Solar Panels and Your EPC Rating: How Much Will They Improve Your Score?

How Solar Panels Improve Your EPC Score

The EPC rating is calculated using the Standard Assessment Procedure (SAP), a government-approved energy model. SAP calculates the energy required to heat and power your home, then offsets this with any energy generated on-site. Solar photovoltaic (PV) panels generate electricity from daylight, and this generated electricity is credited directly against your home's energy demand in the SAP model.

In practice, a 4kWp south-facing system in the UK generates around 3,400–3,800 kWh of electricity per year. Under SAP 10.2 (the current version), the assessor calculates how much of this generation is consumed on-site (typically 50–60%) and how much is exported. Both are credited, but self-consumed energy has a larger effect on the score.

* EPC improvements shown are indicative. Actual improvement depends on current property score, roof pitch, shading, and orientation. Costs include installation by an MCS-certified installer.

Does Roof Orientation Matter?

Yes — and it matters significantly. A south-facing roof at a 30–40° pitch is ideal and produces 100% of the estimated generation figure. Other orientations are less productive:

SAP assessors use orientation data when calculating the output of your system. An east–west split (panels on both sides of a pitched roof) often performs comparably to a single south-facing array and has the advantage of generating power earlier in the morning and later in the afternoon.

Does Battery Storage Improve Your EPC?

A battery storage system (such as a Tesla Powerwall or GivEnergy unit) allows you to store surplus solar generation during the day and use it in the evening. From a financial standpoint this is very beneficial — you shift your own free electricity to replace peak grid power.

Under the current SAP 10.2 methodology, battery storage does not directly increase the EPC score itself — the assessed generation from the panels is the same whether or not a battery is fitted. However, a battery increases your self-consumption, which can marginally affect the credit applied in the SAP calculation in some assessors' models.

Earning Money: The Smart Export Guarantee

Since January 2020, homeowners with solar panels have been able to earn money by exporting surplus electricity to the grid under the Smart Export Guarantee (SEG). You must use a smart meter and register with an SEG-licensed energy supplier.

A typical 4kWp system exports around 1,500–2,000 kWh per year. At 4p/kWh that is £60–£80 per year in export earnings, on top of the £300–£500 saved by self-consuming solar electricity.

Can You Get Free Solar Panels?

Yes — if you qualify for the ECO4 scheme or the Great British Insulation Scheme, you may be eligible for a fully funded solar panel installation. These government-backed schemes require large energy suppliers to fund energy improvements for qualifying households.

The SAP Methodology: How Assessors Calculate the Improvement

When an EPC assessor visits after solar installation, they record the installed capacity (kWp), the orientation, pitch angle, and any shading. This data is entered into the SAP 10.2 calculation engine, which uses historical irradiance data for your location to estimate annual generation.

The generated electricity is split into an estimated self-consumption fraction (based on property size and occupancy assumptions) and an export fraction. Self-consumed electricity offsets the calculated electricity demand; exported electricity receives a partial credit. The result is a reduced energy demand figure, which translates directly into a higher SAP score.

One practical implication: the EPC improvement from solar is assessed on assumed behaviour, not actual usage. A property with solar in an unoccupied state would still receive a meaningful EPC credit because SAP uses standardised occupancy assumptions rather than real meter data.

Further Reading