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Solar panel size captures both a panel’s power and its physical dimensions. Find out what size of solar panel system you need with our guide.
Solar panel size matters. Not only in terms of the physical dimensions of the solar panels – your roof can only fit so many – but in the amount of power they produce. Striking the right balance between the two will give you more bang for your buck, helping cut the cost of your energy bills.
Our guide walks you through what solar panel size means when it comes to output, the average dimensions of solar panels, and the size of the solar panel system needed for your home.
When people talk about the size of solar panels, they can mean two different things: its wattage, or its physical dimensions.
A solar panel’s wattage determines how much energy your system can generate, while a solar panel’s dimensions inform how many you can fit onto your roof. Both can vary significantly from panel to panel depending on:
It’s worth noting that, while a solar panel with a higher wattage will normally be larger than a less powerful panel (because more power usually requires more solar cells), this isn’t always the case.
When comparing solar panels, you will see a panel’s power listed in watts (W), for example 450W or 485W. This is the maximum amount of energy the solar panel can generate in an hour, under standard test conditions (STC). The higher the number, the more energy a panel can produce.
The maximum energy your solar panel system can generate is typically described by its kilowatt peak (kWp). This figure is found by multiplying the number of panels by the model’s wattage. For example, since there are 1,000 watts in a kilowatt, 12 panels with at 375W wattage each would produce a 4.5kWp system – our recommended system size for the average three-bedroom home in the UK.
However, a panel won’t necessarily always produce its STC wattage, nor will your system always hit its kWp. That’s because the amount of energy your solar panels generate each hour can be affected by a range of factors, including weather conditions, the shade that falls on your home, and the angle of your roof.
According to solar panel installer Sunsave, UK weather conditions will typically generate around 85 per cent of a panel’s STC peak output. If every 1kWp your system can generate equates to 1,000 kilowatt hours (kWH) per year, a 4.5kWp solar panel system in the UK would roughly produce 3,825kWh annually.
Wattage isn’t the only consideration, however. The more efficient a panel is, the better it will be at converting sunlight to electricity, without taking up as much space as less efficient panels. This is because you calculate a solar panel’s efficiency using its power and its dimensions.
For example, if a solar panel has a power rating of 500W, but is 2.6m2, it will be less efficient than a panel that has a power rating of 450W but is only 2.2m2. Therefore, it’s important not to be blinded by a panel’s power rating and consider its size as well.
It’s worth noting that high efficiency solar panels are typically more expensive. Choosing the best solar panel involves finding the sweet spot between power, efficiency and price to get the most out of your system.
The average wattage of FMB’s best solar panels is 506W. The panels range from the SunPower Maxeon 6AC 445W – our best solar panel – at one end, and the Jinko Tiger Neo 72HL4 605W at the other.
In terms of efficiency, meanwhile, the average is 23 per cent, ranging from 22.1 per cent to the AIKO ABC Neostar 3N54 495W’s 24.8 per cent.
While the size of a solar panel in wattage will help determine the number you need to generate the energy your household requires, a panel’s physical dimensions will dictate how many you can actually fit on your roof.
When you look at the dimensions of a solar panel, you’ll have:
Your installer will use these figures to calculate what size of solar panel system you can have, both in terms of the available space and the weight your roof can bear.
When installing solar panels on your roof, you’ll only need to apply for planning permission if the dimensions of your system mean it will:
Based on FMB’s best solar panels, the average solar panel dimensions in the UK are:
While there isn’t much variation in width (six of our eight best panels measured 1,134mm) and height (all but one was 30mm tall), there were significantly different lengths. For example, the JA Solar JAM72S30 LR 585W – the longest panel at 2,333mm – is 611mm longer than the Perlight PLM-435 DH8N 450W.
As for weight, the lightest solar panel we’ve reviewed is the AIKO ABC Neostar 3N54 495W at 21.0kg, compared to JA Solar’s hefty 28.0kg JAM72S30 LR 585W.
When you get quotes from the installers you’re considering, they should outline the size of the solar panel system you need based on your energy consumption and available space.
However, it can be useful to go into those conversations with an idea of what to expect – especially as your system size influences the cost of solar panels. Below is the size of solar panel system we recommend for various house sizes in the UK:
| House size | Estimated annual energy consumption (kWh) | Size of solar panel system (kWp) | Number of panels | Roof space (m2)* | Cost of system (including battery) |
|---|---|---|---|---|---|
| 1 bedroom | 2,500kWh | 1.5kWp | 4 | 8.8m2 | £6,200 |
| 2 bedrooms | 2,900kWh | 3kWp | 8 | 17.6m2 | £8,200 |
| 3 bedrooms | 3,350kWh | 4.5kWp | 12 | 26.4m2 | £9,600 |
| 4 bedrooms or more | 4,000kWh | 6kWp | 16 | 35.2m2 | £12,000 |
The average solar panel is 2.2m2, with a height of around 30mm, and a weight of 23.6kg, according to FMB’s research into the best solar panels.
The size of a 400W solar panel will depend on the manufacturer. Our research has found that they typically range between 1.8m2 and 1.95m2, with a height of 30mm to 35mm.
A 5kW solar panel system will likely require 13 to 14 solar panels, requiring between 28.6m2 and 30.8m2 in roof space.
