Steps To Calculate How Many Solar Panels You Need

It’s a question we’re asked by nearly every client and while it can be difficult to calculate, there are a few easy things anyone can do before contacting a Clean Energy Council accredited solar professional.

Find your Average Daily Usage on your electricity bill

Electricity bills are similar to cracking The DaVinci Code, they’re extremely complicated and can be impossible to understand. The single most important information to extract from your electricity bill to calculate how many solar panels you’ll need is your ‘Average Daily Usage’ which is measure in kWh. This can be found on all electricity bills ( Yes, this is one of our clients bills, $2! ).

Why is your average daily usage important?

Much like an architect designing a house, you aren’t going to build a 5 bedroom home for 2 people or a 2 bedroom home for 5 people! You could but it wouldn’t exactly be comfortable, or you’ll spend a lot more than you need to. The same applies for designing a solar panel system. Once we understand our energy requirements, we can then design a solar panel system that meets them.

The Simple Calculation Using The Peak Sun Hours Table


Brisbane averages 5.4 peak sun hours per day which ranks 3rd in Australian cities. What does this mean? It’s a complicated way of saying that for an average of 5.4 hours per day, your solar panel system will be producing power!

If we use the average daily usage in the electricity bill at the top of this page (10kWh), take our 5.4 peak sun hours into consideration and use a 300W solar panel as an example we can use the following formula to calculate how many solar panels we need to cover our average daily usage –

10kWh divided by 5.4 Peak sun hours =1.85kW or 6 x 300W solar panels.

20kWh divided by 5.4 Peak sun hours = 3.7kW or 12 x 300W solar panels

30kWh divided by 5.4 Peak sun hours = 5.5kW or 18 x 300W solar panels

You get the point…

Then why do solar companies recommend installing the biggest system possible?


More commonly know as ‘The Government Rebate’, eligible small-scale renewable energy systems are entitled to a number of small-scale technology certificates. For example, a 5kW solar panel system is entitled to 82 STC’s valued at around $36 per certificate or $2952. A common reason for oversizing a solar panel system can be purely financial as illustrated below –

5kW solar panel system cost before STC’s =$10,000

5kW solar panel system STC rebate = $2952

5kW solar panel system cost after STC rebate = $7048


6.6kW solar panel system = $12,000

6.6kW solar panel system STC rebate = $3924

6.6kW solar panel system cost after STC rebate = $8076

As you can see for an extra $1000 you can increase your solar panels system size by 1.6kW. Resulting in 8.64kW of extra solar power being produced every day!


Solar panels have a combination of factors that will contribute to power losses. Dirt and grime, cable losses, manufacturers output tolerances and inverter efficiency. All of these losses combined can contribute to a solar panel systems overall output being much less than what the ‘sticker’ says. For example a 250W panel can have losses up to 60W turning the panel into a 190w module. Adding these losses up over a ‘5kW system’ can quickly turn into a 3.8kW system. Yet another reason oversizing your solar system can be a good idea..

Future proofing your solar panel system

It’s no secret that Australian’s are fed up of increasing electricity prices and our reliance on fossil fuels. We’re taking matters into our own hands and taking control of our energy. A major plan for a lot of Australian’s transitioning to a clean energy household is to adopt battery storage technology which is coming down in price and powering forward with innovation. If you can’t afford a battery or the investment isn’t yet viable for your situation, a great way to prepare for this technology is to install a solar system that generates excess solar power. You can reap the benefits from your excess solar power by receiving a reasonably generous feed in tariff from your energy retailer. They credit you for each kWh of solar power you export to the grid which offsets the cost of electricity you use at night.


Selecting the right solar products and preparing for the future

The solar industry is a complicated beast and selecting the right solar products becomes harder every day. One very important question to ask yourself is ‘Have I selected solar panels, inverters and materials that are easy to adapt and scale to new technologies like battery storage and one day micro-grids?’ Unfortunately Australian’s get far too caught up in price and aren’t thinking long term about their investments. We strongly believe the day will come when we have a decentralised electricity grid that will allow communities to trade and share energy amongst each other. We’re preparing for it, are you?