An old solar-powered house
While my sister is experimenting
with Plug and play solar backup, I am in the process of learning
to live at a isolated, off the grid, solar powered house.
This house was built in the mid 90's, and designed for both passive solar power (with its southern exposure and earth-sheltered rear), and solar power, with a wiring system that is entirely 12 volt throughout. But 15 years is a long time for a solar system to age, and as it degraded, the occupants adapted to living with less and less power.
That is an adaptation I have not made yet, so will this aging system be able to meet my needs? Like Anna, I am starting off with some experiments. The first was to go live there for a week and use as much power as I wanted.
Today I'm back in town. After approximatly 4 full days of use, the first battery bank dropped to 9 volts, my cutoff point for safe use. Which turned out to be below the safe use point of my laptop power adapter, which burnt out the last evening I was there.
I decided to come back while the other bank is still relatively full, leaving the low one connected to the four 64 watt solar panels to charge.
Hurrying downtown to grab lunch in between work on Branchable, I noticed it was a beautiful sunny day, and I realized that this makes such days even better, because besides enjoying them, I know I'll be enjoying the yield on chilly nights sometime later.
Well, in theory. Actually, the very antique charge controller in the house was dead and bypassed, so I removed it. I called its manufacturer wondering if it could be refurbished, but they suggested it belonged in a museum. So I've ordered a new controller, a Xantrex C-35. Until that comes, pretty days like today will charge, or possibly over-charge the batteries, which will then drain back out at night.
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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.
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I'm jealous. One day...
So do you have Internet at that house? :P $DAY_JOB requires me to be connected at most times.
The batteries are old (and were recycled into this house from a vehicle), but have been taken good care of and still seem to be doing well for their age. Almost all the ones in use charge up to their original 6+ volts.
Still, I don't know if they're holding a charge as well as some newer batteries might. If the system can't meet my needs, I'll be looking at newer batteries first. And probably last, as more PV panels is outside my budget.
Joey,
Does your charge controller include a maximum power point tracker? It doesn't appear so from the specs I found.
If not, you might want to consider getting another charge controller! Unless the battery voltage is close to the maximum power point of the panel (which varies with irradiation, by the way), efficiency is going to be suboptimal.
I had to make one for the solar-powered battery-less vehicle that was the graduation project for my B.Sc in the early nineties. I've read they're increasingly built into panels nowadays to optimize individual panel efficiency. But your panels are old enough that they probably haven't got them.
MPPT is a neat optimisation, especially since it improves efficiency in winter. But controllers with it cost 3 to 4 times the one I bought.
If I had to choose between more panels and MPPT, trading up to a better controller with it would likely be a good choice.
An MPPT isn't that hard to make. You need the following parts;
I can send you the schematic if you're interested. I cannot recall the precise components I used then, it was almost 18 years ago.
An op-amp is a component that produces an output signal based on two input signals. It is used to produce the pulsed DC signal based on the voltage of the panel and that of the sawtooth voltage generator.
A mosfet is basically a transistor (electronic switch) that is switched by a voltage instead of a current like a normal transistor. In the MPPT it is used to control the total current from the panels which would fry an op-amp. Think of it as a kind of small and super-fast relay.
I'd guess you would be able to find schematics for an MPPT in electronics hobbyist magazines. The mppt article on wikipedia has some pointers as well.