Solar Panel ROI: How to Work Out Payback

Solar panels are a significant investment: the Energy Saving Trust puts a typical 4.5kWp home system at around £7,600. This guide shows how to work out payback for your own home, which figures to include, and the assumptions that can change the answer by years.

Understanding Solar Panel ROI: The Key Components

Solar panel return on investment compares what the system saves and earns with what it costs. The returns come from:

1. Electricity bill savings: every unit of solar electricity you use is one you don't buy from your supplier
2. Smart Export Guarantee (SEG) payments: suppliers pay you for electricity you export to the grid (Great Britain only)
3. Less exposure to price rises: the less electricity you buy, the less price changes affect you (prices can also fall)

Step 1: Work Out Your Installation Cost

The installation cost is the starting point. It depends on system size, your roof, access and scaffolding, and the equipment you choose.

Typical Solar Installation Costs

Sources: Energy Saving Trust and DESNZ solar PV cost data. These are typical ranges, not quotes. Use the price from a quote for your own home in your calculation.

0% VAT on Solar Installations

Installed solar panels and batteries are zero-rated for VAT until 31 March 2027. From 1 April 2027 the rate is due to go back to 5%. Check that your quote shows no VAT on the installation.

Adding Battery Storage

A battery stores daytime solar power for use in the evening instead of exporting it. That can raise your savings, but at around £5,000 to £8,000 it also adds a lot to the cost you need to pay back.

Step 2: Estimate Your Solar Generation

How much electricity your panels generate depends on system size, location, roof direction and pitch, and shading. Which? says home systems are typically around 4kWp and that a system of this size can generate more than 3,000kWh of electricity a year.

Roof Direction and Shading

• South-facing roofs generally generate the most
• East or west-facing roofs generate less, but can still be worthwhile
• North-facing roofs are generally not recommended
• Shading from trees, chimneys or nearby buildings can cut output significantly

Your quote should include a generation estimate for your roof. Ask how it was worked out and what shading was assumed.

Step 3: Calculate Electricity Bill Savings

Your main return usually comes from the electricity you generate and use yourself. Not all of it is used at the time: if you are at home during the day you use more of it, if you are out all day you export more, and a battery lets you use more of your own.

Step 4: Calculate Smart Export Guarantee Income

The Smart Export Guarantee (SEG) requires larger suppliers to offer a tariff that pays you for exported electricity. There is no set rate, but any SEG tariff must pay more than zero. You need an MCS-certified (or equivalent) installation and a meter capable of half-hourly export readings, and SEG is not available in Northern Ireland.

SEG Export Rates in May 2026

Source: Solar Energy UK league table, updated 12 May 2026. Rates change often, so check suppliers' websites. If a tariff requires you to buy electricity from that supplier, include its import price in your savings calculation too. See the full list in our SEG tariff guide.

Step 5: Add Up Your Annual Return

Your annual return is your bill saving plus your SEG income. For comparison, here are the Energy Saving Trust's estimates:

Energy Saving Trust estimates for a four-bedroom detached home, based on fuel prices as of July 2026. Ranges run from "out all day" to "home all day". EST does not state the system size or export rate it assumes. Typical figures, last reviewed September 2026; not a guarantee of savings.

Step 6: Calculate Payback Period

The payback period is how many years it takes for your savings to add up to what you paid.

Allowing for Price Changes

The simple calculation assumes prices stay the same. If electricity prices rise, your savings are worth more and payback comes sooner; if they fall, or your export rate drops, it takes longer. Ofgem reviews the price cap every quarter, and the next announcement is due on 25 November 2026.

Step 7: Think About the Whole Life of the System

Solar panels are a long-term purchase, and returns are not guaranteed. When you work out lifetime value, include:

• The length of the panel and inverter warranties in your quote, and what they cover
• The likely cost of replacing the inverter at some point during the system's life
• Any repair or maintenance costs, including scaffolding if it is needed again
• Whether you expect to stay in the home long enough to reach payback

If you have or are planning a heat pump, it can increase how much of your solar power you use, although heat pumps use the most electricity in winter, when panels generate the least.

Factors That Improve Solar ROI

1. Use More of Your Own Solar Power

• Run washing machines and dishwashers during the day
• Charge an electric vehicle while the panels are generating
• Use timers or smart controls to shift usage to sunny periods

2. Choose Your Export Tariff Carefully

• Compare SEG tariffs from time to time, as rates change
• Higher rates often require you to buy electricity, or your installation, from that supplier
• Compare the import price as well as the export rate

3. Get the System Size Right

• Match the system to your roof and your electricity use
• Exported units usually earn less than the units you use yourself are worth
• Ask each installer to explain why they recommend a particular size

4. Look After Your System

• Check performance through your inverter or monitoring app
• Deal with new shading, such as trees that have grown
• Have faults checked by a qualified installer and keep your warranty paperwork

Should You Add Battery Storage?

At around £5,000 to £8,000, a battery usually lengthens payback unless it adds enough savings. It depends on your circumstances:

A Battery May Make Sense If:

• You use most of your electricity in the evening or at night
• You can make use of a time-of-use electricity tariff
• You want backup power in a power cut (only some batteries can do this, so check)

You Might Skip a Battery If:

• You are at home during the day and already use much of your solar power
• Your budget is limited and you want the quickest payback
• You would rather see how the panels perform and decide later

Other Benefits of Solar

• Carbon: the Energy Saving Trust says a typical home system could save around one tonne of carbon a year
• Price changes: buying less electricity means price rises affect you less
• Backup power: possible with a battery designed to provide it

When Solar ROI Doesn't Stack Up

• Heavily shaded roofs
• North-facing roofs with no alternative mounting options
• Expecting to move before the system pays back
• Very low electricity use
• Roofs that need replacing or repairing soon

In these cases, deal with the roof or shading first, or look at other ways to cut your bills.

Your Solar ROI Action Plan

1. Find your annual electricity use and unit rate on recent bills
2. Assess your roof (direction, pitch and shading)
3. Get more than one quote, each with a generation estimate
4. Estimate how much of the generation you will use yourself
5. Compare SEG tariffs and their conditions
6. Add up bill savings and SEG income for your annual return
7. Divide the installation cost by the annual return to get payback
8. Allow for warranties, inverter replacement and how long you will stay

The Energy Saving Trust's estimates put payback at around 9 to 12 years with export payments, but your own figure depends on your price, roof and usage. With 0% VAT on installation until 31 March 2027, check the numbers for your home before you commit.

UK Energy Partnership is run by Harber Glaves Trading Ltd. We are not a government body or an energy supplier. The figures on this page are general estimates, not a quote or a guarantee of savings.