Putting the Sun to Work

　　It's a hot summer day, and you, your family, and friends decide to drive to the beach for a cookout.

　　When you get to the beach, the sand and the rocks are so hot that they hurt your bare feet. You put on sneakers in a hurry. The water is so bright and shining in the sun that you can hardly look at it. While the charcoal (木炭) fire is starting to burn in the cookout stove, every one goes for a swim. The water feels good—warm at the top, but cooler down around your toes.

　　A little wind is blowing when you come out. The fire isn't quite ready for cooking yet, so you play tag (兒童捉人游戲) or read.

　　For lunch there are hot dog, corn, salad and rolls, sodas, fruit, and coffee for the adults. By the time the coffee water boils and the corn and hot dogs are cooked, all the bathing suits are dry. So are the towels spread out on the rocks, in the sun.

　　Lunch is good. Just as you are finishing, it starts to rain so you pack up and run. But nobody minds the rain. It will cool things off.

　　At the same time you were having fun at the beach, work was being done. Energy from the sun was doing work. Energy, in one form or another, does all the work in the world.

　　Heat energy from the sun dried the towels. It heated the sand and the rocks, the water and the air. It even made the rain and the wind. Heat from the sun does small work and big work, all over the earth.

　　Light energy from the sun was working on the beach too. It supplied the daylight.

　　It lit the earth and made the sand bright and the water sparkling.

　　The sun also supplied the energy that grew the food you ate.

　　Plants use light energy from the sun to make food for themselves. The food is a kind of sugar. It is also a kind of energy called chemical energy. Green plants change light energy from the sun into chemical energy.

　　Plants use some of that energy for everyday living and growing. They store the rest in their leaves and seeds, in fruit, roots, stems, and berries.

　　The salad and the corn, the rolls, fruit, and coffee all came from plants. You and all animals depend on plants for food.

　　The charcoal you used for cooking began as a plant too. Once, that charcoal was a living tree that used sunlight to make food and then stored part of the food it made. The energy in this stored food remained, even after the tree died. You used that energy when you burned the charcoal.

　　The gasoline you used for driving to the beach began with energy from the sun, too. It was made from oil.

　　Oil was formed from the remains of plants and animals that lived on earth millions of years ago. The remains of ancient living things are called fossils. This is why oil is called a fossil fuel. Coal and natural gas are fossil fuels, too.

　　Now fossil fuels are beginning to be used up.

　　That's why people worry about running out of energy.

　　But as long as the sun shines, the earth will not run out of energy. The sun pours more energy on earth than we can ever use. Most of that energy comes to us as heat and light. Energy from the sun is called solar energy.

　　Solar energy is a safe kind of energy. It doesn't make pollution or have dangerous leftovers. That is why scientists and inventors are experimenting with ways of harnessing the sun to do some of the jobs fossil fuels have been doing.

　　But to make the sun do work like that, they have to solve some problems.

　　They have to collect the sun's energy. Collecting sunshine isn't easy, unless you are a plant.

　　Sunshine isn't easy to store, either. You can't fill a tank with it or put it in the wood box. You can't move it through a pipe or a wire. You can't turn it on.

　　Still, people have been using solar energy to help do their work for a long time. There are old ways and new ways of catching sunshine and putting it to work.

　　Suppose you were living in a cold place and going to spend the winter in a cave. Would you choose a cave that faced the winter sun or a cave that faced away from it?

　　You might make the same choice if you were building a house in a cold place. You would probably build the house, so the winter sun would pour in the windows to warm it. People have been building houses that way for a long time.

　　Is it possible to catch still more of the sun's heat in a house? Yes, Some houses also collect heat on the roof, move it indoors, store some, use some to make hot water and the rest for heating. A house like that is called a solar house.

　　People who build solar houses have learned how to do those things by observing how the earth itself uses solar energy.