The most common solar system size on Australian roofs is 1.5kW. There are three reasons for this; it is the smallest available size and so is the cheapest, it requires the least space and, it is suitable to meet the energy needs of most 1-2 person households.
Important numbers for 1.5kW solar systems are:
|Average Price ($)||How many panels?||Average Energy Generated Daily (kWh)|
|$2,600 – $4,300||6 – 8 (depending on panel size e.g. 190W)||6 units|
*Note that the energy generated daily is an average for the year; in summer this will be higher but conversely in winter it will be lower. Also this is an average across all of Australia and so there will be a variation depending on exact location.
1.5kW systems are recommended for households whose bills have an average daily consumption of around 10-12 units per day. In most cases, this would be a house of 1 – 2 people.
Calculating this from a financial perspective, the payback period for a 1.5kW system would be between 4.5 – 7.5 years. Considering the average pricing, energy use and also taking into account the rising cost of electricity, however, you’d expect a positive return on your investment in around 5 years.
These calculations use the assumption that energy produced by the system is energy not purchased from the grid. In this way, every unit not bought from the grid saves you about $0.22. While sounding small, this adds up quickly, and over the course of a year amounts to about $500 on a 1.5kW system. These savings only increase if (when) the price of electricity increases.
When considering the placement of a 1.5kW system attention needs to be given to the energy usage of the household. 1.5kW systems can only be placed facing in one direction because of reasons to do with voltage on the inverter. Most household’s peak energy usage is concentrated in the late afternoon/early evening, when everyone arrives home from work and school. One way to maximise the usage of the system in these cases is to have the system facing west so that less power is drawn from the grid during the household’s maximum usage period.
Obviously, for households where someone is home during the day and energy usage is higher during the day, a north facing system would be smarter. The aim for any system nowadays is to use as much of the power you produce and limit the amount of power drawn from the grid.