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Chris Olson
Posts: 84
Location: Northern Wisconsin
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One of the folks on the forum asked me if I could post about our off-grid power system. I don't really know what section of the forum to put it in. So I put it here in the solar part, as most people who attempt a move to off-grid will face the challenge of producing enough power for their home to make it livable, and solar energy will more than likely be the prime power source. If it is not the correct place to put it, admins please move it to a more appropriate section of the forum.

I don't know all what to tell about our system except an overview. If folks have specific questions then I could probably expand on that topic. So to keep the post reasonably short, my wife and I have lived off-grid here for over 12 years. We generate all our own power, grow all our own food, heat our house with wood harvested from our property, and we have an apple orchard that we harvest apples from to sell to other folks, as well as honey bees. Our power consumption is about 12-15 kWh/day in summer and 20-25 kWh/day in winter. Sometimes more. Never less. Our power system is not as large as some, but considerably larger than most.

Our home is totally electric. We do not use propane as my wife will not allow a propane tank on the property. We have all the things that anybody on grid power would have including electric water heating, electric high-efficiency range with induction cooktop and convection oven, clothes washer and electric dryer, large screen HDTV in our living room, air conditioning in our house, etc.. In addition I have a small machine shop - also powered by our off-grid system.

We have solar arrays pointing in three directions - east, south and west. This provides us with a "flatter" power curve thru the day without using any moving parts on trackers. We also have wind power and our turbines are quite large machines - they are not little pinwheels 40 feet off the ground on a piece of pipe. Our power system itself is a Schneider Electric Conext/Xantrex XW system. We have diesel prime power and gasoline standby generators. The standby generator is automatic start/stop, controlled by our XW Power System.

Here is a few photos of the highlights. This first photo is a current take of our utility/battery room. There is some wires there hanging out in the open between a DC disconnect and the XW controller, and that is temporary as I am waiting for another new XW-MPPT60 150V solar controller that will be installed there.



This is a photo of two of our solar arrays - total 3.0 kW in this photo:



This is one of our wind turbines on its tower - this is a 3.5 meter 2.7 kW machine:



This is me standing by one of our other wind turbines with the tower laid down to service the turbine (at night in the winter time) - this is a 4.0 meter 3.0 kW machine:



This is a photo of the inside of our powerhouse where the generators are. This is a sound attenuated building so we cannot hear the the generators running when either one is going:



And this is a photo of our kitchen - it is a totally modern kitchen with all-electric appliances, except my wife does not like dish washing machines (she doesn't like the way they smell inside) so we don't have one of those.



And the System Control Panel for our XW Power System is also on the wall in the kitchen, which is the highest power draw area of our home, so the loads on the inverter and generators can be easily monitored when my wife is drawing a lot of power in the kitchen



That's kind of a "walk thru" of it. If folks have any specific questions I can attempt to answer them.
--
Chris
 
Marcos Buenijo
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Posts: 583
Location: Southwest U.S.
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Hi Chris. Thanks for the post. These forums are long on theoretical and short on experience (myself included). Your off grid experience is most appreciated.

I have all kinds of questions, but I don't want to overwhelm you. I am most curious in particular with real world figures and how they compare with a theoretical analysis. For example, I understand from another post that you have 6 KW rated solar PV at the moment. However, you state here that you consume 12-15 KWh of electricity each day during the summer. This seems quite low by most "theoretical" accounts, but then again most accounts consider a grid tied solar system. Perhaps you can confirm or correct the following line of thought: The way I see it, it's not practical to store and/or use all the production from a large solar array in the off grid setting. Let's say the array sees a solar flux that will permit a 5 KW output. The battery charge rate is limited by the controller ratings and battery state of charge, so if the home is not consuming electricity at a very high rate, then a lot of the potential production from the array may not be seen. There is also the problem of battery charging being extremely inefficient when at a high state of charge. Well, this is kind of a catch 22 in the off grid setting since one desires a large battery to carry the system through inclimate weather and protect against excessive battery discharge which likes to kill batteries. Grid tied solar PV systems get around this entirely by using the solar array production real time. So it seems the only way to pull this off in the off grid setting is to have a way to put most of the production to use while the panels are producing. Do you try to do this? For example, it seems prudent to run large loads like a/c and water heating when the solar array is generating and leave any excess production for battery charging at lower rates to minimize losses there. This might be done during winter months by using any excess production during the day in electric space heaters. It seems there are many possible ways to optimize production from an off grid solar array, but it seems a practical solution can be had by simply using a really large array. Was this your thinking as well (that is, don't overthink it - just get lots of panels and a big battery)?

I have a particular interest in a/c as I will likely settle in a hot and humid climate, but it seems you have little need for it in Wisconsin. What kind of electricity consumption per day do you see during very hot days when a/c is used?

Also, I understand your space heating during winter is done primarily with a wood furnace. What kind of wood consumption do you see during winter months?
 
Chris Olson
Posts: 84
Location: Northern Wisconsin
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Marcos Buenijo wrote:Perhaps you can confirm or correct the following line of thought: The way I see it, it's not practical to store and/or use all the production from a large solar array in the off grid setting.


Hi Marcos, and the above quote is basically correct. We size our stuff here for winter. In the summer we "waste" it for the most part. During the month of July when we had our A/C going in the house we consumed roughly 50-60 kWh/day - a 2-ton A/C unit can consume 70 kWh/day all by itself if the compressor runs around the clock. So even our over-capacity on solar power cannot run the A/C 24 hours per day. We use diesel prime power being fed into the inverter, with the inverter operating in Generator Support Mode, roughly 12 hours a day when the A/C is running.

In the winter, from December to end of January here, a 6.0 kW array will only produce 9-10 kWh/day. So we don't have enough solar power for winter to even cover 50% of our loads. In the summer that same solar array will produce about 25-30 kWh/day if it could run wide open all day. So you need to arrive at a reasonable balance between what you can get by with in winter when you add in other power sources like wind, hydro or generator, compared to what you feel you can "waste" in the summer. There is no sense to trying to optimize output of your equipment year 'round for off-grid - you have to size everything for the poorest times of the year. If you don't, you will not last long in your off-grid adventure.

There are advanced ways to manage generator power, using the generator for peak and prime loads to reduce the load on the RE system, that extends the capability of your RE system during poor RE production. Using these advanced generator management methods yields higher kWh/gallon of fuel burned than the simple traditional way of running batteries down and using generator to charge batteries. The simple way is the only way most people know. So this is a whole different topic. But the generator is either an integral part of your off-grid system, or you will again not last long in your off-grid adventure. How you manage it determines how expensive, or how frugal, your off-grid lifestyle will be.


Also, I understand your space heating during winter is done primarily with a wood furnace. What kind of wood consumption do you see during winter months?


We typically burn 18 face cord here in the house in winter and another 10-12 face cord in the shop - all seasoned red oak, elm, maple or birch. Our house is 2,000 sq ft.
--
Chris
 
Linda Potter
Posts: 31
Location: In the Sierra de Bazas, Andalucia, Spain
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Hi Chris ! We have a VERY small solar system with a pin wheel. We live about 2500 ft up in a semi arid area of Andalucia, Spain. We are self taught mostly as finding people with experience is proving difficult. Our batteries keep dying on us and we will be re-investing in new ones in the next few months. We are obviously using more than the system is generating and storing, so we will be buying more solar panels as we can afford them. One question, is it better we buy a battery with a large capacity and keep it topped up. Or should the battery be small because our input is small ? Hope this makes sense. Thanks, Linda
 
thomas rubino
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Location: latitude 47 N.W. montana zone 6A
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HI linda; I'm sure that chris will respond to this ,but I thought i would give my input also. You don't say how small your system is or if you have alternet power sourse (generator-alternater) to help charge your battery. But battery heart ofyour system, think of it as a big tank of water, the more you have the longer you can get water from it. That said invest,in better batterys and find a way to help keep them charged when the solar is not enough.Could be as simple as using a vehical with jumper cables or a fuel powered generater. Or use a bicycle to spin an alternater if need be. Remember you can ruin a big set of batterys as easy as a small one by running them to long in a discharged state. You must find a way to help your solar panel keep your battery up or use less power untill you can afford more panels. Find a way to moniter your batterys state of charge, invest in a hydrometer to check the specific gravity of your battery (this is the best way) or at the very least moniter your battery voltage and stop using power when it falls below 12 vt (that is the poorest way) If you don't take care of your battery you will never be happy off grid. I have lived offgrid for over 30 years now and i learned the hard way about TAKING CARE OF MY BATTERYS!!! My system is solar and micro hydro and no where near as large or nice as chris has but it has supplied me with all my power needs. I have a remote start genset for when we are using more power than the system is making, and i use a (trimetric meter) to moniter my battery state of charge. I started with one 2.2 amp solar panel with a wire run thru a window and cliped onto a car battery and i have learned and grown since then. Good Luck , Ask Questions, Keep Learning, Never Give UP Tom
 
Linda Potter
Posts: 31
Location: In the Sierra de Bazas, Andalucia, Spain
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Wow, thanks Tom. Our system is tiny. We have.a 160 watt solar panel and a 200 watt wind generator which mostly works the 12 v lights. Then we have a 250 watt 24 v panel for small things like charging our laptop, running and old fashioned washing machine. And a small generator for the vacuum cleaner and other short, high power needs. We have a small fridge which I can't use at the moment, we heat with two wood stoves and a/c is unnecessary as it is a converted cave dwelling. I was thinking about how to test the batteries properly with a hygrometer... working with acid is definitely scarey. Aren't most leisure batteries sealed nowadays ? The ones we have at the moment are. What kind of batteries would you need to get ? Thanks again.... i have sooooooooo many questions !
 
Marcos Buenijo
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Location: Southwest U.S.
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Linda Potter wrote:Hi Chris ! We have a VERY small solar system with a pin wheel. We live about 2500 ft up in a semi arid area of Andalucia, Spain. We are self taught mostly as finding people with experience is proving difficult. Our batteries keep dying on us and we will be re-investing in new ones in the next few months. We are obviously using more than the system is generating and storing, so we will be buying more solar panels as we can afford them. One question, is it better we buy a battery with a large capacity and keep it topped up. Or should the battery be small because our input is small ? Hope this makes sense. Thanks, Linda


Addressing this question is straightforward. The battery must be sized to minimize or eliminate the incidence of significant battery discharge. The single most important consideration in sizing a battery is the average daily electricity consumption. Next, one must consider the average daily production from the solar/wind system. If production is highly variable, then this justifies the use of a larger battery to supply the balance of energy required during days with low production. A battery (even one designed for "deep cycle" use) should not be discharged below 50% state of charge. This is problematic for a couple of reasons. One reason not generally understood is that the efficiency in charging a battery is very low while the battery is at a relatively high state of charge. So, maintaining a battery at a relatively high state of charge necessitates a relatively low efficiency in battery charging. This dynamic is responsible for many people undersizing a solar array. The only way to mitigate this in the off grid setting is to make use of as much electricity as possible while the solar/wind system is producing as this will reduce the effective battery charge rate. However, this is often not a practical solution. The best way to protect a battery from significant discharge is to use a large solar array along with a large battery.

Note that excessive discharge of a battery is the number one killer along with not keeping water level. Also, a battery should not remain in a partially discharged state for long, and the lower the state of charge the less time the battery should remain there. Generally, a battery should be fully charged at least weekly, and should never be allowed to drop below 50% state of charge (only an emergency situation should permit this). Poor temperature control is often a factor. Over charging is another killer, but this is less often seen with the use of modern charge controllers.

If you discuss your system in more detail (including the loads), then there are those among us who could recommend specific advice. I suspect that a combination of enlarging your solar array significantly while reducing the discharge on the battery during evenings will be a solution (eliminating phantom loads, curtailing bad habits, use of a thermal mass in freezer/refrigerator)... or, you might also need to upgrade to a larger battery system.
 
thomas rubino
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Location: latitude 47 N.W. montana zone 6A
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Hi linda; I recomend a deep cycle battery , Trojan L-16 6 volt batterys are the industry standard . Yes , alot of (leisure) batterys are sealed. They are a poor choice for off grid. You need a battey that you can moniter the eletrolite (water) level in. If your finances are low then buying 2 6 volt L-16 batterys is probly out of the question at this time but... save your pennys to upgrade at a later time. Till then you need a 12vt deep cycle battery that has removable caps to check your specific gravity and water level. Yes battery acid is corrosive and it will at the very least make your clothing look very (holey) after you wash them. Wash your hands or use gloves when dealing with electrolite, never touch your clothes. always use distilled water when adding to your batterys. I have never had a burn from electrolite but I have ruined alot of pants by letting them touch a battery. Tom
 
thomas rubino
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Posts: 883
Location: latitude 47 N.W. montana zone 6A
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Hi Linda ; I just read marcos response and he is quite rite in all he says. I also relized that you are using a 24 vt system not a 12 vt. You make no mention of an inverter? Do you use one ? Any of the better ones have a battery charger built in that will charge your batterys while your generater is running all the loads. Look at outback or magnum energy inverters to learn what they are capable of. On another subject, you mention that you use wood heat, I do also and I recently learned about rocket mass heaters, They are realy neat! Look them up here in permies, i am building mine now. Tom
 
Chris Olson
Posts: 84
Location: Northern Wisconsin
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Linda Potter wrote:We are obviously using more than the system is generating and storing, so we will be buying more solar panels as we can afford them. One question, is it better we buy a battery with a large capacity and keep it topped up. Or should the battery be small because our input is small ? Hope this makes sense. Thanks, Linda


Hi Linda,

Sizing the battery to loads and having adequate power to charge it can be a juggling act. You will typically want enough battery capacity to carry normal loads for 24 hours with no incoming power. But your charging capacity has to be minimum C/10 (amp-hours divided by 10) + what it takes to run your loads during charging.

Example, say you have 1,000 amp-hours of battery capacity @ 24V and your normal average loads are 200 watts. Then you need 100 amps of charging capacity (C/10) plus an additional 200 watts to run loads while the battery is charging. So at 24V nominal you need 2,600 watts to charge the battery in this example at the proper rate to get the job done, plus carry loads.

The reason you need C/10 charge rate, minimum, is because of the time you have in a normal "good" day to get your battery charged before you run out of solar power and can't get the job done. Lead sulfate collects on the plates during normal discharge and the electrolyte in the cells loses density, or specific gravity, as they discharge. Charging the battery reverses that process, returning sulfate on the plates back into solution in the electrolyte and cause SG (Specific Gravity) in the cells to rise as the electrolyte becomes more dense. If you don't fully charge the battery some of the sulfate remains on the plates. This is called deficit charging and it is the most common cause of early battery failure. The sulfate, if it not returned into solution at least once a month, hardens into crystal like formations on the plates. Once that stage is reached, the battery has lost capacity and the sulfate can never be returned into solution. A corrective equalization can remove it, causing it to fall off the plates and into the battery's sump. This will regain some of the lost capacity of the battery, but it will never be the same and is well on its way to early death.

Buying the most expensive and best batteries on earth will not prevent early failure from chronic deficit charging. So charge rate is extremely important to properly de-sulfating and charging your battery for best life. I always tell people that are first time off-gridders to buy cheap batteries like Trojan T-105's or L-16's the first time around to gain plenty of experience on how to wreck batteries before spending money on premium batteries. The absolute best batteries for off-grid are Crown or GB industrial forklift or traction batteries. They are designed to be discharged to 20% SOC for usually over 1,700 cycles. The downside to these batteries is that they are heavy. A small forklift battery is probably 700-1,000 lbs. Large 48V forklift batteries are going to weigh up to 2 tons. We have Rolls-Surrette industrial traction batteries and our battery bank weighs over 4 tons. So it is no simple or easy task to even install industrial batteries in the typical off-grid utility or battery room.

The lower end deep cycles like L-16's or T-105's are what most people use because a human can actually move one without having to have heavy equipment on-site to get your battery bank in place. If you take care of them and charge them properly they will typically last 5-7 years. The premium industrial batteries typically last 12-15 years. When you factor in the higher up-front cost of the premium industrial-type batteries, they will cost you about 75%/kWh over the long term as compared to the cheaper L-16 or T-105 golf cart type.

Hope this helps.
--
Chris
 
Linda Potter
Posts: 31
Location: In the Sierra de Bazas, Andalucia, Spain
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Thank you very much Tom, Marcos and Chris. A lot of food for thought in each of your answers. I will need some time to digest it properly.

My last question, for the time being, I would like to know how to roughly calculate just how big an array and battery capacity we need. We really are very low tech. The only things running consistently, throughout the day, would be the 12v lights (2 amps in the evening, in the winter), a small fridge (300w), a laptop (200w), mobile phones charging, and a 180 watt dehumidifier. Other than that we have a low energy washing machine (350w - runs 30 mins/week), some kitchen appliances (nothing greater than 300w - runs 10 mins/week), power tools of my husbands (up to 800w- runs 1 hour/week) - his bigger tools and my vacuum (1400w) run off the generator at the moment, but it would be great to have these work on solar as well. We have kept our energy needs really low I think, which is why I'm so disappointed we haven't been able to get it to work . Bonus. We are in Spain. The sun does shine quite a lot here!

Thanks again for all your great advice, Tom, Marcos and Chris.
 
Chris Olson
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Location: Northern Wisconsin
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Linda Potter wrote:
My last question, for the time being, I would like to know how to roughly calculate just how big an array and battery capacity we need.


Hi Linda,

I added up the loads you listed, estimating hours of operation for the lights, fridge compressor run time**, etc.. I came up with about 44 kWh/week, or roughly 6.3 kWh/day. You would need 12 kW of battery capacity for 24 hours (from fully charged to 50% SOC), which at 12V nominal is 1,000 amp-hours and at 24V nominal is 500 amp-hours.

With either voltage system (either 12 or 24V) you need 1,200 watts of charging capacity. Plus thrown in a little extra to carry normal daytime loads while the batteries are in bulk and the early absorb stage. The battery charging requirement will drop after the internal resistance in the batteries start to come up during absorb.

The thing with solar panels is that 1,200 watts is not really 1,200 watts. They'll make that under perfect test conditions in perfect sun at 25C. But more typically you'll get 80% of their nameplate rating on the "perfect" day and only see nameplate output when you either get cloud edge effect or the exceptionally clear, cold day. So 1,200 watts of required charging capacity really turns into 1,500 watts of actual installed solar capacity.

**300 watts for a small fridge? We have a large 'fridge and it only draws 185. It pulls about 500 watts when the auto-defrost heater is going in it. But otherwise it does not pull anywhere close to 300 watts in normal operation.
--
Chris
 
Linda Potter
Posts: 31
Location: In the Sierra de Bazas, Andalucia, Spain
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Thanks again ! I'll double check on the fridge. It doesn't sound right does it ? This is really helpful and my hubby and I will be using it to see what we can afford and what we get first. It really is a steep learning curve, isn't it ! Abrazos ! Linda
 
Marcos Buenijo
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Linda Potter wrote:Thanks again ! I'll double check on the fridge. It doesn't sound right does it ? This is really helpful and my hubby and I will be using it to see what we can afford and what we get first. It really is a steep learning curve, isn't it ! Abrazos ! Linda


A small modern refrigerator should consume less than one KWh of electricity per day. Check the laptop also. My laptop draws less than 50 watts at all times, and virtually nothing in sleep mode. Consider getting a kill-a-watt meter to verify these things. This little meter is very useful.

As far as how to determine the size of the solar array and battery system you require, the first step entails knowing how much electricity you actually consume on a daily basis. Note the difference between watts and watt hours (the former is a measure of the rate of energy use - also known as "power", and the latter is a measure of energy... you want to know the energy). For example, your 180 watt dehumidifier consumes 180 watt hours (or 0.18 KWh) of electricity during one hour. It consumes twice this amount of energy in two hours, and 24 times this amount of energy when operating all day nonstop. However, it always consumes this electricity at a RATE of 180 watts. The meter will be very valuable here. You can connect the meter to your refrigerator, and it will compute the total energy consumed over a 24 hour period while also providing an indication of the real time power consumption... not bad for $20.

Next, you have to consider the average solar insolation at your location. After this it's a matter of estimating the production from the solar panels based on their efficiency and position, then knowing the losses involved which are generally quite high in off grid installations. A conservative estimate for an off grid installation is to use a derate factor of 0.5. Use solar insolation maps to find the number of sun hours your location sees during an average day. I recommend you try PV Watts Calculator here http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/ to estimate the size of the array you require. You can select from among four different cities in Spain, so choose the one closest to you. Also, make sure to change the derate factor from 0.77 to 0.5. You can also change the array tilt angle on the program, but you may wish to do so since it provides the optimal angle for production during winter months by default. Once you figure how many panels you need, then you can decide how many days of storage capacity you desire. However, this can further complicate things since a much larger battery might require a slightly lower derate factor. Personally, I recommend that you get a battery large enough to provide a full 24 hours of electricity (assuming zero charging) without dropping below 50% state of charge, then keep a small generator around for charging the battery on those rare occasions when it's truly necessary. Also, one extra panel is better than one too few.

NOTE: Think of a battery as a water tank, and think of the solar panels as a rain catchment system. When drawing water from the system the water comes from the tank and/or the rain catchment system. Likewise, the electricity from an off grid solar power system comes from the battery and/or the solar panels. There are losses in batteries (you don't get back everything that goes in), and this might be considered as leakage in the water tank. You can avoid a lot of this "leakage" if you use more electricity from a solar array while it's producing. As long as the solar array is providing electricity at a rate greater than what the home consumes, then the electricity consumed by the home is not coming from the battery... therefore, a lot of battery losses can be avoided. For this reason it's more efficient to use as much electricity as you can while the solar array is producing. You might do this by putting your dehumidifier on a timer so that it operates only during the day when the solar panels are producing. A refrigerator might also be modified by adding a thermal mass along with a timer. Strategies like this have been used to both increase overall efficiency from a solar system while also significantly reducing battery discharge and even allowing for the use of a smaller battery system.

 
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