A solar water array in Esbjerg, Denmark.
Frank Bach

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.

Solar Hot Water

Reduce SourcesElectricityEnhance Efficiency
Reduce SourcesBuildingsShift Energy Sources
CO2 Equivalent
Reduced / Sequestered
Trillion $US
Net First Cost
(To Implement Solution)
Trillion $US
Lifetime Net
Operational Savings
Solar hot water taps the sun’s radiation, rather than fuel or electricity. By replacing conventional energy sources with a clean alternative, they reduce emissions.

Solution Summary*

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 solar hot water has been mandated since the 1980s, 90 percent of homes have systems. Throughout its history, solar hot water has risen and fallen based on the price of energy, as well as government intervention to support it.

All told, solar hot water 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.

* excerpted from the book, Drawdown

If solar water heating grows from 8 percent of the addressable market in 2018 to 15–30 percent, the technology can deliver emissions reductions of 3.6–14.3 gigatons of carbon dioxide. However, if energy costs remain as low as they are today, they may save only US$293–1143 billion over the unit lifetimes for investments of $729–2736 billion. In our calculations of up-front costs, we assume solar water heaters supplement and do not replace electric and gas boilers hence these investment costs already assume availability of a conventional heater for backup heating.

Note: August 2021 corrections appear in boldface.