CHAPTER ONE NOTHING NEW UNDER THE SUN THE SUN IS THE ULTIMATE SERVANT It doesn’t argue never takes a day off and even works for free Ancient peoples recognized that the sun just like a hard-working servant provided everything in their lives Its heat gave them warmth Food came from plants nourished by sunshine Grateful for its power and energy many cultures worshiped the sun viewing it as a deity Today people are less likely to worship the sun but it’s still the source of virtually all Earth’s energy Although 93 million miles 150 million km away this is one long-distance relationship that’s not going to fizzle out Ancient Egyptians thought of the sun as a great boat that carried the gods across the sky 6
People can save money and make use of passive solar energy for drying clothes or heating buildings Each second the sun burns up millions of tons of its own mass turning it into light and heat Only a tiny fraction of that energy ever reaches Earth Even so in less than an hour and a half the sun delivers enough energy to power the world’s people for an entire year It’s estimated that just 20 days of sunlight provide as much energy as is stored in all the world’s reserves of fossil fuels Of course people can capture only a very small portion of all that solar energy but fortunately that’s all they need At its most basic level solar energy is easy to use All it requires is the sun and something that absorbs heat Drying clothes outside uses solar energy So does frying an egg on the sidewalk on a hot summer day Make sure it’s a clean sidewalk first This passive solar energy is simply heat and light that is collected from the sun It does not involve converting the sun’s energy into another form such as electricity as active solar technology does People have used passive solar energy for thousands of years In ancient Greece and Rome architects and engineers designed towns and cities to have as many homes as possible facing south where they could get the most sun in the winter As cities grew more buildings sometimes blocked the sun from reaching existing structures In the sixth century A D the Romans passed a law making it illegal to construct a building 7
In a greenhouse warm air rises through a process called convection and is trapped by the walls and roof that would prevent sunlight from reaching the buildings around it The people had a right to light Later people discovered the power of glass to trap heat They put windows in their houses and constructed greenhouses to grow plants even when it was cold outside Solar power was also used to heat water Water tanks were painted black since black absorbs more heat than other colors The warm water was used for cooking washing clothes and dishes and bathing In one story from the third century B C the Greek mathematician and scientist Archimedes told soldiers to direct their bronze shields toward the sun and then mirror them at enemy Roman ships making them catch fire It’s the same basic principle as using a magnifying glass to focus sunlight on a dry leaf heating the leaf until it ignites This incident is probably more legend than truth but it shows that people recognized that the sun’s power could also be concentrated Today concentrated solar power CSP using the same fundamental methods of focused sunlight is applied in commercial solar power plants Getting more power out of the sun is a goal for the modern solar industry Direct solar heat is helpful but it’s not enough to meet the power needs of today’s societies 8
Wind can supplement solar power providing after-dark energy People want hot showers but solar heated water is often just warm Solar-heated houses are warmer than the outdoors but that’s not always enough during a cold winter People also want enough energy to run appliances such as refrigerators televisions and computers Much of this power comes from electricity an extremely versatile means of delivering energy The main challenge for solar power today is converting it into electricity This is accomplished in either of two ways One is concentrated solar power This captures the sun’s heat energy The heat is collected and then used to make steam The pressure of the steam spins the blades of a turbine which in turn powers a magnet that generates electricity Another solar technology is photovoltaics This word is a combination of two words Photo means light in Greek and voltaic refers to electricity In a photovoltaic PV system the sun’s light is converted directly into electricity when it interacts with certain elements 9
