I've been at the cabin, on solar power, for a year now. I have a year of data!

Everything went pretty well until last month. There was an April rainy spell where power felt slightly tight. Then over the summer, plenty of power, no need to conserve. The last month though had what seemed like weeks of continual grey clouds, where I never saw the sun.

high noon today

Of course, even on a sunny day in winter, it does not get far above the hills, and the peak production window is only a few hours. This bad combination had my battery power dipping below the 10 volts that I consider low, down to 9, and even to 8 volts.

I use kerosine lamps in the winter. (I prefer the light anway.) I've also started unplugging my Thecus server at night to conserve power, meaning no internet late or early. For four or so nights, I had no power to run even my laptop after sunset. On one notable day, there was no power even in the daytime.

Even when it turned sunny again, I found that the batteries would seem to charge to 12 volts during the day, but then precipitously drop to 10 and 9 volts at night. I think the problem was not damaged batteries, but that these Nicads charge most efficiently above 12 volts (14 volts is best), and there was never enough power saved up to get them full enough that they could charge really efficiently.

So, I reluctantly spent three days away this week, to let the batteries soak up sun and recover. It seems to have worked; they've been holding a 12 volt charge overnight again.

Off Grid

Joey,

I find this very fascinating! Less than a month ago I put a PV array on my house and have been much more attuned to the weather and its effect on my production. Our system is 3.8kW and I was amazed to see that even on a very overcast day the system would put out nearly a kW. I am really looking forward to the summer when we start generating more each day than we consume. We also have a family friend who grew up off grid and her parents continue to live in their cabin. They get their power from a micro-hydro setup and have an array of golf cart batteries to store their power.

Can you tell me more about your setup?

Comment by Keith
comment 2

My PV system is only 256 watts, and it's nearly 2 decades old (and the recycled batteries are older still). I wrote some more about it in getting to know my batteries.

It is neat to get a little power on cloudy days. Works as long as the clouds are not so thick that the day is entirely dim. My PV only produces enough on such days to "break even" with my running the laptop all day though.

I also like the effect where, on an overcast day with snowfall, the snow on the surrounding hills acts as a reflector and I get much more production that I normally would.

Comment by joey
comment 3

To put it in perspective, about the highest I've seen my panels produce is 125 watts. Not that many lightbulbs worth.

I'm sometimes asked why I don't add more solar panels, and that's a good question; I have mostly enjoyed finding ways to make do with so little power, however.

Comment by joey
Tracking software?

Hi Joey,

Thanks for this, quite interesting really. What software are you using to talk to your inverter? I maintain a GPL package in Ubuntu called Aurora (authored by Curt Blank), and publish my data to pvoutput.org (where there seems to be quite a number of open source developers who publish their PV data).

Thanks! :-Dustin

Comment by Dustin