Understanding Solar Energy

Solar energy is a renewable and inexhaustable source of energy which can be converted into useable energy such as electricity through technologies such as photovoltaic devices. Solar energy, combined with wind energy can potentially help us reduce our reliance on fossil fuel consumption and thereby cutting down on greenhouse gas emissions.

Scientifically, incoming energy from the sun is referred to as "insolation" which arrives on earth predominantly in the form of visible light, ultraviolet and infrared energy. A portion of the energy arriving is reflected back into space by the earth's atmosphere before reaching the earth's surface is called "shortwave reflectance" amounting to approximately 34% of the energy received. The majority of the energy arriving is absorbed into the earth's heat cycle, water evaporation and weather cycles (climate). Approximately 1-2% of the energy can be attributed to the generation of wind. Interestingly, only approximately 0.023% of the energy is absorbed into the photosynthesis process.

How much solar energy is available?

To calculate the amount of energy received on earth, the basic formula to use is: ENERGY = POWER x TIME. For example, if 1KWH of energy is consumed (1 kilowatt hour), that is to say:

1000 W (power) x 1 hour (time) = 1000WH or 1KWH (energy)

which is equivalent to ten 100 watt light bulbs left on for an hour.

Given the percentages with respect to "shortwave reflectance" and the portion of energy absorbed into the earth's heat cycle, water evaporation and weather cycles, the incidential solar energy received on the earth's surface is approximately 164W per sq. meter over a 24 hour day (averaged over the entire earth). Solar energy received on a typical 8 hour summer day, situated 40 degrees latitude will result in approximately 600W per sq. meter.

Given these figures, during an 8 hour day, the solar energy can be calculated as:

600 W (power per sq. m.) x 8 hours (time) = 4800WH per sq.m. (energy) or 4.8KWH per sq.m.

This energy is roughly equivalent to the energy produced by 0.13 gallons of gasoline. Extending this further, for a 1000 sq. feet. (~93 sq. m.) of horizontal area such as a roof area, could capture approximately 447KWH which is equivalent to the burning of roughly 12 gallons of gasoline!

Capturing Solar Energy

The method of capturing solar energy and converting it into useable energy is done with what is commonly known as "solar cells".[1] A solar cell, or more correctly, a photovoltaic device is a semiconductor, typically constructed of silicon crystal in layers which becomes active when the surface of the photovoltaic cell is exposed to sunlight. The solar energy excites the silicon crystal's electrons, knocking them loose from their elemental structure to cross the diode junction of the solar panel to create current. By afixing metal contacts to the top and bottom of the photovoltaic device (solar cell), current can be drawn to power external loads such as lights, appliances, etc.

Given the current generated from these individual cells is small and the voltage is low, are combined to form solar modules, which are then connected into large series-parallel arrays (solar arrays) in order to capture the necessary solar energy to generate useful amounts of electrical energy. However, despite the immense solar energy available per sq. m., solar modules typically perform at approximately 10% to 15% efficiency. The combination of wind energy and solar energy renewable energy technologies (hybrid systems) will provide a relatively stable and continuous source of renewable energy.

The US Department of Energy - Energy Efficiency and Renewable Energy has an excellent page entitled How Small Solar Systems Work offering a combination of excellent textual content, graphics and animation which effectively describe this subject. For more details on the subjects of wind and solar technologies, click wind turbines and photovoltaic systems for more detailed technical information, enough to glaze one's eyes.

Footnotes

1. Photovoltaic systems is the technology that Solar Wind Canada deploys inconjunction with wind turbines (hybrid RETS) or stand-alone solar systems, despite other variations of solar energy devices available such as solar water heating or cooling systems.

References

1. YouTube. "Solar Energy Basics for Your Home". 2007. Last accessed January 21, 2010.
2. househunting.ca. "Solar-powered Homes". 2008. Last accessed January 21, 2010.
3. US Department of Energy. "How Small Solar Electric Systems Work". Energy Efficiency and Renewable Energy. September 19, 2005.
4. Scott Aldous. "How Solar Cells Work". howstuffworks.com. 1998 - 2006.
5. Wikipedia. "Solar power". March 2006.