Multiple MatchingExercício 1 de 70

Solar power turns sunlight directly into electricity using panels made of special materials. One of its great advantages is flexibility: a single panel can charge a phone, while thousands together can supply a town, and the cost has fallen so far that many ordinary households now fit panels to their own roofs without much expense. The obvious drawback is that it depends entirely on the sun. Output drops on cloudy days and stops altogether at night, so unless the electricity is stored in batteries, other sources must take over once it gets dark.

Wind power uses tall turbines whose long blades are turned by moving air, driving a generator at the top of the tower. Modern turbines are huge and efficient, and large groups of them, on hills or out at sea, can power many thousands of homes cheaply. Like solar, though, wind is not constant: on a still day the blades barely move and little electricity is produced. The technology also has vocal opponents, who complain that the towers spoil open landscapes and that the constant turning creates an irritating background noise.

Hydroelectric power is generated by releasing water stored behind a large dam, letting it rush down through turbines as it falls. Unlike sun and wind, it is highly reliable: operators can hold the water back and then release it the moment extra electricity is needed, which makes it valuable for meeting sudden peaks in demand. The cost, however, is paid at the start. Building a dam usually means flooding an entire valley behind it, drowning farmland and forcing communities to move. Once built, though, a hydro plant can keep working for a hundred years.

Geothermal power taps the natural heat of the earth itself. By drilling deep wells, engineers reach hot rock or underground water and use the steam to drive turbines. Because that heat is always there, a geothermal plant runs steadily day and night, in any weather, providing dependable power around the clock. Its great limitation is location: useful heat lies close enough to the surface only in regions of past or present volcanic activity, so most of the world cannot use it. Where conditions are right, however, it takes up little space and produces almost no pollution.