Remote Area Power Supply (RAPS)
In Australia, most electricity is supplied by utilities or electricity corporations from power stations, via supply networks called grids. These main grids provide electricity to the majority of Australians using mainly large coal and gas fired power stations and large hydro generation schemes. More recently some smaller scale wind farms and photovoltaic systems have been introduced. Remote towns like Port Hedland, Mt Isa and Coober Pedy are not serviced by the main grid and have diesel or gas fired power stations to provide electricity via a mini grid.
In the absence of a grid, RAPS systems can be located near a home to meet electricity requirements. RAPS systems consist of power generation equipment such as solar electric panels, wind turbines and micro hydro turbines usually combined with petrol or diesel generators, control equipment and storage batteries. A RAPS system that has a combination of energy sources is termed a hybrid RAPS system.
How does a RAPS system work?
Electricity is generated by solar panels, wind turbines or micro hydro turbines, and is fed into a bank of specially designed batteries via a regulator or other form of power controller, to be stored for use when required. The power can then be used directly from the batteries with DC appliances, or passed via an inverter for use with normal mains appliances.
Solar power
Solar panels (photovoltaic panels) convert sunlight into electricity and can be placed on the roof of a house, or nearby, to gain the greatest access to the sun. Panels can be mounted on moving racks that track the sun for greater efficiency. The working life of a solar panel should be over 20 years. They require virtually no maintenance, but dust or grime accumulating on solar panels will reduce the output, so they should be cleaned periodically. More information about solar panels is available in Your home - Photovoltaic systems.
Wind turbines
Wind turbines, which are also known as wind generators, produce electricity from the wind. The wind turbines that generate electricity are different from the windmills commonly seen on Australian properties used to pump water.
Electricity-producing wind turbines come in many shapes and sizes, and range from those that can produce small amounts of electricity for small power demands like keeping boat batteries topped up, right up to huge machines that can run hundreds of homes.
They consist of a set of blades connected to a generator or alternator, which produces electricity as it is turned by the spinning blades. By far the most common type is the 'horizontal axis' turbine, which has blades like an aircraft propeller, and a tail or vane to direct it into the wind.
The average sized turbine used in domestic installations is somewhere between 200 and 2000 watts, and most homes will require a turbine somewhere in this range. Like solar panels, the electricity from the turbine is used to charge batteries for later use, so a regulator is required for use with wind turbines, though some smaller machines have the regulator built into them.
Choosing the best site for a wind turbine is important. You need an area with relatively high average wind speeds, with little or no turbulence (rapid fluctuations in wind speed and direction caused by buildings, trees and other obstructions). To achieve this, the turbine is normally mounted on a high tower well above all obstructions. Tower height ranges from 12 metres to 30 metres or more, depending on the site. A tower that is too short will provide disappointing results.
More information about wind systems is available in Your home - Wind systems
Micro hydro
A micro hydro turbine works by taking water from a river or creek and using it to drive a set of turbine blades, much like wind pushes a wind turbine's blades. The hydro turbine drives a generator or alternator that produces electricity. Once the water has left the turbine, it is usually returned to the creek. Flow rates of the creek affect the energy generated.
There are many different designs of micro hydros that work in fast or slow flowing waterways at high or low pressures.
Regulators
Solar panels, wind and micro hydro turbines usually produce unregulated, highly variable power flow. In order that the system batteries are not damaged, they must be used in conjunction with a device called a regulator (sometimes called a controller). This device stops the battery bank from being overcharged when it is full, often diverting excess power somewhere else, such as to a water heater.
Inverters
Most household appliances use alternating current (AC) electricity, which is what comes out of the power point of a mains-grid connected house. However, the batteries used in RAPS supply (DC) electricity. To make conventional appliances run in a RAPS house, this DC electricity must be converted to AC.
This conversion is done by a device called an inverter. The inverter is connected to the battery bank, and provides mains-type AC electricity to the house. The inverter needs to be sized to suit the house's electrical requirements, a common size being around 2000 watts, or 2 kilowatts.
Batteries
Energy is stored in large batteries, similar to a car battery but designed specifically for RAPS. They are usually of the lead-acid variety, either 'sealed' or 'flooded cell'. A properly sized, well maintained battery bank is vital to guarantee a reliable, long lasting system.
Batteries require regular maintenance, flooded cells need to be topped up with distilled water from time to time and charged and discharged to a timetable.
Backup generators
Most RAPS systems use some form of petrol or diesel backup generator.
System costs
A RAPS system to provide all of the power requirements for an energy-efficient house with a typical range of appliances can cost between $15,000 and $50,000. The size of the system needed will depend on the number of people in the home, what appliances are in use, and how often they are used. Rebates are available to pay for up to half of the system costs.
Connecting to a grid may cost $10,000 per kilometre of power lines, making the option of a RAPS system a viable alternative.
The cost of a small renewable energy system to run a farm shed light using one panel and a small battery can be as low as $200.
Installing a system
All RAPS systems need to be designed and installed by qualified personnel. See the Clean Energy Council web site for registered installers in your area - Select Solar Accreditation.
Rebates & grants
Related sites
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