Saturday, January 8, 2011

Solar Gain Saturday

You know it's cold in the house when your cat crawls into your empty suitcase to get warm.

I slept over at Ma'ikwe's house last night, and we were awakened by Kyre clawing her way past the zipper to get into my wife's Samsonite. It was a first for me. Temperatures got down to around 10 degrees (outside) and after a cloudy day Friday, we were happy to see the sun peek in around the insulated curtains once we peeked out from under the covers. It was going to be a solar gain Saturday! While there was no frozen water in the house this morning, that first cup of coffee sure was nice to wrap my hands around.

Ma'ikwe lives at Dancing Rabbit, where all power is off the grid. As hers comes from photovoltaics (others use wind generators instead of—or in addition to—solar panels for their line power, and wood stoves for space heating) it's all about the sunshine. With an array of eight 175-watt panels, she can handle cloudy days better than some. Her system is geared to supply the electric power for three houses, but the second one is not yet occupied and the third hasn't even been started. Thus, she doesn't have to share what her panels crank out this winter. With care, she can go about three cloudy days in a row on battery power (supplemented by the minimal solar gain that trickles in even through complete cloud cover) and still have power enough for reading at night, checking her email, and keeping pace with her 700+ Facebook friends.

The beauty of relying on solar panels is that the need for juice is greatest when the temperatures are lowest, and the temperatures are lowest on clear days—meaning the solar gain is greatest when you need it most. In fact, if she gets two clear days in a row, she's able to "float," which means the panels are producing electricity fast enough that the batteries have been topped off and the extra energy is just being spilled. In those conditions she'll run an electric space heater to augment the BTUs generated by her overworked wood stove (more about that below).

This is fairly amusing in that electric space heaters are generally considered the spawn of the devil among people serious about energy conservation. Electricity is a highly concentrated energy and using it for space heating—a low grade use—is generally considered incredibly wasteful.

With grid electricity it would work like this: in our rural area, power is delivered via the distribution lines of a local power co-op: Tri-County Electric. They, in turn, buy power generated by Northeast Missouri Power, which supplies eight regional co-ops. Northeast Power's nearest generators are a trio of coal-fired plants located in Moberly, 86 miles away. The heat derived from burning the coal is used to drive turbines that generate electricity. The juice is then stepped up to high-voltage and transmitted via high wire lines to Tri-County Electric, stepped down to line voltage near the final user, and then converted to heat through resistance in a floor heater. After all these shenanigans only a fraction of the heat generated by the lumps of coal in Moberly are translated into sensible heat in houses near Rutledge. You can begin to picture why environmentalists want to throw up when asked about electric space heaters.

However, the equation is completely different in Ma'ikwe's case, where the electricity is generated about 25 feet from where it's used; and once her batteries are floating, it's use it or lose it.

All of that said, it's only an occasional luxury that Ma'ikwe can use her space heater to boost her indoor temperatures in short spurts on January days. Her main strategy for space heating is hydronics: radiant heating that comes from circulating hot water through polyethylene PEX tubing buried in her concrete floor. Although the floor slab (with tubing in place) was poured in spring 2009, she has yet to start the building that will house the wood-fired boiler that will generate the hot water for the system. Thus, for the last two winters she's relied solely on her wood stove, which was sized to be the auxiliary heat source—not the primary one—resulting in a lot of chilly mornings.

Maybe what we need to do to get through the winter is figure out how to use the cat as an auxiliary heat source… if we can ever get her out of the suitcase.

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