The Simple Explanation:

Many people ask the question – how many panels do I need? The answer can be very complex, or as we prefer, very simple.  For residential systems we tend to install roughly 2 sizes.

If you are a small household or apartment, with 1-2 people and low power bills (less than $150 per month), a 2-3 kilowatt inverter and 6-8 panels should be sufficient.

If you are a larger household with electricity bills above $150 a month, you should consider a system comprising of a 5 -10 kilowatt inverter and 15 – 30 panels.  Increasingly we are seeing households install a 10kw inverter and 30 panels. This sized system still attracts a generous government rebate (approximately $4700 in 2024) and is useful if extra power is required for air-conditioning, electric vehicles and/or batteries.

Onto the Technicalities:

The electricity industry is very, very complex. Let’s be honest…very few people understand it. So the first thing to do is try not to understand it (in too much detail). For example, when you bought your last computer or iPad, did you delve into the detail about microprocessor systems, bit rates and other technical jargon? Probably not. You trusted the brand and wanted some basic performance data to determine that you were making the right decision.

It’s the same with solar. Stick to known brands and a solar retailer that has operated in your region for five years (at least) and employs experienced installers, and you are on the right path.

The question about what size solar system can be estimated very simply.

5 Factors to Determine Solar System Size

1. Have a look at your power bill.

Usually, your power bill states how many kilowatt hours (or units) of electricity your premises consumes on average per day. This number can vary a lot. Depending on the size of your premises – whether you have a pool, air conditioning, how much you cook, clean etc. – all are valid factors in determining how much power you use.

2. Determine when you use the most power. 

Any power you use during the night will come from your electricity grid and cost you money – usually around $0.30 per kilowatt hour. Most homes will consume between 20 and 30 units of power in 24 hours. Depending on your lifestyle, you will consume a proportion of this power during the day. This is the proportion that can benefit from solar power. A rough idea is all that is required. Checking your meter reading first thing in the morning and at sunset. Do this a few times a week.

Let’s say on average you use 20 units per day during daylight hours on average throughout the year. The idea is to match, as closely as possible, the solar system to this known value. 

3. Divide Your Daytime Use By 4

A basic rule of thumb is you divide your daytime use by 4, and you land at roughly the right solar system size. If you use 20 units a day, then a 5 kilowatt system may be right for you. If you use 15 units during the day, then a 3 kilowatt system may be about right.

4. Roof Space

Often the decision also depends on how much roof space you have, and your expectations for future power use.

5. Government Financial Incentive (Solar Rebate)

Given the larger the system size the greater the government financial benefits, it pays to put on a system that is probably a little larger than you really need. Why? You may install aircon in the future, you may buy yourself a nice electric car or scooter or put that pool in you’ve always wanted. You might also put in a battery that will need extra panels to cover your night-time requirements.  For most homes this usually means a 5 kilowatt inverter and up to 6.6 kilowatts of panel capacity.