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

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If you’re thinking of switching to solar power, you’re probably wondering how many panels 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.



solar panels on a house with an orange roof

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.

If you’d like to know more about the highest quality panels you could be putting on your roof, check out our guide to the 36 best solar panels of 2019. Meanwhile, to start receiving free quotes for solar panel installation, simply fill in the short form at the top of this page.


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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 tall 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 world adds approximately 70,000 solar panels every hour. Fill out this form to start receiving free solar panel quotes today.


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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.

If you’re interested in the panels with more watts than they know what to do with, check out our list of the most powerful solar panels on the market.


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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
1kWp
£1.5 - £3k
4
8sqm
850kWh
2kWp
£3k - £5k
8
16sqm
1,700kWh
3kWp
£3k - £5k
12
24sqm
2,550kWh
4kWp
£6k - £8k
16
32sqm
3,800kWh


Information updated in July 2019.


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Average annual yield from solar panels

As you can see in the table above, the larger your solar PV system, the greater its annual energy output (or its ‘average annual yield’). A 1kWp system will produce about 850 kilowatt hours (kWh) of electricity, while a 4kWp system will churn out a whopping 3,800kWh.

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 1kWh of electricity. In contrast, a 2,000-watt oven would use 1kWh 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 850kWh of electricity each year, in reality this figure will vary depending on the number of peak sun-hours your panels experience.

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 2018, as reported by the Department for Business, Energy & Industrial Strategy.

Month of 2018
Average number of daily peak sun-hours
January
1.9
February
3.7
March
2.8
April
4.3
May
7.8
June
8.1
July
8.7
August
5.6
September
5.3
October
4.4
November
2.5
December
1.4


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.


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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 OVO Energy, the typical UK household uses 3,760 kilowatt hours (kWh) of electricity each year. (Point of interest: compare that to the staggering 12,300kWh that the average US household annually churns through).

Here’s the typical annual consumption broken down by property type, again from the folks at OVO Energy.

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


Information updated in July 2019.


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): 3,100kWh per year

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

Naturally, bigger houses with more people living in them will use more electricity. Unless those people are Amish.

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.


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Should you buy a solar battery?

If you want your solar PV system to pretty much cover all of your energy needs, you’ll also require a solar battery.

If you don’t use solar-generated electricity immediately after it is created, then it will go back into the grid. Homeowners with solar 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 even more expensive in the evenings when demand is higher, so you’re dodging 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).


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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.

According to a study by Which?, the average price of a 3.4-4kWp solar PV system between 2015 and 2018 was £6,672. To learn more, take a look at our detailed guide to solar panel costs in 2019.

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.

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