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Subject Solar electricty versus solar thermal for water heating
Author James Cormican
You said in the knowledge base that "Photovoltaic (or PV) panels are meant to create electricity which is very inefficient for heating water", and you recommend going thermal.

i live in the Detroit MI area, where the sun is brighter than it is warm for some months of the year (eg april, may, oct, november). would not PV outperform thermal in those months of the year where the sun is still very bright, yet not very warm?

thanx... ed.

Hello Ed,

Thank you for your interest in The Alternative Energy Store. The best way I can answer your question is to say that it is a matter of efficiency. While it is possible to heat water using PV, the conversion must be made from light to electricity and then from electricity to heat. Also PV modules are not so efficient themselves, averaging 10 to 15%. On the other hand, solar thermal panels are typically 50 to 70% efficient and only convert direct sunlight into heating the liquid or at least a liquid (glycol) that heats the water. Even if the water is not heated to a sufficient temperature by the sun alone, the water will be heated above the incoming plumbing temperature so as to displace the energy demands on a more tradional (electric or gas) water heater.

The other factor is that solar electric is much more expensive than solar thermal. Solar electric is great, but not so much for heating and it is not price competitive at all with a properly designed solar thermal system for heating applications. For example, a solar electric system designed to heat water could cost over $20,000, while a solar thermal system could do the same job for about $2500.

hopefully this answers your question,

Feel free to contact me any time via telephone or e-mail.

Thanks again,


I have included a link to the solar water heating section of our web page. There is a lot of good infromation about water heating products there.

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