Medium Temperature Collectors

Medium temperature collectors could be used to produce approximately 50% and more of the hot water needed for residential and commercial use in the United States.In the United States, a typical system costs $4000–$6000 and 30% of the system qualifies for a federal tax credit + additional state credit exists in about half of the states. With this incentive, the payback time for a typical household is four to nine years, depending on the state. Similar subsidies exist in parts of Europe. A crew of one solar plumber and two assistants with minimal training can install a system per day.

Thermosiphon installation have negligible maintenance costs (costs rise if antifreeze and mains power are used for circulation) and in the US reduces a households’ operating costs by $6 per person per month.

 Solar water heating can reduce CO2 emissions by 1 ton/year (if replacing natural gas for hot water heating) or 3 ton/year.

Medium-temperature installations can use any of several designs:

  • common designs are pressurized glycol, d
  • rain back,
  • batch systems and newer low pressure freeze tolerant systems using polymer pipes containing water with photovoltaic pumping.


European and International standards are being reviewed to accommodate innovations in design and operation of medium temperature collectors. Operational innovations include “permanently wetted collector” operation. This innovation reduces or even eliminates the occurrence of no-flow high temperature stresses called stagnation which would otherwise reduce the life expectancy of collectors.

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