Here is the house we have built. It is not finished, but we moved in mid October 2017 about 3 years after putting the footings down, 5 years after starting a shop and ten years after buying the property. The details will never be in a blog, but it is as promised. Off grid and rain water supplied, with a Trombe wall for solar heating and a grey water recirc system for flushing the toilet. I am willing to share details with those seriously interested, but not willing to show the whole world or extend an open invitation to the curious. The fifth wheel is abandoned out in back and will be for sale come spring if anybody wants a 20 year old one that is really only suitable for use as a cabin or temporary housing while building. I wonder if HandyBob’s trailer is a collector’s item worth a lot of money?
The first thing I have to say is that rules of thumb don’t work. The most common and often repeated misinformation is that you can size your solar array based on what batteries you have or the other way around. This goes back years and years to when people trying to make solar power work started by adding batteries to systems that didn’t have the ability to charge them. Yes, there are some minimums and maximums that need to be followed, but even there you will find a lot of bad info on the internet. If you want your power system to work, it has to be designed around use of energy, not guesses, and that means metering your use. Unfortunately, this isn’t as easy as it needs to be, especially for those who are trying to design in advance of building, so people keep asking all sorts of questions that I tell them nobody can answer. Solar panels can power anything from little campers all the way up to huge hunting lodges and everything in between, so this is definitely not a “one size fits all” world. Now that I have built our off grid home , plus repaired and built systems for a few others, after spending MANY years off grid in an RV, I do have a bit of experience with this problem. Therefore, I am going to try to shed some light on the subject. I will try to give some insight based on my experience. Here I will admit something that is not said anywhere else in my blog… I did not just install or repair a few systems over the years. I supported us doing so for a few years. My records show that I bought and resold well over 50 Trimetrics and that was after I had figured out how important metering was, a few years in. So, based on helping many people and living the life for years, here goes…
This is not written for the newbie who knows nothing about the subject. You need to already know amps, volts, watts, amp hours, C20, SOC, DOD, etc. I cannot repeat and repeat and you can Google these things. Reading my RV Battery Charging Puzzle will help.
Campers: A small camper that is used on weekends or the occasional vacation trip is not the same thing as a full time RV or a house. Remember that you can let the batteries catch up after a camping trip if you put the panels on the roof where they should be. We used to go camping for 3 day holidays with no solar and no generator, so you don’t need to be charged every day. Portable panels may be fine for some, but a panel that is stored will not charge and it is a bit difficult to arrive at camp with charged batteries if your panel is not connected. Many just want to run lights, water pump, the control circuit for the propane fridge (about half an amp 24 hours per day), charge the cell phone, maybe a bit of TV or stereo. This adds up to maybe 15 amp hours per day now that we have LED lights. One single 100W panel flat on the roof will work for most, IF they don’t run the furnace fan or expect to use any heat producing appliances. I won’t talk about charge controllers since I have covered them before. Simply put, buy a Morningstar Sunsaver without load control (LVD) or spring for the Trimetric TM2030 and SC2030 pair and don’t ask me about all of the bad crap you can find really, really cheap. Most of them don’t work for anything other than a maintenance float charge on batteries that were already full. If that was what you wanted, you would not be here. If designing for summer camping only, you can ignore all of my comments about short charging days and tilting panels. Again, that is not the same as full time living on solar power.
For the rest of the world, those who want to live on solar provided electricity every day, things are more complicated. First you need to size your solar array based on what you will really use in 24 hours and then size your batteries based on how much back up you need. Get this in the proper order. Whether you tilt or not has to be included in sizing the array. It used to be that tilting was not optional when panels were costing $5 per watt. It simply had to be done unless you were made of money. Now, at a buck a watt and less, figuring that you need about 60% more panels on short winter days than the panel rating would have you believe, it makes sense to mount them flat on the roof of an RV or on a south facing slope of a home if not in snow country. Guessing here can either leave you short or have you spending way more than you needed to, but oversizing is needed if you want to live without running a generator every cloudy day. Once I figured out how to make it work (The RV Battery Charging Puzzle) my RV system early on had the capability of providing over double the 75 to 100 amp hours we used most days. It turned out to be a very good place to start, giving us the power needed to recover from 3 or 4 cloudy days when camped out in the desert. We really tilted only so I could run tools. The one time we spent a week sitting in a park while waiting for the truck transmission to be fixed, we were parked the wrong way so we couldn’t tilt and we still didn’t plug in while watching old movies on the park’s cable TV all day long in our boredom. I had customers who were happy with only 300W or so, but most full time RV couples will not be successful with anything less than 600W of solar panels flat on their roofs. People are all different and most motor homes need more. We have friends who have systems up to 1000W, but all who try to power electric refrigeration or other big loads end up having problems. They spend and spend, but a couple of cloudy days is their undoing. There are solar dealers who will be happy to sell you huge systems that won’t work. Go see them; don’t bother me.
Of course you should tilt the panels for maximum power on home systems and that means 15 degrees higher than latitude in winter, 15 degrees lower in summer. In summer you can leave them up high and the longer daylight hours will make up for not optimizing tilt. Up here in the great white north, mine are even higher so they will shed some of the snow that falls on them. Mine are at 80 degrees, at 45 degrees latitude and I leave them there all year long. My system is only 2000W and no solar dealer I ever talked to thought it would work. Our daily use is around 2KW minimum and we do things like laundry only when the sun shines, so I don’t include it. The 2000W of panels on our roof can give us 5KW on a sunny late December day and most days we are floating by 1PM, so guess what? We have about double what we need if the sun were bright every winter day.
Batteries are the next issue. You will have somebody tell you to size the batteries for 24hr of use, times the days you want to be able to go. Baloney… Even on cloudy days we get something from the sun. When the above pic was taken we were getting about 300W and that comes very close to keeping up with the basic necessities. In some climates it can be very little, but it’s not zero unless the panels are covered with snow. Then somebody will go the other way and tell you to size for a 50% use overnight. Wait, you want to go only one day and have to start the generator? A five hour winter charging day will not recover that 50% anyway. The math doesn’t work when you find that batteries start pushing back when you reach absorption at around 90 – 95% SOC after pumping amps in for hours and that last 5% takes a couple of hours, no matter how big the array is and more than two hours if you did run down to 50%. Plus, the quality of the voltage regulation varies tremendously from one brand of controller to another and the number of amps going into a battery near the end of absorption due to better voltage control can really change how much time is required. I will never forget an argument I had early on with some idiot on an RV forum. He was telling everybody that solar power would never work because it could not recharge from a 50% discharge. I told him that I had been successfully been living on solar power for over three years at that time and I was living proof that it was possible, if you just get it through your head that a 50% discharge daily is the wrong thing to do. He still argued and suggested that I was lying. Yep, I got kicked off of that forum. I do NOT react well to idjits calling me a liar.
I suggest that you size for less than 15% draw down overnight. Mine is working at around 10% most long winter nights and boy in summer, it is really ridiculously low. This way we can go for several cloudy days. It also gives me much better voltage under load for starting big motors. Typically in the dead of winter we are able to go for nearly a week before getting low enough to need to start the generator at something under 50%. That is perfect because the rule in the battery world is that you must completely recharge at least weekly to avoid damage. More often is better, but if running them down is not a weekly occurrence, this is fine. Usually the sun comes out at least every other day for a while and keeps us from going too low. In fairly solid clouds we still see 5 – 10% of the system’s potential. We have gone for months with no generator use. It simply depends on the weather patterns and where you are located. Backwoods Solar would tell you that what I am doing doesn’t work in northern Idaho and they are absolutely right. Over here in eastern MT in the rain shadow of the Rockies it is much better even though we occasionally do get that 5 day stretch of clouds. Maybe I should say that choosing where you build might be smart, eh?
So how do you size batteries if you are guessing? Ours in both the RV and now in the house have a C20 rating about 12x our nightly use. The house system has 1200ah of storage after I de-rated it 20% for typical winter battery temps between 45 and 50F. 10% draw down over night is 120ah at 24V and 12 times that equals the C20 rating of the batteries. Now you will see that I don’t have as much solar power on the roof that anybody in the battery world will tell you I need. My 2000W is about 5% of my C20 rating. The typical recommendation has been a minimum of 10%. Remember what I said about the last 5% of charging taking 2 hours, no longer how big the array is? A bigger array would let me charge up to 95% SOC faster, but by not going below 90% most days I have found this is enough, when adding the generator once in a blue moon if going way down and I need more amps to charge faster. We typically start absorption with the system producing around 1700W, but it can be higher if the panels are cold. I have seen 2200W in bright winter sun with the panels below zero, but it doesn’t last long. I watch the charging drop once in absorption until we are putting in around 600W a couple of hours later when the batteries are full. This one thing is what confuses people more than any other… “Where are my amps?” Answer: The batteries are nearly full and will not accept the amps your panels are capable of producing. You can run things like laundry to use the extra amps that are going to waste.
To give you a better idea, I am typing this on a December morning with snow outside, have not seen the sun since two days ago and the forecast isn’t looking good. In a while I’ll have to go sweep the snow off the panels, but I’m no hurry since until the sun gets up a bit higher it won’t make much difference. The batteries are at 79% after making coffee with a 1200W drip unit. I know, it doesn’t seem to add up. If we go down 10% over night, why don’t we go down at least two or three times that in 24 hours? The answer is that it is very unusual for us to not get at least enough from the sun on a cloudy day to do a little charging. Our typical state of charge after three days of clouds is over 75% and we can recover from that in one sunny day, even in December. I plan to run the generator tomorrow if the sun doesn’t cooperate. If I was made of money, I would love to have about 1000W more up on the roof, but we don’t really need it. Occasional equalizing can be done on sunny days with only 3% of C20, no matter what some “expert” tells you. A healthy battery will not accept more than about 5% anyway since you only equalize fully charged batteries and you don’t need to do the EQ any set day. You can wait for a good sunny day. OK, you can also start up your noise maker and waste a bunch of fossil fuel, but that just does not agree with the whole idea.
Yes, people who have electric refrigeration must own a noise maker. This one was recommended by my friend who has the Kings Vista blog; advice goes both ways. We use it to stay above 50% and then if needed to recharge us up to around 80% and let the sun do the rest. However, I need to make a point here because people keep telling me they heard going below 50% will damage batteries. That is NOT true and never has been. You can run them down to 20% without damage, but in the off grid world it simply takes too long to recover from that, even with a generator. Even my big Magnum charger would take over a dozen hours of generator time to recover from that.
The general consensus in this off grid world has been that eight L-16 batteries are enough for a home like ours. We have sixteen. While that is a big investment and doubles the cost when replacement time comes around, they will last a lot longer since they are used half as much daily as eight would be. We had only eight when building and killed them in four years of over use, hot conditions and charging at too high of voltage. That voltage recommendation went up & up in reaction to people trying to charge on short winter days with too little power, plus most people sulfating their batteries by undercharging and now it has been going down as the manufacturers have seen failures from over doing it. I have charging recommendations in my 2018 WARNING for those who are dying to know and they are based on experience, not what people who live connected to the grid told me. The brutal truth is that we get only five decent hours of charging in the dead of winter and the only way to be successful with that is to be recovering from shallow discharges daily or maybe every other day most of the time, or in an effort to charge faster, turn the voltage up to the point where you risk damage from that. The old idea of going lower in state of charge and then cranking the generator nearly every day it is cloudy was not acceptable to me. Instead of spending $8K on a big permanently installed electric start generator, I bought a cheap portable unit that I wheel outside occasionally when needed and put the money I saved toward more batteries. This way my generator is always warm enough to start on the 2nd pull (it does get very cold here) and if I have problems with it, I am not looking for some expensive repair guy to come out and work on it. I can replace it for the cost of one or two service calls, less than $500. and it will last a LONG time with the few hours I use it. My way is to use the generator just a few times over the winter and put it away for the summer. I simply shut the gas off and let the carburetor run dry so it isn’t gummed up with old gas for the long periods it won’t be used. This will not work in all climates, but it does for me. The only improvement I would love to consider is using a propane powered unit or add a $100 conversion to this one and have a quick disconnect outside where I park it, so I wouldn’t have to deal with gasoline. Some day.
The next thing that somebody will bring up is that warning you can find about not having more than two strings of batteries or you will have imbalance problems. Connect them right! Stop doing it the wrong way and this problem goes away. Look at this pic carefully. All series interconnects are all the same. The load cables from the ends of paralleled strings are connected at diagonally opposite corners and those cables are also all exactly the same. The negative and positive cables don’t have to be the same as each other, but all negatives need to be the same. The same goes for the positives. They are sized to meet Magnum’s requirements. This issue is getting very old with me. Even battery suppliers don’t understand it, but then again, if you do it wrong your whole set will fail when the first battery does (the one that was used the most) and they get to sell you a whole new bank. Hmmm… Coincidence? The last thing is that you need space between your batteries for cooling and that 1/2” general consensus is not enough. The more, the better. I went for 1.5” when rebuilding the box.
A bit more info about this house might help a bit. Our home is wired in the normal way with an inverter that is on 24/7. Most things do not draw enough phantom load to worry about and there is still a lot of bad info about this on the internet. People visiting would not know we are off grid unless told so. (You think they might be told?) I found that sleep mode in inverters simply does not work unless you are running only a couple of big things. Trying to make it work with an entire house connected lead to having LED lights not come on or the TV keeping it on all night. We have a small super efficient refrigerator that uses less than 750W in 24 hours, while the usual things are double that. We also have a small freezer that has been modified with better insulation so it is about the same. So refrigeration is well over half of our electrical budget. Our range is a carefully chosen propane one that has spark ignition in the oven, no glow bar. We have no well, using a standard 1/2HP pump to feed the house from a cistern. Where we get water is another discussion, but many in this world fill their cistern by running a generator to power the well pump. It doesn’t take much to pump the 20 gallons or so per day that we use, no matter what size or type the pump is. I’m not sure I believe what people say about a DC pump being 20% more efficient than an AC one, but even if it was, that 20% would only amount to about 1% of our energy use, so it is of no consequence. We also have no teenage kids who don’t know how to turn things off or to conserve water. No air conditioning, even though we could run something on long sunny summer days. We have no furnace blowers and no pumps running hot water floor heating. These things are why many who try solar power in the north fail. Having to power heating systems on the worst solar days of the year doesn’t make sense. It looks fine on paper, but after it has been cloudy for a week, the truth is exposed. All of our heaters are propane with no fans. All lights are LED. The water heater is propane, with a solar preheat system, but that is something I talked about in my warning: Forums are Still Dangerous. BTW, that system does have a tiny pump, but it is controlled by an aquastat so it only runs once in a while. The only indulgence is a big TV and stereo that we don’t use every day and then not for hours and hours. Plus, all of that is on a switch that we can leave off because the phantom load is over 20 watts. Forgetting to turn that off can waste more than our freezer needs. Don’t obsess about things like built in clocks or LED lamps in appliances. Measure first. Most won’t even show up on the meter. Oh, we also have a whole house vacuum system that is a BIG load, but we only run it when the sun is shining and the same goes for my wood working tools out in the shop. Some of those things are HUGE and they were run without a generator when building, teaching me what that leads to. Laundry is a super efficient front load washer and propane dryer that we only run if the sun is shining. BTW, the dryer uses more energy than the washer. I was very surprised to figure that out.
If you are smart enough to look out a window to figure out if you need an umbrella, why can’t you figure out when using the toaster, waffle maker, hair dryer or laundry is a bad idea? We use all of them if the sun is cooperating, but we still make toast on the broiler pan in the gas oven many days and we let the laundry pile up until either the sun is shining or we are running the generator some morning to do supplemental charging. However, we do make coffee the same way every day and put the coffee in a thermos as soon as the Braun is done, not only in winter. Doing things the same every day is how you get your energy use in check. The things like the sewing machine and a small TV in the sewing room are so small they are not worth talking about. The electric iron the quilter uses only gets plugged in if the meter says 85% or better. To most, this sounds like minimalism, but compared to how the off grid life used to be, this is living in the lap of luxury. I don’t know how many times I have talked with people who thought running a generator was needed to use a vacuum or some other motorized thing that doesn’t really take much, if their solar system only worked. That drives me crazy. I like to tell them about how we never even bought a generator for our RV and we carried two vacuums, plus wood working tools and we did not go to RV parks before we used them. Now we use the generator only when we must and never to charge all the way up… That is a terrible waste of both fossil fuels and equipment.
To summarize… Size your solar power for what you use, not somebody’s estimating chart that was designed so they could sell you more equipment. Realize that the people who made that chart probably don’t live off grid. Use your brain to conserve as much as possible and realize that you don’t have to be a slave to high energy use appliances. Be very careful when buying appliances, realizing that the people who sell them probably don’t live off grid. If I hear from one more person who bought a gas range with a big electric heating element in the oven, I am going to scream.
USE YOUR BRAIN PEOPLE!