Passive house using PV electricity for heating.

I designed and build my own house in Saskatchewan Canada (quite cold here)
Is a relatively small house depending of what you think is small 65sqm (700sqft)
It has an unusual construction made of staked 2x4 wall similar to a log house I think.
The concrete floor that acts as a large thermal mass is completely isolated from outside with expanded polystyrene.
I decided to use small and inexpensive dual pane windows to limit the heat loss. The solar gain with large triple plane windows is not worth the investment. Gain will be to small even with expensive triple pane windows when compared with solar PV.
Solar PV panel can heat 100% my house. I need about 7 to 9kW of PV panels to heat the house 100% with solar electricity. The house requires in the worst month 1000kWh for heating and since the heating season is long it requires about 4.5MWh per year.
There will be no batteries involved with the solar PV heating just PV panels and restive heat elements embedded in the concrete floor. I will need to design and build something that I call a Digital MPPT for the heating part but it will be simple and inexpensive (I will also make that open source as all my projects)

Here is a video of how my house is build so you have a better idea of how the house looks like. The PV heating is not installed as of now I will need to get the funds first for that.

interesting idea.
if i understand it correctly, you would be using the concrete mass to store the electricity generated from PV in the form of heat, right?

what kind/type of embedded heaters will you use?

thanks for posting that video also, i enjoyed watching it.

Kelly Smith wrote:interesting idea.
if i understand it correctly, you would be using the concrete mass to store the electricity generated from PV in the form of heat, right?

what kind/type of embedded heaters will you use?

thanks for posting that video also, i enjoyed watching it.

Yes you are correct the mass of the concrete floor will act as a thermal battery that will store the energy from PV panels as heat.
I will probably use just normal enamel coper wires nut sure I will see. Since the max power point voltage of the PV panels will be around 30V and I wan to keep the voltage that low coper wires have high enough resistance to work as heaters similar to what you see on some cars as rear defrost for windows.
I will need an electronic device I call Digital MPPT (no such think exist as of now to my knowledge so I will need to design and build one) That will connect more or less of those resistive heaters to keep the max power point to a good value. If you just connect a fixed resistive element to PV the losses will be significant so that simple inexpensive Digital MPPT makes sense.
Thanks for the question glad you enjoyed the video.

What do you expect the total cost of solar panels and controls to be?

How much for the thermal mass, heating elements and other costs associated with your plan?

Dale Hodgins wrote:What do you expect the total cost of solar panels and controls to be?

How much for the thermal mass, heating elements and other costs associated with your plan?

PV panels are now here at around 80 cent/Watt so PV panels are 7.2k$ then I need some ground support (I will probably keep that simple) about 1k$ max another $500 for copper conductors from the PV array to the house The Digital MPPT will be a lot of work for me but the cost of parts should be relatively low probably $300.
The wires for resistive loops will also not be expensive under 1k$ So all this should be around 10k$
The concrete is a part of the house structure and was needed anyway there is no cost associated with that.

All this is solid state so I assume no maintenance cost will be needed over 25 years life of the panels so 10k$ / 25 = $400 / year for heating.
This 400$ is amortisation cost if I use this just for heating.
The amount of heating for this house is 1000kWh in the coldest month and about 4.5MWh for the season (winter is long and cold here)
so $400/4500kWh = 8.8 cent/kWh for heating only.
But I have all that extra energy in the summer and even in winter I can use that energy for anything else inside the house and the result will still be heat.
I already found a good use for the extra energy I just need to find more.
We drink distilled water and we used to do our own distilled water when we where on grid about 100kWh/month to run that distiller to produce about 4 litres (one gallon) /day but now we get the ware from the store at about 2$ / day that is about 700$/year
So that 700$ for distilled water as saving alone will more than amortise the heating PV array and when we do distilled water in winter all that energy 100kWh/month will still be heat inside the house so no loss from that and in summer we will need to get the distiller outside the house not to contribute to heating the house.
In summer even with that distilled water there is a huge amount of extra energy that I want to find some use for cooling is not required here so I need to find something else.

I'm confused is that your house already built in the video with what looks like pex tubing in the floor or is that copper wire of what gage or are you adding copper wire some where?

"If you just connect a fixed resistive element to PV the losses will be significant so that simple inexpensive Digital MPPT makes sense. "

Can you please explain this more what "fixed resistant losses" and what does MPPT stand for? Are you referring to inverter efficiency? Will you have AC for appliances? Or perhaps an AC controller that backs off voltage supply as air temperature rises per zone?

Terry Ruth wrote:I'm confused is that your house already built in the video with what looks like pex tubing in the floor or is that copper wire of what gage or are you adding copper wire some where?

Yes that house was designed about 4 year ago and start building about 3 years where PV panels were about 2 to 3x more expensive. I did not imagine I will heat with solar PV panels at that time.
So that is a PEX tube and use that currently to circulate warm water heated by a thankless propane heater as a temporary heating solution.
I will add the copper wires on top of the concrete and then add an ceramic tiles on top of them (Is good that I did not installed the ceramic tiles before thinking about this heating solution).

Terry Ruth wrote:
"If you just connect a fixed resistive element to PV the losses will be significant so that simple inexpensive Digital MPPT makes sense. "

Can you please explain this more what "fixed resistant losses" and what does MPPT stand for? Are you referring to inverter efficiency? Will you have AC for appliances? Or perhaps an AC controller that backs off voltage supply as air temperature rises per zone?

MPPT stands from (Maximum Power Point Tracking). It will be a bit harder to explain if you do not have knowledge about how a solar PV panel work but I will try.
The heating PV array will have nothing to do with the current PV array used for electricity in the house this one has batteries and a solar charge controller + inverter for AC that I use less than one hour per day for cooking usually and I mostly use directly 24V DC for all other stuff (computers, light, refrigeration ...)
The PV array fro heating will be a separate one and will have no battery or AC inverter that will heat the concrete slab that needs about 10kWh for each degree Celsius in temperature rise. Since the total heat elements are about 6000W it needs about two hours of full sun to rise the temperature of the concrete slab with one degree Celsius. There will be a thermostat control but that will mostly work in spring in winter all the energy will go in to concrete during the day.

Let me get back to PV panels and how they work. Say you have a single 240W PV panel with 60 cells so a open circuit voltage of about 37V and maximum power point voltage of around 30V and a max power point current of around 8A (8A x 30V = 240W)
The only parameter that will vary with the amount of sun is current here is a typical current voltage curve based on the amount of sun available.

As you can see max power point voltage is always around 30V and current is directly dependent on the amount of sun.

So let me give an example now with that 240W PV panel and a fixed resistive heater that is exactly 240W at 30V so it will have a resistance of 3.75 ohm (30V / 3.75ohm = 8A)
So now if you connect this fixed resistance of 3.75ohm to PV panel and there is full sun in the afternoon on the panel 1000W/sqm you get max 8A and 240W on the resistor.
But say sun is later in the afternoon or there is a small cloud and now the sun available to panel is 500W/sqm the current will drop to 4A but since the resistance is the same 3.75ohm the voltage drop on that resistor at 4A is just 15V (3.75ohm x 4A)
Then 4A x 15V is just 60W is just 50% of the max you can have if you can change that resistance value. I deal you will want now a resistor that has 2x the value say two of this resistors in series 7.5ohm then at 4A voltage drop will be ideal at 30V and so 4A x 30V = 120W (100% of what the panel can provide)

What my Digital MPPT do is connect a number of 200W resistive load to a large array 7kW to 9kW in my case. I will probably have around 31 loops of 200W so 6100W total around 100W/square meter (65sqm house)
Now those 31 loops can be connected this way
16 loops in parallel for 3200W
8 loops in parallel for 1600W
4 loops in parallel for 800W
2 loops in parallel for 400W
1 loop as 200W

So I need 5 switches probably mosfets since relays will not last that long but the idea is the same if you are more familiar with relays.
Now this 5 switches I can control the power (or resistance of the loop) from 200W up to 6100W in 200W increments so about 31 combinations 32 if you count zero or completely off.
For example I can get 4200W by switching on the 16 loops + 8 loops + 1loop = 3200W + 800W + 200W
By doing so I can always maintain a max power point. All I need to do is monitor PV voltage and try to keep that around 30V in the case of this panels by connecting more or less loops.
And all I need are 5 switches that can create a value with a 32 step resolution that is a close enough approximation to keep the PV array working wery close to the max power point.
I do not think anyone did this before so do not take a patent on this all this will be freely available and open source.

Currently I work on a different open source project is right now on Kickstarter if you are curios search for Solar BMS (Battery Management System) or look at my webpage http://electrodacus.com

Dacian.

Thank you for the explainations.

"I deal you will want now a resistor that has 2x the value say two of this resistors in series 7.5ohm then at 4A voltage drop will be ideal at 30V and so 4A x 30V = 120W (100% of what the panel can provide) "

I think you mean increase the thermal conductivity area for the the same resistance (EG: 7.5 OHM), 2 loops vs 1 . To get that effect you are adding alot more loops in parrallel?

"All I need to do is monitor PV voltage and try to keep that around 30V in the case of this panels by connecting more or less loops. "

How will you do this and know when to connect or disconnect. If you disconnect sub-sections in a room that can lead to un-even heat, hot and cold spots. I'm sure someone has figured out how to control loops (zones) and has a smart monitor-controller that reads array voltages and current (should not be that hard to develop long ago). I have not looked deep yet since I am not sure if resistance makes more sense than hydronic. HR panels are easy to make I hear although I have not tried it. The heat does not come on as fast as resistance but there are aluminum fins that help, they fit over PEX and Copper : Also HR provides domestic hot water, I guess PV tied resistant DHW can work too but, less efficient?. HR keeps the indoor relative humidity @ 45-50%, electric needs a humidifier. HR needs a boiler and tanks(s). Many say minisplits tied to PV is the highest cost of performance, here again I don't think these people understand it has been proven by ASHREA it takes around 30-40% less radiant heat to get the same convective heat feel to the human body that couples to "asymmetric" (walls, ceiling) radiant more efficiently that also drops the building HVAC load.


These days many are going to wall radiant heat, cool ceiling's, since ASHRAE did a focus group study that showed it is the most comfortable to most humans. Floors were found to be the least comfortable by far, and cause a decease in the feet called varicose veins. I think too often people are designing HVAC systems to building's (now PV low cost) not humans. You can learn more about that here, how the skin and brain work: http://www.healthyheating.com/Thermal_Comfort_Working_Copy/HH_physiology_4_nerves.htm#.VRlJy_nF_UV

How are you keeping those studs from thermally bridging from low r-value, high conductivity? I bet all those studs cost some money vs insulation. Wood studs do not have that great of solar heat storage capacity or are hygroscopic to regulate humidity. I have a thread here that explains, well worth the read: https://permies.com/t/43637/natural-building/Breathable-Walls
Water is highest, concrete is ok, air is terrible. Short wave solar gains to the room space and walls will depend on the floor covering and color, dark if very absorbent, the longer waves that emit to the body and walls will not depend on color, more on surround mass including people to draw heat out. The EPS will not do much to stop radiant heat loss that depends more on the floor covering, materials, but will stop conductive heat loss. More needs to be learned on how foam creeps (looses memory) or fatigues over time. I'm not a fan. People are trying to figure how how to accurately account for people in HVAC designs. Learn more at HealthHeating.com.

A Masonry heater along with more internal thermal and hygroscopic mass makes better sense than triple pane windows, more PV panels, and more electrical loops or mechanical devices. You may be able to drop that 4.5 MWH/year down with plaster. You are fortunate to have experienced solar passive before determining active loads, most could not take the cold, discomfort. Then again, I have seen massive homes (IE: rammed earth) in freezing temps never get below 65 : http://www.sirewall.com/portfolio/residential-projects/otter-limits/ . It can be done and what I hope for, very low HVAC active loads due to robust solar passive.

Absolutely brilliant and elegantly simple. Capture solar energy in the summer when the sun is higher in the sky and use the captured energy in the winter when the sun is much lower in the sky and when there are many more overcast days. There's a solar-powered subdivision in a community just outside Calgary that does a similar thing of capturing summer energy for winter use - http://www.dlsc.ca/index.htm. The execution of the idea is completely different and more complex though.

Terry Ruth wrote:Thank you for the explainations.
"I deal you will want now a resistor that has 2x the value say two of this resistors in series 7.5ohm then at 4A voltage drop will be ideal at 30V and so 4A x 30V = 120W (100% of what the panel can provide) "
I think you mean increase the thermal conductivity area for the the same resistance (EG: 7.5 OHM), 2 loops vs 1 . To get that effect you are adding alot more loops in parrallel?

Adding loops in paralegals will decrease the resistivity so I can switch from 7.5Ohm 120W at 30V (say 1sqm area ) to 3.75Ohm that will do 240W at 30V ( double 2sqm area) This is just an example my house will have 200W loops so only steps in 200W increments.

Terry Ruth wrote:
"All I need to do is monitor PV voltage and try to keep that around 30V in the case of this panels by connecting more or less loops. "

How will you do this and know when to connect or disconnect. If you disconnect sub-sections in a room that can lead to un-even heat, hot and cold spots. I'm sure someone has figured out how to control loops (zones) and has a smart monitor-controller that reads array voltages and current (should not be that hard to develop long ago). I have not looked deep yet since I am not sure if resistance makes more sense than hydronic. HR panels are easy to make I hear although I have not tried it. The heat does not come on as fast as resistance but there are aluminum fins that help, they fit over PEX and Copper : Also HR provides domestic hot water, I guess PV tied resistant DHW can work too but, less efficient?. HR keeps the indoor relative humidity @ 45-50%, electric needs a humidifier. HR needs a boiler and tanks(s). Many say minisplits tied to PV is the highest cost of performance, here again I don't think these people understand it has been proven by ASHREA it takes around 30-40% less radiant heat to get the same convective heat feel to the human body that couples to "asymmetric" (walls, ceiling) radiant more efficiently that also drops the building HVAC load.

I will use a microcontroller and ADC input to monitor the PV voltage then increase or decrease the number of parallel loops so that voltage it kept around 30V for the maximum power point.
While this is not hard to do I'm quite sure no one has done this since this is required for PV panels and resistive heating and this makes sense only in the last two years or do to dramatic cost reduction of solar PV panels.
If you are referring to Thermal solar when you mention HR panels those can only be the vacuum tube type of panels and those are at the moment at the same price with PV panels.
PV panels use about 2.5x more space than vacuum tubes but the rest of the system is simpler and less expensive for PV and resistive heating + no maintenance needed (no hot fluids and mechanical pumps).
So the difference in efficiency only affects the space needed for panels and in my case that is not an issue I will have the panels ground mount and not on the roof.
HR (if you are talking about thermal solar) will perform the same when if comes to air humidity vs PV electric there is no reason to be different.

Terry Ruth wrote:
These days many are going to wall radiant heat, cool ceiling's, since ASHRAE did a focus group study that showed it is the most comfortable to most humans. Floors were found to be the least comfortable by far, and cause a decease in the feet called varicose veins. I think too often people are designing HVAC systems to building's (now PV low cost) not humans. You can learn more about that here, how the skin and brain work: http://www.healthyheating.com/Thermal_Comfort_Working_Copy/HH_physiology_4_nerves.htm#.VRlJy_nF_UV

Varicose veins I sure has nothing to do with the way you heat the house. It is probably related to genetics predisposition and a bit less about your life style (sedentary, prolonged standing, things of this nature).
The concrete floor will not exceed 27C so I can not see any problem at this sort of temperatures. I heat in about the same way now just use warm water trough PEX embedded in concrete to do so at the moment.

Terry Ruth wrote:
How are you keeping those studs from thermally bridging from low r-value, high conductivity? I bet all those studs cost some money vs insulation. Wood studs do not have that great of solar heat storage capacity or are hygroscopic to regulate humidity. I have a thread here that explains, well worth the read: https://permies.com/t/43637/natural-building/Breathable-Walls
Water is highest, concrete is ok, air is terrible. Short wave solar gains to the room space and walls will depend on the floor covering and color, dark if very absorbent, the longer waves that emit to the body and walls will not depend on color, more on surround mass including people to draw heat out. The EPS will not do much to stop radiant heat loss that depends more on the floor covering, materials, but will stop conductive heat loss. More needs to be learned on how foam creeps (looses memory) or fatigues over time. I'm not a fan. People are trying to figure how how to accurately account for people in HVAC designs. Learn more at HealthHeating.com.

Wood is not that thermally conductive and there are a few air breaks between the studs and the solid wood wall. Yes stoods are a bit more expensive than EPS (expanded polystyrene) insulation but not by much about 1.5x by volume but those wood studs are needed to support the thermal insulation in high winds other solutions like long screws will be more costly and worse for the point of view of thermal bridging.
There is almost no direct thermal gain do to relatively small windows so that is not important since PV is way better than triple glass windows. In this climate even triple glaze will not have a net gain or a very small one while PV only has net gain there is no loss back as with windows.
Expanded polystyrene the type of thermal isolation I used on the walls and foundation will not degrade over time or absorb water unlike the other type the extruded polystyrene.

Terry Ruth wrote:
A Masonry heater along with more internal thermal and hygroscopic mass makes better sense than triple pane windows, more PV panels, and more electrical loops or mechanical devices. You may be able to drop that 4.5 MWH/year down with plaster. You are fortunate to have experienced solar passive before determining active loads, most could not take the cold, discomfort. Then again, I have seen massive homes (IE: rammed earth) in freezing temps never get below 65 : http://www.sirewall.com/portfolio/residential-projects/otter-limits/ . It can be done and what I hope for, very low HVAC active loads due to robust solar passive.

That 4.5MWh is based on my propane use this winter. The propane heater is probably around 80% efficient so I will need about 20% with electric heating. There is almost no passive solar and I had done all the calculations before and they are within a 10 to 20% accurate (errors do to simplification).
Discomfort is usually only present on insufficient isolated house (over 90% of them those made at the minimum code requirement) or those with a lot of thermal bridging problem or not good enough air seal.
The heat recovery ventilation is not done as of now it will need to be custom made and I do not need cooling in summer thanks to the great thermal mass thermal insulation and no solar gain in summer (the roof completely shadows the windows in summer).

Mike Haych wrote:Absolutely brilliant and elegantly simple. Capture solar energy in the summer when the sun is higher in the sky and use the captured energy in the winter when the sun is much lower in the sky and when there are many more overcast days. There's a solar-powered subdivision in a community just outside Calgary that does a similar thing of capturing summer energy for winter use - http://www.dlsc.ca/index.htm. The execution of the idea is completely different and more complex though.

I did researched the seasonal storage idea but is to expensive it makes absolutely no economic sense.
I think I mentioned I need max 9kW of PV panels for direct heating in winter and If I where to reduce that to half and store energy in summer for winter use that storage should cost the same or less than those saved PV panels 4.5kW of panels cost around $3600 and for that or less to build a 2.5MWh energy storage solution is just impossible.
Maybe at a much larger scale like a community the seasonal storage economics work but I'm not sure.

Hi Dacian, I'm struggling with the math since it is going in alot of different directions and I have not taken electrical for a while. Lets start with simple series vs parallel circuits.

Lets say we have 3 resistant loops in series @ R1= 8 ohm, R2= 8 ohm, R3 = 4 ohm, @ 30 volt PV.

I (Amps) = V(voltage) / R(Ohms) = 30V/ 20-ohm (resistance is additive in series) = 1. 5 amp (the current through each resistor). Voltage drops at each resistor: V=IR , R1=12, R2= 12, R3=6, total voltage drops = 30V according to OHMs law.


Now Parallel,

Current is NOT the same through each resistor, it splits up.

Total Resistance = 1/R = 1/8+1/8+1/4 = 1/2, Reciprocal = 2-ohm.
Total Current VR = 30/2 = 15 amps

I (current drops) = V/R = (I-1 = 30/8= 3.75, I-2 =3.75, I-3= 7.5) = 15 amps

Observation: Resistance causes conductive heat to mortar there is alot less in parallel circuits ( 2 ohms (parallel) vs 20 ohms series) in the example above) given a constant voltage of 30 PV. In other words, the same three resistors will produce more heat if connected in series than parallel. The current flow in parallel is also higher yielding less heat from the wires (heating elements) at the resistors.

Are you planning on designing your own wires or using mats? There is alot to that, sheathing that cancels EMF, wires that are gagged-sized to not burn. I know nichrome in ceramics perform well. I know there are special wires for hot asphalt snow melt not sure what they are made of, the manufactures call them proprietary.

I still don't see where energy efficiency is gained, even with the most complex storage systems. When one heats with pv electric, one must convert and store energy, with a loss. If you have sufficient sun light to heat via sun light, there has to be enough energy to heat passively as well.
I really dont understand the need to make a new storage system that already exists, with the need for pv. Sounds like making a solar powered clothes dryer, when all you need is a rope.

But if you have some surplus pv energy, do not store it with heat, pump some water or run a compressor. Passive heat gain is great, but if you have electric to spare, please use it on load bearing applications, sun heat does not need moving parts or electronics to help heating. Moving stuff does.

Just making a guess that where you live gets about the same amount of solar radiation as Moscow, Russia, it would seem that in January and February you area of Canada probably gets about 1 kilowatt hour per day per meter square in January and February.
http://www.pveducation.org/pvcdrom/properties-of-sunlight/average-solar-radiation
You stated that you use 1000 kWH per month in the winter, which works out to be 31 kWh per day. At 100% solar panel efficiency, that means you would need roughly 30 square meters (322 square feet) of solar panels. With a more realistic 14% efficiency, you would need 2300 square feet of panels.

EDIT: Those numbers require that everything be average. Unless you are willing to get really cold on week of overcast days, you would probably need to make the system several times larger if you want to rely exclusively on solar energy during the winter.

Terry Ruth wrote:Hi Dacian, I'm struggling with the math since it is going in alot of different directions and I have not taken electrical for a while. Lets start with simple series vs parallel circuits.

Lets say we have 3 resistant loops in series @ R1= 8 ohm, R2= 8 ohm, R3 = 4 ohm, @ 30 volt PV.

I (Amps) = V(voltage) / R(Ohms) = 30V/ 20-ohm (resistance is additive in series) = 1. 5 amp (the current through each resistor). Voltage drops at each resistor: V=IR , R1=12, R2= 12, R3=6, total voltage drops = 30V according to OHMs law.


Now Parallel,

Current is NOT the same through each resistor, it splits up.

Total Resistance = 1/R = 1/8+1/8+1/4 = 1/2, Reciprocal = 2-ohm.
Total Current VR = 30/2 = 15 amps

I (current drops) = V/R = (I-1 = 30/8= 3.75, I-2 =3.75, I-3= 7.5) = 15 amps

Observation: Resistance causes conductive heat to mortar there is alot less in parallel circuits ( 2 amps (parallel) vs 20 amps series) in the example above) given a constant voltage of 30 PV. In other words, the same three resistors will produce more heat if connected in series than parallel. The current flow in parallel is also higher yielding less heat from the wires (heating elements) at the resistors.

Are you planning on designing your own wires or using mats? There is alot to that, sheathing that cancels EMF, wires that are gagged-sized to not burn. I know nichrome in ceramics perform well. I know there are special wires for hot asphalt snow melt not sure what they are made of, the manufactures call them proprietary.

Hi Terry,

Not sure what you try to demonstrate with the above. I will try to me more simple with my explanation and give more details.
First thing you need to understand is PV panels are constant current power supply not sure you understand the concept of constant current so I will try to explain that a bit.

A 60 cell 240W PV panel that I used in the first example and you can refer to that IV curve will output at most 8A with full sun even if you short circuit the PV panel current will stay around 8A max maybe 8.5 or 9A
If you have the panel open circuit it will output as much as 36 or 37V.
In both cases open circuit or short circuit there is no usable power in one case current is zero and in the other voltage is zero.
In order to get the most out of it you will need to connect a resistor value that will drop 30V at 8A so
R=V/I = 30V / 8A = 3.75ohm
So if you connect a 3.75ohm resistor to that PV panel in a sunny day with panel facing the sun and cells at 25C based on spec you will get that 8A and at 30V drop on that resistor you get the 240W dissipated on that resistor.
Now let say a cloud comes in and now your PV panel can only output half 4A do to less solar radiation on the panel.

If you do nothing and keep the same resistor 3.75ohm how much power will you get dissipated on that resistor?
Voltage drop on that resistor at 4A will be 4A x 3.75ohm = 15V now power will be P= 15V x 4A = 60W

But as you notice the power is just a quarter of the full PV power and I mentioned that solar energy drooped to half only.
The reason for that is that with that 3.75ohm resistor the panel dose not work at the max power point.

To do so you need to change the resistor to a value that allows a voltage drop of 30V that is optimal for this panel
So 30V /4A = 7.5ohm Now if you connect a 7.5ohm to this panel you get P = 30Vx4A = 120W

You may ask what happens if you use a 15ohm resistor will you get more power?

Voltage drop at 4A on a 15ohm resistor can be 4Ax15ohm = 60V but if you remember that panel open circuit voltage is 36V at 0A so it will not go higher than that even without any current.
So what will happen is based on the current-voltage graph of that panel is that current will drop at around 2A and voltage will increase just slightly say 32V in that case current will be 32V/15ohm = 2.13A and power will be at around 68W less than ideal max power point 120W

Now say you want to build a realy small heater for a small room or something with just one of this 240W PV panels and 4 loops.

The best way to do that is have all 4 loops of 15ohm and connect them in parallel for a total off 3.75ohm.
You will have 3 relays or mosfets one connected to 2 loops in parallel and and the other two to each of the other resistive loops.
With this configuration you can have 0 ohm all loops disconnected.
a) 15ohm a single loop connected (any of the two will work)
b) 7.5ohm two loops in parallel (can be the two loops already connected in parallel to one relay or the other two relays each with one loop)
c) 5ohm three 15 ohm loops in parallel (the two loops connected to one relay and any one of the other two single loops)
d) 3.5ohm all 4 loops in parallel

Now all you have to do is monitor the voltage and select one of the 4 variants from a) to d) (that can be done automatically by a microcontroller)

Say now the available energy from the sun is not 50% as in the example above but around 62% or 5A
If you connect all loops version d) you will see that voltage drop will be 5A x 3.5ohm = 17.5V and you will know you need to increase the resistance by disconnecting some of the loops to get more power (P= 17.5V x 5A = 87.5W )
So now you disconnect one of the loops like version c) voltage drop this time is 5A x 5ohm = 25V still less than ideal (P=25V x 5A = 125W)
Next you can try version b) and voltage drop will be 5A x 7.5ohm = 37.5V but not possible remember that panel can put out at most 36 or 37V with no current so this is a bit more complicated but current will probably drop a bit so that voltage drop is around 31V or so and then 31V / 7.5ohm = 4.13A (P = 31V x 4.133A = 128W)
Controller will stop here and will probably select the 5ohm 3 parallel loop version if you set your max power point voltage as closest to 30V but less than 30V or you can set that to 31V and then the 7.5ohm version will be selected in any case quite close to max possible of 30Vx5A = 150W

While in this example I used just 4 loops for simplicity with more loops you can get much closer to the ideal 150W in this case but even with just 4 loop you are extremely close compared to a single fixed 3.75ohm resistive loop that will give you just 87.5W vs 125 or 128W with 4 loops and an algorithm based on voltage.

Hope it was more clear this time but we can discus more if you want.
So my house will have 31 loops in parallel and by disconnecting or connecting more or less of them I get a much closer to max power point value.
For 31 loops I only need like I think I mentioned 5 relays or mosfets that is not much more than 3 needed for 4 loops or two need with 3 loops.


Dacian.

chad Christopher wrote:I still don't see where energy efficiency is gained, even with the most complex storage systems. When one heats with pv electric, one must convert and store energy, with a loss. If you have sufficient sun light to heat via sun light, there has to be enough energy to heat passively as well.
I really dont understand the need to make a new storage system that already exists, with the need for pv. Sounds like making a solar powered clothes dryer, when all you need is a rope.

But if you have some surplus pv energy, do not store it with heat, pump some water or run a compressor. Passive heat gain is great, but if you have electric to spare, please use it on load bearing applications, sun heat does not need moving parts or electronics to help heating. Moving stuff does.

Not sure you understand what I meant by energy efficiency (I was referring to the digital MPPT probably ).
As for heating with PV that is about the cost.
I can use large triple pane windows to heat the house directly from sun but those windows will cost more than PV panels and will also have much higher loss than the typical wall. Same surface of wall is R35 thermal insulation and cost less than the least expensive 2 pane window that has typical R3.5 so 10x more heat loss for same area.
Installing much larger windows to have enough surface area to passive heat the house will cost way more than PV panels and also heat loss during the night or cloudy days will increase significantly even with 3 pane windows so in that case you will need way more heat storage again contributing even more to cost.
Hope this explains your questions.

John Wolfram wrote:Just making a guess that where you live gets about the same amount of solar radiation as Moscow, Russia, it would seem that in January and February you area of Canada probably gets about 1 kilowatt hour per day per meter square in January and February.
http://www.pveducation.org/pvcdrom/properties-of-sunlight/average-solar-radiation
You stated that you use 1000 kWH per month in the winter, which works out to be 31 kWh per day. At 100% solar panel efficiency, that means you would need roughly 30 square meters (322 square feet) of solar panels. With a more realistic 14% efficiency, you would need 2300 square feet of panels.

EDIT: Those numbers require that everything be average. Unless you are willing to get really cold on week of overcast days, you would probably need to make the system several times larger if you want to rely exclusively on solar energy during the winter.

Yes this will not work great everywhere. You should move to Saskatchewan Canada
You have an average 0.91kWh/m2 in January and I get here 4.26kWh/m2 in the same month.
That is a huge difference so unfortunately your location is quite bad for solar.
Average over a year you get 2.75kWh/m2 where I get here 4.65kWh/m2 difference dose not look that bad here but in winter difference is huge.
I use this for comparison http://rredc.nrel.gov/solar/calculators/pvwatts/version1/ selected Europe RUS Moscow for your location and Canada SA Regina for my location.
As for averaging the the temperature I have 14 cubic meters of concrete floor that can store up to 100kWh at 10C delta say +17C to +27C

Dacian.

Dacian Todea wrote:in January and I get here 4.26kWh/m2 in the same month...Average over a year you get 2.75kWh/m2 where I get here 4.65kWh/m2 difference dose not look that bad here but in winter difference is huge.

Are you saying that you get 4.26 kWh/m2 per day in the winter, but only average 4.65 kWh/m2 per day for the entire year? To average out the 4.26 in January, you would need just 5.04 kWh/m2 per day in July, and that would seem a bit odd since you get almost twice as many hours of daylight in July as you do in January.

John Wolfram wrote:

Dacian Todea wrote:in January and I get here 4.26kWh/m2 in the same month...Average over a year you get 2.75kWh/m2 where I get here 4.65kWh/m2 difference dose not look that bad here but in winter difference is huge.

Are you saying that you get 4.26 kWh/m2 per day in the winter, but only average 4.65 kWh/m2 per day for the entire year? To average out the 4.26 in January, you would need just 5.04 kWh/m2 per day in July, and that would seem a bit odd since you get almost twice as many hours of daylight in July as you do in January.

Yes that is right since my panels are set at 70 degree tilt for most gain during winter. I have less use for energy in summer. There is anyway a lot of unused energy so I want to get the best of what is possible when I need that in winter when day is shorter.
You can check that link for my heating array I use 95% efficiency allowing for up to 5% loss on outside cables there is no DC AC conversion loss or battery charging efficiency involved for heating and tilt 70 degree.
If you do that for a 9kW array at my location you will get this numbers.
November 867kWh
December 943kWh
January 1222kWh
February 1279kWh
March 1367kWh

July 1173kWh

Awesome replies Dacian, it will take a while for your info to reach our head. Esp here, where we like natural system that doesn't use electronic.

I did like the point about failure rate of the resistors and how we would replace them with a water/space heater, I have to replace it every 15yrs how long would your resistor last and how easy is it to replace them. Would it last as long as a pex pipe.

I also like redundancy, if you were to go out of biz where could I get said resistor controller from. Is your project opensource.

S Bengi wrote:Awesome replies Dacian, it will take a while for your info to reach our head. Esp here, where we like natural system that doesn't use electronic.

I did like the point about failure rate of the resistors and how we would replace them with a water/space heater, I have to replace it every 15yrs how long would your resistor last and how easy is it to replace them. Would it last as long as a pex pipe.

I also like redundancy, if you were to go out of biz where could I get said resistor controller from. Is your project opensource.

In my case the resistors will be just normal copper cable and max temperature will be extremely low about the same as PEX so those will last forever much more than PEX and probably more than the house. Thy have a large area and only about 4W/m or less is dissipated about 100W/sqare meter with at least 25m of cable on each square meter.
On water heaters you have a few thousand watt on just less than one meter of heat element.
I currently use hot water and PEX but for PV heating those resistive heat loops will be embedded on the concrete floor directly it makes no sense to heat water and then use pups to move that water. So no moving parts and low temperature copper wire that will heat the house.
The project will be open source as all my projects are and that is not done currently I do a Kickstarter for the Solar BMS project and I will probably do the same thing for this Digital MPPT when I'm done with the Solar BMS. The Digital MPPT will be relatively simple construction and should last at least 30 years same as PV panels if not more all solid state noting to fail there and it will be protected form short circuit or overcurrent.
I used to work as HW engineer in safety electronics designing airbag control units for cars at Siemens Automotive.

Dacian, I figured you were an EE or something, your getting into circuit design that needs to be on a EE site. I can tell by the responses your over most peoples head but thanks for the challenge, it reminds why I leave it you sparky's I call them for fun! I did understand your response to me, thank you!

1. The point I was trying to illustrate in my last post is the low resistance in parallel vs series does not provide as much heat to the surroundng concrete or mortar. Correct me if I am wrong but, it is current through a resistor that generates heat, not power or watts?

2. If I understand correctly current is constant (8 amp, 4 ) and does not vary incrementally (IE: 5.6 amps) depending on sun?

3. Is the only loss conductive from the wire to concrete? The PV to wire has low loss?

But if you say that wire heat will generate as much as hydroponic systems do I believe you. Pumps are not that expensive. Wire can fatigue, hard to replace, dig out mortar maybe not that bad.

There are plenty of wire/mats manufacures out there that design safe no EMF (Electric Magnetic Field ) design that are certified by third parties backed by warranties. Are these parallel or series desgins? I have not checked yet. EMF is a health factor permies avoid electronics for one. I gave you a link with data on vericose disease from floors since the feet withdraw heat or conduct it depending on floor temps, there is proven data you can choose to ignore if you want, HVAC systems can effect the body and more even distribution to it should make sense, just like a wall or building, even, monolithic is better. Amazing how we just look to our body for building design guides, ehh? Rising heat or stack affect does not provide it, nor the highest comfort level. We permies like to avoid electronics but rather design efficient envelopes to avoid or reduce them, use it as a secondary source once natural and passive solar has been optimized, or other systems that burn cheap and clean such as rocket mass heaters. It is far, far, stretch of the imagination to claim stacked wood studs wrapped in plastic and foam is the more optimized natural solar passive design on the planet, so lets not get the wrong impression and not put the cart before the horse.

We are not big fans of other manufactured products such as plastics or foams with health hazards miles long including blowing agents and fire retardants. The proof and data why there are better more natural inert, non combustible, low or no fire rated, low impact from cradle to grave on the environment building materials can be found on my thread called "Breathable Walls" your welcome to dispute the data with data after reviewing the data. I already brought up creep allowables in foam you will not find on any manufactures specs stuctures engineers need for a complete analysis along with max deflection, max compression is lower than others discussed, plastics very low point load capability, tear, toxic (see MSDS) etc...nor are there any life cycle test as there are with more natural building materials. These barriers cause issues and do not help take down HVAC/PV heating and cooling loads. Earth and lime plasters with lots of empirical data do better as seen in the specs on the thread: https://permies.com/t/43637/natural-building/Breathable-Walls

What is your take on the 98% efficient condensing boilers? I've read conflicting reports of reliability issues, some claiming the average life cycle is 6 years vs 20+, parts are expensive, etc.

Yes please do keep us informed on your design including when it will pass building codes, reliability life cycle testing, maintenance cost data, when you have third party and/or complied to applicable ASTM testing, proven field builds, all the bugs worked out. That will cost some money.

Thanks again for the EE refresher course It's been over 30 years for me.

Dacian, thanks for all that explaining!

For those who are worried about the heating controller, while my electrical/electronics experience is far short of a completed degree, and a decade stale, I can still say this would be a pretty simple thing to build. Probably could be hacked together on an Arduino, though I'm sure Dacian's will be better.

Terry, thanks for the interesting link about heating comfort. Do you have a link for the vericose veins study? Couldn't find it at first Google, only some sites describing this as a myth!

Checking your link (http://www.healthyheating.com/Thermal_Comfort_Working_Copy/Definitions/floor_temps.htm#.VRwyWeHkqsw), they say that 'Humans appreciate floors temperatures that are controlled to above 66˚F minimum in cooling and below 84˚F maximum in heating.' 84f=28.89C, so Dacian's floor is within range. It is above the 23.88 point of lowest predicted dissatisfaction, but not by a lot, and presumably will not always be at it's maximum temperature.

Furthermore, it looks like a concrete floor(closest thing to tile that's listed) results in a higher preferred temperature of 79-83f for people with bare feet, because of the greater contact coefficient, so Dacian's floor at max would again be within range.


Perhaps someday we will have the option of floors which track occupants preferences and footwear, and heat each zone separately to suit... but I think most Permies would have a fit at the thought of the supporting electronics!

Terry Ruth wrote:Dacian, I figured you were an EE or something, your getting into circuit design that needs to be on a EE site. I can tell by the responses your over most peoples head but thanks for the challenge, it reminds why I leave it you sparky's I call them for fun! I did understand your response to me, thank you!

1. The point I was trying to illustrate in my last post is the low resistance in parallel vs series does not provide as much heat to the surroundng concrete or mortar. Correct me if I am wrong but, it is current through a resistor that generates heat, not power or watts?

It is not important is loops are parallel or series as an example two loops of 15ohm in parallel = 7.5ohm where two loops of 3.75ohm in series will have the same 7.5ohm value and so connected to the same voltage will generate the same amount of heat.
If you only know the current you will have no idea how much heat is generated you need to know at least one more parameter like voltage or resistance and then you can find out the power (and that is the one you care about). One step further is energy but you need to know power and the amount of time that power was applied.

Terry Ruth wrote:
2. If I understand correctly current is constant (8 amp, 4 ) and does not vary incrementally (IE: 5.6 amps) depending on sun?

PV solar panels have the output current directly proportional with the amount of sun you can see that in the graph I posted in one of the replays above.
The value written on the label on the back of the panel called max power point current say 8A is for STC (Standard Test Conditions) and those are done at 1000W/m2 solar irradiation and 25C cell temperature
You normally get around 1000W/m2 in a sunny day in the afternoon and cells can be at 25C in the winter spring when ambient is probably around freezing 0C then you will get 8A from the PV panel.
Of course those 8A will be if you have a load that can take that so say is a 60 cell PV panel with about 36V open circuit and around 30v max power point voltage and sun is 1000W/m2 25C cell temperature
Then you connect a 15ohm resistor to the panel and if you do that all you will get is a bit above 2A 30V/15ohm =2A but since you do not use all the power available panel is somewhere between max power point voltage and open circuit voltage so around 2A voltage will probably be 31V or 32V and current just a bit larger on 15ohm maybe 2.1A
You will need to connect a 3.75ohm resistor to get the full 8A out of the panel and also max power since 8A x 3.75ohm = 30V so 30V x 8A = 240W
Now if you connect a say 1ohm resistor what will the current be ? Answer is approximatively 8A that is because that is the max no matter what even if you short the wires so almost 0ohm you still get 8A (a bit more is specified on the PV label as short circuit current maybe 8.5A or so in this example)
So if you connect a 1ohm to that panel and current is about 8A maybe 8.2A then voltage drop on that resistor is 8.2V and total power dissipated as heat since is just a resistor will be 8.2V x 8.2A = 67.3W

Terry Ruth wrote:
3. Is the only loss conductive from the wire to concrete? The PV to wire has low loss?

Yes the loss to the wire to concrete is conductive. Not sure what is the second question about. Wires from PV to concrete are thicker so less resistance and less loss even if they carry the same current they are also much shorter so the loss on them is extremely insignificant probably up to 3% or less.

Terry Ruth wrote:
But if you say that wire heat will generate as much as hydroponic systems do I believe you. Pumps are not that expensive. Wire can fatigue, hard to replace, dig out mortar maybe not that bad.

Copper wire at 60C or even 100C will have no degradation since melting point is way higher at copper an order of magnitude higher than on PEX.
One example of copper wire used as a heater is on your car back or even front glass and used to defrost your window. That is a very thin layer of copper deposited on the glass and the amount of power there per surface area is way higher than what I will be using in concrete.
There are also commercial available electric heating wires even if those are made for 120 or 240AC and are quite a bit different and I will not enter in details not to confuse things.

Terry Ruth wrote:
There are plenty of wire/mats manufacures out there that design safe no EMF (Electric Magnetic Field ) design that are certified by third parties backed by warranties. Are these parallel or series desgins? I have not checked yet. EMF is a health factor permies avoid electronics for one. I gave you a link with data on vericose disease from floors since the feet withdraw heat or conduct it depending on floor temps, there is proven data you can choose to ignore if you want, HVAC systems can effect the body and more even distribution to it should make sense, just like a wall or building, even, monolithic is better. Amazing how we just look to our body for building design guides, ehh? Rising heat or stack affect does not provide it, nor the highest comfort level. We permies like to avoid electronics but rather design efficient envelopes to avoid or reduce them, use it as a secondary source once natural and passive solar has been optimized, or other systems that burn cheap and clean such as rocket mass heaters. It is far, far, stretch of the imagination to claim stacked wood studs wrapped in plastic and foam is the more optimized natural solar passive design on the planet, so lets not get the wrong impression and not put the cart before the horse.

There is no EMF with DC heating. There are so many unfounded concerns related to health. Even breading is bad for your health and that is a proven fact it will eventually kill you

Terry Ruth wrote:
We are not big fans of other manufactured products such as plastics or foams with health hazards miles long including blowing agents and fire retardants. The proof and data why there are better more natural inert, non combustible, low or no fire rated, low impact from cradle to grave on the environment building materials can be found on my thread called "Breathable Walls" your welcome to dispute the data with data after reviewing the data. I already brought up creep allowables in foam you will not find on any manufactures specs stuctures engineers need for a complete analysis along with max deflection, max compression is lower than others discussed, plastics very low point load capability, tear, toxic (see MSDS) etc...nor are there any life cycle test as there are with more natural building materials. These barriers cause issues and do not help take down HVAC/PV heating and cooling loads. Earth and lime plasters with lots of empirical data do better as seen in the specs on the thread: https://permies.com/t/43637/natural-building/Breathable-Walls

What is your take on the 98% efficient condensing boilers? I've read conflicting reports of reliability issues, some claiming the average life cycle is 6 years vs 20+, parts are expensive, etc.

Yes please do keep us informed on your design including when it will pass building codes, reliability life cycle testing, maintenance cost data, when you have third party and/or complied to applicable ASTM testing, proven field builds, all the bugs worked out. That will cost some money.

Thanks again for the EE refresher course It's been over 30 years for me.

I studied all type of thermal insulation materials and EPS was my choice for walls. EPS (Expanded polystyrene) has no health impact the blowing agent is steam. Yes this may last a long time or never degrade but I want the house to last for at least 100 years or more (you never know how long I can live).
I used to live in Europe and there the 98% efficient condensing boilers are the norm for quite some time a few decades. The technology is well perfected and they use mostly stainless steel to prevent corrosion on those parts that can be affected.
You need to be well below 90% for a non condensing boiler so that 10% may be worth more than the extra cost of high efficiency condensing boilers.
I use as temporary heating a non condensing boiler with a claimed efficiency of around 80% but that is because that was easy to find here and I paid just $150 for it. It only needs to last two or three years before I can do the PV direct electric heating.
I will make sure to document all my work on the solar electric heating and all other things that I will do related to OffGrid house.

Dillon Nichols wrote:Dacian, thanks for all that explaining!

For those who are worried about the heating controller, while my electrical/electronics experience is far short of a completed degree, and a decade stale, I can still say this would be a pretty simple thing to build. Probably could be hacked together on an Arduino, though I'm sure Dacian's will be better.

Terry, thanks for the interesting link about heating comfort. Do you have a link for the vericose veins study? Couldn't find it at first Google, only some sites describing this as a myth!

Checking your link (http://www.healthyheating.com/Thermal_Comfort_Working_Copy/Definitions/floor_temps.htm#.VRwyWeHkqsw), they say that 'Humans appreciate floors temperatures that are controlled to above 66˚F minimum in cooling and below 84˚F maximum in heating.' 84f=28.89C, so Dacian's floor is within range. It is above the 23.88 point of lowest predicted dissatisfaction, but not by a lot, and presumably will not always be at it's maximum temperature.

Furthermore, it looks like a concrete floor(closest thing to tile that's listed) results in a higher preferred temperature of 79-83f for people with bare feet, because of the greater contact coefficient, so Dacian's floor at max would again be within range.


Perhaps someday we will have the option of floors which track occupants preferences and footwear, and heat each zone separately to suit... but I think most Permies would have a fit at the thought of the supporting electronics!

Yes it can be build with arduino no problem is relatively simple and I encourage anyone to do that.
I'm never bare feet unless on a beach somewhere and that is a good example of natural and much higher temperatures then you go in the water where temperatures are much lower
There are many heated floors especially in northern Europe for quite a long time and there is no relations to that and any sort of medical problems. I'm not worried about that at all.

Dillon Nichols wrote:Dacian, thanks for all that explaining!

For those who are worried about the heating controller, while my electrical/electronics experience is far short of a completed degree, and a decade stale, I can still say this would be a pretty simple thing to build. Probably could be hacked together on an Arduino, though I'm sure Dacian's will be better.

Terry, thanks for the interesting link about heating comfort. Do you have a link for the vericose veins study? Couldn't find it at first Google, only some sites describing this as a myth!

Checking your link (http://www.healthyheating.com/Thermal_Comfort_Working_Copy/Definitions/floor_temps.htm#.VRwyWeHkqsw), they say that 'Humans appreciate floors temperatures that are controlled to above 66˚F minimum in cooling and below 84˚F maximum in heating.' 84f=28.89C, so Dacian's floor is within range. It is above the 23.88 point of lowest predicted dissatisfaction, but not by a lot, and presumably will not always be at it's maximum temperature.

Furthermore, it looks like a concrete floor(closest thing to tile that's listed) results in a higher preferred temperature of 79-83f for people with bare feet, because of the greater contact coefficient, so Dacian's floor at max would again be within range.


Perhaps someday we will have the option of floors which track occupants preferences and footwear, and heat each zone separately to suit... but I think most Permies would have a fit at the thought of the supporting electronics!

Dillon, I must have missed where Dacian calculated is floor temperature. That has to be tough. I can not remember the calculations, lets see heat transfer from a wire I guess power in watts to generate a heat flux load that gets distributed by connecting to other radiant heat sources like in walls, furniture, people, etc...just thinking about it gives me a headace. I do not think WUFI could accurately do it, and with the 20-30% inaccurate load calcs he did do without mass it can only get less accuate. You would need all materials properties such as density, specific heat, thickness, perm rating, hygroscopic adsorption/desorption, capillarry adsorption/desorption, air or ACH flow, etc... Going to need more than a EE, here, thermo, aero, fluid, dynamics and a good modeler for some better than WUFI software. Lots of R&D money. Thermal mass and hygroscopic properties of materials really complicate matters. If you want to make it easier just wrap the interior inner wall with plastic and foam like ICF . An outer wrap the has to dry in like this may yield some interesting results, I can only imagine. I prefer drying and properties as such in both directions, that can get complicated in the wall too where I prefer it.

HealthyHeating.com has a lot of great info I plan on reading it all as time permits.

I posted a graph out of ASHRA 55-2004 that shows that floor heating is by far the least comfortable according to a focus group. The best source for this info based on masses and controlled testing are the Engineers and Scientist Teams at ASHREA. If you want to design a home to personal preferences you ignore it, until you want to sell against a builder like me that did not. The vericose test results should be in that spec. It is on my list to read: http://www.almasesepahan.com/fh/download/ASHRAE_Thermal_Comfort_Standard.pdf

Walls are proven to provide the most comfort according to it and the focus group. The Germans are moving towards walls since some realized that heating the lower 1/3 of the body disrupts the cardivascular system an can cause vericose disease. I guess we say as Dacian likes to use to dismiss health related issues proven to be related to buildings, but common lets use some common sense. An even load to the body, less localized heat load, is only simple logic. Why are the Germans always light years ahead of the USA in realizing things? There are also as many proven founded health related issues that have risen post industrialized revolution due to the factory products (man made chemicals), and I'm not say that is not possible in the natural building communities where people that are not chemist combine materials they do not understand.

From what I gather most of the mat manufactures are running AC so they market no EMF wires. DC has a low static field equal to or lower than the earth they say is not harmful to human body. I'm not sure what happens when you are surrounded by 4 walls with DC? I favor magnesium board and/or foam insulation since is non-magnetic, thermally non-conductive, and the properties much higher than EPS/XPS, Poliso, PU, wood sheathing like OSB and plywood, great for slabs too. I also will keep AC power lines a good 6 feet away from where people sleep.

I'll have some more questions and comments later. So many choices.

Terry Ruth wrote:
Dillon, I must have missed where Dacian calculated is floor temperature. That has to be tough. I can not remember the calculations, lets see heat transfer from a wire I guess power in watts to generate a heat flux load that gets distributed by connecting to other radiant heat sources like in walls, furniture, people, etc...just thinking about it gives me a headace. I do not think WUFI could accurately do it, and with the 20-30% inaccurate load calcs he did do without mass it can only get less accuate. You would need all materials properties such as density, specific heat, thickness, perm rating, hygroscopic adsorption/desorption, capillarry adsorption/desorption, air or ACH flow, etc... Going to need more than a EE, here, thermo, aero, fluid, dynamics and a good modeler for some better than WUFI software. Lots of R&D money. Thermal mass and hygroscopic properties of materials really complicate matters. If you want to make it easier just wrap the interior inner wall with plastic and foam like ICF . An outer wrap the has to dry in like this may yield some interesting results, I can only imagine. I prefer drying and properties as such in both directions, that can get complicated in the wall too where I prefer it.

Yes thermal calculations are not that simple but simplification can give you a good enough approximation. I have the advantage that I already heat the concrete with PEX and I can know the exact amount of power I deliver to concrete floor by knowing the hot water flow rate and temp delta at input and output of the concrete floor.
I did all those thermo, fluid mechanics in the EE during the 5 years engineering school in Romania . I must admit not much was left in my brain but as an engineer in general you can read graphs and interpret data of any types. I did a thermal calculation for the entire house and I was accurate within 20% tolerance of the amount of heat I needed. All I used was a spread sheet but could have done that even with pen and paper not as convenient but possible.
Having those calculations done in a spread sheet glowed me to play with different house parameters that is how I decided how much thermal insulation is optimum and how large or small the windows should be. I also was lucky to have good weather data for my location so I can do an accurate enough model.

Terry Ruth wrote:
HealthyHeating.com has a lot of great info I plan on reading it all as time permits.

I posted a graph out of ASHRA 55-2004 that shows that floor heating is by far the least comfortable according to a focus group. The best source for this info based on masses and controlled testing are the Engineers and Scientist Teams at ASHREA. If you want to design a home to personal preferences you ignore it, until you want to sell against a builder like me that did not. The vericose test results should be in that spec. It is on my list to read: http://www.almasesepahan.com/fh/download/ASHRAE_Thermal_Comfort_Standard.pdf

Walls are proven to provide the most comfort according to it and the focus group. The Germans are moving towards walls since some realized that heating the lower 1/3 of the body disrupts the cardivascular system an can cause vericose disease. I guess we say as Dacian likes to use to dismiss health related issues proven to be related to buildings, but common lets use some common sense. An even load to the body, less localized heat load, is only simple logic. Why are the Germans always light years ahead of the USA in realizing things? There are also as many proven founded health related issues that have risen post industrialized revolution due to the factory products (man made chemicals), and I'm not say that is not possible in the natural building communities where people that are not chemist combine materials they do not understand.

I will take a look at those studies but as long as floor temperature is lower than 27C that is 10C lower than body temperature I can not see how that will influence health. The floor can be close to that temperature even in a house without in floor heating.
Keep in mind this is a house designed based on passive standard so there is a lot of thermal insulation and a lot of thermal mass. The wall also contribute to thermal mass since they are solid wood and no thermal insulation on the inside.
To heat a house done to code with solar PV and floor heating is impossible. Floor heating is barely possible if you heat the floor all the time say with hot water or electricity from the grid.
The way my heating works is just a few hours a day of heating the rest there is no heat.
I just took a quick look and did a search in that 30 page pdf document and there is no mention of the word vericose or varicose.

Terry Ruth wrote:
From what I gather most of the mat manufactures are running AC so they market no EMF wires. DC has a low static field equal to or lower than the earth they say is not harmful to human body. I'm not sure what happens when you are surrounded by 4 walls with DC? I favor magnesium board and/or foam insulation since is non-magnetic, thermally non-conductive, and the properties much higher than EPS/XPS, Poliso, PU, wood sheathing like OSB and plywood, great for slabs too. I also will keep AC power lines a good 6 feet away from where people sleep.

I'll have some more questions and comments later. So many choices.

Yes is normal that most use AC because that is available for grid tie connections. DC has no EMF.
The heating is in the floor not walls in may case but I'm sure walls will be no problem also.
I have no AC lines the inverter is connected 1 feet away from the AC outlet in the kitchen and that has power only when is in use maybe one hour a day at most not that I have any concern with AC is because is more efficient to run my electronics directly from low voltage DC.
Are you referring to magnesium oxide boards. Those seems more as a replacement to gypsum panel boards. And when you say foam insulation what is that exactly ?
From my research EPS is the best thermal insulation from thermal insulation point of view durability and health (the only down side is that is not biodegradable but I do not care as much about that the house is designed for 100+ years by that time this will not be an issue humans as we know them will be extinct or irrelevant).

Yes I did those calcs too back in Aerospace Engineering school. I graduated back in 1984. I went to Northrop University in Inglewood, CA that had a muti-cultural class body. The Romanians were there, very nice culture and I have some friends that are Romanian. The more wealthy cultures came there because we are a top nation in Aerospace and Aircraft. Since then I have designed many top military and commercial aircraft. As a "Design--Build" Engineer my focus is creative new tech design that can be manufactured at low cost. Companies with lot of $ have MANY engineers, teams, Aero, Thermo, Fluds, EE, Electronics, etc...that supported and review my designs, I did not so I did not use the math. I also focused on Modeling using AutoCad and CATIA is very expensive used the most these days. It also has CFD we get flux loads then import them to FEM then back to the Design model. So I am not that good with the math and Science as I am design-build. I know what to look for and when to get professional help. I have only looked at Construction industry for about two years. Of course I pick it up fast, lots of parallels in technology but quit a mess in the mainstream tech. So I really enjoy talking to Engineers such as yourself with expertise in EE. I think this industry needs more and people without the knowledge need to seek help. In natural building it is more Chemistry and Stuctures in rural areas without building codes, that is the issue, a lack of knowledge. I have learned more about it reaching out to Chemist than my entire 30 year career in Aerospace. Still learning. Now human Factors we call it is Aircraft it has expert Engineers for the cockpit, etc...is another highly misunderstood I see. Now one discusses rarely yet we spend a lot of time in building's that need to be design to us, not as building put people. ASHREA and HealthyHeating is the best I found so far on the subject. I was lead to it by a book I read Breathable Walls. Authors are a Chemist with a MS, Biologist with a BS, Industrialist with a BS named George Swanson that has as much experience in building homes as I do in aerospace. I will see him soon since he has a lot of experience around the world including visits to China, Europe including Germany where the data is concerning vericose disease in his book. I don't need the data, again it makes sense to distribute heat evenly to the body that is what I will design to.

Walls may make better sense for your design since you can shut down adjacent walls and still have the other two for even distribution. If you shut down a section of floor say in a living room you may get hot and cold spots unless you place and space the wires to minimize it. If I understand your intent to put more loops in more square meters to take down resistance and optimize max power point the walls would give more surface area. I'm sure you will figure out what is best and I wish you all the luck, good job! I hope we can to all AC homes, not inverters just AC. I hope the cost of tracking devices comes down to. A single axis may be worth that cost of performance analysis.

When you say Passive House and charts are you referring to PHPP, Passhaus House Power Point? American or German standard? You purchased the Power And are below .6 ACH @ 50 pascal? By blower door test? There is a guy in Germany that build a Passhaus with breathable walls that air exchange, forgot his name. He did with not mechanical ventilation HRV/ERV, just some small exhaust since its design is not effected by pressure drops in the building.

I will add some info on SIPS to my blog soon (this weekend in my signature) about how seams are failing due to not being able to dry and food for fungi trampment. Perhaps another opportunity for you to design and sell a controller that turns on a whole building dehumidifier that is smartly controlled by the relative humidity in the seams or dry them by resistors and RH difference in the building for designs that dry in but can not. You can see such a design in my blog we are doing not where the Architect did not think, dark roof, no seam ventilation but through T&G inward if it can. Polyurethane foam with OSB fungi, rot. Here are some that only last 8-12 years. Now very expensive to tear out a roof. We install standing seams roof at $10/SF, to tear out and replace $20. Since you like foam seams I thought you might be interested. You may want to check that EPS data sheet again for the word "inert" and does not react to any oxidizing found in plastic and concrete you mated it to. If all the materials are not insert and stable, non-reactive, and you did not have a chemist review if the are not, there is a good chance you have fungi food in the assembly. Also, I'm not going to go look for the study since this is obvious. There is one I found in CAN that is tearing out foam, plastic, under slabs that are not suspended with not load to the foam, to find the plastic has torn so some codes are requiring 30 mil min, more use 6. Look at the point load test by dropping at dart and ask yourself if you as an Engineering think that is enough to resist ground pressures from a expansive clays and slap deflections that are much higher 6-10xs) more than foam and plastic can take? Do the math. Think about what a tear can do to a wall when you run a nail through it to hang a picture, what happens to pressure at the tear point relative to pressure accross the inner and outer wall? Does the tear make matters worse? Yes!

Edit: I forgot I put the SIP foam seam failure out here: https://permies.com/t/45572/natural-building/SIPS-Seam-Failures
Seamless monolithic Hempcrete or limecrete roofs that breath in both directions do not have these drying issues or require the indoor humidity to be controlled to keep seam RH or EMC to less than 70% and dry in a 48 hour period to stop mold germination.

There are much better natural mixes with Geo polymers like MGO, hemp, low density fiber boards, membranes that air rate and do not cause mold. Stick around, you will learn a few things. Bill Bradbury restores all natural buildings for a living and J.C. White Cloud has alot of natural Timber experience just don;t get him started on studs or let him see your build Both have alot to offer in all natural building materials, methods, and means. I have learned alot from them, thank you! I agree, the pine inner mass coupled with the concrete should provide decent properties. There is a EMC and other data on my breathable wall thread that explains why. I can think of better wood and slab material but that is another thread. There is a thread on Geopolymers and lots of discussions on natural cements with MGO and lime on the site.

Aircrete makes a MGO insulation that is far superior to many: http://www.airkrete.com/ The gun and tooling up front cost is steep, like $40,000 they can finance. I'm thinking about it I bet I could recoup my investments fast.

Premier is mining MGO in the US and this will continue to drop prices. MGO is not a "subs" for drywall, it replaces it and sheathing with far better properties you can look up. You can purchase a "light burnt" MOC from Premier, add a phosphate or chloride for low cost to spray on walls and put in slabs that neutralizes most materials making them inert and makes a great isolator for dissimilar materials that are reactive. They also offer a shotcrete mix you spray on to biofoam that will outperform any foam wrap or SIP, called Structural Concrete Insulated Panel. There are such products on the Market like GCT using Portland cement but, the MGO is so strong by itself some like Crancrete eliminated the steel mesh reinforcement in some load cases. The building I am designing will have a high content of MGO, I may persue the MGO shotcrete manufacturing especially if a PE determines for my load can no wire corrosive mesh is needed, if so I'll use basalt.

Sorry to take your thread of topic I tired not to but you asked for it and for the spelling and typos, I am not a very good writer.

Terry Ruth wrote: As a "Design--Build" Engineer my focus is creative new tech design that can be manufactured at low cost. Companies with lot of $ have MANY engineers, teams, Aero, Thermo, Fluds, EE, Electronics, etc...that supported and review my designs, I did not so I did not use the math. I also focused on Modeling using AutoCad and CATIA is very expensive used the most these days.

I used to work for a large multinational company with a large team for support so I know what you want to say. I worked as a HW engineer to design airbag control units for cars at Siemens Automotive for about 6 years and we used expensive software tools for simulation and calculations but also less expensive and complex ones to double check the results (that is a requirement in safety electronics). Now I need to do all those things that 10 to 12 people team did for my products and use free open source software tools for design But I enjoy this so I do not complain.

Terry Ruth wrote:
Walls may make better sense for your design since you can shut down adjacent walls and still have the other two for even distribution. If you shut down a section of floor say in a living room you may get hot and cold spots unless you place and space the wires to minimize it. If I understand your intent to put more loops in more square meters to take down resistance and optimize max power point the walls would give more surface area. I'm sure you will figure out what is best and I wish you all the luck, good job! I hope we can to all AC homes, not inverters just AC. I hope the cost of tracking devices comes down to. A single axis may be worth that cost of performance analysis.

The digital MPPT will be more complex than that for now is just in my brain since I just got founding on Kickstarter for the new version of Solar BMS so the Digital MPPT is for much later.
But to answer your question, when I discontent a loop to maintain a max power point that will be done for a few minutes then switch to the other loop to maintain a uniform heating for the entire floor. The software will be more complex than just following max power point will also count the amound of energy delivered to each loop over time and make sure that heating is uniform distributed.

Terry Ruth wrote:
When you say Passive House and charts are you referring to PHPP, Passhaus House Power Point? American or German standard? You purchased the Power And are below .6 ACH @ 50 pascal? By blower door test? There is a guy in Germany that build a Passhaus with breathable walls that air exchange, forgot his name. He did with not mechanical ventilation HRV/ERV, just some small exhaust since its design is not effected by pressure drops in the building.

I was trying to use German passive house standards as a rule in my design but I'm not interested in certifications or any other things like that. It was a guide to check my targets and calculations. I will use a mechanical air to air heat exchanger for now I use the windows for ventilation I just did not had the time to build and install that. Those already made that I found here did not meat my standards. For one they are all with AC power and relatively inefficient motor they are also designed for a much larger house. I have the core heat exchanger and DC brushless fans is just a matter of building a good box that can deal with condensation and did not had the time for that up to this point.

Terry Ruth wrote:
I will add some info on SIPS to my blog soon (this weekend in my signature) about how seams are failing due to not being able to dry and food for fungi trampment. Perhaps another opportunity for you to design and sell a controller that turns on a whole building dehumidifier that is smartly controlled by the relative humidity in the seams or dry them by resistors and RH difference in the building for designs that dry in but can not. You can see such a design in my blog we are doing not where the Architect did not think, dark roof, no seam ventilation but through T&G inward if it can. Polyurethane foam with OSB fungi, rot. Here are some that only last 8-12 years. Now very expensive to tear out a roof. We install standing seams roof at $10/SF, to tear out and replace $20. Since you like foam seams I thought you might be interested. You may want to check that EPS data sheet again for the word "inert" and does not react to any oxidizing found in plastic and concrete you mated it to. If all the materials are not insert and stable, non-reactive, and you did not have a chemist review if the are not, there is a good chance you have fungi food in the assembly. Also, I'm not going to go look for the study since this is obvious. There is one I found in CAN that is tearing out foam, plastic, under slabs that are not suspended with not load to the foam, to find the plastic has torn so some codes are requiring 30 mil min, more use 6. Look at the point load test by dropping at dart and ask yourself if you as an Engineering think that is enough to resist ground pressures from a expansive clays and slap deflections that are much higher 6-10xs) more than foam and plastic can take? Do the math. Think about what a tear can do to a wall when you run a nail through it to hang a picture, what happens to pressure at the tear point relative to pressure accross the inner and outer wall? Does the tear make matters worse? Yes!

Edit: I forgot I put the SIP foam seam failure out here: https://permies.com/t/45572/natural-building/SIPS-Seam-Failures
Seamless monolithic Hempcrete or limecrete roofs that breath in both directions do not have these drying issues or require the indoor humidity to be controlled to keep seam RH or EMC to less than 70% and dry in a 48 hour period to stop mold germination.

There are much better natural mixes with Geo polymers like MGO, hemp, low density fiber boards, membranes that air rate and do not cause mold. Stick around, you will learn a few things. Bill Bradbury restores all natural buildings for a living and J.C. White Cloud has alot of natural Timber experience just don;t get him started on studs or let him see your build Both have alot to offer in all natural building materials, methods, and means. I have learned alot from them, thank you! I agree, the pine inner mass coupled with the concrete should provide decent properties. There is a EMC and other data on my breathable wall thread that explains why. I can think of better wood and slab material but that is another thread. There is a thread on Geopolymers and lots of discussions on natural cements with MGO and lime on the site.

Aircrete makes a MGO insulation that is far superior to many: http://www.airkrete.com/ The gun and tooling up front cost is steep, like $40,000 they can finance. I'm thinking about it I bet I could recoup my investments fast.

Premier is mining MGO in the US and this will continue to drop prices. MGO is not a "subs" for drywall, it replaces it and sheathing with far better properties you can look up. You can purchase a "light burnt" MOC from Premier, add a phosphate or chloride for low cost to spray on walls and put in slabs that neutralizes most materials making them inert and makes a great isolator for dissimilar materials that are reactive. They also offer a shotcrete mix you spray on to biofoam that will outperform any foam wrap or SIP, called Structural Concrete Insulated Panel. There are such products on the Market like GCT using Portland cement but, the MGO is so strong by itself some like Crancrete eliminated the steel mesh reinforcement in some load cases. The building I am designing will have a high content of MGO, I may persue the MGO shotcrete manufacturing especially if a PE determines for my load can no wire corrosive mesh is needed, if so I'll use basalt.

This is the second house that I build the first one was in Romania with totally different construction method more traditional to that place. The first house used reinforced concrete columns and bricks made out of a concrete sponge (aerate concrete blocks) the brand was Ytong that had both some mechanical proprieties and excellent thermal insulation proprieties was light weight and easy to build with.
They looked like this and were easy to build with glued by a very thin layer of special adhesive similar to what is used for ceramic tiles


I needed to build with wood here since this is the material of choice in North America and is easy and inexpensive to get. Even concrete was quite expensive at my location.

Yes those AAC blocks are a good breathable material if you are wanting to go the factory product route. Durisol and Faswall makes the best ICF...the low density clay-wood chip-binder composite has great properties far beyond the EPS used by other ICFs you can see on my thread. The best materials are not at Lowes and Home Depot they have to be shipped in which adds to cost and environmental damage.

Did you do a blower door test? How are you determining your ventilation ACH? ASHREA 62.2? What DC air-to-air heat xchanger and fans do you recommend that are efficient? Can we hook them straight to PV? Yes right? What do you mean by a condensation box. Are you going with an ERV or HRV? Do you have a schematic of the design yet you would like to share? What CFM? Where are you going to run your ducts? Another tuff one. I'm thinking about sizing it and my HVAC after the built and I understand solar passive thermal mass and natural ventilation for at least one season but that probably won't happen the bank will pressure me to get it done and the interest on the construction loan is high. I building commercial to codes, not cheap.

Terry Ruth wrote:Yes those AAC blocks are a good breathable material if you are wanting to go the factory product route. Durisol and Faswall makes the best ICF...the low density clay-wood chip-binder composite has great properties far beyond the EPS used by other ICFs you can see on my thread. The best materials are not at Lowes and Home Depot they have to be shipped in which adds to cost and environmental damage.

Did you do a blower door test? How are you determining your ventilation ACH? ASHREA 62.2? What DC air-to-air heat xchanger and fans do you recommend that are efficient? Can we hook them straight to PV? Yes right? What do you mean by a condensation box. Are you going with an ERV or HRV? Do you have a schematic of the design yet you would like to share? What CFM? Where are you going to run your ducts? Another tuff one. I'm thinking about sizing it and my HVAC after the built and I understand solar passive thermal mass and natural ventilation for at least one season but that probably won't happen the bank will pressure me to get it done and the interest on the construction loan is high. I building commercial to codes, not cheap.

I'm not going to enter in details about thermal isolation but for me EPS was the best choice in my opinion is the perfect thermal insulation a bit expensive compared to many other alternatives but no impact on health since is just plastic with no VOC and the blowing agent is steam so juts air is in those plastic bubbles. Is true that they are not biodegradable but for me personalty that is a plus it means it will not degrade.

My house is well sealed but I did not had the chance to do a blower test nor am I interested in. I will use a HRV since I live in a cold climate the air flow rate will be determined based on a digital CO2 monitor. Based on that value I will create an algorithm to control the amount of air flow needed. Power consumption will be extremely small so I have no worries about that and it will work on 24V DC since the fans are DC brushless extremely efficient and digital speed control and my house is small almost zero ducts.
My house is 65sqm (about 700sqft) single floor and the HRV will be mounted in the middle in my Lab and extract air from there and bathroom this have access to a hall way where one one side is the bedroom and on the other is the living room and air will be pushed in to those you can imagine the air flow in the house as a letter B in the middle air is extracted out and on the two ends fresh air is inserted. so there will be just 3 ducts in total one about 2 feet long pushing air in to living room other also 2 feet long sucking air from bathroom no duct to suck air from lab that is directly where the HRV is and the longest duct will be to bring air to bedroom about 8ft (2.4m) long.
The intake and exhaust ducts are just the thickens of the wall no bends or anything so there will be no air restriction. Everything is designed that way for this house to be used in the most efficient way possible.
I was lucky to use my own money so I di not had to deal with loans and requirements. But on the first house I had to deal with all that not fun.

Dacian.

What DC air-to-air heat xchanger and fans do you recommend that are efficient? Can we hook them straight to PV? Yes right? What do you mean by a condensation box?

Terry Ruth wrote: What DC air-to-air heat xchanger and fans do you recommend that are efficient? Can we hook them straight to PV? Yes right? What do you mean by a condensation box?

Sorry I do not know any DC air to air heat exchanger. I seen one some time ago but was only available in UK do not remember what brand. I will build my own custom one.
You can not hook them one strait to PV since they need to work all the time even when there is no sun and at night so there needs to be a battery.
I have here -40C in the winter and the heat exchange core will freeze do to condensation in the air then when I defrost that I need a way to collect the water. The outside of the box my also condense If is not well sealed and thermally insulated. So I need to be extremely careful on how I design the box so that I do not have water dripping from my heat exchanger.

Ok, thanks! Yeah I read some of the HRV manufactures have defrost in the heat xchanger. If I need one I'll probably just buy, my time is valuable to.

Dacian, I was looking at the PV Watts V1 link you posted, it got replaced in 2014. You can review the changes here: http://pvwatts.nrel.gov/version_5.php

I ran the new one for a lot I am looking at and got this report: http://pvwatts.nrel.gov/pvwatts.php (it won't direct link just pick the "results" tab at top) It accounts for grid incentives if you want, taxes, cost of money @ 7.5% amortized over 25 years in my location, inflation @ 2.5%, etc, you can see in the help section defined. Alot different than V1 KWh/M2/day and Energy value output that has old data: http://rredc.nrel.gov/solar/calculators/pvwatts/version1/US/code/pvwattsv1.cgi

In the "Economic Comparison" at bottom, I'm not cash flowing that well, negative, for pay back period -. 4KW system generates .12 $/kwh, grid cost .10 when I purchase @ "installed" price of 3.30 $/WDC it cost $13,200. That means I need to install lower cost.

That is a quick and dirty look, there is a better calculator here: SAM : https://sam.nrel.gov/

Didn't you say your buying you panels @ .80 $/wdc? Where, what type and manufacturer?

Did you run this new calc to get a full analysis? These panels with crystalline silicon or thin film modules loose around 1% efficiency/year the new calculator includes it and alot more. 14% PV system losses, 96% inverter efficency....There are better ones but cost more.

I did read about hybrids, PV and Solar thermal combo that keep it cooler and extends live. I wonder with your hybrid lines if that would not have been a better choice? Save some ground and roof space too, isn't PV how many more meters required for the same output?

There is no difference between the old PVWatts and the new one. I think the new one is much more confusing to use.
They changed the default derate factor that is why the results are a bit different but you will get the same results if you change that to the same level.
In the old one they used the default tilt same as Latitude and now they default to 20 degree tilt at my location and that will give realy bad performance here especially in winter when I need them the most.
They have now system losses and inverter efficiency instead of de-rate factor.
Default system losses 14% again confusing since they do not explain what that includes last time they mentioned that de-rate factor include battery and that was by far the largest loss for Lead Acid.
This 14% is way to small for Lead Acid but it can not be something else since cable losses are usually around 3%.

I tested my system 0.72kW with the old PV Watts and used 86% DC to AC de-rate factor to get the same 14% system losses and I get the same result almost 1031kWh/year vs 1034kWh/year with the new one the difference is probably related to the last few years of solar data included in the average not significant.
Personally I dislike the look of the new one and most people will do mistakes when using the new one.
For me the most important data was the solar energy I do not care about all the other stuff like derate factors and efficiency since they are just simplifications anyway and do not work in real world.

How did you calculate your return on investment ? What is that 3.30 $/WDC it includes just PV panels or PV panels + mounts and installation ? Are the wires included, Battery ? Inverter ?
On the last calculator they where clear that it was for OffGrid now is not so clear if this can be used for grid tie or offgrid and will get confusing for many.
At 1$/Watt PV panels with 20% degradation over 25 years used at my location have an amortisation cost of around 3 cent/kWh but that is just for PV panels and it assumes you will use all the available energy that is only possible in grid tie connection.
The $0.8/Watt is for Canadian Solar PV panels or similar if you by a large number like 20+ pcs a complete pellet. But I will need that many for my large array for heating.
I paid for mine a few years ago 1.4$/Watt this price including the shipping.

Solar thermal is obsolete in any form more expensive than PV. And those hybrid are even worse. Heat is realy not that big of a problem you have some loss but in offgrid that makes no difference.
Panels are hot in summer when is sunny in the afternoon and then is where you waste most of the energy in OffGrid so it does not mater.

Dacian Todea wrote:There is no difference between the old PVWatts and the new one. I think the new one is much more confusing to use.
They changed the default derate factor that is why the results are a bit different but you will get the same results if you change that to the same level.
In the old one they used the default tilt same as Latitude and now they default to 20 degree tilt at my location and that will give realy bad performance here especially in winter when I need them the most.
They have now system losses and inverter efficiency instead of de-rate factor.
Default system losses 14% again confusing since they do not explain what that includes last time they mentioned that de-rate factor include battery and that was by far the largest loss for Lead Acid.
This 14% is way to small for Lead Acid but it can not be something else since cable losses are usually around 3%.

I tested my system 0.72kW with the old PV Watts and used 86% DC to AC de-rate factor to get the same 14% system losses and I get the same result almost 1031kWh/year vs 1034kWh/year with the new one the difference is probably related to the last few years of solar data included in the average not significant. Personally I dislike the look of the new one and most people will do mistakes when using the new one. For me the most important data was the solar energy I do not care about all the other stuff like derate factors and efficiency since they are just simplifications anyway and do not work in real world.

There is quite a bit of difference between old and new. New gives more control and better financial analysis. See below.

The new one is more enhanced with abilities to change the losses in a calculator attached including wires, resistive, age, shade, snow and soil(dirty) cover etc, for a more accurate reading. You also have the option to change the weather data from TMY 2 1990 default in both to TMY 3 2005 which in your case did not make a difference but could to another reader. Advanced features offer "AC-DC size ratio, Inverter Efficency, Ground Cover Ratio" the old did not have.

I’m getting 1055 year old vs new for your location for the same 14% loss both weather data sources without manipulating the other data you speak of.
http://pvwatts.nrel.gov/pvwatts.php

How did you calculate your return on investment ? What is that 3.30 $/WDC it includes just PV panels or PV panels + mounts and installation ? Are the wires included, Battery ? Inverter ?

You might want to read the help section on the new and you will see it does more than the old. One would have to get an "installed" cost in their area for a proper financial analysis. Unless you are a DIY labor cost is a factor is usually 2/4 higher than parts. I put in a conservative 3.30 $/WDC for you since I know your time is valuable, so is your money that can earn money elsewhere since you are all about comparing investments in your OPs. See attached Economic Comparision. Your systems in negative cash flowing since you can buy @ .09 $/WDC from your grid and your system cost is .18 (double) all things being equal to everyone else in your area and assuming 3.30 $ installed cost amortized per the data in the calculator.

On the last calculator they where clear that it was for OffGrid now is not so clear if this can be used for grid tie or offgrid and will get confusing for many.

Not at all! I think they did a great job explaining if you read it. It is comparing what you can buy from the grid compared to what your system cost installed in your area. You can add tax break and other incentives, they produce and large list of them so you can apply and know about them. You can factor in more complex cost analysis such as time of day and tiered to compare your PV output cost to what you can buy from grid. It assumes all energy is being consumed and AC you can remove if you want. If you are using DC that makes cash flow better. Again, nothing "confusing to most'. The old was misleading. SAM is even more accurate.

Energy value, net-metering policy, and customer use habits

The cost savings are determined as the product of the number of kilowatt hours (kWh) and the cost of electricity per kWh. These cost savings occur if the owner uses all the electricity produced by the PV system, or if the owner has a net-metering agreement with the utility and receives credit at the electricity rate for all of the power generated by the system.
If net-metering isn’t available and the PV system sends surplus electricity to the utility grid, the utility generally buys the electricity from the owner at a lower price than the owner pays the utility for electricity. In this case, the cost savings shown in the table will be higher than the actual savings.

Besides the cost savings shown in the table, other benefits of photovoltaic systems include greater energy independence and a reduction in fossil fuel usage and air pollution. For commercial customers, additional cost savings may come from reducing demand charges. Homeowners can often include the cost of the photovoltaic system in their home mortgage as a way of accommodating the system’s initial cost.

The PVWatts® economics model uses the System Advisor Model (SAM) residential or commercial cash flow model with a flat utility rate. For more detailed financial analysis using complex utility rates, building load profiles, and other financial structures, we recommend using NREL's System Advisor Model (SAM).

Another tool for financial analysis of renewable energy technologies is NREL's CREST model, available as an Excel spreadsheet. CREST does not require installing any software, but does not include a system performance model.

At 1$/Watt PV panels with 20% degradation over 25 years used at my location have an amortisation cost of around 3 cent/kWh but that is just for PV panels and it assumes you will use all the available energy that is only possible in grid tie connection.

Not sure where the 3 cents is coming from, use the calculators for proper cost analysis.

The $0.8/Watt is for Canadian Solar PV panels or similar if you by a large number like 20+ pcs a complete pellet. But I will need that many for my large array for heating. I paid for mine a few years ago 1.4$/Watt this price including the shipping.

http://pvwatts.nrel.gov/pvwatts.php

At .08 $ your positive cash flowing @ 3 cents kwh, not sure what your pay back period is. Saving about $.13/day (grid cost vs PV) on average 4.76 annual production, or $4/month, $48/year very long pay back due to your and my low grid cost. If we had tiers, time of use, high tax, more efficient lower cost PV, single or double axis, better. That does not include incentives. Check my math.

Thats all the time I got today for PV, on to the rest of the design. I'll try SAM tommorow they say it has more accurate cost analysis. PV is not looking like a good investment where there is low grid cost like ours (my state $.97 kwh). Leases and leveled cost of money make it worse.

Got another question for you: I called an HRV the sales guys said they use a transformer to covert AC from wall to DC to run the fan motors, they use plastic core for heat recovery 93% efficient something like that. So could we take the transformer out and hook to PV direct? Avoid the inverter and transformer losses? Save some time $ building DIY?

Terry Ruth wrote:
The new one is more enhanced with abilities to change the losses in a calculator attached including wires, resistive, age, shade, snow and soil(dirty) cover etc, for a more accurate reading. You also have the option to change the weather data from TMY 2 1990 default in both to TMY 3 2005 which in your case did not make a difference but could to another reader. Advanced features offer "AC-DC size ratio, Inverter Efficency, Ground Cover Ratio" the old did not have.

I’m getting 1055 year old vs new for your location for the same 14% loss both weather data sources without manipulating the other data you speak of.
http://pvwatts.nrel.gov/pvwatts.php

First I'm offgrid the largest cost of amortisation is batter even if it is a LiFePO4.
I have no idea how much will have cost to connect my new house to grid but I guess at least $20000 ($5000 is about minimum if you have the electricity in front of your house)
I did all DIY but there is very little time to install maybe two days for my small installation.
My total cost for equipment is
PV panels 3x 240W = 720W each panel is now 200$ so total $600
Solar BMS SBMS4080 $179
Battery 100Ah 24V GBS LiFePO4 $1200
2400W inverter $500 (I got mine used for a bit less $300 if I remember correctly)
DC breakers and cables $120
PV array mount is wood at most $50 cost for material and two hours to assemble.

So total $600 + $179 + $1200 + $500 + $120 + $50 = $2649

For 25 years I will need to replace the battery hopefully just one I will see this spring when I test the capacity loss after 2 years of full offgrid and PV aray mount will also need a replacement all the others should last at least 25 years.
I use in average 80kWh/month so x 12 month x 25 years = 24000kWh

$2649 initial investment + $1200 new battery + $50 new PV mount = $3899

$3899 / 24000kWh = 16 cent / kWh most of this by far is battery.

When I was living in a rented apartment in the city the power consumption was 250kWh/month and bill was $50 so 20cent/kWh (the kWh was less around 11 cent but with all the takes it gets to 20 cent /kWh)

I hope you see I did not needed any PV solar calculator to have precise amortisation cost.

All I need from that calculator is pure solar data for my location I do not care for all effluence and loss since I can calculate that way better.

You can only use all the available solar energy if you are grid tie since you can sell all the excess to the grid in Offgrid you only use a smaller percentage of what can ideally be available since battery has a finite size once that if full the rest is unused.

In the same way I did the above calculation I can get the cost amortisation for solar PV panel.

Say you can by PV panels at $1/Watt (is just a round number I can find now at 80 cent/Watt)

At my location each Watt of solar PV will produce 1.432kWh/year
PV panel at the end of life is usually around 80% of initial so as simplification I will use a 90% average

1.432kWh x 0.9 x 25 years = 32.22kWh
$1 / 32.22kWh = 3.1 cent /kWh the amortisation cost if you can use all the energy available from a solar PV panel and the initial cost is 1$/Watt.


Here are the data from old PV Watts for my location for 720W array mounted at 70 degree tilt and with a de-rate factor of 0.86 that is equivalent with 14% loss in the new one see result 1031kWh/year


City: Regina
Country/Province: SA
Latitude: 50.43° N
Longitude: 104.67° W
Elevation: 577 m
Weather Data: CWEC
PV System Specifications
DC Rating: 0.72 kW
DC to AC Derate Factor: 0.860
AC Rating: 0.62 kW
Array Type: Fixed Tilt
Array Tilt: 70.0°
Array Azimuth: 180.0°
Energy Specifications
Energy Cost: 0.0862 dollars CAN/kWh

Results

Month
Solar Radiation
(kWh/m2/day) AC
Energy
(kWh) Energy
Value
(dollars CAN)
1 4.26 90 7.76
2 5.11 95 8.19
3 4.98 100 8.62
4 5.51 100 8.62
5 4.83 86 7.41
6 4.69 79 6.81
7 5.00 85 7.33
8 5.37 94 8.10
9 4.93 85 7.33
10 4.57 87 7.50
11 3.27 63 5.43
12 3.31 68 5.86
Year 4.65 1031 88.87


Using the new one input same location 0.72kW array and 70 degree tilt the rest is default here is the result the difference from 1031kWh to 1034kWh for the new one is only based on some small changes to PV panels if you look at the first column with kWh/m2/day is exactly the same and that is all I care about the amount of sun I receive.

January 4.26 86 N/A
February 5.11 91 N/A
March 4.98 97 N/A
April 5.51 99 N/A
May 4.83 90 N/A
June 4.69 87 N/A
July 5.00 92 N/A
August 5.37 95 N/A
September4.93 84 N/A
October 4.57 85 N/A
November3.27 62 N/A
December3.31 66 N/A
Annual 4.65 1,034 0


Dacian.

Terry Ruth wrote:Got another question for you: I called an HRV the sales guys said they use a transformer to covert AC from wall to DC to run the fan motors, they use plastic core for heat recovery 93% efficient something like that. So could we take the transformer out and hook to PV direct? Avoid the inverter and transformer losses? Save some time $ building DIY?

Assuming all else can work on DC it should be possible to run that from DC It will depend what DC voltage level they use. The core efficiency will depend on the temperature delta and flow rate and total surface of the core and less about material used to build the core. My core is made of aluminium but wont be much better than plastic.