The story of solar water heating began in the 1760s in Geneva, Switzerland, where Horace-Bénédict de Saussure, a Swiss naturalist, observed that it is always hotter when sun rays pass through a glass-covered structure, whether in a coach or a building, than into a site unprotected by such material.
To put his hypothesis to scientific scrutiny, in 1767 he built an insulated box, its bottom painted black to absorb as much sun energy as possible, with two panes of glass covering the top — the prototype for all solar water heaters. De Saussure found that when he exposed the box perpendicular to the sun, the inside heated to temperatures far above the boiling point of water.
The Swiss scientist had demonstrated, for the first time, the greenhouse effect.
Carbon dioxide in the atmosphere, like the glass covers of his box, allows sunlight to easily pass to the Earth’s surface. Like the black bottom of de Saussure’s box, the Earth’s surface heats up when struck by sunlight. The longer heat waves that had entered the box as sunlight find it difficult to escape through the glass, just as they cannot easily pass through carbon dioxide blanketing the sky. The Earth, like de Saussure’s box, gets hotter than usual. That’s why we call the phenomenon global warming.
De Saussure speculated, “Someday some usefulness might be drawn from this device for it is actually quite small, inexpensive and easy to make.”
But more than a century passed before de Saussure’s hope was realized.
In 1891, Clarence Kemp, an American plumbing and heating manufacturer, placed a black-painted water tank inside a glass-covered box with a similar design to de Saussure’s. As the bottom of the box heated, the colder water inside the tank absorbed the heat and became hot enough to be drawn for bathing or dishwashing. Here was the first commercial solar water heater. Kemp called it the Climax.
As California had lots of sunshine, in the late 19th century thousands of citizens affluent enough to be willing to pay for hot water but who had no local or cheap source of fuel were willing to spend $15 for Kemp’s invention.
The Climax had one drawback: The water was heated and stored in the tanks, which were exposed to the elements at night and during bad weather. Under such conditions, they cooled down sometimes to such a degree that customers would have to forego a morning bath or washing up for breakfast with hot water.
In 1909, William J. Bailey found a way out of the dilemma: separating the solar heating of the water from its storage. His solar collector consisted of water pipes attached to a black-painted metal plate inside a glass-covered box and connected to an insulated remote storage tank located above the collector. As the sun heated the water, it became lighter than the heavier, cooler water entering from the bottom, forcing the hotter water to naturally rise into the storage tank and remain warm during the night and the following morning. Bailey called his company the Day and Night Solar Water Heater Company to emphasize his product’s advantage. Day and Night solar water heaters soon drove the Climax out of business to dominate the burgeoning solar water heater business in California, Arizona and Hawaii.
The discovery of plentiful oil and natural gas in southern California in the 1920s killed the local solar water heater business.
But Bailey’s configuration — separation of solar water heating and storage — lived on to become the design of choice for millions throughout the world relying on the sun to heat their water. It first moved to Florida, where real estate in the 1920s was selling like hot cakes but no means existed to heat water cheaply and reliably. The only means besides solar — electricity — was too dear. By World War II, solar water heaters dominated the rooftops of Miami and its surroundings.
When war broke out, however, the government froze the use of copper — a principal element required by solar manufacturers — forcing the industry to shut down. After the war, servicemen remained in the Miami area, increasing the customer base for Florida Power & Light and therefore lowering electrical rates enough to compete with solar. The utility offered those using solar water heaters the electric equivalent at reduced rates in order to totally eliminate the solar industry in southern Florida.
The solar water heater, though, did not die; rather, it relocated farther east to Israel. The new Jewish state had so little electricity that it prohibited its daytime use for household water heating — a rule enforced by energy police. Seeing in this a business opportunity, an engineer who had visited Florida adapted the design for Israel’s special needs.
With the capture of oil fields in Egypt’s Sinai Peninsula during the Six-Day War, Israelis had sufficient fuel supplies to run electric water heaters cheaply, driving solar water heaters nearly out of business. Six years later, with the Arab oil embargo, the subsequent loss of Sinai and the rise of an unfriendly government in Iran turning off its oil spigot to Israel, the solar water heater business moved out of the shade. The government mandated the use of solar water heaters on all buildings less than 27 meters in height. The law coincided with a huge influx of immigrants requiring immediate housing, which set off an unprecedented boom for both the construction and the solar industries — industries that are selling the most current technology back to the United States.
Currently, Israel shares with Cyprus the highest per-capita use of solar water heaters in the world, and more than 90 percent of Israeli households heat their water with the sun. Interestingly, neither nation provides any monetary incentives for using solar water heaters.
Cyprus, like Israel, has only one natural energy resource: the sun. Otherwise, like Israel, it totally depends on imported oil to run its power needs. The knowledge of solar water heating came to Cyprus from Israel in the 1960s. The Cypriots knew a good idea when they saw it. To set an example to its citizens of good energy husbandry, the national government committed to installing solar water heaters on all state buildings. Unexpectedly, the government’s role in promoting solar became paramount when, in 1974, the Turks invaded the island, uprooting thousands of Greek Cypriots from their homes. The government had to house nearly one-third of the island’s population and, since it built the homes, had to put up solar water heaters. When the remaining population saw how well the heaters worked, they too soon became users.
Thousands of miles away on sunny Barbados, islanders saw their water heating bills rise after the two oil shocks of the 1970s. Prime Minister Tom Adams had a locally manufactured solar water heater placed on the roof of his residence. Impressed by its performance, Adams had Parliament pass a series of laws to encourage solar water heating, which included removal of duties on imports specifically directed to the island’s solar water heater industry, tax breaks for those buying solar water heaters and a stiff tax on electric water heaters. Later on, rebates were added to reward those making the change to solar.
The number of solar units on the island increased over the last 30 years by a factor of nearly 3,000, making Barbados the third highest per-capita user of solar water heaters in the world. The Barbados example shows that incentives pay for themselves. For a minuscule investment, the nation has saved tens of millions of dollars on oil it would have otherwise had to import, not to mention gained the added security of greater energy independence and cleaner air.
A recent observer commented, “The island now has most houses and buildings fitted with solar panels for water heating. In comparison, another West Indian island, Trinidad and Tobago — similar to Barbados in every way but having extremely low electric rates — has had little success in promoting the use of solar water heaters.”
A sunny climate is not required for success in solar water heating. Austria is tied with Barbados for per-capita use of solar water panels.
Also breaking the pattern, the environmental consciousness of Austrians drove the local market for solar. In 1978, a referendum whether to turn to nuclear power jump-started a national discussion on solar. A grassroots movement emerged with local communities developing do-it-yourself networks that supplied the initiative, know-how and training for the construction and installation of solar water heaters.
The disaster at the Soviet Union’s Chernobyl nuclear plant and concerns over global warming added fuel to the solar flame. Lobbying by concerned citizens got various Austrian states to provide subsidies. Seeing solar water heaters go up on neighbors’ houses started a snowball effect. Manufacturers that had been producing electric water heaters jumped into the solar business. By the mid-1990s, Austrians began extending their solar water systems to also provide heat for their homes. Under such friendly conditions, the use of solar heating panes has grown tenfold since 1984.
The real goliath of solar water heaters, based on the sheer number of solar water heaters in use, is China. More than 30 million Chinese households rely on the sun to heat their water. Over the last six years, the number of solar consumers has grown sixfold. The motivation is simple. A solar water heater in China costs less than $200. Without one, a family wishing for hot water would have to buy an electric water heater for about the same price and pay up to $120 per year for electricity. The payback is almost instantaneous.
Huang Ming, the founder of the solar water heater business in China, built a prototype so his aging mother would avoid having her rheumatism flare up by washing the dishes and floor with cold water. Word spread, and soon everyone in his neighborhood wanted a solar water heater. Huang listened and built what became the largest solar water heater business in China.
The largest city in the region where Huang lives also got the message. Rizhao, a city of 3 million people, provided funding to Huang’s firm to bring down the price and increase its efficiency and simplicity. The municipality also informed the public by holding educational seminars and conducting advertising campaigns in the old Communist tradition of parades and mass gatherings.
Their efforts paid off. Almost every household in Rizhao — located in the oil-rich Shandong province — now uses a solar water heater. The city has benefited as well. By relying on the sun, the citizens of Rizhao have cut carbon dioxide emissions by almost 53 thousand tons per year. Air quality has remained much better than in most urban areas of China, luring foreign investors and increasing tourism. The eco-friendliness of the city has also gained it national recognition resulting in leading Chinese universities establishing campuses here.
Experts project that by 2010 the number of solar water heaters installed in China will equal the thermal equivalent of electrical capacity of 40 large nuclear power plants. Globally, solar water heaters have the capacity to produce as much energy as more than 140 nukes. Their energy production dwarfs photovoltaics by a factor of 30 and equals the electrical capacity of wind, thought by most to be the most widely used renewable energy source. Solar water heaters saved, in 2005, the consumption of almost 70 million barrels of oil and cut carbon emissions by 29,000,000 tons — not bad for a technology, so simple it can be built in a tool shop, that will celebrate its centennial next year, born in America yet now primarily used elsewhere.
John Perlin is the author of From Space to Earth: The Story of Solar Electricity,A Golden Thread: 2500 Years of Solar Architecture and Technology (with Ken Butti), and A Forest Journey: The Role of Wood in the Development of Civilization. He worked with Nobel laureates Walter Kohn and Alan Heeger in the 2005 film The Power of the Sun. He can be contacted at johnperlin@physics.ucsb.edu.
