This was supposed to be straight-forward. We had ordered a bunch of catalogs from solar equipment distributors and installers. The material was good. They all included chapters explaining how solar energy systems work; what to buy; how to configure them; etc. We knew we needed the following equipment: batteries for storing the electricity captured by the solar panels, the solar panels themselves (frequently called PVs, as in photo-voltaics; see http://en.wikipedia.org/wiki/Photovoltaics), an inverter for converting the DC voltage to AC voltage. After doing our homework, we understood that we also needed to buy something called a charge controller, whose job was to control the voltage and current from the panels to the batteries.
Our system isn’t small. We have 24 6-volt batteries, configured to put out 48 volts. Each battery weighs 67 pounds!
We have 8 solar panels that put out about 1200 watts of power on a good day.
So is that enough to power our entire house in Maine? We don’t really know yet — ask us after this winter! But it does seem to be close, perhaps too close. In a future post we willl write about the appliances and other electrical items in the house that were specifically chosen due to their small electrical footprint. (Just to give you an example, our Whirlpool refrigerator consumes about 340 kilowatt hours of power per year! That’s the lowest rated power consuming fridge of its size (19 cu ft) on the market today.)
And just to be on the safe side, we have two backup systems in place. Our house is about 500 feet from the road where there is grid power courtesy of Central Maine Power (CMP). When we originally started to build our home, we decided to bring power up to the house (even though we knew, a priori, that we wanted to live off-grid) for a couple of different reasons. We knew the solar system wouldn’t be in place until the house was finished. Also, the contractors that were building our home, were going through gas with their portable generators as if it was water — and of course charging us for the gas and the rental of the generator that they needed to power their tools. Lastly, we thought that whoever one day would buy our home, might not want to rely on solar power and would therefore appreciate a grid connection.
So CMP is our backup system if the battery voltage goes below a certain predefined threshold. In addition, we installed an 8.5 kilowatt generator as a secondary backup. That double backup system is how I viewed our electricial power solution. It seems that our solar guy, our electrician, and our generator man didn’t have that same view or vision.
When the generator was installed, we had only been using grid power from CMP. The contractors tested the system; and indeed, when we cut the power from CMP, the generator kicked in and completely powered our house. Very cool!
And then the solar panels and assorted hardware were installed. Suddenly, the house was being powered by the sun. It was such an incredibly cool feeling. I loved the idea.
But that cool feeling didn’t last that long. After a couple of weeks of living in our solar powered house, we suddenly noticed all the lights went out for an instant and then came back on. We also heard our generator kick on. Uh oh. We were on generator power and I had no idea why. I had myself to blame, really. Our solar system had two display panels that could show all sorts of information about our system. I just (a) didn’t look at it; (b) wouldn’t have known what to look for as I had not really read any of the manuals nor asked sufficiently detailed questions. But now it was too late.
I called our solar guy and explained the problem to him. I also mentioned that we were going back to our other home for a few weeks and hoped the problem would be resolved before we got back.
A subsequent email from him said that everything is working fine. The batteries had been drained too low and he simply had them recharged. Had I been running on batteries the whole time without solar recharging? That was my first (and incorrect) thought. It wasn’t until months later that I realized our solar panels had simply not been able to keep up with our electrical demand. I now monitor our system on a daily basis and this is, I believe, the correct thing to do — unless you are rich enough to buy sufficient panels to cover any amount of power consumption you might have.
Everything I have said up to now is, more or less, historical and simply background information. As a result of the incident above, I realized something rather quirky. When our house is being powered by the generator, the batteries are not being recharged. When the house is powered by CMP, the batteries are being recharged. What’s worse is that if I turn on the big CMP breaker switch, our house automatically switches from solar to CMP (and the batteries start charging). There is no way for the system to automatically go from solar to CMP when the batteries are too low. Rather the system goes from solar to generator; and then the batteries don’t get recharged.
So this is where we are today. We have hired a new solar person who is also an electrician (eliminates the need to talk to two contractors). He understands what we want — but he doesn’t (yet) know how to get there. He is speaking to the company that makes the hardware we purchased and hopes that with their help, a solution will be found (that hopefully won’t be overly expensive). They all said that had we wanted only one backup solution to our solar system (that is, CMP or a generator), then the wiring would have been straight-forward.
So yes there eventually will be a follow-up to this story. I hope it’s soon, before the winter comes, as we would really like to spend much of that season in our cabin/house in Maine.