Commercial solar: what UK businesses need to know before installing

Why commercial solar economics are better than residential

Residential solar achieves 8–10 year paybacks. Commercial systems typically pay back in 3–5 years. The difference comes from three factors: economies of scale (cost per kWp drops at 50kW+ system sizes), business electricity rates (often higher than residential — SMEs pay 25–35p/kWh vs the residential cap of ~24p), and the simple fact that businesses use most electricity during daylight hours when solar is generating.

A 50kWp commercial system (approximately 120–130 panels) costs £35,000–50,000 installed, or £700–1,000/kWp compared to £1,250–1,500/kWp for a 4kW residential system. The cost per unit of capacity drops substantially with scale.

What a 50kWp system actually delivers

Generation: ~47,500 kWh/year (assuming UK average of 950 kWh/kWp for a south-facing system). At a business electricity rate of 28p/kWh (realistic SME rate in 2026), self-consumed solar saves £13,300/year if 100% is used on-site. For a business operating 08:00–18:00 Monday to Friday, self-consumption is typically 85–95% — most generation aligns directly with operating hours.

Payback at £42,000 installation cost and £12,500/year savings: approximately 3.4 years. 25-year net benefit: £250,000+. If Full Expensing is applied: £10,500 corporation tax saved in year one (at 25% CT rate), reducing effective net cost to £31,500. Payback drops to approximately 2.5 years.

Roof structure: the issue that kills projects

Commercial roofs come in two main types: pitched (profile metal sheet, typically trapezoidal) and flat. Each has structural implications:

- **Profile metal roofs:** Most UK warehouses and industrial units built since 1980 use this system. Solar adds 10–15 kg/m² distributed load. Most roofs designed in that era have adequate spare capacity, but a structural engineer's assessment is mandatory. The key check: whether the existing purlins and cladding rails can take the additional load without reinforcement.

- **Flat roofs:** Bituminous felt or single-ply membrane systems. Solar adds 15–25 kg/m² including ballast if using a non-penetrating mounting system (which preserves roof warranty). Flat roof systems can be oriented south without the constraints of the building's orientation, improving yield. The trade-off: ballasted systems are heavier.

A structural survey costs £1,000–3,000 but is essential. If reinforcement is needed, budget £5,000–20,000 depending on scope. If the roof is nearing end-of-life (felt roof over 15 years old, metal sheets showing corrosion), replacement before solar installation is strongly advisable — removing and reinstalling panels mid-life adds significant cost.

Grid connection: the hidden bottleneck

Systems above 50kW (or any system where the local grid has limited capacity) require a G99 application to the Distribution Network Operator. The process: submit application with system design → DNO assesses local network capacity → approval, approval with constraints (export limitation), or refusal/quotation for reinforcement.

In areas with high renewable penetration (parts of the South West, East Anglia, and some rural areas), grid constraints are becoming common. Export limitation — where the system is capped at a maximum export level — adds £1,000–3,000 for a G100-compliant export limitation device but gets projects through approval. Network reinforcement costs, if required, can run from £10,000 to £100,000+ depending on upgrade scope. This is the single biggest risk in commercial solar project planning — always budget time and money for DNO engagement.

Power Purchase Agreements (PPAs): the alternative to capital investment

If capital expenditure isn't feasible, a PPA is a zero-upfront-cost model. The PPA provider funds, installs, owns, and maintains the system on your roof. You agree to buy the electricity it generates at a fixed or indexed rate (typically 6–10p/kWh) for 15–25 years. You save the difference between the PPA rate and your normal business electricity rate (28p – 8p = 20p/kWh saved on all solar electricity consumed).

PPAs work well for businesses with: strong credit ratings, long-term occupancy of the premises, good roof space, and daytime electricity usage. The drawback: less total savings than owning the system outright. On a 50kWp system over 25 years, ownership delivers ~£250,000 net benefit; a PPA at 8p/kWh delivers ~£190,000 in savings. The difference is the PPA provider's profit margin — but if the alternative is doing nothing, £190,000 in savings is still a substantial gain.

Tax: the benefits beyond energy savings

- **Full Expensing (100% First-Year Allowance):** Deduct the entire capital cost from taxable profits in year one. At 25% corporation tax, this is an effective 25% government contribution to the capital cost. Permanent (not temporary). Applies to plant and machinery — solar PV, battery storage, EV chargers, heat pumps all qualify.

- **Enhanced Capital Allowances (ECA):** 100% FYA specifically for equipment on the Energy Technology List (separate scheme from Full Expensing). Still available alongside Full Expensing for designated high-efficiency equipment.

- **Climate Change Levy (CCL) exemption:** Electricity generated from qualifying renewable sources and consumed on-site may be exempt from CCL. Combined with a Climate Change Agreement, this can reduce your effective electricity cost by an additional 10–15%.

- **VAT:** Commercial solar installations are standard-rated (20% VAT), unlike residential (0%). However, the VAT is recoverable for VAT-registered businesses — it's a cashflow consideration, not a net cost. The input VAT is reclaimed on the next VAT return.

Battery storage for commercial: shifting demand, cutting charges

Commercial battery storage serves different purposes than residential. The primary uses:

1. **Peak shaving / DUoS reduction:** Distribution Use of System charges include a capacity-based element for peak demand. If your business draws 150kW at 10:00 but only 30kW the rest of the day, you pay DUoS based on the 150kW peak. A battery discharging during that peak hour reduces the recorded maximum demand, cutting DUoS charges by 10–20%. For energy-intensive businesses, this can save £2,000–10,000/year.

2. **Time-of-use arbitrage:** Import at cheap overnight rates, discharge during expensive daytime periods. Works with business-specific TOU tariffs.

3. **Grid services:** Larger battery systems (100kW+) can participate in National Grid ESO's frequency response, balancing mechanism, and capacity market — but this requires specialist aggregator services and is beyond the scope of most SME installations.

Planning permission thresholds

In England, solar panels on commercial roofs are permitted development (no planning permission required) under Part 43 of the GPDO, provided: panels do not protrude more than 200mm above the roof plane, are not on a listed building or in a conservation area (where different rules apply), and do not exceed the highest part of the roof (excluding chimney). Ground-mounted commercial solar exceeding 9m² may need planning permission. Always confirm with the local planning authority.

Listed buildings and scheduled monuments require listed building consent and/or scheduled monument consent. Conservation areas require planning permission if panels are on a wall or roof slope fronting a highway. These are absolute blockers — not solvable through permitted development rights.

The decision framework

Commercial solar makes financial sense for a business if: (a) you own or have a long lease on the premises (10+ years to recoup costs), (b) you use electricity during daylight hours, (c) your roof is structurally sound with 10+ years remaining life, and (d) the DNO approves the connection. If most of those boxes are ticked, the numbers almost always work. At Sunlit Solutions, we provide a full commercial assessment including structural survey coordination, DNO application management, PPA brokerage, and tax benefit modelling. Commercial solar isn't just an environmental decision — at 2026 energy prices, it's a strong financial one.