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What Size Solar PV System Do I Need for My Home?

A typical three-bedroom house would need a 3.5 kW solar panel system

This equates to 10 panels, which typically costs £5,420

Solar panels typically save 17.5 tonnes of CO2 over their lifespan

If you’re thinking of switching to solar power, you’re probably wondering what size solar PV system you need.

It’s a reasonable thing to wonder – solar photovoltaic (PV) systems come in a significant range of sizes, from just a couple of panels to something that covers an entire roof. It all depends on how much electricity your household uses, how much space you have, and how much money you’re willing to spend.

In this article, we’ll explain the basics of how to calculate the right size solar PV system for your home.

This includes information about average UK household electricity usage, as well as typical solar panel dimensions.

And to receive free quotes for the best solar panels, simply fill in this quick form.


What's on this page?

01 | How big is a solar panel?
02 | What is a solar array?
03 | The different sizes of solar PV system
04 | Small solar panels
05 | Large solar panels
06 | What size solar PV system do you need?
07 | How heavy are solar panels?
08 | Average annual yield from solar panels
09 | How much electricity does your house use?
10 | Should you buy a solar battery?
11 | How do I calculate the right size solar array for my home?
12 | Next steps


How big is a solar panel?

The vast majority of residential solar panels are rectangular in shape, measuring approximately 2 square metres.

They’re usually about 2 metres long and 1 metre wide, with a thickness of 3-5cm.

However, some manufacturers have recognised the need for compact panels, which are ideal for households with small roofs. If you’re looking for something particularly compact, check out:

Sharp’s 258.4W NQ-R Series, measuring 1.29 square metres

Panasonic’s 300W N300, measuring 1.54 square metres

SunPower’s 370W X-Series X22, measuring 1.63 square metres

You can also get around the issue of limited roof space with high-efficiency solar panels. These premium panels are particularly good at converting sunlight into electricity, offering conversion rates of around 20-22% (the industry standard is closer to 18%).

Did You Know?

The UK generates enough solar energy per year to power the creation of 11 million mugs of tea. Fill in this form to start saving money and the planet today by receiving free solar panel quotes.

 

Average solar panel dimensions


What is a solar array?

A ‘solar array’ is just a nicer way of saying ‘solar PV system’. Once you’ve combined multiple solar panels and connected them to your household, you’ve got yourself a solar array.

 

What’s the typical power output of a solar panel?

The typical wattage of a residential solar panel is around 300W, although you can find panels that exceed 400W if you really want your PV system to pack a punch.

Consequently, if you wanted to create a 1.2 kilowatt peak (kWp) solar array, you would need four 300W panels (because 4 x 300W = 1,200W). Similarly, eight 300W solar panels would create a 2.4kWp system. You get the idea.

 


The different sizes of solar PV system

See below for a breakdown of the four key solar PV system sizes, and all the specifications that come with them.

Please note that the ‘annual energy output’ figures are just estimates, as the output of your solar PV system will vary widely depending on numerous environmental factors. Likewise, the costs are also estimates.

To learn more about how much you’re likely to pay for a new solar array, take a look at our guide to solar panel costs.

Solar PV system
Cost
Number of 250W panels
Roof space
Annual energy output
1 kWp
£1,630
3
4.9
790 kWh
2 kWp
£3,250
6
9.8 m²
1,590 kWh
3 kWp
£4,880
9
14.7
2,380 kWh
4 kWp
£6,500
12
19.6 m²
3,170 kWh

Information updated in July 2022.

 


person installs solar panels

The more solar panels you have, the more money you can save


Small solar panels

There are plenty of small solar panels you can use to power a variety of off-grid systems based on batteries – most commonly leisure vehicles like caravans and boats.

They wouldn’t normally be considered for houses, as the number of connections to create a reasonably sized array would increase the cost by too much.

Instead of the standard size of two square metres, these are typically four times smaller, at 0.5 square metres – though the output is also smaller, naturally.

The 50W panel is a popular model among small solar customers, but you can get anything from a 10W panel to a 100W panel, depending on your needs.

The best attribute of small solar panels is their flexibility. You can use their different outputs and sizes to get exactly what you need for your battery.

Speaking of which, you'll need a solar battery if you want to save solar energy for later, instead of only using it while the sun's shining.

 


Large solar panels

Solar panels as big as 3.1 square metres are now available for domestic use.

Companies like Risen Energy produce panels this size that can generate up to 670W – around twice as much as a typical panel – which makes sense considering its size.

Large panels aren't necessarily any more efficient, and it can be complicated to fit them around obstacles on your roof, but they can look neater and more uniform.

You don't have to get large solar panels, even if you have a big roof or large off-grid building to power – but sometimes it makes more financial sense to go big for your home.

Of course, cost considerations also come into this calculation, and large panels are often prohibitively expensive.

That's why they're normally only produced for commercial use.

 


What size solar PV system do you need?

The size and output of your solar array depends on the size of your home, and your annual electricity usage.

The average three-bedroom house will use 2,900 kWh per year, meaning you'll need a system rated at around 3.5 kW to generate the same amount of electricity each year.

That would require 10 panels rated at 350 kW each.

This should take up around 20 square metres on the average roof – but your home isn't average, which is why you should consult our definitive guide to how many solar panels you need.

 

Should you use small or large solar panels?

When it comes down to it, it doesn't matter whether you use small or large panels.

What matters is that your solar panels fit on your roof, generate enough electricity for you, and do both of these tasks in a cost-effective manner.

Small off-grid buildings and vehicles may not be able to fit or support large or medium-sized solar panels, and therefore must use small solar panels.

But when it comes to standard roofs, it's all about making sure your overall solar array fits your budget, your roof, and your energy needs – whether the panels are small, medium, or large.

 


How heavy are solar panels?

Residential solar panels usually weigh between 18kg and 20kg.

That means the typical 10-panel solar array weighs more than two fully grown men, on average.

This is an excellent reason to hire a professional installer to get you all set up with solar power – along with the fact that they'll install the panels properly.

If you're buying solar panels for a vehicle or small off-grid building, you should consider flexible solar panels, which can bend around a corner or over a bump, and are also lighter, typically weighing in at between 0.8kg and 3kg.

 


Average annual yield from solar panels

The larger your solar PV system, the greater its annual energy output (or its ‘average annual yield’). A 1 kWp system will produce about 895 kilowatt hours (kWh) of electricity, while a 4 kWp system will churn out a whopping 3,580 kWh.

But what actually is a ‘kilowatt hour’? Quite simply, it’s the quantity of energy that a 1,000-watt appliance would use if it was switched on for one hour. For example, if you turned on a 50-watt light bulb, it would take 20 hours for it to use 1 kWh of electricity. In contrast, a 2,000-watt oven would use 1 kWh of electricity in just 30 minutes.

You’ll notice in your energy bills that your monthly electricity usage is measured in ‘kWh’, so it makes sense to quantify a solar panel’s electricity output in the same way.

 

What are peak sun-hours?

It’s also important to bear in mind that environmental conditions can affect the amount of energy that your solar panels produce. While a 1kWp solar PV system is expected to produce roughly 895 kWh of electricity each year, in reality this figure will vary depending on the number of peak sun-hours you enjoy, the direction your panels face, and their efficiency.

A ‘peak sun-hour’ is an hour in the day when the intensity of sunlight is at least 1,000 watts per square metre. Naturally, the amount of solar radiation (also known as ‘insolation’) increases each day towards noon, and then decreases again as the sun starts to set. The seasons will also determine how many peak sun-hours there are, with the summer (when the sun is highest in the sky) bringing the most, and winter bringing the least.

Here is the average number of daily peak sun-hours in the UK for each month in 2019, as reported by the Department for Business, Energy & Industrial Strategy.

Month
Average number of daily peak sun-hours
January
1.7
February
4.4
March
4.2
April
5.8
May
6.6
June
5.7
July
6.8
August
6.7
September
5.4
October
2.7
November
1.7
December
1.9

Once you know how many peak sun-hours you can expect, use this equation to calculate how much electricity your solar panels will generate per day:

Daily peak sun-hours x PV system’s rated output (kWp) x 0.85

Why 0.85? Well, when solar irradiance exceeds 1,000 watts per square metre, solar panels are rarely able to absorb more than about 85%.

So, if you have a 3kWp solar PV system, this would be its expected electricity output in the UK in July:

8.7 x 3 x 0.85 = 22.2kWh per day in July.

Meanwhile, its output in the middle of winter would be much lower:

1.4 x 3 x 0.85 = 3.6kWh per day in December.

Along with the seasons, your location in the UK will also affect the number of peak sun-hours that your panels receive. A household located in the south of England will naturally receive a stronger level of solar irradiance than one up in Scotland, for example.

 


house with solar panels

This could be your home, saving money and energy


How much electricity does your house use?

The most important factor in calculating the size of a new residential solar array is your household’s annual electricity usage. Once you know that, you can then work out what system size will be right for you.

According to Ofgem, the typical UK household uses 2,900 kWh of electricity each year. (Compare that to the staggering 12,300 kWh that the average US household annually churns through).

Here’s the typical annual consumption broken down by property type.

Type of property
Annual electricity consumption
Mid terrace
2,779 kWh
Flat
2,829 kWh
End terrace
3,442 kWh
Semi-detached
3,847 kWh
Bungalow
3,866 kWh
Detached
4,153 kWh

Information updated in July 2022.

 

If you want to think about it in terms of number of bedrooms or number of occupants, here are some estimates from Ofgem:

• 1-2 bed flat (1-2 occupants): 2,000kWh per year

• 3-bedroom house (3-4 occupants): 2,900kWh per year

• 4+-bedroom house (5+ occupants): 4,600kWh per year

Naturally, bigger houses with more people living in them will use more electricity.

So, how do you actually go about calculating your own household’s electricity usage? Well, you might not like looking at them, but your electricity bills will hold the answer. Solar panel installers will usually require your daily average consumption, so take the figure (in kWh) on your monthly bill and divide it by 30.

If you think this task sounds fairly daunting, don’t worry. Once you’re in touch with a professional solar panel installer, they can help you out.

 


Should you buy a solar battery?

If you want your solar PV system to cover the large majority of your electricity needs, you’ll also require a solar battery.

If you don’t use all your solar electricity at the time it's generated, the remaining energy will go to the grid. Homeowners with panels need to be in their house during the daytime in order to use their solar energy, or else it will go to waste.

However, with a solar battery, you can store up all the solar energy that doesn’t get used. Then, once you’re back home in the evenings and the sun has gone down, you can still power all your appliances with solar energy. What’s more, electricity from the grid is usually even more expensive in the evenings when demand is higher, so it may allow you to dodge the priciest time for grid power.

You can find out more in our complete guide to solar batteries, which includes information about typical costs, pros and cons, and the best models on the market. Naturally, it’s the biggest batteries that are most capable of taking you entirely off-grid, such as the Tesla Powerwall 2.0 (13.5kWh) or the Sonnen Batterie eco (11.25kWh).

 


How do I calculate the right size solar array for my home?

To work this one out, you need to ask yourself three questions:

1) How much power does your household use?

2) How big is your roof?

3) What's your budget?

Number three is the most important consideration. Irrespective of your energy usage and roof size, cost is surely the deciding factor when it comes to choosing a solar PV system.

The average price of a 3.5 kWp solar PV system is £5,420. To learn more, take a look at our detailed guide to solar panel costs.

 


Next steps

The size of solar PV system you need for your home will depend on a variety of factors, including your roof space, energy requirements, and budget.

The next step is to work out which solar panels – and how many – you need.

With 65% of people telling our latest National Home Energy Survey that they'd buy a house with solar panels, there's never been a better time to go solar.

If you’d like to find out how much solar panels will cost you, simply fill in this short form, and our professional installers will be in touch.

Charlie Clissitt Editor

Charlie has been researching and writing about solar power for four years, which makes him great fun at parties. Ever since he can remember, Charlie has worried about the planet, and he one day dreams of owning his own solar power farm.

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