A Solar Choice broker will help you, at no charge, decide what size solar energy installation best suits your needs and budget. In the meantime, we hope the following article will assist you in making the right decision.
(This article was originally published in 2009 – we updated in January 2016 to reflect the new realities of Australia’s solar market landscape.)
How to calculate the size of solar system for your home
1. Look at your energy bill
The best place to start is by taking a look at your most recent energy bills. Most energy companies have a graph on the back of your bill which sets out your average daily energy consumption. An energy efficient Australian three bedroom home, with an average sized family and reasonable use of air conditioning, will usually have an average daily consumption of around 12 kilowatt-hours (kWh) to 16kWh.
Depending on where you are in Australia and how much daylight you receive on average per day, a 1kW solar power system will usually produce around 4kWh to 5kWh of energy per day. PVWatts is a great tool that you can use to estimate how much solar energy you can expect to produce if you go solar; the tool lets you adjust for variables like your system size and location.
2. Estimate how much electricity you use during daylight hours
But remember that unless you have battery storage, your solar panels will only meet your electricity needs during the daytime hours. Unless you have access to a generous solar feed-in tariff (which most new solar homes do not), your solar energy is worth the most to you when you use it directly. The electricity from your solar panels will flow first into any appliances in use within your home at the time, saving you money by reducing the amount of electricity you need to purchase from your electricity retailer (usually at a rate of 20-30c/kWh). Any surplus solar will go into the grid, to net you only 6-10c/kWh. This means that you want a solar system that generates enough electricity to meet your daytime electricity usage.
This can most easily be done by estimating what percentage of your total electricity consumption happens when the sun is shining. For example, if you use 20kWh of electricity per day on average, but only about 1/3 of that during the day, then you’ll want a solar PV system that generates about 7kWh per day. (Remember, these are rough estimates – consult with an accredited solar installer to work out more precise estimate based on your circumstances.)
Interested in exploring how much you can save with solar? Check out our Solar Power System ROI Calculator!
3. Choose a solar system size that will generate enough electricity to meet daytime demand
So with an average daily household electricity demand of 20kWh with about 33% of that occurring during daylight hours, a 2kW solar system would probably be the best solar system size – it would generate just enough solar energy to offset a chunk of your daytime energy usage without ‘wasting’ too much solar by exporting it into the grid (a ‘self-consumption’ rate of about 60%).
The ‘double hump’ electricity usage pattern, common in homes with school-age children. The times of highest electricity consumption happen outside of peak solar production times – the trough in the middle of the graph. Red bars represent ‘wasted’ solar going into the grid.
A 3kW solar energy installation, on the other hand, would probably be slightly too large for your home if it’s not occupied during the day, exporting nearly 50% of the energy produced on average. However, if you are home during the day (retired or have a home office, for example), it would make a good fit, with only 30% of the solar energy going back to the grid on average.
The ‘day focus’ electricity usage pattern, common in homes occupied by retirees or those who work from home. With the appropriately-sized solar system, such homes can easily use a significant portion of the solar energy produced, sending only a small amount into the grid.
Learn more about solar system sizing:
4. Consider whether battery storage is a worthwhile option for you
Not all solar PV systems come with battery storage systems, which may actually be sold separately or fitted onto existing solar systems retroactively. If you’re interested in battery storage for your solar system, there are a number of things you should consider before making a decision. What are your goals in installing batteries, for example – do you want to go ‘off the grid’, or just want to save a bit of your solar energy for nighttime usage? We break down your options in our article, “How much battery storage capacity do you need?”
Get free and instant quotes from installers in your area
We hope the above points are helpful to you. Take 30 seconds to complete our Solar Quote Comparison Request form, or feel free to give your Solar Choice broker a call on 1300 78 72 73 to further discuss what size installation best suits your budget and energy needs. Our service is 100% free to our residential customers. (We can also help you compare battery storage system quotes.)
© 2016 Solar Choice Pty Ltd