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Battery Storage (BESS) Sizing & Payback

Size domestic battery storage against a solar PV array: self-consumption uplift, annual import avoided, export forgone and simple payback.

System Size

kWp

Σ of module STC ratings (MCS MIS 3002)

Reference Yield

kWh/kWp

Pre-loss yield — PR is applied below

Performance Ratio

0–1

IEC 61724-1 system losses

Annual Consumption

kWh/yr

Total property electricity use (MGD 003 'Annual Electricity Consumption')

Baseline Self-Consumption

0–1

Share used on-site WITHOUT a battery. UK no-battery ≈ 0.30

Battery Usable Capacity

kWh

Capacity available for self-consumption (MGD 003 §4.5)

Round-Trip Efficiency

MGD 003 scope floor 80% (BS EN IEC 62933-2); typical Li-ion ≈ 90%

Battery-Boosted Self-Consumption

0–1

No clean public uplift curve — user-set. Default 0.65 is grounded in one MGD 003 datapoint, not a formula (see docs)

Import Tariff

£/kWh

Ofgem cap Jul–Sep 2026 ≈ 0.2611

Export Rate

£/kWh

Smart Export Guarantee — supplier-set; default illustrative

Grid Carbon Factor

kgCO₂e/kWh

DESNZ/Defra 2026 'electricity generated' ≈ 0.13096

Battery Installed Cost

Market-set; 2026 UK typical £3,500–£10,500 installed

Battery-boosted self-consumption cannot be lower than the baseline