Solar energy

By: David Walker, Executive Officer
July 12, 2010

In just one hour the sun beams down more energy than the world uses in a whole year. This is not just the amount of energy radiated by the sun, but that tiny proportion intercepted by planet Earth. (see http://www.gmagazine.com.au/75/solar-energy)

Arrays of solar sells (photo USAF)

There are three main ways we use the sun's light and heat energy:

1. Photovoltaic cells

Photovoltaics (PVs) or solar cells convert the sun's light into electricity. The photovoltaic effect was discovered in the late 19th century by French researcher Edmund Becquerel who found that when sunlight hits certain materials a spark of electricity is generated.

Since there are no moving parts, photovoltaics are relatively maintenance free and are expected to last up to 50 years. Limitations, however, include needing a lot of space for installation and not being able to operate at night or in low light.

They are also very expensive. But costs are expected to plummet in the next few years with development of thin cell technology that uses over 100 times less silicon. Relative costs will also decline once carbon trading comes into action, because it will create a more accurate price for coal-fired electricity.

2. Solar thermal

Another approach is to use the suns heat to warm a liquid - this is called solar thermal.

The best-known example of solar thermal is solar hot water, which uses relatively simple technology: a black box with a clear lid is located on the roof and liquid (usually water) is run through it. The water absorbs the sun's heat and is then pumped into your home to use as hot water or for ‘hydronic’ heating. (Hydronic heating is the piping of water through the home to provide whole home heating. This can be through panel heaters or convectors which warm the air, or through ‘in slab’ floor coils.)

While it was initially expensive, increased global production of solar hot water systems has helped to lower costs, as have rebates, making them quite competitive with other hot water systems.

On a larger scale solar thermal can be used to run power stations. By using mirrors to concentrate the sun, fluids are heated to create steam, which is then used to drive a turbine that generates electricity, much like a coal power station.

The great advantage of this system is it can store heat later to be used to generate electricity. Australians are leaders in this technology, and have developed a pilot power plant in the Hunter Valley.

3. Passive solar

The oldest and cheapest approach to using the sun is called passive solar.

For centuries, well-designed houses have made the most of the sun to help maintain comfortable temperatures. By allowing the winter sun through big windows on the north (in the southern hemisphere) to heat up brick walls and concrete floors it is possible to minimise the need for heating. Conversely, insulation and shading on the north and westerly sides will keep the house cool in summer.

This age old technique is still being used today – and if considered at time of construction the cost is usually negligible.

Our recent Sustainable House Expo featured houses and apartments that utilised this technology.

There is tremendous potential to increase the use of solar energy particularly for electricity generation. Yet at this stage, it will provide only part of a solution because of inherent inefficiencies of solar.

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