The invention: The first commercially practical plant for generating electricity from solar energy.
The people behind the invention:
Frank Shuman (1862-1918), an American inventor John Ericsson (1803-1889), an American engineer Augustin Mouchout (1825-1911), a French physics professor
Power from the Sun
According to tradition, the Greek scholar Archimedes used reflective mirrors to concentrate the rays of the Sun and set afire the ships of an attacking Roman fleet in 212 b.c.e. The story illustrates the long tradition of using mirrors to concentrate solar energy from a large area onto a small one, producing very high temperatures.
With the backing of Napoleon III, the Frenchman Augustin Mouchout built, between 1864 and 1872, several steam engines that were powered by the Sun. Mirrors concentrated the sun’s rays to a point, producing a temperature that would boil water. The steam drove an engine that operated a water pump. The largest engine had a cone-shaped collector, or “axicon,” lined with silver-plated metal. The French government operated the engine for six months but decided it was too expensive to be practical.
John Ericsson, the American famous for designing and building the Civil War ironclad ship Monitor, built seven steam-driven solar engines between 1871 and 1878. In Ericsson’s design, rays were focused onto a line rather than a point. Long mirrors, curved into a parabolic shape, tracked the Sun. The rays were focused onto a water-filled tube mounted above the reflectors to produce steam. The engineer’s largest engine, which used an 11- x 16-foot trough-shaped mirror, delivered nearly 2 horsepower. Because his solar engines were ten times more expensive than conventional steam engines, Ericsson converted them to run on coal to avoid financial loss.
Frank Shuman, a well-known inventor in Philadelphia, Pennsylvania, entered the field of solar energy in 1906. The self-taught engineer believed that curved, movable mirrors were too expensive. His first large solar engine was a hot-box, or flat-plate, collector. It lay flat on the ground and had blackened pipes filled with a liquid that had a low boiling point. The solar-heated vapor ran a 3.5-horse-power engine.
Shuman’s wealthy investors formed the Sun Power Company to develop and construct the largest solar plant ever built. The site chosen was in Egypt, but the plant was built near Shuman’s home for testing before it was sent to Egypt.
When the inventor added ordinary flat mirrors to reflect more sunlight into each collector, he doubled the heat production of the collectors. The 572 trough-type collectors were assembled in twenty-six rows. Water was piped through the troughs and converted to steam. A condenser converted the steam to water, which reentered the collectors. The engine pumped 3,000 gallons of water per minute and produced 14 horsepower per day; performance was expected to improve 25 percent in the sunny climate of Egypt.
British investors requested that professor C. V. Boys review the solar plant before it was shipped to Egypt. Boys pointed out that the bottom of each collector was not receiving any direct solar energy; in fact, heat was being lost through the bottom. He suggested that each row of flat mirrors be replaced by a single parabolic reflector, and Shuman agreed. Shuman thought Boys’s idea was original, but he later realized it was based on Ericsson’s design.
The company finally constructed the improved plant in Meadi, Egypt, a farming district on the Nile River. Five solar collectors, spaced 25 feet apart, were built in a north-south line. Each was about 200 feet long and 10 feet wide. Trough-shaped reflectors were made of mirrors held in place by brass springs that expanded and contracted with changing temperatures. The parabolic mirrors shifted automatically so that the rays were always focused on the boiler. Inside the 15-inch boiler that ran down the middle of the collector, water was heated and converted to steam. The engine produced more than 55 horsepower, which was enough to pump 6,000 gallons of water per minute.
The purchase price of Shuman’s solar plant was twice as high as
Trough-shaped collectors with flat mirrors (above) produced enough solar thermal energy to pump 3,000 gallons of water per minute. Trough-shaped collectors with parabolic mirrors ((below) produced enough solar thermal energy to pump 6,000 gallons of water per minute.
that of a coal-fired plant, but its operating costs were far lower. In Egypt, where coal was expensive, the entire purchase price would be recouped in four years. Afterward, the plant would operate for practically nothing. The first practical solar engine was now in operation, providing enough energy to drive a large-scale irrigation system in the floodplain of the Nile River.
By 1914, Shuman’s work was enthusiastically supported, and solar plants were planned for India and Africa. Shuman hoped to build 20,000 reflectors in the Sahara Desert and generate energy equal to all the coal mined in one year, but the outbreak of World
War I ended his dreams of large-scale solar developments. The Meadi project was abandoned in 1915, and Shuman died before the war ended. Powerful nations lost interest in solar power and began to replace coal with oil. Rich oil reserves were discovered in many desert zones that were ideal locations for solar power.
Impact
Although World War I ended Frank Shuman’s career, his breakthrough proved to the world that solar power held great promise for the future. His ideas were revived in 1957, when the Soviet Union planned a huge solar project for Siberia. A large boiler was fixed on a platform 140 feet high. Parabolic mirrors, mounted on 1,300 railroad cars, revolved on circular tracks to focus light on the boiler. The full-scale model was never built, but the design inspired the solar power tower.
In the Mojave desert near Barstow, California, an experimental power tower, Solar One, began operation in 1982. The system collects solar energy to deliver steam to turbines that produce electric power. The 30-story tower is surrounded by more than 1,800 mirrors that adjust continually to track the Sun. Solar One generates about 10 megawatts per day, enough power for 5,000 people.
Solar One was expensive, but future power towers will generate electricity as cheaply as fossil fuels can. If the costs of the air and water pollution caused by coal burning were considered, solar power plants would already be recognized as cost effective. Meanwhile, Frank Shuman’s success in establishing and operating a thoroughly practical large-scale solar engine continues to inspire research and development.
See also Compressed-air-accumulating power plant; Fuel cell; Geothermal power; Nuclear power plant; Photoelectric cell; Photovoltaic cell; Tidal power plant.
