UK Commercial Solar Calculator
Every figure below is an estimate derived from the assumptions you set. Solar generation is split between electricity used on-site and electricity exported, and each is valued separately — exported units are not valued at the retail price.
1. System sizing
Modelling assumption only. Usable roof area accounts for roof edges, access paths, roof structures, skylights, vents, fire/access requirements and installation constraints. Actual usable area must be confirmed by a qualified installer.
2. Generation assumptions
Actual generation depends on location, orientation, roof pitch, shading, module technology, inverter losses, temperature and other system losses. A professional design should use a site-specific PV simulation such as PVGIS, PVsyst or PVSol. Orientation and shading factors are simplified modelling assumptions only.
3. Consumption & tariffs
Tariffs are assumptions, not quoted prices. Exported electricity is valued at the assumed export rate, which is normally well below the purchase price.
4. Battery storage (optional)
Simplified annual model — not an hourly dispatch simulation
5. Cost, VAT & maintenance
Many qualifying UK installations attract 0% VAT, and VAT-registered businesses can often recover VAT charged. Confirm your position with your accountant. The default cost per kWp is a modelling benchmark, not an official market price — commercial pricing varies with roof structure, electrical infrastructure, grid connection, access, mounting, switchgear, cabling and site conditions.
100% AIA up to £1m, then 50% first-year allowance
6. Long-term modelling assumptions
These are modelling assumptions, not forecasts. Electricity prices may rise, fall or stay flat. Grid emissions factors change over time.
Panels
252
System size
110.9 kWp
Annual generation (est.)
105,336 kWh
Self-consumption (effective)
60%
Solar used on-site
63,202 kWh
Solar exported
42,134 kWh
Estimated system cost
£99,792
£900 / kWp · ex VAT
Indicative capital allowance relief
£24,948
AIA / 50% FYA at 25% corporation tax — subject to your tax position
Net investment (estimate)
£74,844
There is no general nationwide capital grant for UK commercial solar. The figure shown is an indicative year-one corporation tax saving from capital allowances (100% Annual Investment Allowance up to £1m, then the 50% first-year allowance on the balance). It is not cash paid to you, depends on your taxable profits and must be confirmed with your accountant. Sector schemes such as IETF (manufacturing) and Salix (public sector) may apply separately.
Electricity bill savings
£16,432
Export revenue
£2,528
Total annual energy benefit
£18,960
Annual maintenance
− £998
Net annual benefit
£17,963
Simple payback
4.2 years
Net investment ÷ net annual benefit
Total 25-year energy benefit
£601,402
Total 25-year maintenance
− £24,948
Initial net investment
£74,844
Estimated 25-year net benefit
£501,610
25-year ROI (illustrative)
670%
COâ‚‚ saved / year
21,805 kg
513.6 tonnes over 25 years
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