solar energy Every hour the sun beams onto Earth more than enough energy to satisfy global energy needs for an entire year. Other solar technologies are passive.
Solar energy is the technology used to harness the sun's energy and make it useable. Today,
the technology produces less than one tenth of one percent of global energy demand. Many people are familiar with so-called photovoltaic cells, or solar panels, found on things like spacecraft, rooftops, and
handheld calculators. The cells are made of semiconductor materials like those found in computer c
hips. When sunlight
hits the cells, it knocks electrons loose from their atoms. As the electrons flow through the cell, they generate electricity. On a much larger scale, solar thermal power plants employ various techniques to concentrate the sun's energy as a heat
source. The heat is then used to boil water to drive a steam turbine that generates electricity in much the same fashion as
coal and nuclear power plants, supplying electricity for thousands of people. In one technique, long troughs of U-shaped mirrors focus sunlight on a pipe of oil that runs through the middle. The hot oil then boils water for electricity generation. Another technique uses moveable mirrors to focus the sun's
rays on a collector tower, where a receiver sits. Molten salt flowing through the receiver is heated to run a generator. For example, big windows placed on the sunny side of a building allow sunlight to
heat-absorbent materials on the floor and walls. These surfaces then release the heat at night to keep the building warm. Similarly, absorbent plates on a roof can heat liquid in tubes that supply a house with hot water. Solar energy is lauded as an inexhaustible fuel source that is pollution and often noise free. The technology is also versatile. For example, solar cells generate energy for far-out places like satellites in
Earth orbit and cabins deep in the Rocky Mountains as easily as they can power do
