Will solar thermal heat up again?
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It used to be that the term “solar panel” connoted a solar thermal panel, which uses sunlight to heat your house or tap water, as opposed to a photovoltaic (PV) panel, which produces electric power. These days, though, attention (not to mention sunlight) focuses on PV. Many people assume that solar hot water heaters are all well and good for, say, Israel, but ill-suited to high-latitude, cloudy, snowy climes such as the U.S. Northeast. But Scott Wilson of Olney, Md., begs to differ.
Responding to my call for stories about solar installations, Wilson sent me a description of his thermal system. His blog provides even more details and makes the case for installing thermal instead of photovoltaic panels:
“I don’t have a grid-tied PV system, but I do have a solar thermal hot water system. As great as PV is, based on cost-efficiency, solar hot water should probably be most people’s first contact with solar. I was on our local tour of solar homes this year, after saving up 1.5 years worth of performance data.
“Our system is a 16 tube evacuated array, with an equivalent power collecting ability of about 1.5 kW. It has a pressurized (34 psi) propylene glycol/water mixture that circulates through a manifold at the top of the array, picking up heat from a ‘hot finger’ that extends from the top of the individual tubes. That fluid travels to a heat exchanger mounted in the bottom of the tank, where it dumps the heat to the surrounding cold water, then travels back up to the roof. The water itself never travels to the roof, unlike the ‘drain-back’ flat plate systems of the ’70s and ’80s, which suffered, I’m told, from inferior quality issues, and gave solar domestic hot water a bad name.
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