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.
Technical summaries for each solution will be available May 1, 2017.