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Focus
On Alternative Energy
Solar Energy
What is Solar Energy?
Energy from the sun travels to the earth in the form of electromagnetic radiation. At any given
time the amount of solar energy depends upon the weather, location, and the time of year. The
amount of solar energy that can be converted to useable energy is dependent upon the technology
and the application used.
Why Solar Energy?
Benefits
Solar and other renewable energy systems can be stand-alone; thereby not requiring connection
to a power or natural gas grid. The sun also provides a virtually unlimited supply of solar energy.
Environmental Benefits
The use of solar energy displaces conventional energy; which usually results in a proportional
decrease in greenhouse gas emissions.
Economic Benefits
The operating costs of solar energy systems are much lower than the cost to operate a combustion
furnace with an air conditioning unit. However, the cost to install a complete solar system can be
higher than the cost to install a furnace and air conditioning unit.
How to Utilize Solar Energy
Solar Heating of Buildings
In the Northern Hemisphere the south side of a building always receives the most sunlight,
therefore buildings designed for solar heating usually have large, south-facing windows.
Materials that absorb and store the sun’s heat can be built into the sunlit floors and walls. The
floors and walls will then heat up during the day and slowly release heat at night, when the heat is
needed most.
Other solar heating design features include sunspaces and trombe walls. A sunspace (which is
much like a greenhouse) is built on the south side of a building. As sunlight passes through glass
or other glazing, it warms the sunspace. Proper ventilation allows the heat to circulate within the
building. A trombe wall is a very thick south-facing wall, which is painted black and made of a
material that absorbs a large amount of heat. A pane of glass or plastic glazing installed a few
inches in front of the wall helps hold in the heat. The wall heats up slowly during the day, then as
it cools gradually during the night it gives off its heat inside the building.
There are many design features that help keep solar buildings cool in the summer. For instance:
overhangs can be designed to shade windows when the sun is high in the summer, sunspaces can
be closed off from the rest of the building, and a building can be designed to use fresh-air
ventilation in the summer.
Solar Water Heating
The sun can be used to heat water with solar water heating systems. Most solar water heating
systems for buildings have two main parts: a solar collector and a storage tank. The most
common collector is called a flat-plate collector. Mounted on the roof, it consists of a thin flat
rectangular box with a transparent cover that faces the sun. Small tubes run through the box and
carry the fluid – either water or other fluid, such as an antifreeze solution – to be heated. The
tubes are attached to an absorber plate, which is painted black to absorb the heat. As heat builds
up in the collector, it heats the fluid passing through the tubes. The storage tank then holds the
hot liquid. It can be a modified water heater, but is usually larger and very well insulated.
Systems that use fluids such as antifreeze can be used to heat the water in a modified water
heater. The hot antifreeze passes through a coil of tubing in the tank transferring the heat to the
water.
Photovoltaic Systems
Photovoltaic (PV) cells convert sunlight directly into electricity. PV cells are the solar cells that
are often used to power calculators and watches. PV cells are made of semiconducting materials
similar to those used in computer chips. When these materials absorb sunlight, the solar energy
knocks electrons loose from their atoms, allowing the electrons to flow through the material to
produce electricity. This process of converting light (photons) to electricity (voltage) is called the
photovoltaic effect.
PV cells are typically combined into modules that hold about 40 cells. Approximately 10 of these
modules can be mounted in PV arrays that measure up to several meters on a side. About 10 to
20 PV arrays can provide enough power for a household. For large electric utilities or industrial
applications, hundreds of arrays can be interconnected to form a single large PV system.
What are Some of the Problems with Solar Energy?
The initial cost of this type of technology can be a drawback depending on the application. Also
the storage of the energy can be an issue, again depending on the application.
For More Information
Katrina Sexton, P. Eng.
3000 College Drive South
Lethbridge, Alberta T1K 1L6
Phone (403) 329-1212
Fax (403) 328-5562
E-mail [email protected]