Calculating warehouse solar ROI is a 6-step process: (1) PVSyst yield model, (2) self-consumption from HH meter data, (3) avoided grid cost, (4) AIA tax shield, (5) 25-year DCF, (6) IRR and payback. Most commercial solar quotes only show payback — this guide covers the full picture.
Step 1: PVSyst yield model
PVSyst is the industry-standard photovoltaic simulation tool. A rigorous PVSyst model uses: site-specific irradiance data (Meteonorm or SolarAnywhere, not UK-average); exact roof orientation (azimuth and tilt from structural drawings); module temperature coefficients for the specific panel selected; system losses (DC cables, AC cables, inverter efficiency, soiling, shading). Output: monthly generation profile (kWh). UK rule of thumb: 920-960 kWh/kWp/yr in the Midlands and North; 1,000-1,050 kWh/kWp/yr in the South East; 1,050-1,100 kWh/kWp/yr in the East.
Step 2: Self-consumption from HH meter data
12 months of half-hourly (HH) meter data is the input. We match the hourly solar generation profile against the HH load profile to calculate: self-consumed kWh (solar displaces grid); exported kWh (solar exceeds load, goes to grid via SEG). Self-consumption varies significantly by warehouse type: cold chain 88-94%; fulfilment 82-89%; distribution centre 72-81%; cross-dock 60-74%; self-storage 50-65%.
Step 3: Avoided grid cost and SEG export revenue
Avoided grid cost = self-consumed kWh × grid retail tariff (2026: 20-24p/kWh for commercial). SEG export revenue = exported kWh × SEG tariff (as at July 2026: roughly 4–12p/kWh depending on supplier and tariff type). Grid retail tariff trajectory over 25 years is the largest financial model uncertainty — we model under central (2.5%/yr escalation) and conservative (1.5%/yr) assumptions.
Step 4: AIA tax shield
100% Annual Investment Allowance on first £1m capex: deducted from taxable profit in year of installation. At 25% corporation tax: £250,000 tax saving per £1m capex. This is a year-one cash flow item — significantly improves IRR relative to simple payback. After-tax payback is typically 1-2 years faster than simple payback. Freeport ECA stacks on top for eligible sites.
Step 5: 25-year discounted cash flow
Full 25-year DCF captures: year-one AIA tax shield (positive); annual avoided grid cost (growing with tariff escalation); annual SEG export revenue; annual O&M cost (£8-15/kW/yr); system degradation (0.4-0.5%/yr, compounding over 25 years); capital cost (year 0, negative); inverter replacement at year 12-15 (approx 10-15% of original capex). Discount rate: typically 6-8% for UK commercial property. NPV at 8% discount rate for a typical 1 MW warehouse install: £600,000-£900,000.
Step 6: IRR and payback
Simple payback (years) = capex ÷ year-1 net saving. After-tax payback = (capex - AIA tax shield) ÷ year-1 net saving. IRR = the discount rate that makes NPV = 0. For typical UK warehouse: IRR 15-25% — well above commercial hurdle rates. Worked example: 1 MW Midlands distribution centre. Capex: £800,000. Year-1 avoided grid cost: £138,000. Year-1 SEG: £9,200. Year-1 O&M: £10,000. Year-1 net saving: £137,200. AIA tax shield: £200,000. Simple payback: 5.8 years. After-tax payback: 4.4 years. IRR: 18.3%.
Common modelling mistakes to avoid
Three mistakes that make commercial solar paybacks look better than they are: (1) Using UK-average irradiance instead of site-specific PVSyst (can overstate yield by 5-15%); (2) Assuming 90%+ self-consumption without modelling actual HH meter data (most warehouses are 70-80%, not 90%); (3) Applying 100% AIA to all capex in a group where multiple subsidiaries have already claimed AIA cap (only £1m AIA per qualifying entity per year).
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Warehouse solar costs and payback: /warehouse-solar-costs/. Tax allowances: /guides/warehouse-solar-tax-allowances/. Free DCF from your meter data: /contact/.
UK warehouse solar economics 2026 — at a glance
UK commercial solar PV for warehouses has fundamentally changed economically between 2019 and 2026. Three structural shifts drive current 4-6 year paybacks: grid electricity has nearly doubled from 12-15p/kWh blended day rate in 2019 to 16-26p/kWh in 2026, with peak Time-of-Use rates now reaching 28-35p/kWh during 16:00-19:00 evening peak; battery system cost has fallen from £700-£900/kWh installed in 2020 to £250-£450/kWh in 2026; and 100% Annual Investment Allowance up to £1m of capex per year delivers immediate 25% corporation tax relief on solar capex. A typical 1 MW warehouse rooftop solar install costs £700,000-£800,000, generates 870,000-950,000 kWh per year, displaces £155,000-£180,000 of grid electricity annually, and pays back in 4-5 years before tax — 3-4 years after AIA tax shield.
Compliance pressure driving warehouse solar adoption in 2026
Four converging UK compliance forces make warehouse solar effectively necessary by 2030. (1) MEES trajectory: the Government has consulted on tightening the minimum standard for let commercial property to EPC B — current expectation is around 2031, applying to larger buildings (over 1,000 sqm expected), with the earlier EPC C 2027 interim milestone dropped. Not yet enacted, but already shaping landlord decisions. Solar PV adds 5-15 EPC points and is often the most cost-effective compliance route for warehouse stock currently at EPC C-D. (2) ESOS Phase 4 (December 2027 deadline): Energy Savings Opportunity Scheme requires large UK businesses to commission energy audits and implement or document rationale for solar recommendations. (3) SECR reporting: mandatory Streamlined Energy and Carbon Reporting requires Scope 1+2 emissions disclosure in annual reports — solar PV directly reduces reported Scope 2 figure. (4) Customer Scope 3 mandates: Amazon Climate Pledge, Tesco Net Zero, M&S Plan A, Sainsbury's Plan for Better, John Lewis Net Zero, JLR/Stellantis Tier-1 supplier programmes all flow Scope 3 supplier requirements through contract weighting and CDP/EcoVadis reporting. 3PL operators and owner-occupied warehouses serving these customers face direct commercial consequences if they fail to demonstrate verifiable renewable generation by 2027-2030.
How we model warehouse solar — half-hourly meter data, not assumptions
Every warehouse solar feasibility we deliver starts with your 12 months of half-hourly meter data and a roof drawing. Standard online solar calculators use generic per-sqft estimates that miss the operational pattern variation driving 30-40% of total payback difference. Our methodology: PVSyst yield model calibrated for your specific roof orientation, tilt and shading; self-consumption profile derived from your actual half-hourly demand at 15-minute resolution; 25-year DCF with monthly cashflow granularity; capital allowance schedule (AIA + ECA where applicable); grant funding scenario where eligible (IETF Phase 3 for manufacturers above 1 GWh/yr); SEG export tariff and REGO income; O&M cost schedule; sensitivity analysis on grid tariff inflation, self-consumption ratio, capex per kW and discount rate. Output: simple payback, after-tax payback, IRR, NPV at 4%/6%/8% discount rates, and 25-year cumulative return. If the numbers do not work for your specific site, we say so — we will tell you plainly when the economics do not justify proceeding.
Get a free desk feasibility — 7 working days
Send us 12 months of half-hourly meter data and a roof drawing (PDF or DWG). Within 7 working days we deliver: indicative system size from PVSyst modelling of your specific roof; financial DCF showing payback, IRR and NPV under three financing routes (outright purchase, asset finance, PPA); customer Scope 3 audit pack template for your supply chain context; grant funding eligibility assessment (IETF, local and devolved grant schemes, Enterprise Zone ECA, Freeport ECA); DNO connection cost estimate from grid heatmap; structural pre-assessment from drawings; honest assessment of whether your site suits solar. No charge, no obligation. Send your meter data via our quote form or email info@solarpanelsforwarehouses.co.uk — quote within 7 working days, guaranteed.