Hotfoot to Heliostat
c200 BC
-200 -200
117.00W34.50N
SCI

BARSTOW, CALIFORNIA
	One somewhat doubtful story says that in about 200 BC the Greek mathematician Archimedes set fire to Roman ships besieging his home town of Syracuse by focusing sunlight on them with mirrors.
	Though that may have been one early use for solar energy, it was far more common to use the sun for such simple tasks as drying fruit or evaporating water to obtain salt from the sea.  But today solar energy is also used for heating, cooling and generating electricity.
	Actually, almost all our energy is solar energy, though it often comes to us indirectly. For example, wood, coal and oil were once plants, which grew because of the sun; windmills are powered by winds caused by the sun; and we can harness rivers because the sun evaporates water from lakes and seas, which then falls as rain and powers hydroelectric plants.
	Though we use solar energy indirectly in many ways, there are just two methods of using solar energy directly: passively and actively.
	To use solar energy passively, architects design buildings to collect the maximum amount of heat on cold winter days and to avoid collecting heat in the summer. On the other hand, active solar systems use collecting devices to convert sunlight into electricity or to heat water which is circulated through a building to warm it.
	Most solar devices have been developed for individual buildings, but some experimental large scale projects, such as one near the desert town of Barstow, California, are designed to feed electricity into the regular power grid.
	Like Archimedes' system, these devices use hundreds of mirrors, called heliostats, to focus the sun's rays on a boiler at the top of a tower.  The vaporized liquid from the boiler then powers a generator.