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Solar Hot Water: Thermal or Photovoltaic panels?

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  • Tue, Oct 22, 2013 - 04:36am



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    Solar Hot Water: Thermal or Photovoltaic panels?

Hi again Mots,

My solar engineer neighbor (who has been out of the business for about 6 years) did a bit of research this evening based on your post and concluded that with the low cost of the new solar panels ($1/watt) and the newer heat pump type of electric water heaters that the PV type of hot water heater now seems to make sense to him, too.  He forwarded a recent summary article of this debate to me.


Solar Hot Water: Which Is Better PV or Thermal?


Hal Slater, Contributor
September 11, 2013

Solar thermal water heating is a temperamental thing. Water weighs a lot, it expands when it freezes, and it can cause scaling damage to pipes when it boils. Solar thermal systems are wonderfully efficient [extracting about 50% of the energy in sunlight], and some systems work just fine for decades, but even these need regular inspection. When a solar thermal system fails, however, it sets about destroying itself, and it has been clear for some time that solar thermal water heating is not the way of the future except for very low-end heat usage, like swimming pools.

Recently, however, reductions in solar electric (PV) costs and maturation of air-to-water heat pump technology have provided a new model: solar-electric assisted heat pump water heating (HPWH). HPWH comes with fewer drawbacks than solar thermal, with a smaller price tag for residential applications. 

PV Advantages

Lower upfront cost

Easier to install.


Uses less space.

Needs no maintenance


Cannot freeze.

Cannot overheat.


No scale build up.

No CO2 emissions.