How Many Solar Panels Do I Need?

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Working out how many solar panels are needed to meet the electricity demands of your home will ensure your solar system is able to generate enough power.

To do that, all we need to know is your annual energy usage – which can be found on your electricity bill.

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Annual Energy Usage

Your average annual electricity usage is one of the biggest deciding factors in how many solar panels are needed for your home.

Energy usage is measured in kilowatt hours (kWh) which measures exactly how much energy is being used – a kWh is different to kilowatts (kW) which are a measurement of power (1,000 watts is equal to 1 kilowatt).

In the UK, the average annual electricity usage stands at around 3,800 kWh but this will go up or down depending on the size of your home, number of people in the property and your energy habits.

Below is a look at the average energy usage of different property types during a year. Detached homes tend to have the highest demand for energy while a mid-terrace home is likely to have lower demand.

person saving money on the Feed-In tariff

Source: OVO Energy

To get a more exact idea of the energy being used in your home each year, you will be able to find it on your electricity bill.

How Much Power Does Your Home Need?

Once you know how much energy you're using over the course of a year we can begin to work out how many solar panels you'll need.

The power output of solar panels is measured in watts (W) and can range from around 245W right up to 400W.

If your home has a particularly high demand for electricity then it makes sense to consider solar panels with a larger power output – more than 325W. Investing in solar panels with a higher output will not only mean they generate more energy, you will need less of them.

To reach the UK average energy usage of 3,800 kWh, only 10 400W solar panels would be needed as part of the solar PV system, whereas 16 250W solar panels would be needed to achieve the same output.

Size of Solar PV System Number of 400 Watt Solar Panels Estimated Annual Output
1.2 kW 3 1,200 kWh
2 kW 5 2,000 kWh
3.2 kW 8 3,200 kWh
4 kW 10 4,000 kWh

While fewer 400W solar panels are needed to reach the national average energy usage, they do come at a higher price which may mean you want to consider solar panels with a smaller output.

Size of Solar PV System Number of 250 Watt Solar Panels Estimated Annual Output
1 kW 4 1,000 kWh
2 kW 8 2,000 kWh
3 kW 12 3,000 kWh
4 kW 16 4,000 kWh

It's worth noting that you don't need to install a solar system that meets your entire demand for electricity. A solar system can also subsidise part of your energy usage, which will help to reduce energy bills and your carbon footprint but mean that you still have a fair amount of reliance on your energy supplier (you can always increase the size of your solar system further down the line).

So, How Many Solar Panels Do I Need?

Different properties will have a varying number of solar panels based on a number of factors:

  • Property size
  • Energy demands
  • Power output of the solar panels

Using your property's annual energy usage, we can work out how many solar panels you will need to meet your demands.

Let's take the average UK annual energy usage as an example – 3,800 kWh.

If we refer back to the table at the beginning of the article, a 4kW solar system is the best suited to meet this demand. This means having enough solar panels as part of the solar system to reach 4,000W (e.g. 16 x 250W panels).

House Type Average Annual Energy Usage (kWh) Number of 320W Solar Panels Total Output of Solar PV System (kW)
Detached 4,153 13 4,160
Bungalow 3,866 12 3,840
Semi-detached 3,847 12 3,840
End Terrace 3,442 11 3,520
Mid-terrace 2,779 9 2,880
Flat 2,829 9 2,880

It's worth remembering that the energy usage in the table above is an average and may well differ depending on your energy habits – if you live alone you might only use 1kW of electricity each year. For that reason, it's important to take a look at how much electricity is used by your home in a year on a recent energy bill.

While a solar PV system might appear to be large enough to meet the energy demands of your home at first, the solar inverter needs to be factored in too.

Solar Inverter

A solar inverter converts the direct current (DC) into alternating current (AC) which can be used to power the electrical appliances around your home. During this process, some of the energy generated by the panels is lost.

While solar inverters only tend to lose between 2-8% of the energy when converting the current that's still enough to have an impact on total generation. So that you can still rely on your solar PV system to meet your entire demand for electricity, your installer might recommend an additional solar panel to your system.

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Is Your Roof Suitable for Solar Panels?

It's one thing to know how many solar panels you might need to power your home with free renewable solar energy but your roof will need to be suitable for solar panels.

On the plus side, most UK homes are perfectly suitable for solar panels but there are a few considerations to make in order to get the most out of them:

  • A south facing roof will deliver optimal generation
  • Free from shading
  • Roof pitch of 30-40 degrees
  • Whether there's enough space (a 4 kW system can take up around 28 square metres of space)

Find out more in Is My Roof Suitable for Solar Panels?

Energy Usage Times

It goes without saying that solar panels are generating the majority of energy during daylight hours. In contrast, we're using more electricity in the evenings between 6pm and 10pm which, especially during the winter months, don't offer much sunlight.

So, if you're at work during the day and returning home in the evening, you've missed out on the best hours to be using the free renewable energy being generated by your solar PV system. This is where a solar battery can help.

What is a Solar Battery?

Solar batteries store any excess energy generated by your solar panels during the day – and they're generating more energy than is used. This way, you can reduce your reliance on your energy supplier in the evenings and even through the night (depending on the capacity of the solar battery).

Alternatives to Solar Panels

As solar technology has developed more people than ever are now able to enjoy the benefits of free renewable solar energy. So, if you can't fit enough conventional solar panels to your roof, then flexible solar panels and solar roof tiles are alternative options.
Flexible solar panels are a lot thinner and lighter than conventional panels which helps to make them much more flexible. This means that anyone living in a home with a roof that might not be able to support the weight of several solar panels doesn't have to rule out renewable solar energy as a way of cutting their energy bills.

Solar roof tiles, or solar shingles, tend to be more expensive than solar panels, don't generate as much energy and aren't suitable for all roof types, however, they're an aesthetically pleasing option that are popular as part of a roof replacement.

How Much Do Solar Panels Cost?

A solar system between 1-4 kW is likely to cost around £1,800 to over £6,000 depending on the manufacturer, model and number of panels.

Size of Solar System Potential Cost (before installation)
1 kW £1,840
2 kW £3,680
3 kW £5,520
4 kW £6,040

Solar panels might be a large investment but when you factor in the energy bills savings over a number of years and potential payments through the Smart Export Guarantee (SEG) you could soon see a return on the initial investment.

Read our guide to 'How Much Does it Cost to Install Solar Panels?' for an indepth look at the potential costs of a solar PV system.

Find a Solar Panel Installer

As well as adding up the cost of the solar PV system itself, you will also need to factor in the installation. To find the most competitive price, we highly recommend comparing quotes from multiple solar installers.

Getting multiple quotes might sound like hard work but at Solar Guide, we've made finding solar panel installers easier than ever. Simply take a few moments to go through our quick online form and we'll match your needs with up to 3 solar installers based in your area. Once you have the quotes then you're free to compare them and be confident that you're not paying a penny more than you should be.

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