How much energy do solar panels produce?

It’s widely known that solar panels generate electricity and reduce people’s reliance on the national grid, but how much electricity do they actually produce? Is it reasonable to expect solar panels to completely cover your electricity needs? 

In this article, we'll explore roughly how much electricity a solar panel system can produce, and explore the various factors that can influence solar output. 

If you’re interested in switching to solar, you can find out how much a solar & battery system could save you by answering a few quick questions below.

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

A solar panel system in the UK will typically generate around 85% of its peak output.

If a system has a peak rating of 4.4 kilowatts-peak (kWp), it would produce 4,400kWh per year in standard test conditions (STC), which is a set of environmental factors used across the industry to measure a panel's capabilities.

But since the average conditions in the UK are around 85% as good as STC, these panels will produce around 3,740kWh per year.

This is more than enough for the average household, which typically uses 3,400kWh of electricity per year, according to government data.

There's some variance in this figure though, which is influenced by a few different factors.

As you can see in the chart above, the main factor behind how much energy your panels generate is the size of the system, which makes sense – the bigger and better your system, the more electricity it'll produce.

But even with identically sized systems, you can see massively different output levels. Check out a few examples here:

How much will this save you on your energy bills?

A solar & battery system will typically reduce your annual electricity bills by 103% – meaning across a year, you'll actually earn more than you spend.

This figure is based on a household experiencing average UK irradiance with a 4.4 kilowatt-peak (kWp) solar panel system and a 5.2 kilowatt-hour (kWh) battery, using 3,500kWh of electricity each year and signed up to the Intelligent Octopus Flux export tariff.

It might sound too good to be true, but technological and tariff developments have made it a reality. Households can now turn to high-performing modern solar panels and storage batteries, as well as solar export tariffs that turn your excess solar electricity into significant profits.

So your panels will dramatically reduce the amount of electricity you need to buy from the grid, and you’ll earn money by selling your excess electricity to the grid.

Octopus's export tariffs have transformed the financial benefit of solar panels, and it's easy to sign up for one – especially if you get Sunsave Plus.

How much energy do solar panels produce per day?

A 4.3kWp solar panel system will produce 10kWh per day in the UK, on average.

However, you shouldn't take this as a hard-and-fast rule, because your system's daily generation levels will depend on a host of factors.

As well as the variables listed above – like orientation, angle, shading, and inverter type – generation will also be affected by each panel's peak output, their location, the weather, and what time of year it is, as this will determine how many hours of daylight there are.

So on average, a 4.3kWp solar panel system in London will produce 8.8kWh per day, while the same system in Exeter will typically generate 12.8kWh per day.

If it's in the ideal situation though, on a south-facing roof with an orientation of 40°, it'll produce even more solar electricity.

And wherever you are, your output will likely be around 55% below the average in winter, and 52% higher than average in summer.

As a result, you'll usually have to buy grid electricity during the colder months to make up the shortfall, but you can then sell your solar energy to the grid when summer comes round again.

How much energy do solar panels produce per hour?

Solar panels produce 0.4kWh per hour on average, but this includes the hours after the sun goes down, when your system won't generate any energy.

Your solar panel system will be most productive at solar noon, when the sun is at its highest point in the sky. Due to the nature of the Earth's orbit, this time is almost never exactly 12pm, but instead occurs between 11:40am and 1:10pm, depending on the time of year.

You should therefore concentrate as much of your electricity consumption as possible during this time and the couple of hours either side, to take advantage of your increased solar output. Run the dishwasher, do the laundry, cook dinner – whatever makes sense for you.

Though of course, if you have a solar battery, you can simply store the extra electricity and use it later.

Solar panel output per m²

The average solar panel output per m² is 186kWh per year.

Solar panels are usually around 2m², which means the typical 430-watt model will produce 372kWh across a year.

A solar panel system will need space on either side, so finding out your roof's area is only one part of working out how much solar electricity you can generate, but it's a great first step.

Solar panel output based on time of year

A solar panel system does not consistently produce the same quantity of electricity throughout the year. In the summer months when the sun is high in the sky (and the days are long), solar panels are at their most productive.

And conversely, in the winter months when the sun is low in the sky (and the days are short), solar panel output drops quite significantly. 

For example, consider the below output chart, which is based on a four-bedroom home in Essex with a 6kWp solar panel system and 5kWh battery.

The system generates almost 25kWh of electricity each day in May and July, but produces just 4.9kWh per day in December.

Solar panel output by season

What factors affect how much energy solar panels can produce?

Solar panel power output depends on a wide range of factors, including:

• Solar panel power and efficiency
• Solar panel degradation
• Quality of installation
• Shading
• High temperatures
• Solar panel cleanliness
• Inverters and optimisers
• Solar panel angle and direction
• Location in the UK
• Transformer losses

Let’s explore these factors in more detail.

Solar panel power and efficiency

When it comes to solar panels, 'power' refers to the maximum amount of electricity a panel can generate (in watts). The panel's 'efficiency' is all about how effectively it can convert daylight into electricity.

Higher power and efficiency mean greater electricity production. This means that, in the exact same conditions, a 430W solar panel with 22% efficiency could generate more electricity than a 350W solar panel with 20% efficiency.

Solar panel degradation

Like all electrical systems, solar panels degrade over time, which means they'll generate slightly less electricity as the years go by.

The average solar panel system in the UK loses between 1% and 3% in its first year, then around 0.5% with each subsequent year.

That means after 25 years, the average system will produce 14% less energy than it did on its first day.

Degradation is more of an issue for solar panel systems in hotter climates, where the heat can negatively affect electrical networks.

Typical solar panel degradation over 30 years

Quality of installation

Solar panel systems are complex networks of electrical equipment that can underperform or malfunction if installed incorrectly.

If your installer doesn't secure the connections between the solar panels and inverter and the inverter and fuse box, your system may not convert DC electricity to AC electricity – which is the type your home runs on – or send all of the converted electricity to your home's devices.

And if they don't connect the diodes properly, your system could produce less solar electricity or be damaged by the battery discharging to the panels at night.

At best, bad connections will mean you get less solar electricity. At worst, a faulty connection can start a fire.

Shading

Shade can have a pretty significant impact on solar panel output, which is why it’s important to make sure there are no trees towering over your solar panel system. 

When solar panels are installed using a traditional string inverter, they’re connected in ‘strings’ (usually around 8-14 panels per string). If something is casting shade on one panel and reducing its output, this will have a detrimental effect on the electricity generation of the entire string.

This is where microinverters come in handy (more on that below).

High temperatures

Solar panels are built to withstand extremely hot weather, which is why there are very productive solar farms located in some of the hottest places in the world.

However, solar panels still see a very slight drop in output once they get particularly hot - in fact, every solar panel loses a tiny sliver of generation for every degree above 25°C. On a solar panel's datasheet, this is called its temperature coefficient.

To clarify, this coefficient refers to the temperature of the solar panel, not the temperature of the air around it.

The average temperature coefficient for a solar panel is -0.32%/°C, which means for every degree above 25°C, a solar panel's output falls by a miniscule 0.32%.

However, even if your solar panels were to reach the dizzying heights of 50°C, they would still be operating at roughly 92% of their original capacity - not a very significant loss at all.

Typical solar panel output loss in high temperatures

Solar panel cleanliness

Solar panels all have a hydrophobic coating, meaning they are essentially self-cleaning. When rainwater lands on a solar panel it rolls right off it, in theory taking any dust or dirt with it. 

However, in certain areas, solar panels can accumulate enough grime that it limits the amount of daylight that can hit the panels.

This phenomenon, which is known as solar panel soiling, can be brought about by detritus as diverse as dust, exhaust fumes, agricultural emissions, and organic material like bird droppings, lichen, and pollen.

In the UK, solar panel soiling can cut your system's output by more than 5%, according to Loughborough University, but it's a far more serious issue in hot, arid areas like China, India, and the Middle East, where losses can reach 70%.

Keep an eye on your solar panels, and get them cleaned every time they get noticeably dirty.

To learn more, check out our guide to solar panel cleaning.

Inverters and optimisers

As mentioned above, if one panel in a string inverter setup goes south, it'll mess up the whole string's output. With microinverters, each panel gets its own dedicated inverter and operates independently, so any malfunctions won't affect the entire system.

It’s also possible to stick to a normal string inverter and add optimisers, which are designed to improve the performance of the weakest panels in a system.

Your system's output could also be affected by solar inverter clipping, which is when your panels produce more electricity than your inverter's peak rating. As your inverter can't process the extra energy, it'll turn into heat and be lost to you.

Correctly sizing your inverters will avoid this happening too often, but don't spend too much in an effort to eradicate all clipping. In many cases, a small amount of clipping over the sunniest months is worth avoiding spending hundreds of pounds on more powerful inverters.

However, buying an efficient inverter is a good investment. Solar inverters are usually between 93% and 98% efficient at turning DC electricity into AC electricity, which is a large enough range to make a significant difference to your output.

Solar panel angle and direction

The angle and direction of solar panels has a big impact on their output. Aim for the sweet spot: facing south and tilted at an angle matching your latitude. The best angle for solar panels in the UK is between 20° to 50°, depending on where you are in the country.

Solar panels can still be very effective if they’re east-facing or west-facing though – it’s just that south-facing is the optimum scenario. Any solar installer worth their salt will design a solar panel system for your property that makes the best use of your available roof space.

Whatever direction your solar panels face, some sunlight will reflect off them instead of being absorbed, reducing their output by around 2% to 4% – or it would, except more than 90% of commercial modules now come with anti-reflective coating.

The coating eliminates the great majority of this loss, so make sure it's included with any panels you buy.

Location in the UK

You won’t be surprised to read that sunshine makes a difference to solar panel output, and the UK sees a pretty wide range of solar irradiance. In the south of England there is an average of 128.4 watts per square metre (m²), whilst in the northwest of Scotland it’s just 71.8m².  

But despite the south coast of England seeing more sunshine than anywhere else in the UK, you can still have a productive solar panel system in any part of the country. Plentiful sunshine is a bonus, but not a key ingredient – and you can see from this list just how many other factors determine how well a solar panel system works.

Transformer losses

Your inverter will usually contain a transformer, which performs a vital function that does unfortunately result in some energy loss.

The transformer converts incoming DC electricity to AC electricity you can use in your home, and also changes the voltage of that energy to match that of the appliances your solar energy will then power.

Unfortunately, like all electrical products, it does produce a small loss in energy – about 1%, usually – because it involves multiple complicated processes.

Some inverters now come without transformers, which avoids this loss – but they're not common just yet.

How to ensure your solar panels produce more energy

If you’re considering having a solar panel system installed, there are a few things you do in order to maximize its output. For example: 

1. Get high-quality solar panels
2. Hire a trustworthy installer
3. Maximise your roof space
4. Use microinverters
5. Monitor your solar panels

1. Get high-quality solar panels

Your household deserves to benefit from some of the best solar panels on the market, with high efficiency rates, hefty peak power ratings, and long lifespans.

Making this choice will maximise your electricity bill savings, cut your carbon footprint by as much as possible, and help increase the value of your home.

You should only go with an installer that uses top-tier panels, both to take advantage of these benefits and because you want an installer with the good judgment and high standards to pick superior models.

​​2. Hire a trustworthy installer

This is the most important step. It doesn't matter how good your panels, battery, or inverter are if they're not properly fitted by a certified installer.

Choosing one of the best solar installers around will ensure that your installation produces as much electricity as possible, has a long lifespan, and doesn't require as much maintenance. This will maximise your savings, and also give you peace of mind.

It's worth paying a little more for a reputable, responsive, competent company that'll stick around for the aftercare, instead of leaving you to it once the panels are on your roof.

3. Make full use of your roof space

The more solar panels you get installed, the more electricity your system will produce, everything else being equal – so instead of trying to calculate how many solar panels you need, consider how many panels will fit on your roof.

Even if your system generates far more energy than your household uses, export tariffs like Intelligent Octopus Flux will pay you a high rate for all the excess electricity you send to the grid. Your profits will climb, and the national supply of electricity will get a bit greener.

It'll also future-proof your household. The UK is in the process of electrifying its transport and heating sectors, meaning electric vehicles and heat pumps are becoming commonplace.

This will result in a 50% increase in demand for electricity by 2035, according to the independent Climate Change Committee.

If you get an EV or heat pump at any point in the coming years, you can use your 'oversized' solar panel system to run them. A heat pump will typically increase the average household's annual consumption from 3,400kWh to 6,600kWh, while an EV charger usually adds another 1,500kWh.

And even if you don't add either of these products, the rapidly rising need for electricity across the nation means the price for your exported electricity should stay high.

4. Use microinverters

Microinverters can potentially increase your system's output, but they aren't always necessary – which is fortunate, since they're more expensive than standard string inverters.

If your roof comes with a significant level of unavoidable shading, you may want to use microinverters, since they allow every panel to operate independently of the others.

This avoids the major issue of using string inverters, which allow shade on one part of the system to affect every panel.

Because of the price difference though, a trustworthy installer will only recommend microinverters if it's absolutely essential.

To read more about the price of going solar, check out our guide to solar panel costs.

5. Monitor your solar panels

Keeping an eye on your solar panel app is the best way to make sure your system's output stays high.

This is time-consuming though, and if your system's generation does fall, most solar panel owners aren't able to identify and fix the problem – and hiring an engineer can be expensive.

Fortunately, we have a solution. The UK’s first solar subscription, Sunsave Plus, comes with 20 years of remote 24/7 monitoring, meaning our solar experts will always keep an eye on your system for you.

You'll also have 20 years of maintenance support, which means we'll alert you if something isn’t working, troubleshoot any issues, and make sure your output gets back to the level it should be at.

Next steps

A solar panel's output depends on multiple factors like your location, your roof, and the quality of the system itself.

Going solar usually means covering a large chunk of your annual electricity needs and massively cutting your energy bills, but to maximise your returns, it's crucial that you choose the right installer.

If you’re interested in switching to solar, you can find out how much a solar & battery system could save you by answering a few quick questions below.

Solar panel output: FAQs