The prevalence of 4kW systems has gone down since it has become more financially viable to meet energy requirements rather than exceed them. Therefore only quite large energy consumers tend to require anything larger than a 3kW system to meet their daytime energy needs.
Some key system details are as follows:
|Average Price ($)||How many panels?||Average Energy Generated Daily (kWh)|
|$5,200 – $8,600||16 – 21 (depending on panel size e.g. 190W)||16 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.
In general, a household of 5+ people and an average daily electricity consumption of 26-28 units would be ideally suited for a 4kW solar system.
If we put all this together and look from a financial point of view, then the payback period for a system like this would be between 4 – 6.5 years. In all likelihood though, if we take average pricing and energy use and also take into account the rising cost of electricity you’d expect a return on investment of approximately 4.7 years.
These figures are based on the fact that you offset your energy usage by not having to buy power from the grid. So for every unit you don’t pay for from the grid you save yourself about $0.22. This may not sound like much but over a year that adds up to about $1,300 on a 4kW system. These savings only increase if (when) the price of electricity increases.
For placing the panels of a 4kW system you have look at what your own energy use is like. The 4kW systems can be placed facing in up to 2 directions. This is because the configuration of inverters this size usually split the panels between two ‘ports’.
The typical household has low load in the middle of the day when people are at work/school and a peak in the late afternoon early evening when everyone gets home. These types of households may benefit more from facing their panels in a more westerly direction to get the peak generation closer to the evening when the most power is being used. However, if people are home during the day then it would be better to have your panels face as north as possible and peak during midday.
Alternatively you can have half panels facing west and half north and have them act like two individual 2kW systems. This will give a smoother power output during the day, but obviously won’t reach the same peaks as all panels facing the same direction.
In the end you want to maximise the use of the solar you generate in order to minimise how much you have to buy from the grid.