Facts about solar energy

The sun is the source all of solar energy on Earth. It takes over eight minutes for sunlight to travel 93 million miles to Earth but once it arrives about one third is reflected back into space. The Earth absorbs the remaining two thirds, about four kilowatts every day for every square meter, enough energy in one year to replace one barrel of oil. The amount of energy received is higher at the equator and lower at the poles. The total solar energy reaching the Earth in one hour is more than our yearly global energy demand.

There are many ways to convert solar energy into heat and electricity. Solar cookers focus sunlight to heat a container of food or water. Solar lighting uses reflecting panels and tubes to direct sunlight into buildings. Small solar collectors absorb light to heat water, and larger collectors create steam that drives turbine and produces electricity. Solar cells produce electricity directly from sunlight without the need for steam or turbines. Solar cells are used to power wristwatches and calculators, and even create enough power for a space station.

Solar collectors have many thin pipes placed over a flat surface facing the sun. The surface is painted black because it converts sunlight to heat better than other colors which reflect part of the light away. A liquid, usually water, flows through the pipes and absorbs this heat before returning to a storage container. The liquid is usually water, but some systems use a water-glycol mixture that absorbs heat better. However, this must be passed through a heat exchanger to transfer the heat to the hot water supply. Solar collectors can provide nearly all household water heating needs in most parts of the world. Unlike solar panels, the efficiency of collectors is reduced in colder climates because of heat loss to the environment.

Solar cells were first discovered in the 1880’s but silicon cells weren’t produced until the 1950’s. The electricity they produce is free and non-polluting, but manufacturing them requires energy and creates pollution. Solar cells are made from semiconductors which use a range of materials, including silicon, cadmium, tin, copper, selenium, gallium, and titanium. Most solar cells are made from silicon, which makes up around one quarter of the Earth’s crust, and is the second most common element after oxygen.

Each solar cell only produces about two volts, so panels use many cells connected in series to produce a useful voltage. An inverter is used to increase this voltage to mains voltage, and batteries are used to store the excess energy. Solar cells can also produce electricity from artificial light, which itself may have been created by solar energy. They can produce electricity for more than twenty years but suffer a gradual reduction in their efficiency past that point. They have no moving parts and are enclosed by damage resistant plastic and glass casings, allowing them to withstand extreme environments.

Solar energy is no longer considered an environmental novelty, and is now a fast growing global industry that employs thousands of people and generates billions of dollars in profit. Demand for solar energy has increased thirty percent per year for the last fifteen years and should accelerate as worldwide energy demand increases. Homeowners have increasingly turned to solar energy in recent years to offset rising energy costs. Corporations are investing in the industry, and governments are providing generous subsidies to use solar energy. The decline in the supply of fossil fuels, combined with the calls for action on global warming, makes solar energy an essential part of our energy supply.

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