Solar power

Solar energy is the most abundant form of energy on Earth. All life on this planet depends on the energy received from the sun. Coal-fired power stations would not exist today were it not for the sun. The plants that became coal stored the sun's energy, which is now burnt to produce electricity.

The most common way solar energy is used directly in Queensland is in solar hot water systems. Large flat plates absorb radiation and this heats the water. Water is stored in an insulated tank until it is used.

More recently, the Australian Federal Government introduced the Solar Cities Program, a $75 million initiative to use solar technology in a grid network similar to an electricity network. The Solar Cities program will investigate the costs associated with the installation and use of solar energy, as well as to trial ways to overcome problems.

There are many research projects looking at ways to produce electricity from the sun. Producing electricity from the sun can be grouped broadly in two quite different technologies:

• solar collectors that convert solar energy to thermal or heat energy
• photovoltaic cells that convert solar energy directly to electric energy.

Solar collectors

Large reflectors concentrate or focus the sun's light to a central, high receiver.

In the receiver water turns to steam that is used to drive an engine, which in turn drives a generator to produce electricity. Sometimes molten salt is used instead of water to store the heat. To generate electricity in useful quantities, an array of solar collectors is necessary. A solar array is a bank of many solar collectors.

A power tower is a separate technology that concentrates the sun’s radiation from many reflectors at a single point. The heat can then be used to generate electricity.

Parabolic dish

Parabolic dish for collecting solar radiation is made of a highly reflective material. The dish reflects the sun's light to the focal point. Because the sun's light is concentrated at one point, high temperatures are developed.



A receiver is situated at the focal point of the parabolic dish where the heat of the sun's radiation is concentrated. A boiler is placed in this position where water is converted to steam. This steam can then be used to generate electricity.

The Australian National University (ANU) in Canberra has constructed a parabolic collector, which is capable of producing 80 kW of electricity.

Photovoltaic cells






Photovoltaic cells convert the sun's energy directly to electricity. These cells contain silicon, the same material used to make computer chips.

Did you know that if all the energy from the sunlight that strikes one square metre of the Earth's surface could be converted to electricity it would produce about 1 kW (1000 Watts) of power? That's enough power to light about seventeen 60 Watt light bulbs.

The typical solar panel today achieves between 10% and 15% conversion. That is, between 10% and 15% of the sun's energy is converted to electricity. Efficiency can be higher, but is a costly matter.

Electricity produced from photovoltaic cells is used in:

• calculators, wristwatches and similar equipment
• water pumps
• lighthouses
• satellites

Unfortunately photovoltaic cells are too expensive at this time to be a viable alternative to produce enough electricity to satisfy the needs of a city.

Find out how a photovoltaic cell works
See the Flash movie on photovoltaic cells

Setting up a solar panel

The efficiency of a solar panel depends on the angle it is positioned, because the sun's light strikes the Earth's surface at an angle. Another factor to consider is that the sun changes position in the sky constantly during the day. One way to counter these conditions is to use a "solar tracker" which allows the solar panel to follow the sun as it moves across the sky.

The other alternative is to set up a solar panel so that the midday sunlight strikes it at an angle roughly equal to the latitude of your position. For example, if you were to set up a solar panel in Brisbane which is longitude 150o E and latitude 30o S, then your solar panel should be set at an angle of about 40o (using the table).

Solar boat

Image supplied courtesy of Solar Sailor.



"Insects evolved wings initially as solar collectors then used them to fly. So why not evolve wings onto boats as solar collectors & use them to sail?"
- Dr Robert Dane, CEO, Solar Sailor

Founded in 1999 in Australia, Solar Sailor developed an award-winning solar boat design. The solar panels are attached to "solar wings" which act as both sails and solar collectors for the boat. Solar Sailor’s technology can use the energy from the wind and sun separately or in combination.

In most respects, Solar Sailor is similar to conventional vessels, but the breakthrough lies in its use of eight unique and aerodynamic solar wings on its roof. These lightweight ‘wingsails’ are embedded with photovoltaic solar energy cells. On Solar Sailor, the panels can track the sun in two planes, providing a proven 40 per cent increase in solar energy which contrasts with the fixed nature of many land-based solar panels.

Solar power is a popular source of power for appliances on many boats.

Costs and benefits of solar power

Benefits:

• Solar energy is a renewable resource.
• Sunlight is free.
• Australia's climate is well suited to solar energy.
• Solar power generation does not produce greenhouse gases or dangerous emissions.
• Solar hot water systems reduce the need for electricity and hence the need for fossil fuels.
• Photovoltaic cells or solar cells convert sunlight directly to electricity.
• Solar power can provide electricity to remote areas of Australia that are not connected to the electricity grid. Australia is a world leader in solar energy research and the sale of the resulting technologies into overseas markets can earn valuable export revenue.

Costs:

• Solar cells and solar thermal generators can impact on the environment.
• Energy collected from solar cells or solar collectors has to be stored in batteries.
• Thermal solar systems used for electricity production are expensive.
• An array of solar collectors takes up a large area.
• For maximum efficiency, solar collectors need tracking devices, which adds to the cost.
• Dust and smoke and weather conditions in general affect the performance of solar collectors.
• The production of ultrapure silicon wafers used for making photovoltaic cells is expensive.

Technology

Solar receptors absorb energy from the sun. Some collectors have flat surfaces. Others have curved surfaces to concentrate the sun’s energy. Solar receptors rely on ultra pure minerals and advanced technologies to meet performance needs. The receptors generate either a solar electric effect or a solar thermal effect.

Solar electric systems require panels made from specially engineered materials called semiconductors. They have unique properties and respond to light by causing electrons to flow from one material layer to another. A major component in these semi conductors is a very pure form of silicon, the element, called ultrapure silicon. The high cost of producing extremely pure single-crystal wafers, and their availability, remain major barriers to the uptake of photovoltaic technology. For Australian National University researchers, crystalline silicon remains the material of choice in a recent development, SLIVER® solar cells. The new technology allows for a reduction of as much as 90% in the amount of ultrapure silicon required.

Solar thermal systems have a number of variations. A low temperature form of this technology is a solar hot water system. Other types of solar receptors with curved surfaces are designed to generate immense heat. The heat is removed by directing fluid to flow over the surface. A solar thermal power generator uses a material such as a pressurized gas to drive turbines.

Problems yet to be solved in this kind of technology include how to:

• produce the components on demand and with cost efficiency
• store the energy on a scale useful to communities; and
• turn turbines for generators with the output of solar cells.