Do Solar Panels Improve Your EPC Rating? How Many Points, Worked Out the SAP Way

How an EPC Counts Solar Panels

An EPC for an existing home is produced with RdSAP 10, which works out the PV part exactly as the full SAP 10.2 method does. There are four steps, and knowing them explains every result in the calculator.

1. How much it makes. Output is 0.8 x the system's kWp x the sunlight on the panels x a shading factor. The sunlight is UK average weather, not your town's, so a Cornish roof and a Scottish one score the same. A south-facing 4kWp array comes out at about 3,450kWh a year.
2. How much you use yourself. SAP estimates, month by month, what share of that output your home uses rather than exports, based on its floor area and the number of people it assumes live there. Without a battery that's usually 25 to 40%.
3. What that's worth. Power used at home is valued at 16.49p a kWh, and exports at 5.59p. Those are SAP's own prices, written into the methodology, not today's.
4. What that does to the score. The saving cuts the home's "energy cost factor", which is the yearly cost divided by floor area plus 45. Above a score of about 43, every £1 of saving per m2 is worth the same number of points, which is why the same panels add more points to a small home than a big one.

If the assessor doesn't know your system's size, RdSAP assumes 0.12kWp per m2 of panel. Keep your MCS certificate: it states the kWp, and that's the number that should go in.

What Changes the Number

Our calculation from the SAP 10.2 formulas, so expect your assessor's figure to be within a point or two rather than identical.

Why a battery helps the EPC more than your bills

SAP values exported power at only 5.59p but power you use at 16.49p, so anything that shifts output from exporting to self-use is worth a lot of points. A 10kWh battery takes self-use from about 31% to about 67% in SAP's model, worth around six extra points on our example home. On your actual bills the gap between import and a good export rate is narrower, which is why we say a battery rarely pays for itself on money alone (see our battery guide). For an EPC, though, it's one of the strongest single additions.

Why your current score barely matters

Above a score of about 43 (most of band E and everything above it), the points solar adds don't depend on where you start. Below that the formula curves, so a band F or G home gains fewer points from the same panels and usually needs insulation or a heating change first.

Landlords: Solar and the 2030 Band C Rule

Privately rented homes in England and Wales need an EPC of at least E now, and the government has confirmed they must meet a standard equivalent to band C by 1 October 2030. The cost cap rises from £3,500 under the E standard to £10,000 under the C standard, and the maximum fine is £5,000 per property.

For a D-rated rental near the top of the band, solar is often the cheapest way over the line, because it adds points without disrupting the tenant (no lifting floors or replacing heating). For a low D or an E, combine it with the cheap fabric measures first. Our EPC improvement calculator compares every measure, and its D to C section sets out the order to do them in.

Getting the New Rating

• Your old EPC won't update itself. You need a new assessment once the panels are in, and a new certificate replaces the old one on the register.
• Have the paperwork ready: the MCS certificate (for the kWp), the battery's usable capacity if you have one, and details of any PV diverter. Without the kWp, the assessor falls back on the 0.12kWp per m2 default, which can undercount a modern system.
• Check the orientation and pitch are recorded. They change the result by several points.

What You Don't Need

• A bigger system "for the EPC". Points rise with size, but the self-use share falls, so each extra kWp is worth a little less. Size it for your roof and your usage.
• A battery bought only for the rating, unless you're a landlord a few points short of a band, where it may be the cheapest route.
• Panels on a north roof to chase points. They score, but about 30% less than south, and they make much less money too.

Thinking about the money as well as the rating? See whether solar panels are worth it, whether they add value to your home, and every scheme that can help pay in our solar panel grants guide. Solar is 0% VAT until 31 March 2027.