Solar energy is the radiant energy (light or heat) that comes from the sun. Only a small amount of the sun’s energy strikes the Earth, one part per two million. However, even that one part is an enormous amount of energy.
Solar energy is the most abundant energy source available. In fact, according to National Geographic, every hour, the sun beams enough energy to meet the entire world’s energy needs for a year. The tricky part is harnessing the energy effectively to meet those needs. Solar power depends on the sun being out—and when it is not, solar panels generate no power. However, storage systems can collect the sun’s energy for use during cloudy weather or at night.
Sunlight can be directly used to create electricity using solar, or photovoltaic (PV) cells. The solar cells are made using silicon, the same thing that makes up sand. Even though silicon is found almost everywhere, making a solar panel is a difficult and expensive process. According to a report in the New York Times, “generating power from photovoltaic panels costs more than four times as much as coal, and more than twice what wind power costs.” Polysilicon, a material made up of small silicon crystals that is used to make photovoltaic cells, is sometimes in short supply, which means prices for solar equipment can be volatile.
The silicon is heated and melted at super high temperatures and then molded into thin wafers. When sunlight strikes the solar cell, electrons are loosened and move toward a treated front surface, making an imbalance between the front and back. Electricity occurs when a connector, such as a wire, joins the negative and positive sides together.
The production of photovoltaic cells, which are used to change sunlight directly into electricity, causes far less pollution than fossil fuel-burning power plants. While manufacturing the cells does require harmful metals such as lead and mercury and also produces some greenhouse gases, the toxic emissions are up to 300 times lower than those created by coal power plants, according to scientists with the Brookhaven National Laboratory in New York.
PV cells by themselves are small, at most about 4 inches across, and do not generate enough power for most applications. That is why, in most photovoltaic systems, PV cells are grouped into larger panels or modules that collect sunlight and convert it into electricity. These panels can be small (like those found on solar-powered calculators) or huge, covering acres of land and providing power for whole buildings. Most photovoltaic cell panels need a lot of space. Because the sun doesn’t deliver that much energy to any one place at any one time, a large surface area is required to collect the energy at a useful rate.
Solar thermal plants also use sunlight to generate power, but in a different way from PV systems. Solar thermal plants use the sun’s rays to heat liquid, which is then used to heat water and produce steam. This steam then powers a turbine to generate electricity. There are three main types of solar thermal power systems: solar dish, solar power tower, and parabolic trough.
Solar dishes are designed to always point at the sun, collecting concentrated energy and, with the help of a turbine and electric generator, turning that energy into electricity. Solar power towers use mirrors to concentrate the sun’s energy into a central receiver tower, which contains fluid that collects heat. A parabolic trough system uses a long reflector to focus the sun’s rays onto a receiver pipe. Fluid moving through the pipe is then heated and used to heat water, creating steam. This steam is then used in a turbine to generate electricity.
Photosynthesis is solar power at work in nature. It is the process of converting carbon dioxide into organic compounds using energy from the sun’s rays. Photosynthesis is needed to make plants, bacteria and algae grow. It is vital for life on Earth—photosynthesis gives us the fruits, vegetables and grains we eat and also maintains the normal level of oxygen in our atmosphere.