The energy potential of the sun is amazing. Solar energy emits no greenhouse gasses, nor does it pollute water or air. If merely 4% of all deserts had solar energy systems covering them, it could create enough energy to fulfill the entire world’s energy demands, according to the International Energy Agency.

There are two major methods of producing power from solar energy. Solar energy can be produced through photovoltaic cells or through direct use in solar thermal power plants. Photovoltaic cells are the popular solar panels that can be seen on many rooftops, or on outdoor lighting. Direct use of solar energy can be seen in the Western US, where solar thermal power plants use parabolic troughs, solar dishes, or solar power towers to capture solar heat.

Photovoltaic

Photovoltaic, or PV, power plants use solar cells that trap the sun’s radiation, converting it directly into electrical energy. Typical PV cells are capable of producing 1-2 watts of electricity each, but they can be connected in a circuit to expand capabilities. PV cells are currently 12% to 15% efficient at producing electricity from solar energy, according to the Solar Energy Society of Canada. Recently, scientists have been able to reach PV cell efficiency of nearly 30%, according to Energy Innovations Inc. These more efficient, highly concentrated PV cells (HCPV) use a proprietary optical system to focus the sun's rays 1,200:1 onto a very small piece of photovoltaic material. HCPV cells will be produced in early 2010.

Energy produced by PV cells must be consumed immediately, or small amounts can be stored short-term, since there is no efficient way to store large amounts of the electricity. Often times, PV cells are used on outdoor electronics, like lighting or emergency telephones. The electricity produced by PV cells is direct current, so unless an appliance uses DC, an inverter will be used in the circuit as well. If the PV cells are connected to the electricity grid, then excess electricity can be sold to an offtake energy company. An offtake energy company is an electrical company that has a contract to buy excess electricity from a producer of electricity, such as a home with PV cells.

Direct solar

Solar thermal power plants produce electricity through the direct use of solar energy. Solar radiation is accumulated by solar collectors. Parabolic troughs, solar dishes, and solar power towers are all solar concentrator collector systems. All three of these systems attract sunlight and reflect it into a concentrated area, where the heat is then absorbed.

The heat generated from solar concentrated collectors can be used to heat liquid for steam turbine use in a power plant.



Commercial use of solar energy

PV cells can be placed on rooftops of large buildings and the electricity they produce can be consumed by the building. If any excess electricity is produced, it can be sold to an offtake electric company. The building will have a meter keeping track of how much electricity is being sold back to an offtake.

Once the sun has set, or it is cloudy outside, the building will take back and consume electricity from the offtake company. The meter will keep track of how much is consumed, and given back by the building. Small amounts of PV cell electricity can be stored in batteries locally and used when the sun is not out as well.

Through the use of solar concentrated collectors, a liquid will be heated up by the solar energy. The liquid travels through tubing into a power plant where steam is then created inside a heat exchange unit. Once steam is created, it is forced through a turbine which generates electricity.

Direct solar energy is collected outside of a solar thermal power plant. The largest solar thermal power plant in the world will be located in Deming, New Mexico. The 300 Megawatt facility will be capable of supplying enough energy for 240,000 homes and is set to open by 2011, according to Green Options.

Residential use

PV cells and solar concentrated collectors can also be used for residential applications. PV cells can be placed on rooftops, and just like in commercial use, an inverter is used and the electricity produced can be consumed by the residence, or sold back to an offtake electrical company. Once the sun sets, or disappears behind clouds, the residence will consume electricity from the electrical company, while a meter on the house keeps track of the consumption and excess electricity trade off.

Solar concentrated collectors as well as nonconcentrated collectors can be placed on rooftops in residential areas as well. Certain types of collectors are more practical than others.

For a concentrated collector, once the collector heats up the liquid that is inside of the tubing, the liquid will be pumped into the house through the tubing and air will be blown past it, and through the air vents of the house. Nonconcentrated collector cells simply absorb heat themselves on rooftops while air from inside the house circulates past the roof through natural convection, or with the help of fans.

Future of solar energy

Since the actual process of collecting solar energy emits no greenhouse gas, air pollution, or water pollution, solar energy fulfills the needs of many renewable energy goals.

Solar energy technology is fairly new, and it has some downsides that have not been resolved yet. The cost of producing electricity via solar energy is 12 cents per kWh using solar thermal and 23 cents per kWh using PV cells, according to Gilbert Metcalf, Federal Tax Policy Toward Energy. In comparison, geothermal energy generates electricity at roughly 4.5 to 7.3 cents per kWh according to the California Energy Commission.

There are also a few environmental concerns that solar energy carries. Birds and insects can be killed if they fly into a beam of concentrated sunlight, typically associated with solar power towers. In addition, the production of PV cells requires the use of a small amount of toxic chemicals. Finally, solar energy plants that use solar concentrated collectors may require the use of a liquid that can be heated quickly; the potentially hazardous liquid must be handled and disposed of properly.

Since the amount of usable solar energy is so abundant, now is a great time for the development of solar power plants to eventually replace hazardous plants. The US government offers many different subsidy programs for solar energy projects to help with start up, and ongoing costs of solar energy.

Between all of the sources for renewable energy, Earth has a great opportunity to become a cleaner, safer place. Through the help of government grants and subsidies to help start new projects, renewable energy can survive and power the future.

- Colvin