Solar panel sizes & dimensions: explained

When considering your switch to solar, there are two ‘sizes’ you need to think about: the power rating of your panels, and whether they’ll actually fit on your roof. 

The configuration you choose will have a big impact on the electricity you’ll produce and consequently the savings you’ll make. 

In this guide, we’ll run through everything you need to know about solar panel sizes, including their typical power rating and physical proportions. 

And if you’re wondering how much a solar & battery system could save you, answer a few quick questions below and we’ll provide you with an estimate.

What size are solar panels in the UK?

There are two ways to talk about solar panel size: watts (W) and physical dimensions, though the more common approach is watts. This refers to the maximum amount of electricity that a solar panel can generate in ‘standard test conditions’. 

Standard test conditions involve a solar irradiance of 1,000W per m² and a cell temperature of 25°C, and is the way manufacturers across the industry measure a solar panel’s output. 

Roughly speaking, in the UK, good solar installers will tend to use panels that have a power rating of about 400-450 watts (W), although some do stretch up to around 500W.

What does this mean? Well, if you take a solar panel that is 430W, this means it will be able to generate 430 kilowatt-hours (kWh) across a year, if conditions are perfect.

It's important to note that W and kWh aren't the same thing; W measures instantaneous power, like water pressure from a tap, while kWh measures quantities of electricity, like the amount of water in a bucket.

Average solar panel dimensions

The average solar panel used in residential installations is approximately 2m long and 1m wide, meaning a surface area of 2m², and is about 4cm thick. This makes them compact enough to fit on most UK rooftops while still providing significant output.

Meanwhile, the average solar panel weighs between 16-20kg. However, it’s important to remember that a complete solar panel system weighs more than just the panels themselves, as it includes metal mounting equipment.

For example, a standard 12-panel system, including mounting equipment, typically weighs around 250kg, with approximately 45-50kg of this weight coming from the mounting hardware.

Fortunately, most sloped residential roofs in the UK are strong enough to support the weight of a solar photovoltaic (PV) array without issue. But residential flat roofs are a different story, and they always need to be carefully assessed before a solar installation can go ahead. 

To learn more, check out our guide to flat roof solar installations.

Is solar panel size important?

When choosing solar panels, focusing solely on their size can be misleading. For instance, you might naturally assume that a 450W panel is superior to a 420W panel, but this isn't always the case.

It all depends on how much material the manufacturer has used in order to achieve this power rating, and consequently how physically large the panel is. 

For instance, a 500W solar panel might sound very appealing, but if it’s disproportionately larger than a 450W solar panel, you’ll be using up valuable roof space for disproportionately small gain. 

The key factor to focus on, therefore, is watts per square metre (W/m²), which adjusts the panel’s power output for its physical size. This is essentially the same measure as solar panel efficiency, and it provides a clearer picture of how much electricity a panel can generate relative to its surface area.

In fact, the ever-increasing power rating of solar panels is chiefly being driven by physically larger panels, rather than meaningful improvements in a panel’s W/m² rating. You can learn more about these developments here.

Residential vs commercial solar panel sizes

For commercial use, installers favour larger and more powerful solar panels, which are built to meet the high energy demands of big industrial buildings, factories, and warehouses.

As a result, commercial solar PV installations require large, open areas (either on the ground or on expansive flat rooftops) which can accommodate these bulkier beasts.

Today's monocrystalline solar panels can now reach power outputs exceeding an impressive 700W, but these ultra-powerful panels are reserved for commercial applications. 

Meanwhile, panels above around 500W tend to be impractical for domestic roofs, as their larger physical dimensions can make it tricky to fit enough of them on.

To learn more, check out our guide to the most powerful solar panels.

How much space do solar panels need on your roof?

As a general rule of thumb, your roof needs to be large enough to accommodate at least six solar panels for an installation to be worthwhile. For example, a 3 kilowatt-peak (kWp) system is around seven or eight solar panels, and it’d require approximately 23m² of usable roof space. 

The average solar panel uses 2m², and installers typically leave around 40cm of space on each side of the array and 3cm between each panel.

Your installer will also need to account for any objects on your roof, like chimneys, skylights, or vent pipes. If your roof has all three, you’ll need an extra 0.81m² of space to work around these obstacles.

It’s also important to note that if your roof has a dormer, the space it occupies doesn’t count as usable, as dormers typically have flat roofs - and most residential flat roofs aren’t strong enough for solar panels. 

Curious about how much a solar & battery system could save you? Answer a few questions below and we’ll provide you with a quick estimate.

The impact of solar cells on solar panel sizes

Crystalline solar panels are made up of solar cells, which are the components responsible for converting ultraviolet (UV) light into electricity through the photovoltaic effect. These cells are typically square-shaped and measure around 6 inches by 6 inches.

Most residential solar panels contain 60 to 72 solar cells, but you may also encounter panels with 120, 132 or 144 cells. These higher cell counts tend to come from the use of half-cut cells, which are literally standard cells cut in half to improve efficiency. 

Adding more cells to a solar panel increases its power output simply because there’s more material capable of generating electricity.

Therefore, panels with higher power ratings tend to have more cells, much like the 720W Hydra panel by Seraphim. This commercial solar panel contains 132 half-cut cells and tops our list of the nine most powerful solar panels available on the market today.

What size solar panels do you need?

Instead of focusing on individual panel sizes, it makes more sense to think about the overall size of your system, as this is what determines output. Once an installer has settled on what size system you need, they can create this using various panel sizes.

For example, a 4kWp system could consist of 10 400W panels, nine 450W panels, or eight 500W panels - it all depends on what will fit best on your roof.

To learn more, check out our guide to working out how many solar panels you need. 

For reference, as of February 2025, the average residential solar PV system in the UK is 4.6kWp, according to the Microgeneration Certificate Scheme (MCS).

How have solar panel sizes changed over time?

In the case of power rating, solar panel sizes have increased significantly over the past few decades. 

For example, the average power rating of a residential solar panel was around 290W in the 2010s, but many modern panels now exceed 500W.

Looking even further back over the past 60 years, the progress in solar power ratings has been remarkable. According to a NASA report, in 1966 its Orbiting Astronomical Observatory satellite boasted 53,000 solar cells but only achieved a peak power output of 0.7kWp.

Today, a solar panel system firmly rooted on Earth could achieve that same power rating with just two solar panels containing fewer than 200 cells - a staggering improvement.

Not to mention NASA’s array also occupied 17.4m² of space, whereas the same area on a modern rooftop could now support a system with a power rating of 3.9kWp. That's over five times the capacity of NASA’s array.

Next steps

Despite manufacturers continuing to release ever larger solar panels - both in terms of watts and physical dimensions - this may not necessarily represent a benefit to homeowners. What really matters is a solar panel’s W/m² rating, which is essentially the same as its efficiency. 

Fortunately, if you opt for a reliable solar panel installer with good reviews, you can trust them to select suitable, high-quality solar panels.

Wondering about how much a solar & battery system could save you? Just pop a few quick details in below and we’ll provide you with an estimate.

Solar panel sizes: FAQs