Installer Online reports a record number of UK households combining renewable technologies — typically solar PV with battery storage, increasingly alongside a heat pump. As an assessment matter, this is more interesting than it sounds, because the certificate does not value these equally.

How the assessment sees each measure

  • Solar PV is generally well rewarded. Generation offsets modelled energy cost, and on a south-facing London roof with reasonable pitch it moves the number meaningfully.
  • Heat pumps can be transformative on a property currently running on electric resistance heating or oil, and more modest on a property with a recent efficient gas boiler — because the comparison baseline is already decent.
  • Battery storage is the one that surprises people. It shifts when you use energy rather than how much the building needs, so its effect on a standard domestic assessment is limited even though the effect on your actual bill can be substantial.

That gap between "good for your bills" and "good for your rating" is worth internalising. They are related but not the same measurement, and a salesperson quoting band improvements for a battery should be asked to show their working.

Where reform changes this

The reformed EPC — now due in the second half of 2027 — replaces the single A–G letter with four separate metrics: fabric performance, heating system, energy cost and smart readiness.

That last one matters here. Smart readiness is precisely where batteries, time-of-use tariffs and controllable heating start to count in their own right rather than being flattened into a single number. Households stacking technologies now are, in effect, building for the metric that does not exist yet.

They are also building toward the rented sector's secondary standard, which requires either heating system performance or smart readiness — the landlord's choice — alongside the C-equivalent rating from 1 October 2030.

The order still holds

Fabric first, then heating, then generation and storage. Not because the technology is not good, but because every kilowatt-hour you do not need is cheaper than every kilowatt-hour you generate.

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