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August 6, 2007

Why isn’t there more Solar Thermal?

Category: Solar Thermal – Dan 6:06 pm

In terms of what you can do at home to make a difference, one of the top items on the “more expensive but worth it” list is solar thermal — essentially hot water generated by rooftop collectors.

We like our hot water. We talk about taking a “long hot shower”, we rely on it to clean our clothes and dishes. A typical family of four uses an estimated 65 to 75 gallons of hot water per day[1]. According to an article by the Renewable Energy Resource Center in Vermont:

By installing a solar water heater, a family of four, who currently use an electric water heater and consume an average of 80 gallons of hot water per day, will prevent 3,400 pounds of greenhouse gas emissions each year. This represents a reduction in household greenhouse gas emissions of 20% or more for a typical household.

If the goal is to achieve 80% reduction in greenhouse gases by 2050, that requires a 2% reduction per year. So solar hot water can buy you the first 10 years down this path. The investment can range from $3,000 to perhaps $10,000, depending on if it’s for new construction or a retrofit, and depending on the size of the installation.

How does Solar Thermal work?

Solar thermal is one of the simplest green technologies. Basically, you pass water through a collector on the roof during the day. Whenever the sun is shining (and really whenever it’s relatively bright outside), the collector heats the water. This water is then stored in a tank for later use. Depending on the configuration, the solar portion of the system could be the only source of heat (if the tank is large and the collector is sufficiently large relative to the daily demands), or a traditional water heating system is provided to boost the heat from the solar system to acceptable levels.

Why is the US so far behind?

The US investment in solar thermal collectors is incredibly small. Look at this chart of data from the German Solar Energy Industry Association for 1999 installations (m2 of collectors):

Country Total Per Person
China 4,000,000 3.09
India 2,000,000 1.92
Japan 1,000,000 7.84
Europe 890,000 1.23
South Korea 500,000 10.55
Turkey 430,000 6.27
Israel 400,000 63.46
USA 25,000 0.09

How depressing. And while I fear China’s ongoing construction of coal fired facilities, you have to admit that their investment in solar thermal is impressive. But it’s not limited to developing countries like India and China, and it’s not limited to mid-latitude countries like Israel or Turkey.

I’d postulate three reasons why the US is so far behind here:

  • Cheap energy – Why worry about additional stuff in your house when gas and electricity is inexpensive.
  • Lack of policy – We don’t have any incentives to encourage developers, homeowners, or businesses to invest in solar thermal.
  • Lack of feedback – Those homeowners who do have solar thermal systems don’t get any sense of how well it’s working, or how much money they are saving by having it.

Installing Solar Thermal

If you can afford the investment ($3K to $10K, depending on your home and size), where do you go and what can you do? Here are several leads for systems:

  • Heliodyne Inc has been manufacturing solar thermal products for 30 years, primarily flat plate collectors and heat transfer appliances. They sell both components and off-the-shelf packaged systems ranging from smaller residential systems to large pool or commercial heating systems.
  • Alternate Energy Technologies, LLC manufactures flat plate solar thermal collectors and fully integrated solar hot water systems for medium and high-temperature commercial, industrial and residential applications. They have a nicely integrated system that reduces the number of overall components and therefore the installation costs.
  • Conergy is a supplier of flat panel collectors and systems for domestic hot water, space heating, and pool and spa heating. Their applications include use of solar powered water pumps to ensure reliability and eliminate dependence on grid power for their operation.

There are many more. You can find companies like this at, or by doing Google searches.