Solar water heating system

Solar Water Heaters: A Renewable Retrospective

By Steve Whitworth

Harnessing the power of the sun may seem like a relatively recent development, but its origins go way back. In fact, as early as the seventh century B.C., people were using magnifying glasses to concentrate the sun’s rays to make fires. And back in 212 B.C., the Greek scientist Archimedes used the reflective properties of bronze shields to focus sunlight and set fire to wooden ships from the Roman Empire, which was besieging Syracuse.1

Of course, it would be another 2,000 years before the first solar collector was invented, and it wasn’t until the 19th century that the first solar water heaters emerged. The following is a look back at how solar water heating systems developed in California and beyond.

Mid to Late 1800s: Catching Some Rays
In the middle of the 19th century, most people were still heating water on a stove by burning wood or coal. Then a much safer, easier and cheaper way to heat water came into vogue: placing into the sun a metal water tank painted black to absorb as much solar energy as possible.

These were the first solar water heaters on record. Unfortunately, even on clear, hot days, it usually took from morning to early afternoon for the water to get hot. And the tanks rapidly lost their heat as soon as the sun went down because they had no protection from the night air.2

Then along came Baltimore inventor Clarence Kemp, who in 1891 patented a way to combine the practice of exposing metal tanks to the sun with the scientific principle of the hot box, which uses glass panels to trap heat from the sun. He called this first commercial solar water heater the Climax. It sold well in California and other states with temperate climates and plentiful sunshine. There were 1,600 of them in Southern California homes by 1900.

As popular as the Climax was, the fact that the hot box and storage tank were one unit meant that the water heated by the sun the day before was exposed to the cooler weather overnight. Consequently, by the time morning came around, the water was cold again.

Early 20th Century: An Overnight Sensation
That all changed in 1909 when William J. Bailey, a mechanical engineer, patented a solar water heater that would revolutionize the business. Bailey’s invention, which he called the Day and Night, separated the solar water heater into two parts: a heating element exposed to the sun and an insulated storage unit that was located inside the house. This design enabled families to have solar-heated water day and night and early the next morning.

Providing hotter water for longer periods put the Day and Night at a great advantage over the competition. Soon the Climax went out of business. By 1918, Bailey’s company had sold more than 4,000 Day and Night Solar Hot Water Heaters.

In the 1920s and 1930s, huge stores of natural gas were discovered in Southern California, effectively killing the solar water heater business. Bailey applied the innovations he had made with the Day and Night to develop a thermostatically controlled gas water heater.

1950s to 1970s: Postwar Booms and Busts
In 1956, architect Frank Bridgers and his partner, mechanical engineer Don Paxton, designed and oversaw the construction of the Bridgers-Paxton Building, the world’s first commercial office building using solar water heating and passive-solar design. Located in Albuquerque, N.M., the building is now in the National Historic Register.

In postwar Japan, cheap sources of energy to supply hot water on demand were scarce. To heat water, rice farmers had to burn rice straw, which they could have otherwise used to feed their cattle or fertilize the earth. So when a Japanese company began marketing a simple solar water heater consisting of a basin with its top covered by glass, it sold more than 100,000 units by the 1960s. Urban dwellers began to buy a model that resembled the old Climax Solar Water Heaters. Nearly 4 million of these solar water heaters sat on rooftops by 1969.

When huge oil tankers started trolling the seas in the 1960s, the Japanese gained access to Middle Eastern oil. As had happened in California, the solar water heater industry collapsed. But not for long. The Oil Embargo of 1973 and the subsequent dramatic increase in the price of petroleum revived the local solar water heater industry. Today, more than 10 million Japanese households heat their water with the sun.

It was a similar story for Israel, whose success in the Yom Kippur War is what led to the 1973 Oil Embargo. The Israelis responded by purchasing mass quantities of solar water heaters. By 1983, 60% of the population heated their water with the sun. When the price of oil dropped in the mid-1980s, the Israeli government did not want people backsliding in their energy habits as had happened in the rest of the world. It therefore required its inhabitants to heat their water with the sun. Today, more than 90% of Israeli households own solar water heaters.

1980s and Beyond: A Sustainable Future
Today’s versions of the solar water heater—active, closed-loop systems that use heat transfer liquids and a heat exchanger, and passive, open-loop systems that heat potable water directly—had their origins in the late 1970s and 1980s. These continue to improve and be the workhorses of commercial solar water heating industry. This proven technology is becoming a crucial component in future efforts to combat climate change and save energy for customers.

You can learn more about financing a solar water heating system and working with a contractor by downloading PG&E’s free eBook, "How to Make Solar Water Heating Affordable for Your Business."

  1. U.S. Department of Energy
  2. California Solar Center

Find out about the origins and history of the solar water heater:
  • SMB Blog Author
    Steve Whitworth
    Senior Program Manager at PG&E, is a recognized leader in the industry for renewables. Steve uses his proven and practical expertise to bring renewable education to residential and business customers. In this vital role, he develops and oversees highly successful initiatives that result in the adoption of more renewable projects throughout PG&E's territory.

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