Иностранный язык (английский яз)

How solar energy works

Solar energy – power from the sun – is free and inexhaustible. This vast, clean energy resource represents a viable alternative to the fossil fuels that currently pollute our air and water, threaten our public health, and contribute to global warming. Failing to take ad­vantage of such a widely available and low-  impact resource would be a grave injustice to our children and all future generations.

     In the broadest sense, solar energy supports all life on Earth and is the basis for almost every form of energy we use. The sun makes plants grow, which can be burned as «biomass» fuel or, if left to rot in swamps and compressed underground for millions of years, in the form of coal and oil. Heat from the sun causes tem­perature differences between areas, producing wind that can power turbines. Water evaporates because of the sun, falls on high eleva­tions, and rushes down to the sea, spinning hydroelectric turbines as it passes. But solar energy usually refers to ways the sun's ener­gy can be used to directly generate heat, lighting, and electricity

The solar resource. The amount of energy from the sun that falls on Earth's surface is enormous. All the energy stored in Earth's reserves of coal, oil, and natural gas is matched by the energy from just 20 days of sunshine. Outside Earth's atmosphere, the sun's en­ergy contains about 1,300 watts per square meter. About one third of this light is reflected back into space, and some is absorbed by the atmosphere (in part causing winds to blow).

By the time it reaches Earth's surface, the energy in sunlight has fallen to about 1,000 watts per square meter at noon on a cloud­less day. Averaged over the entire surface of the planet, 24 hours per day for a year, each square meter collects the approximate en­ergy equivalent of almost a barrel of oil each year, or 4,2 kilowatt hours of energy every day.

This figure varies by location and weather patterns. Deserts, with very dry air and little cloud cover, receive the most sun more than six kilowatt hours per day per square meter. Northern climes get closer lo 3.6 kilowatt hours.

Passive solar design for buildings. One simple, obvious use of sunlight is to light our buildings. If properly designed, buildings can capture the sun's heat in the winter and minimize it in the summer, while using daylight year round. Buildings designed in such a way are utilizing passive solar energy a resource that can be tapped with­out mechanical means to help heat, cool, or light a building. South   facing windows, skylights, awnings, and shade trees with the sun in mind can be comfortable and beautiful places to live and work.

Solar heat collectors. Besides using design features to maxi­mize their use of the sun, some buildings have systems that actively gather and store solar energy. Solar collectors, for example, sit on the rooftops of buildings to collect solar energy for space heating, water heating, and space cooling. Most are large, flat boxes painted black on the inside and covered with glass. In the most common design, pipes in the box carry liquids that transfer the heat from the box into the building. This heated liquid usually a water alcohol mixture to prevent freezing  is used to heat water in a tank or is passed through radiators that heat the air. Oddly enough, solar heat can also power a cooling system. Today, about 1,5 million U.S. homes and businesses use solar water heaters. In other countries, solar collectors are much more common; Israel requires all new homes and apartments to use solar water heating, and 92 percent of the existing homes in Cyprus already have solar water heaters. With natural gas prices at historically high levels, solar water and space heaters have become much more economic.

The future of solar energy. Solar energy technologies poised for significant growth in the 21st century. More and more architects and contractors are recognizing the value of passive solar and learning how to effectively incorporate it into building designs. Solar hot water systems can compete economically conventional systems in some areas. And as the cost of solar PV continues to decline, these systems will penetrate increasingly larger markets. In fact, the solar PV industry aims to provide all new U.S. electricity generation by 2025.

     Aggressive financial incentives in Germany and Japan have made these countries global leaders in solar deployment for years.

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