Peter VanDerWal

pollinator
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since May 28, 2017
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bee bike fish greening the desert solar woodworking
Working on setting up a sustainable household. Currently have a solar array that produces more than we use, an expanding garden, small (3000 gallon) rainwater collection system, L2L system, kitchen rinse sink grey water system. working on shower grey water, expanding rainwater collection and building an aquaponics greenhouse.
Southern Arizona. Zone 8b
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Recent posts by Peter VanDerWal

Joseph Lofthouse wrote:

Creighton Samuiels wrote:I haven't run the numbers, but I would strongly suspect that photovoltic panels have dropped enough in price that it now makes sense to use extra panels to electrically heat water,



Solar electric panels are about 20% or less efficient at converting sunlight to electricity.
Solar thermal panels are about 80% efficient at converting sunlight to heat.
It would be really hard for the solar electric panels to compete in any application that was generating heat.



Thermal panels do not have a fixed efficiency, their efficiency is effected by the temperature differential between input and output, the flow rate, the outdoor temperature, solar insolation, etc.  When it's very cold out, many solar thermal systems don't produce any usable output, however when it's really cold out, PV panels produce MORE output.

However, efficiency is irrelevant to cost.  What matters to most people is the COST of the system.

If you live somewhere it never freeze you could use something like a batch heater which tend to be really cheap.  But folks that live in areas that experience freezing conditions typically use indirect systems with antifreeze, pumps, heat exchangers, etc.  Not only does this reduce the efficiency of the system, it drives up the cost, PLUS they usually require energy to run the pumps.  Even around here folks with these types of systems need a backup water heater for 3-4 weeks a year, when it's too cold to harvest thermal energy. 
The energy needed to run the back up systems and the pumps, is almost the same as I use to run my heat-pump water heater.
So the total cost is thousands more, AND it uses almost the same amount of electricity.
3 hours ago
A couple things to consider:  Solar panels produce more power when they are cold than they do when they're hot. Inverters can also run at over their rated output when cold.  My system will often produce 5% over rated output during the winter and 5% less than rated during the summer.

Heat pumps also work better in heating mode than cooling.  All of the energy used to run the heat pump gets added to their hot side.  This is a bonus during the winter, but a negative during the summer.

If you have a connection to the Natural Gas grid, then that 'might' be cheaper than heating with solar PV, unless you also need cooling during the summer.  If you need cooling, then you already have to buy the equipment (AirConditioning and perhaps PV array) and its silly not to buy something that can also provide free heat.

If you're off grid and have access to lots of free wood, then that is going to be cheaper than a heat-pump...unless you need cooling.  If you need cooling then again you might as well use the heat-pump for heating, and supplement it with wood burning as needed.

If your choice is between heating with propane and heating with PV, PV is almost always going to be the winner (unless you live way up north)

You really need to do an individual analysis for your particular location. 

My point is that solar PV prices have fallen so far recently that the old assumption that you should always use propane, etc. for heating is no longer valid and in most cases these days it's wrong.
PV prices have dropped so far that even using PV to heat water is now cheaper than direct solar water heaters in most areas.
17 hours ago
Check with the fire department.  In a lot of areas they will deliver water to you.

A lot of people haul in water where I live, often 500-1,000 gallons at a time.
1 day ago

Pearl Sutton wrote:
One of the things I want is DIY installation, any idea if this is something I can do? I hate dealing with insatiably techs, they tend to piss me off...



Well, it's definitely doable, I did mine.  Whether  or not you can do it depends on you.

You'll need a good vacuum pump, I spent about $115 on mine(new).  Probably not the pump I'd select if I did this for a living, but for doing 2-3 installs it was more than adequate.
I splurged and bought a micron vacuum gauge,  that cost another $132.  If you want to be absolutely sure you don't have any leaks (or water left in the system) you really need something that can measure down to 100 microns or less.

Typical cheap vacuum gauges have a needle that is almost 1 psi wide(or even wider), there are about 51,715 microns in 1 psi.  So not only can't you tell the difference between 50 microns(great) and 50,000 microns (horrible), but you could be leaking hundreds of microns per hour (that's bad) ,or even thousands, and not be able to tell with a cheap gauge.

Altogether I spent about $350 or so on tools.  Around here the HVAC guys wanted $2,000-$3,000 for installation.  $350 and a few hours work were worth it to me.
1 day ago

Creighton Samuiels wrote:

Peter VanDerWal wrote:
You don't need a huge array if your house is efficient.



Granted, but living in Arizona probably helps in that regard.



Less heat needed, more cooling.   Pick your poison.

Arizona is right at the median (by state) for household energy consumption.
1 day ago
The problem I have with solutions like this is that you are dedicating the entire output of the solar panel to the heat-pump.  If the heat-pump doesn't need the all the energy the panel produces, the rest is wasted.

You can pickup a 9,000 btu Pioneer mini-split heat-pump that runs on 110V for less than $600, and it will produce heat as well as cooling.

You can buy a lot of inverters, batteries, etc. for the $1200 you save over buying the above unit.

9,000 btus is more than enough for a tiny house.  If you have a larger house they are available in larger sizes.  I use the 12,000 btu unit in my 1500 sq ft house.
2 days ago
Dry soil is a moderately good insulator.  If you can bury the pipe 0.5 - 1 meter down, that would help.  To make sure the soil stays dry you can install an 'umbrella'  above it, basically bury a sheet of plastic just below the surface (and above the pipe) that slopes away from the pipe, so any water in the soil will be directed away from the pipe and the soil under the plastic sheet will stay dry.

As for the pipe in a pipe idea, you can build that yourself.  Just run the hot water pipe through a larger pipe, like a plastic drain pipe.  The outer pipe doesn't have to be anything special, even some used pipe will work. Every 2-3 meters add some kind of support(wooden bushing, etc.) to keep the internal pipe in the middle of the external pipe.  The air space between the two pipes will work as an insulator.  If you have access to cheap perlite or even some used Styrofoam, you could use that as both an insulator and a support for the internal pipe.

Be aware that if there is any chance that outside air will get into the outer pipe, then eventually you'll end up with condensation (water) inside the pipe and water is a poor insulator.  So you'll want to add some weep holes to the bottom of the external pipe to let the water drain out. 
2 days ago

Mick Fisch wrote:making corn into ethanol is also a bad use of land.  When they started doing it all the food prices took a pretty hefty jump as I recall.  You just can't get enough alcohol out of an acre of corn to be worth it.  If later, we can get the conversion rate improved a 1000% or so, then maybe.



It's worse than that.  Growing ethanol uses petroleum (diesel fuel for the tractors, fertilizer made from petroleum, diesel fuel to haul the corn to the distillery, energy to convert the corn to ethanol, etc.)  when you add everything up, the amount of petroleum used to grow/make the ethanol is equal to the amount of petroleum saved by using the ethanol instead of petroleum.

So not only do you not save any petroleum, you end up producing MORE pollution in the process than you would if you'd just stick to using petroleum.

It's a stupid idea squared.
2 days ago
A large thermal store could be useful during the winter, but not so useful the rest of the year.  Batteries are useful all year round.

Plus a large, well insulated, holding tank is not going to be cheap.  Batteries might actually be cheaper.

Something else to think about, as your thermal store starts cooling off, it becomes more and more difficult to extract energy from it.  With Lithium type batteries the energy output is pretty flat until close to the end.

Adding a heat-pump to the battery system can further improve its advantages.  With the right pump you can get heating AND cooling, either way they tend to have a COP of 3-4, which means you get 3-4 kwh of heat/cooling for every 1kwh of electricity.

FWIW I did a lot of research into thermal storage systems, including phase change systems that fix some of the issues with using something like water.  After crunching all the numbers I decided it was much cheaper just to use a mini-split heat pump and electricity.  With a well insulated house you can get by with a surprisingly small heat-pump.  I use a 12,000 btu unit to heat/cool my 1500 sq ft house.
3 days ago
I heat, cool, and cook with electricity, its the ONLY energy source for my house. 

My grid tied array is rated at 2850 watts (AC), although it rarely produces that much.   Before I bought the Chevy Volt we produced about 1.8-2 MWh a year surplus. 
We bought the volt a little over a year ago and in the year since we bought it we went slightly(~250kwh)  in the hole, so I'm going to be adding another panel.
When we go off grid I'll probably add another 4-5 panels.

FWIW the Chevy Volt accounts for ~30% of our electricity use over the last year.  It will be going up quite a bit this year because my Grand daughter is living with us and we have to drive her to school right now, that is about 45 miles a day, once she gets her driver's license that will go down.

You don't need a huge array if your house is efficient.
3 days ago