Solar Energy

Solar energy has been with us since the Earth was formed. It is the heat and light from the Sun that warms our planet and drives our weather systems. Solar technologies are wide ranging. Energy from the Sun can be used to heat and cool buildings, provide natural light, heat water and cook food. Although all solar energy technologies have an important role to play in energy conservation and the reduction of greenhouse gas emissions, this section will discuss only photoelectric or the conversion of light into electricity.

Photovoltaic system
Photovoltaic solar panels.

A solar cell or photoelectric cell is a device that converts light into electricity using the photoelectric effect. The first working solar cells were constructed by Charles Fritts in 1883. The photoelectric effect occurs when certain materials give off or emit electrons after absorbing electromagnetic energy such as light or x-rays. Most photovoltaic (PV) cells use semi-conductor materials usually made of silicon. One side is a p-type conductor and the other is an n–type conductor. Photons of light can be used to create an excess positive charge in the p-type material and an excess negative charge in the n-type layer which then creates a small electric current. You see this technology at work whenever you use your solar calculator.

Photoelectric cell
Photoelectric cells convert light into electricity.

Photoelectric cells have wide ranging applications. They are extremely useful for powering small electronic devices or for providing electricity in remote locations. The space program also uses photoelectric cells to power satellites and small spacecraft. As for large scale electrical production, photoelectric cells are not yet practical from either an economic or efficiency point of view.

The efficiency of photoelectric cells is quite low (ranging from 5–15%), meaning that large numbers of them have to be used together in what is called an array in order to produce any significant amount of electricity. If you covered the entire roof of an average house with photoelectric cells you might get enough electricity to go about your business during the day time. However, as technology improves, the efficiency of photoelectric cells will increase and already some homeowners and businesses are using them to reduce their yearly energy costs and carbon emissions.

The International Space Station uses photoelectric cells to help run computers, life support and other vital equipment — demonstrating that photoelectric cells are reliable energy converters. However if you take into account that the station is roughly the size of three school buses, you can see how many photoelectric cells are needed to power it. The amount of land area that would be required to provide enough electricity for a city or town would be enormous.

The province of Ontario has decided to build what will be one of the world’s largest solar farms. Solar farms are planned to be built in Sarnia and Sault Ste. Marie, together producing 60 MW (enough electricity for 9,000 homes). From a financial point of view, producing electricity using photoelectric cells is much more costly than producing electricity using other sources such as fossil fuels, hydroelectricity or nuclear power and presently relies on government subsidies with a view to developing the industry.

Sources:

Canadian Energy Research Institute, World Energy: The Past and Possible Futures, p. 81, 2008,
www.cna.ca/english/pdf/Studies/CERI/CNA_CERI07_EN.pdf.
The Physics of Photoelectric Cells, http://www.jgsee.kmutt.ac.th/exell/Solar/PVCells.rtf.
Image source: NASA.