Do Solar Thermal Hot Water Heaters Still Make Sense?

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solar thermal vs photovoltaic
CC BY 2.0. Lloyd Alter (left image)

Over at NRDC Switchboard, Pierre Bull makes the case for solar thermal hot water heating. It has been around a long time, and the development of evacuated tube heat pipes, along with cheap Chinese manufacture has made it simpler and more effective. Pierre writes:

  • Passed over in many of our attentions by its sexier cousin - solar photovoltaics, solar thermal has much to offer. In fact, a recent report by the Solar Energy Industries Association estimates that solar heating and cooling (SHC) in the U.S. could, by 2050:
    Generate almost 8 percent of the nation’s heating and cooling.
  • Create more than 50,000 good paying jobs.
  • Save $61 billion annually on energy.
  • Cut carbon dioxide emissions by 226 million tons every year(the equivalent of taking 64 coal-fired power plants offline for good).

I used complain that people would put photovoltaics on their roof because they were sexy, even though I calculated that a kilowatt of energy cost ten times as much as that generated by solar thermal. I demanded Big Steps in Building: Put Solar Hot Water Heaters on Every Roof. But then Martin Holladay made the case that Solar thermal is dead. In summary,

  • Solar thermal systems generate a lot of energy in the summer, far more than you need. But you can't really store it and put it away for the winter very easily. With a grid-tied PV system, you can sell the electricity that you don't need. You can buy it back when you need it in winter. This makes a watt of electricity a LOT more valuable than a watt of heat.
  • Solar thermal systems have lots of piping, valves and pumps. I have learned from the sad experience of my interconnected hydronic heating and domestic hot water system that you don't want your basement looking like the set for Das Boot, that simplicity matters a lot.

Holladay concluded that "unless you’re building a laundromat or college dorm, solar thermal is dead." That's an overstatement; there are many southern, sunny parts of America where it makes a lot of sense. But with the continuing drop in the price of photovoltaics, the ability to tie them into a much bigger system, the increasing efficiency of electric heat pump water heaters and the simplicity of having just one solar system instead of two, I wonder if solar thermal hot water heating is still hot.