Solar thermal engine

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 silverplated
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 CivilWar 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- ×
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-horsepower
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 twentysix
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

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. Alarge 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; Photovoltaiccell ; Solar Power