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The average home can save up to £1,190 on their energy bills each year by installing solar panels, but before you can start seeing those savings, you’ll need to know which solar panel system size and wattage is right for you. Otherwise, you could end up with a system that doesn’t suit your needs, whether it’s too large or too weak to sufficiently supply your household with solar energy.
The typical solar panel in the UK is 350W, which can produce up to 1,128.75Wh of electricity per day – enough to cover almost a sixth of the average UK home’s electricity needs by itself. However, solar panels come in a range of different sizes, with varying levels of efficiency and power outputs. In this guide we’ll walk you through solar panel sizes, explain what panel wattage is, and help you to calculate exactly how many solar panels your home will need.
Watt (W) = the amount of power the solar panels are capable of producing
Kilowatt (kW) = 1,000 Watts
Watt-hour (Wh) = the amount of watts solar panels produce over an hour
You should note that when this guide talks about a solar panel’s size, it’s referring to its physical measurements – its dimensions. As such, solar panel size shouldn’t be confused with solar array (or, if you prefer, solar system) size.
Solar system is the term for a collection of solar panels, rather than the panels individually, and in the UK and abroad, the size of a solar system is often denoted by its power output, which is measured in watts (W) – not in the metres or centimetres of its physical dimensions.
So, if you ask a solar panel installer or supplier in the UK what size your solar array or system should be, they’ll often quote you on the wattage rather than the exact physical dimensions. They’ll be using solar system “size” to refer to the combined total of each solar panel’s wattage or power output.
In the UK, a standard 350W residential solar panel is around 1.89m long, 1m wide and 3.99cm thick and contains approximately 60 solar cells.
This means that a 350W solar panel will take up around 1.89m² of roof space – although more efficient panels can be smaller but produce the same amount of power.
Solar panel wattage refers to the amount of power a solar panel can generate under standard test conditions (STC). Measured in watts, solar panel wattage refers to the maximum power output a solar panel can produce when exposed to sunlight.
Common domestic solar panel wattages in the UK include 250W, 300W, 350W and 400W, but even higher wattages are available – and all the best solar panels are at least 400W. (The most powerful solar panel we recommend, the JA Solar JAM72S30 Mono PERC Half-Cell MBB, has a power output of between 525W and 550W.)
Understanding solar panel wattage is vital to picking a solar panel powerful enough to meet your home’s electricity needs.
A 250W panel should, under ideal conditions, produce 250 watt-hours (Wh) for every hour of sunlight it receives. If you multiply 250W by the average daily sunlight hours in the UK – which across all 12 months in 2023 was 4.3 – you get 1,075Wh per day. But you also need to take into account sunlight fluctuations and suboptimal orientation, so to do that, you can multiply 1,075Wh by a modifier of 0.75. Therefore, a 250W panel should generate about 806.25Wh in a day.
| Solar panel wattage | Daily electricity provided | Roof space required (m²) |
|---|---|---|
| 200W | 645Wh | 1.30 |
| 250W | 806.25Wh | 1.37 |
| 300W | 967.5Wh | 1.62 |
| 350W | 1,128.75Wh | 1.89 |
| 400W | 1,290Wh | 1.92 |
| 450W | 1,451.25Wh | 2.17 |
| 500W | 1,612.5Wh | 2.55 |
Given that the average household electricity usage in the UK is 7.5kWh (kilowatt-hours) per day for a medium-use household, you’d need at least 10 250W panels (or fewer panels with a higher wattage) to meet those needs. But what would the power output of a full domestic solar array be?
As they’re made up of multiple solar panels (and, as such, generate a lot of power), solar arrays or systems are measured in kilowatts (kW), with 1kW = 1,000W.
| Solar system size | Yearly electricity production* | Household size | Roof space required | Number of panels |
|---|---|---|---|---|
| 3kW | 2,199kWh | One to two people | 15m2 | 8 |
| 4kW | 2,826kWh | Two to three people | 22m2 | 12 |
| 5kW | 3,532kWh | Three to four people | 30m2 | 16 |
| 6kW | 4,238kWh | Four to five people | 37m2 | 20 |
STC refers to a set of standardised conditions that enable manufacturers to measure and rate the performance of different solar panels. STC controls for:
Understanding STC is important because the solar panel wattages and efficiencies (which we’ll get to shortly) that manufacturers advertise will be based on STC. Since solar panels are developed in standardised, ideal conditions, the actual performance of solar panels – ie under real-world conditions – may differ.
Real-world conditions include a range of factors that affect solar panel performance, such as fluctuations in sunlight intensity, daytime temperature and any shade that falls on your house throughout the day. Whether you decide to install a tracking system that keeps your panels continuously oriented towards the sun will also affect solar panel performance. So, bear in mind that STC ratings are a baseline for performance comparison – not a guarantee of minimum performance in the real world.
Some of the factors that affect the wattage of a solar panel include:
A solar panel’s physical size tends to strongly correlate with its wattage. As a general rule, larger solar panels have higher power output than smaller ones.
This is because larger solar panels have more surface area, meaning they can accommodate more solar cells. Since solar cells are responsible for capturing sunlight and converting it into electricity, the equation is simple: more cells = more power.
That said, you don’t always have to buy the solar panels with the largest physical dimensions to get the most power – as we’ve discussed, efficiency also plays a role. A smaller panel with more efficient cells can produce as much power as a larger panel with cells that aren’t as efficient. So, while the physical size of a panel does matter, it’s not the be-all and end-all – which is why a solar panel’s wattage and efficiency are more reliable indicators of its performance and capabilities than its physical dimensions.
Yes, solar panel size – that is, its physical dimensions – has an impact on efficiency. In fact, a solar panel’s efficiency can only be calculated by factoring in the amount of space it takes up.
For example, a solar panel rated at 400W with a surface area of 2m² will have an efficiency rating of 20 per cent ([0.4kW/2m2] × 100 = 20 per cent). So a panel’s efficiency is dictated by both its physical dimensions and its power output.
This means that panels with the highest wattage – vis a vis their size – will be the most efficient. So why is panel efficiency so important?
Well, the more efficient your panels are, the more electricity they produce for your home. And the more electricity your home produces, the less you’ll have to rely on the National Grid for the bulk of your household’s energy needs – which means your electricity bills will be lower. Better still, maximising your home’s renewable energy production means you can take advantage of the UK’s solar panel grants – namely, the Smart Export Guarantee (SEG).
Effectively, the SEG allows you to sell any excess electricity your home’s solar panels generate back to the grid for a profit – thus augmenting the savings you’re already getting from lower electricity bills and reducing the amount of time it’ll take to break even on your solar panel installation.
| System size | Estimated installation cost | Energy generated per year | SEG payments (15p/kWh) | SEG payments (10p/kWh) | SEG payments (5p/kWh) |
|---|---|---|---|---|---|
| 3kW | £4,957 | 2,199kWh | £243 | £162 | £81 |
| 4kW | £5,942 | 2,826kWh | £342 | £228 | £114 |
| 5kW | £6,928 | 3,532kWh | £441 | £294 | £147 |
| 6kW | £7,913 | 4,238kWh | £540 | £360 | £180 |
| 7kW | £8,899 | 4,945kWh | £642 | £428 | £214 |
To calculate how large your solar array should be, you’ll first need to crunch some numbers to find out how many panels you’ll need.
To do this, you’ll need a recent electricity bill to understand how much electricity your home currently consumes per day. As an example, take the average figure for the UK as the starting point. According to OVO Energy, the figure for a medium-use household in 2023 was 7.5kWh, or 7,500Wh, per day.
Next, you need to work out how much of your electricity needs you want your solar system to cover. You might want the system to cover only 75 per cent or even 50 per cent if you’re on a tighter budget. But for this example, assume you want to reduce your electricity bill as much as possible, so you’d opt for a solar array that will meet the entirety – that is, 100 per cent – of your home’s electricity needs.
Now you need to determine how much sunlight your home gets per day. This will vary depending on where in the UK you live, so you can explore our regional guides for more details:
For this example, we’ll go with the average daily sunlight hours in the UK: 4.3. However, you should also incorporate a 0.75 modifier to account for any variables that could affect the year-round performance of your solar panels – such as shade or suboptimal panel orientation – and to reflect that their real-world performance won’t ever meet that achieved under STC.
Finally, it’s time to utilise your new knowledge of solar panel wattage and pick a solar panel with a power output that’s appropriate for your home. As you know, solar panels come in various wattages, but for this example, let’s choose a robust 400W system.
Now, you have all the information you need to calculate how many solar panels your home will need. First, calculate the output of one panel:
Solar panel wattage x sunshine hours x modifier = solar panel power output
Plugging in the figures from our hypothetical example, you get:
400W x 4.3 x 0.75 = 1,290Wh
Now, all you need to do is divide your home’s daily electricity needs by this figure to find out how many solar panels you’d need to power your home.
Electricity needs % solar panel output = how many panels requires
So, for our hypothetical household, you get:
7,500 % 1,290 = 5.81
The household will need at least six 400W solar panels.
| Solar panel wattage | Daily electricity provided | Panels required | Panel size (m²) | Roof space required (m²)* |
|---|---|---|---|---|
| 200W | 645W | 12 | 1.30 | 15.6 |
| 250W | 806.25W | 10 | 1.37 | 13.7 |
| 300W | 967.5W | 8 | 1.62 | 12.96 |
| 350W | 1,128.75W | 7 | 1.89 | 13.23 |
| 400W | 1,290W | 6 | 1.92 | 11.52 |
| 450W | 1,451.25W | 6 | 2.17 | 13.02 |
| 500W | 1,612.5W | 5 | 2.55 | 12.75 |
As we’ve discussed – and as the table demonstrates – the more powerful the panel, the fewer you’ll need to satisfy your home’s electricity needs. (But remember that the number of panels needed will also depend on the efficiency of the panel you choose.) Before you proceed on the basis of solar panel wattage alone, you’ll also need to factor in solar panel size – that is, the physical dimensions – and make sure there’s enough space on your home’s roof to support the appropriate solar array.
Remember, one standard-sized 350W solar panel takes up 1.89m2 of precious roof real estate, with more powerful panels hogging yet more – so it’s a good idea to make sure you have between 25m² and 35m² of roof space available before scouring the market for solar panel quotes. (After all, you may want to generate more electricity than the average UK home demands and sell what you don’t use back to the grid for a profit.)
When you’re ready to start comparing, our guide to solar panel costs will help – as will our free quote-finding service.
Yes, it’s highly likely that solar panels will continue to get smaller and more efficient as the technology advances and the field matures.
Solar roof tiles, for example (also known as solar shingles or solar slates) are a type of solar technology that, rather than being mounted on your roof, are your roof – they look and behave exactly like traditional roof tiles but generate clean, renewable energy for your home. They’re much smaller than conventional solar panels and come with none of the aesthetic drawbacks.
Other emerging solar technologies include solar thermal panels – which convert sunlight into heat, rather than electricity, to warm your home’s water and spaces – and flexible solar panels, which can be bent to fit the surface you’re mounting them on. Flexible solar panels are made of silicon wafers that are just a few micrometres thick and are a striking example of how solar panels are becoming not only smaller as the technology evolves but thinner, too.
Finally, there’s a whole new generation of solar cells and panel types with the promises of higher efficiency, quicker times to market and exciting new designs and use cases.
It might be rather clichéd or eye roll-inducing to say that the future of the solar industry looks bright. But it certainly does look exciting – and, as solar technology becomes more accessible, more available, more affordable and more aesthetically pleasing, this can only bode well for UK homeowners looking to help the environment (and their wallets) by going solar.
Under STC, a 350W solar panel will produce a maximum of 350 watts of power – which, in every hour of ideal sunlight conditions, should equate to 350Wh of electricity. Based on the UK’s average daily sunlight hours of 4.3, you’ll need at least seven 350W solar panels to cover the average daily electricity needs (7.5kWh) of a UK home.
When deciding on solar panel size and wattage, consider factors such as: how much electricity your home currently consumes; whether you will be taking advantage of solar panel grants and schemes; how much roof space you have; how efficient your panels will need to be, and more.
Most domestic solar panel systems in the UK won’t require planning permission, as they qualify under Permitted Development rights – providing you meet certain conditions. However, if your property is a conservation or listed building, you may need permission, so it’s always worth checking with your local authority before installation.
Our calculations indicate that you’ll need around seven 350W solar panels to meet the average electricity needs (7.5kWh/day) of a medium-use UK homeowner. You could also meet these needs with five 500W panels or twelve 200W panels.
On average, the power output of solar panels ranges from 250W to 400W per panel. This figure will vary based on how much sunlight the panel is exposed to, how efficient it is and how it’s oriented and positioned on your roof.
Most solar panels weigh around 18kg each, although larger varieties (such as 72-cell panels) can weigh as much as 22-25kg each.
