How many solar panels do I need?

When you're investing in solar for your home, you want to choose the right number of panels.

A system usually costs thousands of pounds upfront, and getting the size wrong can either inflate this cost further or needlessly limit your energy bill savings.

In this guide, we'll explain how to use your annual electricity consumption to decide on your system's size, how your location and roof's angle and direction affect the calculation, and which solar panel types can reduce the number of panels you need.

To find out how much a solar & battery system could save you in the long run, answer a few quick questions below and we'll generate an estimate.

How many solar panels do you need for your home?

Solar generation vs electricity consumption

The amount of solar electricity your system generates each year won't usually line up with your usage pattern.

Solar panels generate much more electricity in summer than they do in winter, at least in the northern hemisphere.

This contrasts with the way households typically use electricity, which is relatively stable, with a peak in winter and a dip in summer.

So even if your system produces all the electricity you need over the course of a year, you may not be able to use them all – though a solar battery does help.

You'll usually rely on the grid for some of your electricity in winter, and export a large proportion of your solar electricity in summer.

You can earn money for this excess energy with a solar export tariff – and to choose the right tariff for you, check out our guide to the best solar export tariffs.

With a smart export tariff, you can use around 66% of your solar electricity, export the rest, and reduce your electricity bills by 103%, on average.

How to calculate how many solar panels you need

To calculate how many solar panels you need, the only piece of information you need to find is your annual electricity usage, which your energy supplier will usually share with you each year.

If you have an online account or solar app from your supplier, you may also be able to find your annual consumption that way.

Once you've found it, all you have to do is divide this number by 366 – the typical annual kilowatt-hour output of a standard 430-watt residential solar panel in the UK – and you’ll get an estimate of how many solar panels you need.

If your annual electricity consumption is 3,500kWh, you would need approximately 10 solar panels – although this will of course vary based on your property and needs.

Without solar panels, you'll pay the grid for the full 3,500kWh, which adds up to £858 per year under the October 2024 price cap.

With a 4.3kWp solar array, you'll generate 3,655kWh per year on average, around 66% of which – 2,412kWh or so – you'll use to power your home. This will save you about £591 on your annual electricity costs.

You can send the other 34% to the grid and earn money doing it, thanks to the existence of solar export tariffs. We’ve used a 15p per kWh tariff here, since it’s the highest rate available to homes without a solar battery.

You'll still need to import around 1,243kWh of electricity from the grid, but you'll cut your electricity bills by around £777 per year.

What happens if you add a battery?

If you get a solar battery with your system, you can use even more of the electricity your panels produce, and benefit from export tariffs like Intelligent Octopus Flux.

This can save you even more money on your energy bills, as you’ll gain access to competitive peak export rates.

Octopus will also maximise your profits by directing your battery to import electricity from the grid at off-peak times and export it back to the grid at peak times.

Overall, the average household can expect to earn £350 per year on this tariff. This is based on a home with a 4.4kWp system, 5.2kWh battery, annual consumption of 3,500kWh, and typical UK solar irradiance, which exports 34% of its solar electricity.

To learn more, read our guide to deciding what size solar battery you need.

Should you get an oversized solar panel system?

It's almost always worth getting as large a solar panel system as you can.

If you get an ‘oversized system’, you’ll generate more solar electricity than you need, which you can sell to the grid to reduce your electricity bills even further than a standard system could.

With export tariffs only getting more profitable for domestic customers, the more panels you get, the more you’ll save – especially as extra panels don’t add much to your overall cost.

And with systems lasting upwards of 30 or even 40 years, you’ll be protected against energy price rises and prepared for your future – whether that involves an electric car, heat pump, air conditioning, or new additions to your household.

To find out more, check out our full guide: 4 reasons to get a larger solar panel system.

Average residential solar panel system size UK, 2020-24

The chart below shows how the average size of a residential solar panel system in the UK has increased between 2020 and 2024, based on data from Ofgem's annual SEG report.

Is it worth buying a very small system in order to save money?

It's not usually worth buying a very small system, especially if your aim is to save money.

Buying a very small solar panel system will slightly reduce your energy bills, and won't cost you much upfront.

However, you'll likely save a negligible amount, and your break-even point will be much higher than it would be with a system that suits your needs.

To go solar, you have to pay for the fixed costs that come with scaffolding, labour, and essential kit like the inverter – so you should make the most of it by getting as many solar panels as you can.

The panels themselves aren't particularly expensive, compared to the other costs, and the savings and revenue you can make from each additional panel means you shouldn't hold back – as long as you can afford the cost.

If you can't, or if you don't want to pay it, Sunsave Plus may be a good option. For no upfront cost, you’ll receive the best-in-class kit, all in one easy package that comes with a 20-year Sunsave Guarantee. Your installation will work seamlessly, look excellent, and save you money from day one.

What factors affect how many solar panels you need?

Here’s a list of factors that usually affect the number of solar panels you’ll need to power your home:

1. Your electricity consumption
2. If your electricity consumption is going to increase soon
3. The direction and angle of your roof
4. Where in the UK you live
5. The type of solar panel

1. Your electricity consumption

This is the main factor that'll help you work out how many solar panels you should get.

Your system should generate roughly as much electricity per year as you currently consume at home.

Even with a battery, you won't be able to use all the solar electricity your panels produce – as they'll generate so much more in summer than in winter – but sizing your system in this way helps to maximise your profits.

2. If your electricity consumption is going to increase soon

3. The direction and angle of your roof

The direction your solar panels face affects the quantity of electricity they can generate – as does the angle they’re installed at. 

If you live in the UK, you’ll ideally want to have your solar panel system facing south, at an angle between 30° and 45°.

The further you are from this ideal situation, the more solar panels you’ll need in order to achieve the required quantity of electricity.

You can still generate lots of electricity throughout the year with an east-facing solar panel system, but it’ll need more panels than a south-facing system to achieve the same output. 

And if you have a large south-facing roof that comes with various obstructions – such as chimneys, skylights, and vent pipes – that cast areas of the roof in shade, you may have to use more panels on other sides of your roof to reach your desired output goal.

If you have a flat roof, you can achieve the optimal angle with a mounting system to prop the solar panels up, though most residential flat roofs in the UK aren't strong enough to support a solar array.

Since drilling into a flat roof is usually a bad idea, the system will need ballasts to secure it to the roof, which weigh around 80kg per panel.

This will usually make an array with 12 solar panels around five times heavier, which is too much for the average roof.

4. Where in the UK you live

Despite the UK’s comparatively small physical size in global terms, there’s a surprisingly large variation in the amount of sunshine hitting different parts of the country. And this, of course, will affect how many solar panels you need in order to meet your consumption levels. 

You won’t be surprised to read that the more southerly parts of the UK, like Cornwall, Dorset, and Essex receive more solar irradiance than the northern parts. 

For instance, the south of England typically sees around 128 watts per square metre (W/m2) of solar irradiance each year, whilst the northwest of Scotland sees just 79W/m2.

Receiving less solar irradiance obviously means you’ll need more panels on your roof to achieve the same power generation as those basking in higher quantities.

5. The type of solar panel

There are several different types of solar panels. Some are much more efficient than others, which can greatly affect how many solar panels you need. 

If you go for black monocrystalline solar panels, which are currently the most efficient on the residential market, then you won’t require as high a number as if you went for blue polycrystalline solar panels.

This is because a more efficient solar PV system provides more power per panel then a less efficient one. 

If roof space is a particular concern, high-efficiency panels are a must. Plus, modern monocrystalline solar panels also have a sleek, black appearance which looks a lot better on rooftops than older blue panels do.

Fortunately, all Sunsave installations use black monocrystalline solar panels.

There's also a range of quality within the monocrystalline category, from efficiency to peak power rating, and even in terms of design.

Depending on the model, it may be better to opt for a bifacial solar panel – which absorbs sunlight on both sides – or one that uses half-cells, which reduce a panel's resistive losses, improve its defences against shade, and make hotspots less likely.

Limitations on the number of solar panels you can have

Legally, there’s no maximum number of solar panels allowed in the UK, but all roofs come with physical limits.

When you’re trying to fit as many solar panels on your roof as you can, there are a couple of main factors that can put a ceiling on your ambitions.

There isn’t much you can do about either of these issues, but the more you know, the better prepared you’ll be.

Roof space

The more solar panels you get, the bigger your roof has to be to fit them.

A panel is usually around 2m², but your installer will need to leave room either side of each panel, and around the system as a whole.

They’ll typically leave 40cm of space on all sides, and at least 3cm between the panels, to match the standards created by bodies like Microgeneration Certification Scheme (MCS) and Flexi-Orb.

This all means that each panel requires more than 3m² – for example, if your installer plans to put 10 solar panels on your roof, they’ll need 31.79m² of space.

And if your roof has extra facets, such as a chimney, skylight, or vent pipe, this will also reduce the amount of usable roof space.

To learn more, check out our guide to whether your roof would be suitable for solar.

Roof strength

A typical solar panel weighs 20kg, or 10kg per square metre.

This is well within the capabilities of most pitched roofs, which can generally hold many times this weight.

However, flat roofs are more problematic. Installers don’t usually drill into flat roofs, since holes can result in leaks, so they’ll ballast your panels – but ballasts weigh around 80kg per panel.

Roughly speaking, this will multiply your solar panel system’s weight by five, so a 10-panel system will go from about 200kg to a tonne. This normally means solar panels aren’t suitable for flat roofs.

How many solar panels do you need to live off grid?

You won't be able to power your entire off-grid setup with solar panels unless you massively reduce your electricity consumption in winter, to match the seasonal decrease in your panels' output.

However, solar panels can still form a large part of your electricity supply.

In order to work out how many solar panels you should get to help power your off-grid life, you'll need to know your annual electricity consumption.

You can also adjust this total based on need – so if you don't fancy paying for a large number of panels, you can cut down on the number of electrical items you use.

If you're successful in minimising your electricity consumption to – for example – 1,200kWh, you may only require three solar panels to power a large chunk of your electrical needs.

Next steps

You now have the tools you need to work out how many solar panels you should get for your home. This means you’re one step closer towards lower energy bills, reduced carbon emissions, and less reliance on the grid. 

To find out roughly how much you could save with a solar & battery system, simply answer a few quick questions below and we’ll provide an estimate.

FAQs