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Solar Water

A solar water array in Esbjerg, Denmark, used for house and district heating, employs buffer tanks for thermal storage. Esbjerg, a port city on the Jutland Peninsula, runs almost entirely on renewable energy and is at the center of Denmark’s offshore wind and wave energy industries.

Water heating is a major energy use. Hot water for showers, laundry, and washing dishes consumes a quarter of residential energy use worldwide; in commercial buildings, that number is roughly 12 percent. Solar water heating—exposing water to the sun to warm it—can reduce that fuel consumption by 50 to 70 percent.

The world’s first commercial solar water heater came to market in the 1890s. In the early 20th century, the technology took a leap forward by adding a separate storage tank. Solar collectors popped up on rooftops across California and Florida, but cheap energy in the post–World War II years stymied the industry in the United States.

Today, the technology is in use in many countries and almost every climate. In Cyprus and Israel, where the use of SWH has been mandated since the 1980s, 90 percent of homes have systems. Throughout its history, SWH has risen and fallen based on the price of energy, as well as government intervention to support it.

All told, SWH is among the most effective ways to convert solar energy into thermal energy. Payback periods are as short as two to four years, depending on specifics of system and location.


Clarence Kemp…The Climax: Perlin, John. Let It Shine: The 6,000 Year Story of Solar Energy. Novato, California: New World Library, 2013.

William Bailey’s Day and Night: Perlin, Shine.

China…70 percent of…capacity: REN21. Renewables 2016 Global Status Report. Paris: REN21 Secretariat, 2016.

Cyprus and Israel…90 percent of homes: IEA-ETSAP and IRENA. Solar Heating and Cooling for Residential Applications. Paris and Abu Dhabi: International Energy Agency and International Renewable Energy Agency, 2015.

large-scale installations [growing]: REN21, Renewables 2016.

“one of the most effective technologies”: Shukla, Ruchi, et al. “Recent Advances in the Solar Water Heating Systems: A Review.” Renewable and Sustainable Energy Reviews 19 (2013): 173-190.

Hot water…energy use: Ürge-Vorsatz, Diana, et al. “Heating and Cooling Energy Trends and Drivers in Buildings.” Renewable and Sustainable Energy Reviews 41 (2015): 85-98.

SWH can reduce…by 50 to 70 percent: IEA-ETSAP and IRENA, Solar.

United States…potential [impact of] SWH: Dutzik, Tony, Rob Kerth, and Rob Sargent. Smart, Clean, and Ready to Go: How Solar Hot Water Can Reduce Pollution and Dependence on Fossil Fuels. Boston: Environment America Research and Policy Center, 2011.

national ambitions for growth: Mauthner, Franz, Werner Weiss, and Monika Spörk-Dür. Solar Heat Worldwide: Markets and Contribution to the Energy Supply 2014. Gleisdorf, Austria: IEA Solar Heating and Cooling Program, 2016.

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