Passive Solar Heated Solar CITIES IBC tank biodigester: A window into a new world.

September 26, 2015

Inspired by the promising data from our experiments at Tamera Solar Test Field, we decided to take one of our soy-based polyurethane foam-insulated biodigesters up to Kathy Puffer’s Homestead Ecosystem in Tillson, NY. We cut out the foam on the south facing side, painted the IBCs exposed wall black, and installed foam in a double pane glass window. At Tamera, we installed a black IBC insulated on three sides and covered with two layers of clear stretch wrap plastic on the south and west sides.

Preliminary results show favorable solar gain on sunny days, keeping the digester in Tillson at or near 25 degrees Celsius, even when ambient drops to three Celsius at night.

There are still thermal losses at night through the window, which we cover with a blanket.  There is also loss through the top of the digester where it is uncovered because of the lid and the feeding pipes. It may not stay active all winter, particularly during cloudy times, but it certainly helps in sunny times and will definitely boost production in fall and spring even if it slows dramatically during the winter. We suggest this now as a standard feature in IBC builds. The marginal cost of an old double pane window (which we got used) is negligible compared to the gains.


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