Solar photovoltaic (PV) panels are generally fitted on the roof in a northerly direction and at an angle to maximise the amount of sunlight that hits the panels.
Solar PV panels on the roofs of homes and businesses generate clean electricity by converting the energy in sunlight. This conversion takes place within modules of specially fabricated materials that make up the solar panels. It is a relatively simple process that requires no moving parts. In most cases, solar panels are connected to the mains power supply through a device called an inverter.
Solar panels are different to solar hot water systems, which are also mounted on household roof-tops but use the heat from the sun to provide hot water for household uses.
The technology to convert sunlight into electricity was developed in the 19th century, but it was only in the second half of the 20th century that development accelerated behind the need to provide reliable supplies of electricity in remote locations – from satellites in space to outback Australia.
Solar panels have been installed on the rooftops of houses and other buildings in Australia since the 1970s. Currently there are more than 1.25 million small-scale solar panel systems safely and reliably delivering clean electricity across Australia.
Grid-connected solar PV systems
Most suburban homes in Australia are connected to the electricity grid, which uses alternating current electricity (AC). But the electricity generated by solar panels is direct current (DC). That means grid-connected (GC) solar PV systems need an inverter to transform the DC electricity into AC electricity suitable for ordinary household needs.
Houses with solar systems use solar power first before sourcing electricity from the grid. At night, when the panels are not producing electricity, power is supplied from the existing electricity grid.
For systems that include a battery backup, the inverter regulates the charging of batteries during the day. The electricity stored in those batteries can then be used at night or during blackouts.
Average daily production of a solar PV system
The power output of a solar PV system depends on its efficiency, size and location. The table below shows the average daily production of some common grid-connected systems throughout Australia.
|City||1 kW system||1.5 kW system||2.0 kW system||3.0 kW system||4.0 kW system|
|Adelaide||4.2 kWh||6.3 kWh||8.4 kWh||12.6 kWh||16.8 kWh|
|Alice Springs||5.0 kWh||7.5 kWh||10.0 kWh||15.0 kWh||20.0 kWh|
|Brisbane||4.2 kWh||6.3 kWh||8.4 kWh||12.6 kWh||16.8 kWh|
|Cairns||4.2 kWh||6.3 kWh||8.4 kWh||12.6 kWh||16.8 kWh|
|Canberra||4.3 kWh||6.45 kWh||8.6 kWh||12.9 kWh||17.2 kWh|
|Darwin||4.4 kWh||6.6 kWh||8.8 kWh||13.2 kWh||17.6 kWh|
|Hobart||3.5 kWh||5.25 kWh||7.0 kWh||10.5 kWh||14.0 kWh|
|Melbourne||3.6 kWh||5.4 kWh||7.2 kWh||10.8 kWh||14.4 kWh|
|Perth||4.4 kWh||6.6 kWh||8.8 kWh||13.2 kWh||17.6 kWh|
|Sydney||3.9 kWh||5.85 kWh||7.8 kWh||11.7 kWh||15.6 kWh|
The rated output is that achieved in perfect laboratory conditions. The Clean Energy Council design summary software takes these de-ratings into account when predicting averages for any given system.
Panels generate more electricity in summer than in winter. The table above reflects the electricity generated averaged across the whole year.
A typical Australian house consumes around 18 kilowatt hours (kWh) of electricty per day. This means that a 1-2 kW system could displace 25-40 per cent of your average electricity bill.
Solar PV system design
The wattage of each solar panel specifies its maximum output over an hour (the electricity your solar PV system generates is measured in kilowatt hours). So, if you have four 250 W panels (making a total of 1 kW of panels), then the maximum output these panels can generate is 1 kW over an hour.
However, panels will never run at 100 per cent efficiency. Losses occur through cabling and at the inverter and will be affected by factors such as location, climate, the time of year and the angle of the panels. A well-designed system will minimise these losses to give you the best possible output for your system.
Angle of solar panels
Solar PV panels produce the most power when they are pointed directly at the sun. In Australia, solar modules should face north for optimum electricity production. The orientation of the panels will often have a greater effect on annual energy production than the angle they are tilted at. However, a minimum tilt of 10° is recommended to ensure self-cleaning by rainfall.
For grid-connected solar PV power systems, the solar panels should be positioned at the angle of latitude to maximise the amount of energy produced annually. Most Australian homes have a roof pitch of 20° to 30°.
If your roof’s slope is not ideal, your accredited designer can create an appropriate mounting frame to correct the orientation and elevation of your panel. Failing this, the designer can advise you on the difference in energy output for different tilt and orientation.
Designing a solar PV system for maximum sunlight
The amount of energy that a solar PV panel receives from sunlight over a day is expressed in peak sun hours. As the amount of energy generated by a panel is directly proportional to the amount of energy it receives from sunlight, it is important to install panels so they receive maximum sunlight.
Your accredited designer will calculate the amount of energy generated by the solar PV panel based on the peak sun hours available. Peak sun hours vary throughout the year.
The effect of shade and dirt on solar panel output
Ideally, solar PV panels should be in full sun from at least 9am to 3pm. They should not be placed in shaded areas and should be kept free from dust and dirt.
Even a small amount of shade can have a large impact on the output of a panel as it will change the flow of electricity through the panel. You need to make sure your solar panels are located away from shade created by things like trees, roof ventilators or antennas.
Shading or dirt on just one of the cells in a solar panel causes a loss of power from many cells, not just the one that is covered.