The Science — What is Solar Energy?

In simple terms, and as the name suggests, solar energy is the energy produced by the earth’s closest star: the sun.

Although the sun is over 150 million kilometers away from the Earth, its energy has no trouble reaching our planet. The sun creates energy through a thermonuclear process, which produces both heat and electromagnetic radiation in the form of visible light, infrared light, and ultra-violet (UV) radiation (the kind that burns your skin on a sunny day).

Only a fraction of that radiation reaches Earth - the rest goes into space - but it is more than enough to provide all of our power needs several times over. More energy from the sun reaches the earth in an hour than the whole world uses in a year. The challenge is harnessing that power and converting it into energy forms more useful to us such as heat and electricity.

The Technology — How is Solar Energy Harnessed?

Solar energy tends to be harnessed in one of three ways: through active, passive, and photovoltaic (PV) solar systems.

Passive solar energy makes use of the energy from the sun as it comes to the earth. As the name suggests, passive solar uses no additional mechanical equipment to convert the sun’s energy into other forms of energy. Passive solar is a cost effective way to use solar energy in your home.

Harnessing passive solar energy often involves appropriate building design and placement building components such as walls, windows, the floor, and the roof to make use of sunlight for daylighting, space heating and/or space cooling. For example, passive solar heating of buildings occurs when sunlight passes through a window. Landscaping can assist building design elements by proving summer shade to control overheating or providing a windbreak in the winter.

Active solar technologies convert the sun’s energy into heat, usually for the purpose of heating water. Solar collectors are positioned so that they are aimed at the sun to collect as much radiant heat as possible.

There are differences in the level of insulation and efficiency, but generally, solar water heaters pump water through pipes located within the panel. The collectors are dark or black to absorb the sun’s heat energy and that energy is used to heat the water in the pipes.

The process of converting small particles of light (photons) into electricity (voltage) is called the photovoltaic effect. Photovoltaic (PV) cells convert sunlight directly into electricity. PV cells are usually made of a semiconducting material similar to that used in computer chips called silicon. When sunlight hits the PV cell, the photons “knock” electrons loose from their atoms creating a flow of electrons known as a current. Cells have metal contacts on the top and bottom to draw off the current to be used as electricity.

Unfortunately, solar cells are not very efficient, since not all solar energies hitting the cell will “knock” electrons loose. Much of the sunlight is either reflected or absorbed by the cell (like heat). Typically, a cell has an efficiency of about 15%, which is why multiple cells arranged into arrays or panels are needed to produce a usable amount of electricity. Although an efficiency of 15% may seem low, this is a vast improvement over the first PV cells built in the 1950s. They had an efficiency of less than 4%!

A great article on how solar PV systems work can be found on the How Stuff Works website. See also CanSIA website, Solarbuzz website, and the Solar Energy Society of Canada website for information on passive, active and photovoltaic technology.

The Applications — What can solar power do?

Solar power has a wide variety of uses. As mentioned above, passive solar energy can be used for heating or cooling a building, and also for light. No other machinery is necessary, just appropriate building and landscaping design.

Active solar systems can be used for many purposes, including the heating of water. Solar collectors can also be used in a variety of locations, including your own home, a cottage, and other commercial and industrial locations.

For example, within your home, a solar hot water system can be used to provide hot water for your showers, laundry, and dishwasher, as well as for applications such as heating your pool or providing radiant floor heating. A system can be designed to provide up to all of your hot water needs, but the average system will provide about 50% to 60% and act as an offset to a traditional water heater.

Your home may not have been designed to make the best use of passive solar energy, and you probably don’t have an active solar water heater yet, but you likely already have a solar cell in your home. The earliest PV cells were used for simple applications including the handy, every-day calculator.

You may even have a set of solar-powered garden lights in your back yard or have solar panels on your camping trailer. Solar panels have also been used for decades to power the space station.

There are many other commercial applications as well, including powering roadside signs and parking meters. PV cells also have potential for rural and developing world electrification because the panels are relatively small and portable and can be used for all sorts of off-grid applications.

Larger solar panels can be used to provide electricity to homes. Homeowners with south-facing roofs in full sun, or similar sunny space on the ground can provide a significant portion of their domestic electricity use through solar panels. If the solar system is connected to the grid, homeowners can avoid the problem of storage and make use of either the net metering program or the SOP in Ontario.

 Finally, panels can be grouped together to create a solar farm. 33,500 150-watt panels were grouped together on a solar farm outside of Leibzig, Germany, to create a 5 MW solar farm. At the time it was built in 2004, it was the largest solar farm in the world. The farm is capable of providing enough energy to power 1,800 homes. An even larger plant is planned near Sarnia, Ontario. If the project goes through, the plant will have a capacity of about 40 MW, and generate enough electricity to power between 10,000 and 15,000 homes.

For more information on solar power applications, see CanREN, Solar Energy Society of Canada Inc, or CanSIA.

Benefits of Solar Power

Solar power has many advantages over conventional energy.

First, solar systems are stand-alone systems and contribute energy at the site where it is being used. This contributes to a more distributed energy system, and helps to mitigate some of the need for expensive transmission system upgrades and the building of new transmission and distribution lines.

Second, unlike conventional fossil fuels, solar energy is free following the initial equipment costs, and is virtually unlimited. Also, the use of the fuel – solar energy – doesn’t produce waste or pollution. Like most renewable energies, solar power offers a way to mitigate climate change by replacing the need for greenhouse gas emitting coal and gas-fired generators.

Finally, solar energy is extremely handy for some of the low-power applications mentioned above, such as calculators and parking meters, and may prove to be essential for rural electrification, especially in developing countries. Like wind power, biomass and small hydro, solar also has much to offer the community power sector in Ontario, including economic benefits to the community.

For more information on solar power, see CanSIA, Solarbuzz, World Energy Council, Paul Gipe's website.

Other information you may be interested in:
OurPower, for information on bulk purchases of solar systems, including links to organizations working on solar projects in Ontario.