UK Commercial Solar Guide 2026

1. Introduction

This guide is a working installer's view of UK commercial solar PV in 2026 — what works, what does not, what costs what and how to make sensible decisions for your business. It is written by Steve Moran and Kieren Myler, the co-founders of KMM Energy Solutions, drawing on 5,000+ installs (team + network). We have tried to be honest about both the strengths and the weaknesses of commercial solar in the current UK market.

2. When commercial solar pays back

Commercial solar PV pays back fastest for businesses that are open during the day, draw a steady electrical load, own or have a long lease on the roof above them, and pay more than around 22p per kWh on their daytime power tariff. That description covers most UK SMEs from 50 employees upwards. The pure financial case for commercial solar in 2026 is the strongest it has ever been in the UK — primarily because of the post-2022 step change in commercial electricity prices, which has lifted average UK commercial unit rates to 26-32p/kWh against a wholesale spot price still in the 8-13p range.

3. System sizing fundamentals

The first question we ask any commercial enquiry is for their MPAN and 12 months of half-hourly consumption data. From that we build a generation overlay — every 30-minute slice of consumption matched against modelled generation for the building's specific roof orientations. Only with that overlay can you correctly size a system. Rule-of-thumb sizing always overshoots (oversizes export) or undershoots (leaves money on the table); HH-data sizing gets you within 3% of optimal.

4. Choosing panels

We work with tier-1 panel manufacturers — JA Solar, Hanchu, Aiko, Perlight, Q Cells. Tier-1 is a BloombergNEF financial-stability ranking; it tells you the company will be around to honour the 25-year linear performance warranty. For most commercial roofs we recommend 430-460W panels which is the current sweet spot of cost-per-watt versus area utilisation. Higher-wattage panels (475-500W) exist but they cost a 10-15% premium per watt for marginal area savings — only worth it on very area-constrained roofs.

5. Choosing inverters

For commercial scale (above 50kWp) the inverter selection narrows to four genuine tier-1 commercial brands: Sungrow, Solis and Huawei. We typically specify Sungrow for systems above 100kWp because their commercial range has the deepest UK service-engineer coverage. Below 100kWp we are agnostic — all four perform well and have similar warranty terms.

6. Battery storage decision

Whether to fit battery storage alongside commercial solar comes down to three questions: (1) what is the self-consumption ratio without battery, (2) is there a peak-shaving opportunity to reduce DUoS charges, and (3) is there a time-of-use arbitrage opportunity. On a continuous-load 24/5 commercial site with 75%+ self-consumption, battery rarely pays back — the marginal kWh saved is not worth the £700-£900/kWh capex. On hospitality, retail and office sites with daytime peak load, batteries lift self-consumption from 40-55% to 75%+ and routinely pay back inside 7 years.

7. Grid connection (G98/G99/G100)

Any commercial generation above 16A per phase requires a G99 application to your local DNO. KMM submits every application as part of the project. The DNO review takes 4-24 weeks depending on system size — 4-10 weeks for sub-50kVA, 12-24 weeks for 50-1000kVA, 6-18 months for above 1MW. Where the DNO refuses an unlimited export offer, we design with G100 export limitation device set to 0kW or matched to your existing import capacity, allowing the install to proceed without grid reinforcement.

8. Planning permission

Most commercial roof solar is Permitted Development under Class J of the GPDO — no planning application needed. Exceptions: listed buildings, conservation areas front-elevation, ground-mount above 9m², any installation more than 200mm above the existing roof line. For ground-mount commercial solar we work with a specialist planning consultant on the application pack — typically 13-16 weeks for determination.

9. Roof structural assessment

Every commercial roof solar project includes a structural review. Most modern steel-portal commercial buildings handle the 12-13 kg/m² imposed load of solar PV without issue. Older buildings (pre-1980s) and unusual structures need a structural engineer to sign off the loading. We coordinate this and the cost (typically £400-£900) is included in our project fee.

10. Finance routes

Three primary finance routes for commercial solar in 2026: CAPEX (buy outright), asset finance / lease (5-10 years), and Power Purchase Agreement (PPA, third-party ownership). The right route depends on your tax position, your working capital appetite and your strategic asset-ownership preference. We model all three for every commercial proposal and disclose every commission.

11. Tax allowances

Businesses can claim a 100% first-year deduction on solar capex under the Annual Investment Allowance, up to £1m a year (solar is special-rate plant, so Full Expensing does not apply). For a company paying 25% corporation tax, effective capex falls by 25%. Charities, schools, NHS and other not-for-profits do not benefit from these allowances — their finance route is almost always Salix loan or PSDS grant.

12. Grants and funding

See our full grants page and the live deadline tracker. The major active routes are Salix (public sector 0% loans), PSDS Phase 5 (when open), regional council grants in Lincolnshire and Nottinghamshire, and the workplace EV charging grants from OZEV.

13. Smart Export Guarantee

SEG is the mandatory tariff that every major UK electricity supplier must offer for exported solar generation. Commercial G99 installations qualify for SEG; rates from suppliers in 2026 range from 4-8p/kWh for commercial export tariffs. We negotiate the export contract as part of the project handover.

14. Installation process

A typical 100kWp commercial install: scaffolding 1 week before mobilisation, panels and inverter delivered week 1, install crew on site for 8-12 working days, electrical first fix concurrent with roof work, commissioning at end of install. The site continues normal operations throughout — no production downtime needed.

15. Commissioning

Commissioning includes: full G99 protection test, witness test by DNO if required, monitoring platform setup, SEG contract registration, customer training on monitoring app, handover documentation pack. Most commissioning visits take 1-2 days for systems above 100kWp.

16. Monitoring

Every KMM commercial install includes manufacturer monitoring (Sungrow iSolarCloud, SolaX SolaXCloud, Solis Cloud) at panel-string level. For larger projects we add RS485 modbus integration into the customer's BMS, allowing production scheduling around predicted solar generation — which routinely lifts self-consumption by 3-7% over passive operation.

17. Maintenance

Commercial solar maintenance typically costs £8-£14 per kWp per year for a comprehensive service plan covering monitoring, annual inspection, annual cleaning, fault response and inverter replacement provisions. Without maintenance, expect to lose 1-2% generation per year on top of panel degradation. See our maintenance page.

18. Warranties

Standard warranties: panels 25-year linear performance + 12-year product; inverters 10-12 years with optional extension; mounting hardware 10-12 years; battery (where fitted) 10 years and 80% capacity retention. The most important warranty document is the inverter — keep it filed.

19. Insurance

Notify your buildings insurer of any solar installation. Most do not increase premiums; some may slightly increase battery installation premiums. We provide a documentation pack for your insurer including system specs, certificates and EN-IEC compliance evidence on batteries.

20. ESG reporting

Every commercial install includes ESG-formatted reporting: kWh generated, tCO2e displaced, equivalent trees planted, equivalent homes powered. We supply these in GRESB-compatible format on a quarterly basis for clients with formal ESG reporting obligations.

21. Pairing with EV charging

Around half of our commercial installs include workplace EV charging. We integrate the chargers behind the same MPAN so solar generation feeds the chargers first, with grid backfill. The OZEV Workplace Charging Scheme covers up to £500 per socket (installs completed from 1 April 2026) on up to 40 sockets per applicant — £20,000 maximum off the EV charger install cost, for staff and fleet parking.

22. Future expansion

Every KMM commercial install is designed with expansion in mind. We specify inverters with 20-25% DC headroom for future panel additions; we leave spare conduit runs for future battery; we leave consumer-unit capacity for future EV chargers. Tomorrow's bolt-on costs are typically 30% less when designed in today.

23. Conclusion

UK commercial solar in 2026 is in the strongest position the industry has ever been in. Tier-1 hardware costs are stable, the tax position is permanent, the grant landscape is reasonable, and the post-2022 electricity price step change has turned every commercial roof in the country into a financial proposition that demands serious analysis. We urge any business with a 250m²+ commercial roof to at least run the numbers — and KMM is happy to do that, free of charge, with no obligation to proceed.