How many solar panels do I need to power my home?

It’s the first question that anyone thinking of going solar asks: how many panels do I need for my roof? Here's how you can calculate that.

Every home is different, and the performance solar panels will be affected by the tilt of your roof, your home location, and even the direction your home faces, so it is always best to speak to an expert or a solar installer to get a full reading on how many panels you will need. However, it is still possible to get a rough idea.

Your energy usage

When asking how many solar panels you will need, first you need to know what your current home power usage is. If you have a recent energy bill lying around you should find this figure on there. Energy usage is sometimes given for the year -- divide this by 365 to calculate your average daily use.

For example, say your yearly use is 4,000 kilowatt hours (kWh). Simply divide this by 365 (days per year) to get an average daily usage of 10.9kWh.

Remember that this is an average and give plenty of room for cloudy days and winter. We’ll use 15kWh to give a buffer.

Measuring the sunlight

Next we need to figure out how much sunlight your home gets. This is easier said than done, and for this we will have to call in the experts. Contact a solar installer or local solar authority to get some information on the sunlight measurements in your area.

Let’s say your home receives a solid 6 hours of sunlight per day, which is a reasonable average accounting for the movement of the sun and possible shade from trees or other structures. So now we divide your daily usage by the amount of hours of sunlight.

The Calculation

15kWh/6 = 2.5kw needed every hours

We now multiply our kilowatt hours by 1,000, which converts the figure into watts, rather than kilowatts (this makes subsequent calculations easier).

2.5 X 1,000 = 2,500 watts

So your solar panel system needs to produce 2,500 watts of energy per hour to power your home. Simple, wasn’t it?

The decision

Solar panels are rated for the amount of watts they produce. Let’s say you want to buy 200-watt solar panels, it’s easy enough to work out that you will need 13 panels to cover your 2,500 watts per hour.

200 watt panels X 13 = 2,600 watts per hour.

Performing these calculations will really help when it comes to comparing quotes or determining whether panels are feasible for your home. Remember that this figure is just a guideline, and when making a decision as big as this you should seek out professional advice early and often.

Shirley Liu

Shirley Liu is a program manager at finder, formerly the publisher for Banking and Investments. She is passionate about helping people make an informed decision, save money and find the best deal for their needs.

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2 Responses

  1. Default Gravatar
    BelindaSeptember 1, 2015

    What is the government rebate for solar panels in nsw ?

    • finder Customer Care
      ShirleySeptember 1, 2015Staff

      Hi Belinda,

      Thanks for your question.

      The NSW government offers a number of rebates. Please see this page for more information as to which rebate you’re eligible for.


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