How many solar panels do you 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?

This table will give you a sense of how many panels are required for households with different levels of electricity consumption, but make sure to only use it as a rough guide.

The number of panels you need will differ depending on a wide range of factors, including your roof's characteristics, how much sunlight your home receives, and your future electricity consumption. 

Every household has unique characteristics, which makes it tricky to provide estimates that work for everyone. For instance, if you have a chimney, vent pipe, or skylight (also known as a Velux window), you’ll need a bit more space on your roof – 0.81 m², if you have all three.

The exact number of panels you need will be best identified during a consultation with an installation expert.

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 if you sign up to Intelligent Octopus Flux, you'll be paid the same price for your electricity as you'll pay to import it from the grid.

With a smart export tariff, you can use 63% of your solar electricity on average, export the rest, and save up to 103% on your electricity bills.

This last figure is based on a household experiencing average UK irradiance that has a 4.4kWp solar panel system and a 5.2kWh battery, uses 3,500kWh of electricity per year, and is signed up to the Intelligent Octopus Flux export tariff.

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 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 – and you’ll get an estimate of how many solar panels you need.

Is it worth covering your whole roof in solar panels?

It's almost always worth covering as much of your roof as possible in solar panels.

Once you take the price of scaffolding, inverter, cables, and labour into account, it doesn't add much to your overall cost to tack on a few more panels – and it can massively increase your savings.

If your roof is north-facing in an area where solar panels output is low, it may not be worth getting solar panels at all, but if it's a good idea to go solar where you are – and that includes most of the UK – then you should maximise your roof space.

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 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.

Can you add extra solar panels to an existing system?

You can always add extra panels to an existing solar panel system, but it’s a good idea to make sure the panels you add are the same type. 

This is because the new solar panels you add might have a different wattage, which will lead to a lower overall power output. In solar panel systems, the lowest wattage panel will be prioritised, pushing the more powerful panels to the back of the queue. 

In turn, your system will generate less power.

It's also often difficult to add solar panels to the same inverter, so you may well need a second inverter. As well as pushing up your costs, this could mean you'll have to use two tracking apps, which isn't ideal.

How many solar panels do you need if you live alone in a large house?

If you live alone in a large house, the average figures you'll see for different sizes of home may not apply to you.

You should instead focus on your annual electricity consumption to find out how many solar panels you should get.

As long as you switch off lights when you're not in the room, and turn off electrical appliances like TVs when you're not using them, you'll typically have a smaller consumption level than most homes.

If you use 2,000kWh of electricity per year, for example, you should typically get a system with five 430-watt solar panels.

How many solar panels do you need in order 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.

Summary

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, click the button below and provide us with a few quick details - then we'll generate an estimate for you.

FAQs