Sizes a domestic/commercial battery storage (BESS) retrofit against an existing or planned solar PV array, the extra self-consumption a battery unlocks, the resulting bill saving, and a simple payback on the installed cost.
Indicative only. Verify final sizing to MCS MGD 003 and a site-specific consumption profile.
For design guidance only. Always verify with a qualified MCS installer.
About this battery storage sizing calculator
This free battery storage sizing calculator estimates what a battery (BESS) retrofit adds to an existing or planned solar PV array, the extra generation you self-consume, the resulting bill saving and a simple payback on the installed cost. It is aimed at UK installers, designers and homeowners scoping a domestic or small commercial battery at survey or quotation stage, so you can sanity-check whether a proposed usable capacity and price stack up before committing. Everything runs in your browser. Nothing is uploaded.
How battery storage payback is calculated
The model builds on the Ensign solar PV generation method: annual generation is E = kWp × reference yield × performance ratio (MCS MIS 3002 / IEC 61724-1). The battery's extra self-consumption is (boosted − baseline) self-consumption fraction × generation, a documented fallback input, because MCS MGD 003 has no closed-form uplift curve. And it is clamped to the remaining annual demand so you can never self-consume more than the site uses. Energy diverted from what would have been exported is uplift ÷ round-trip efficiency, so battery losses are accounted for. Net extra saving is the added import saving minus the export earnings forgone, and simple payback is installed cost ÷ net annual saving. Carbon saved uses the DESNZ/Defra grid emission factor.
Frequently asked questions
What self-consumption figures should I enter?
MCS MGD 003 gives no fixed uplift curve, so you enter both fractions directly: a baseline (UK domestic with no battery is roughly 0.30) and a boosted figure with the battery (around 0.65 for a well-matched system). The boosted value must be at least the baseline. A battery should never reduce self-consumption, and the uplift is capped at the remaining annual demand headroom.
Does it account for round-trip efficiency?
Yes. The energy forgone from export equals the import avoided divided by the round-trip efficiency, so charge/discharge losses are included. The default is 90%; MGD 003's scope floor is 80% AC round-trip.
Is the payback a full financial appraisal?
No. It is a simple payback, installed cost divided by the net annual saving, with no discounting, tariff escalation or battery degradation modelled. Treat it as an indicative screen and verify final sizing to MCS MGD 003 and a site-specific consumption profile.