How much money can solar panels really save on my energy bills? – UK Times

If you are trying to work out whether solar panels are worth it for your home, the answer depends on more than the headline price of a system. For most households, the appeal is clear: lower electricity costs, less reliance on the grid and, over time, a chance to generate a meaningful return on the upfront investment. But calculating those savings is not always straightforward.

How much you save will depend on several factors, including the cost of solar panels, how much electricity your home uses, when you use it, and whether you are paid for exporting surplus power back to the grid. Any solar panel grants or financing support can also affect the overall picture.

In general, UK homeowners can expect solar panels to pay for themselves in around 8 to 13 years, depending on system size, roof orientation, local sunlight levels, and how much electricity they use during the day. After that, a well-performing system can continue to deliver years of significantly lower electricity costs, making solar one of the more compelling long-term home energy upgrades.

How much can solar panels save on energy bills?

How much energy your solar panels generate depends on the size of the system you install, but the table below shows typical outputs for various system sizes.

There are a lot of variables to account for. In the table, we use an address in London, assuming a family of three and typical use (no heat pumps, high daytime usage or electric car charging).

Other assumptions include no shading on the panels, someone at home using electricity for roughly half the day, and an export rate such as Octopus’s 15p per kilowatt hour Outgoing Octopus tariff. Other than a new inverter, no other maintenance costs are assumed, and the use of savings rather than a loan is factored in. The roof is roughly south-east facing.

Much will depend on what price you get for your exported electricity. Tariffs vary widely. If you keep on top of things, however, you should be able to get the 15p per kilowatt hour rate we use below.

Read more: Compare free solar panel quotes

How much can solar panels save on your electricity bill?

As you can see, with a bigger system you can be making instant savings. When calculating how much solar panels can save there are, of course, a number of variables to consider, but with a 5.4kW system you could potentially cover most of your annual electricity usage and even generate a modest surplus — around £70 per year, under ideal conditions.

Naturally these numbers will vary from year to year. Sunny years where you use more of your own power will see better returns. Less sunny periods and using more grid power mean it will take longer to recoup your money.

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So, how much do solar panels save in real terms? It depends on your usage, location and how much energy you’re able to consume during the day.

These numbers also rely on there being no downtime. If your inverter breaks and you don’t notice for a few days, those are lost days with no power being used or stored.

Luckily the Energy Saving Trust has a neat tool you can use to work out how much you could save and how long it will take to recoup your investment.

How much can I save with solar panels per month?

Monthly savings from solar panels vary widely, but for many UK households, they are likely to fall somewhere between modest double digits and well over £100 in stronger-performing setups. The exact figure depends on how much electricity your system generates, how much of that power you use at home rather than export, your import tariff, and whether you also have a battery to store surplus electricity for later. Homes that use more electricity during the day tend to see the biggest immediate reduction in bills, because they can make direct use of solar generation instead of buying as much power from the grid.

In practical terms, the households that save the most are usually those with a well-sited roof, a correctly sized system and consumption patterns that match solar production. If you are out all day and use most of your power in the evening, your direct savings may be lower unless you have a battery or can earn a worthwhile rate for exported electricity. That is why monthly savings can look very different from one home to the next, even when the systems are similar on paper.

Do solar batteries increase how much solar panels save you?

Phil Steele, Future Technologies Evangelist at Octopus Energy, says the strongest results tend to come when solar is paired with a battery, because households can store surplus daytime generation and use it later instead of buying power back from the grid. He says that, once you have solar, you are generating your own energy and storing any excess rather than relying entirely on imported electricity.

For many, the problem with solar power is that the energy is available during the day when it’s generally not needed as much. Using solar panels to charge a battery, which then powers your lighting, heating and appliances in the evening, could be a good idea. A solar battery can increase how much solar panels save you, particularly if you’re often away during the day and use more electricity in the evening.

Steele points to a common example: if a homeowner exports surplus solar at 15p per kWh but would otherwise need to buy electricity later at around 27p per kWh, storing that unit for later use can effectively be worth about 12p more than exporting it immediately. He says that with a large enough solar array, a well-sized battery and the right tariff, some households can drive bills down dramatically.

However, Steele warns that households should be careful about long-term savings calculations built around today’s tariff spreads, because off-peak import and export rates can change. In his view, that makes the battery-only case less predictable over time than solar generation itself, which delivers a more direct benefit because you are producing your own electricity.

Battery systems also typically have a shorter lifespan than solar panels and can add up to 50 per cent to the overall cost of installation.

If you want to get off the grid, batteries are a good idea. As a purely money-saving investment, they’re harder to justify purely from a financial perspective.

If you can get a decent rate selling your unused energy to the grid and you don’t mind switching to get the best deal for that, then it may be best to wait until battery prices fall further.

What is the ‘20% rule’ for solar?

The so-called ‘20% rule’ for solar is usually a rule of thumb for system sizing, not a law. In most cases, it means designing a solar panel system to generate roughly 20 per cent more electricity than your average usage, giving you a buffer for cloudy weather, winter performance, inverter losses and future changes in demand. Put simply, if your household normally uses a certain amount of electricity over a year, the installer may recommend a system sized to cover a little more than that on paper rather than matching it exactly.

Do solar panels work on cloudy days – and does it affect how much they save?

Yes, they do. Modern panels work well throughout most weather, though their efficiency is reduced in overcast conditions. Direct sun will offer the most power. As you can imagine, you get less power at dusk and dawn, and zero at night. For more on this, see our guide to whether solar panels work in winter and on cloudy days.

Read more: My honest review of Octopus solar panels