Category Archives: 2009 blog posts

for off-grid northerners, at least.

Bob was drafted by one of our local farmers to help her design a greenhouse with heated beds — using no electricity. He spent a whole evening bouncing ideas around with me (not that I have any expertise, mind you — it was sort of an exercise where he could think out loud). We imagined variations on thermo-siphons, where you heat water in pipes that go through a woodstove, and then the pipes would carry the heated water beneath the soil in the beds… But the problem is that this kind of system would require terraced beds, since hot water in a thermo-siphon has to travel upwards — and if you imagine trying to split the system between several beds, some closer to the heat source than others — it quickly takes on too many finicky variables to be practical. And we envisioned stoves (like “rocket stoves”) where the exhaust pipe would go under the beds, heating them with its gases. But again, multiple beds posed some difficulties.

“She needs a little electric water pump,” we kept saying. The elegance of multiple small water pipes was hard to beat, but the water would need to be propelled by a power source.

“But what about the hot stove that she’ll have right there? Isn’t there some way to generate electricity from all that heat?”

We both looked at the little fan we have on top of our own woodstove, a pricey little gadget that seems more toy than tool. It doesn’t move much air, honestly (if you put your hand right in front of it you can’t even feel any breeze) … but there is some technology there which turns heat into electricity. We dove into the computer to research how heat can be turned into electricity — and suddenly our whole vision for our own home electrical system was transformed.

It turns out that you can now buy thermo-electric generator modules which you can attach to the outside of your woodstove, and hook up to a reservoir of cool water. The temperature difference between the hot stove and the cool water generates electricity… at less than the cost of an equivalent solar panel! The cold side of the thermocouple would be supplied by a reservoir of cold water, kept outside and piped in. It will be the way out of our wintertime propane dependence, during these dark days when no amount of solar panels can produce any power to speak of! Our woodstove is hot probably 20 hours a day right now; if we could be generating power during all those hours? It would be amazing.

So, when we come back from Nicaragua in February, my project will be bees and Bob’s will be to set us up with a thermoelectric generating system. If it works as promised, I think almost everyone who lives off-grid in these cloudy northern regions would be as excited as we are. Check out the Tegpower website — it’s truly a revolutionary technology.

Plus a tiny one would power our neighbor’s hot water through pipes for her greenhouse beds.

Oh, and yes… our truck is once again running. I live with an Engine Whisperer… it took him 10 minutes to charm it out of its dark oily little sulk.