One of the most common questions people have before investing in solar is how many panels they need.

The simplest way to find this out is to ask an expert solar installer.

They will conduct an audit of your energy usage and your homes capacity for a solar installation and provide you with a recommendation based on their findings.

As our world is moving from fossil fuels to electrified cars, and as the cost of battery storage is becoming affordable, many people are now installing the largest solar systems possible so they can offset the cost of not only their energy costs for their homes, but also the fuel costs for their cars.

The right size system for you depends on a number of factors such as;

  • How much electricity you use in your home
  • When you use your electricity in your home
  • The expected output of the solar panels
  • Where the panels are located
  • How they are oriented on the roof
  • What feed in tariffs are available from your electricity retailer
  • Are you planning to install a battery storage system as well

You can attempt the estimate yourself.

To do this, you need to figure out your average daily use of power.

You can probably find this on your most recent bill, but if it only shows your yearly use, simply divide this number by 365 to get a daily average. For example, let’s assume your yearly use is 5,000 kilowatt hours (kWh). Divide this by 365 to get a 13.7 kWh daily average.

Whatever way you use to determine your needs, it’s best to build in a buffer. Solar panels don’t work at 100 percent efficiency. There will be times when their output is reduced. So add a little extra – say another 25 percent. To do this, multiply the daily average by 1.25. Using the example above, this comes to 17.1 kWh.

You also need to take into account the amount of sunshine your home receives. While Australia is mostly sunny – and receives more solar energy than any other continent – the southern states don’t receive as much solar radiation as the northern states.

Ask your installer or local solar authority about the amount of sunlight you can expect to receive on your roof.

You then need to divide your daily average by the number of daylight hours. This figure will tell you how many kilowatts are needed each hour by your panels to absorb solar energy. Let’s assume your suburb receives 6 hours of daylight. Divide 17.1 by 6 to get 2.85 kW needed every hour. Times that by 1,000 to convert the sum into 2,854 watts.

These system sizes allow you to run your home on solar as much as possible while minimising the wasted electricity sent back to the grid.

We asked Stephen Jenkins, a homeowner on the NSW Central Coast and proud solar owner since May 2017, to share his energy bills with us before and after installing a 5kW solar system. Some data on the bills below have been blurred due to privacy reasons.