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Fogão solar
During the 1980s, Gaviotas designed and built a new hospital to serve Gaviotans and people in surrounding villages. They used solar technology and adapted various techniques in order to make the hospital energy- and self-sufficient. The engineers decided to circulate solar-heated, low-viscosity cottonseed oil around the pressure cookers in the kitchen because oil presented fewer problems than water in maintaining the necessary high temperatures.

As sunlight super-heated the oil, a heat siphon sucked it into a holding tank. At the flip of a toggle switch, a forty-watt micro-pump, run on batteries charged by photovoltaic cells, forced the hot cottonseed oil through coils that looped around six stainless-steel pressure cookers, then back up to the roof to re-heat. Insulation in the roof-top oil tank kept the closed system hot enough to operate twenty-four hours a day, and there was adequate charge left in the battery bank to illuminate the hospital all night with compact fluorescent bulbs, designed to operate on twelve-volt direct current.