Questions are being asked about why quite a few domestic EPCs appear to be getting very limited increases in the rating from just adding solar PV, but a much higher rating increase if it is combined with either an export capable meter or battery storage.

Some clients may mistakenly think that the rating benefit from solar PV should simply be down to how much it can generate, but it is not that straightforward. This is the simple explanation in respect of whether or not there is an export capable meter. (The principle is very similar for battery storage).

The improvement in the EPC rating is going to depend on how much of the generation is expected to be used in the property. For example...

If the property is expected to use 80% of it, there should still be a significant rating benefit in all cases. The gain from an export capable meter is only 20% of the generation.

If the property is only expected to use 20% of it, the rating benefit will be much lower without an export capable meter or battery storage. The gain from an export capable meter will then be 80% of the generation.

In dwellings it is unusual to have cooling, so electricity demand is lowest when electricity generation is highest. Hence the highest benefit only coming if you can save it for later (when it gets dark) or export it.

For a more detailed explanation, this is the relevant sections of the methodology:

RdSAP10
The savings associated with generated electricity depends on whether it is used directly within the dwelling or exported. Savings depend on factor β (from 0 to 1) which indicates proportion of electricity used in the dwelling.
See Section M in SAP10.2 specification.

SAP 10.2 (Section M)
At times of high solar radiation the PV array may generate more electricity than the instantaneous electricity demand within the dwelling. An estimate is made in SAP of this surplus, taking account of battery storage, and this surplus is assumed to be exported to the grid if the PV is connected to an export-capable meter.

Proficiency 27/7/2025