The Short Answer
We'd pay cash if you comfortably can: no interest, and the quickest payback. A 4kW system costs about £6,200 to £6,600 and is worth about £599 a year on our model. If you borrow, compare the APR and total payable, and check whether your savings and export earnings cover the repayments (the calculator below does that).
In Wales, Green Homes Wales lends £1,000 to £25,000 interest-free, with no means test. In Scotland, Home Energy Scotland doesn't fund standard solar panels. In England and Northern Ireland we found no government loan for solar. And 0% VAT on installed solar ends on 31 March 2027.
What Finance Costs You
Solar Finance Calculator
See what solar costs on finance, and whether your savings and export earnings cover the monthly repayments. Set the APR to 0 to model an interest-free deal.
DESNZ's average for 4kW is about £6,600; use your quote
Whatever your quote asks for, if anything
Starts at 9.9% as an example; put in the APR on your quote, or 0 for an interest-free deal
Use the term on your quote
On our model, 4kW in central England is worth about £600 a year; our solar costs calculator gives a figure for your home
Monthly payment
£140
Net each month
-£90
Interest over term
£1,794
Repayments are about £90/month more than your savings, so you'd top up by roughly that much until it's paid off in 5 years, then the savings are all yours. A longer term or a 0% deal can narrow or close the gap.
Get quotes with finance optionsMonthly payment uses a standard amortising loan formula. Real finance agreements vary in fees, deposit terms and whether they're regulated credit. Always check the APR and total amount payable on the actual agreement. This is an estimate to help you compare options, not a credit quote.
Paying Cash
On our model, £599 a year on £6,600 is about 9% in the first year at today's prices, and the system pays for itself in 10 to 11 years across the DESNZ cost range. The catch is that the money is in your roof, not your bank. In our view, clear expensive debt and keep an emergency fund first. Adding a battery costs another £5,000 to £8,000 on the Energy Saving Trust's figures (it gives no size); our battery guide covers whether it pays.
Borrowing
- Installer finance. Some deals are interest-free; others charge interest. Compare by APR and the total amount payable, not the monthly figure, and check it's regulated credit.
- A further advance or remortgage. Ask your mortgage lender what it would cost and compare the APR. It's secured on your home, so missing payments puts the house at risk, and spreading a small sum over a long mortgage can mean paying interest for years. Overpay if you can.
- A personal loan. Unsecured, so check the APR against the other two.
Set the calculator to your quote's APR and term. If the monthly repayment is less than the savings, the system pays its way from the start.
Wales: Green Homes Wales
The Development Bank of Wales offers interest-free loans of £1,000 to £25,000, with terms up to 10 years (longer for larger projects) and a six-month repayment holiday at the start. It isn't means tested, but every application has credit and affordability checks. The home has to be in Wales and owned by you. Listed buildings aren't currently supported and private landlords can't apply. Solar panels are on its list of measures. We'd start here before any installer finance: an interest-free loan is as good as cash if you'd otherwise borrow. Nest gives free advice on 0808 808 2244. More in our Wales solar grants guide.
Scotland
Home Energy Scotland doesn't fund standard solar panels by grant or loan. It does offer an interest-free loan of up to £5,000 for solar thermal (hot water) and hybrid PV-T panels, with no grant. For ordinary panels, Scottish homes have 0% VAT and the Smart Export Guarantee like the rest of Great Britain.
England, Northern Ireland and the Warm Homes Plan
We found no government solar loan open in England or Northern Ireland. The Warm Homes Plan says homeowners across Great Britain (not Northern Ireland) should be able to get low-cost finance through a new zero and low-interest loan offer, backed with an initial £2 billion. It could include solar panels and batteries, but it isn't open yet and the details are still to come. We wouldn't delay a sensible install for it, given the VAT date below. Free schemes for lower incomes are in our free solar panels guide.
The VAT Deadline
HMRC's VAT Notice 708/6 zero-rates solar panels and batteries installed in homes until 31 March 2027; from 1 April 2027 it's 5%. On a 4kW system that's about £310 to £330 more. Our VAT guide has the detail.
What You Don't Need
- A "free solar" roof lease, in our view. The company owns the panels and you sign a long lease of your roof. Before signing one, ask a conveyancer and your mortgage lender what it would mean when you sell or remortgage.
- The monthly figure alone. Judge finance on the APR and total payable.
Compare quotes, and finance options
Some installers offer finance alongside the install, sometimes interest-free. Get free quotes to compare the system price and the payment options side by side.
