Business Solar FAQs: Sizing, Cost and Payback Answered

Size to your annual consumption, capped by your roof. Divide annual kWh by your regional yield (800–1,050 kWh per kWp across the UK) for the consumption-matched size, then check it fits at roughly 6.5 m² of clear roof per kWp. A business using 115,000 kWh a year in the Midlands needs about 120kWp to match consumption — but if only 500 m² of roof is usable, 75kWp is the practical answer. The calculator on the homepage runs this logic automatically.

Roughly £900–£1,100 per kWp fully installed for systems below 50kWp, falling to £750–£900 per kWp between 50kWp and 250kWp. "Fully installed" should include panels, inverters, mounting, electrical work, scaffolding, the G99 grid application and commissioning — treat any quote that excludes those items as incomparable until corrected. Above 250kWp, pricing is genuinely site-specific.

Most well-sized 2026 UK systems land between 4 and 7 years before tax relief. The three biggest levers are your import rate (every penny above 26p/kWh shortens payback), your on-site use percentage, and system size (larger systems cost less per kWp). The worked examples page shows 4.1–4.5 year paybacks across an office, a warehouse and a factory at default assumptions.

For a business running five or six days a week with normal daytime load, 60–70% is realistic, which is why the calculator defaults to 65%. Sites with continuous load — cold storage, data rooms, 24/7 manufacturing — reach 85–95%. A strictly 9-to-5, five-day office may manage only 45–55%. Check the figure against your operating hours; it moves the result more than any other input.

Smart Export Guarantee rates for businesses in 2026 typically run between 5p and 15p/kWh depending on supplier and tariff structure; the calculator defaults to a realistic mid-range 12p. Larger systems can sometimes do better through merchant PPAs for export. Either way, export is worth less than half of on-site displacement — design for self-consumption first and treat export income as a bonus.

Usually not. Most non-domestic rooftop installations in England fall under permitted development, subject to conditions — panels must not protrude more than 200mm from the roof plane, and listed buildings and some conservation-area sites need consent. Ground mounts above 9 m² and installations on flats have additional rules. Your installer should confirm the position in writing as part of the proposal.

G99 is the engineering recommendation governing connection of generation to the distribution network. Any commercial-scale system needs DNO approval before it can connect, and on constrained parts of the network the DNO may limit export or require reinforcement — occasionally at material cost. Timescales run from a few weeks for straightforward connections to several months at larger scale. It is the main reason commercial solar projects take 3–9 months end to end.

Only if the numbers say so, and in 2026 they often do not — yet. Commercial batteries add £300–£500 per kWh of storage, and a business already using 65%+ of its generation on-site has limited surplus to shift. Batteries earn their keep where on-site use is low, where half-hourly tariffs create big peak/off-peak spreads, or where capacity charges can be shaved. Run the solar-only case first; add storage as a separately justified line.

As accurate as their assumptions are honest — which is why ours publishes every one and lets you edit them. The genuinely site-specific factors no online tool can know are roof condition, shading, your half-hourly load profile and your DNO position. Expect a good calculator to land within 10–15% of a professional desk feasibility, and treat anything that promises an exact figure without seeing your meter data with suspicion.

Savings scale almost linearly with your import rate, so a fall from 26p to 22p stretches the warehouse example payback from about 4.1 to 4.8 years — still comfortably inside the system warranty period. The structural pressures on UK delivered prices (network reinforcement, electrification of heat and transport) point upward over the medium term, but the calculator deliberately assumes zero inflation either way: flat prices for 25 years is the cautious middle.

Yes — at 800–850 kWh per kWp rather than the south's 1,050, a 20–25% yield discount, not a disqualification. Panels are also marginally more efficient in cooler temperatures. A northern site with strong daytime load regularly out-earns a southern site without one: the worked-examples factory near Sheffield posts a 4.2-year payback at 850 kWh/kWp because its 80% on-site use converts generation at the full import rate.

Modest but not zero. Budget 1–2% of capex a year: annual electrical inspection, occasional panel cleaning (more often near aggregate dust or under flight paths), inverter monitoring, and one inverter replacement around year 12–15 — typically £5,000–£8,000 on a 100kWp system. Panel performance warranties from tier-1 manufacturers guarantee 84–87% of original output at year 25; the calculator degrades output by 0.5% a year to match.

Yes, with the landlord's written consent — and the conversation is usually easier than tenants expect, since solar raises the building's EPC rating and lettable value. The practical threshold is lease length: under five years remaining, the payback maths rarely works for a tenant-funded system, and funders will not write a PPA. Options include landlord-funded installs with a rent adjustment, or simply making solar part of the next lease renewal negotiation.

Direct grants are scarce for ordinary commercial installs — the meaningful support is fiscal: the Annual Investment Allowance gives a 100% year-one deduction on the full system cost, and rooftop solar plant is exempt from business rates valuation in England until 2035. Sector schemes exist for some public and third-sector buildings. Be wary of anyone selling "free solar grants" to ordinary limited companies; what they are usually describing is a PPA.

Because it does not need one. The maths runs entirely in your browser — no backend, no stored data, no follow-up sequence. The quote form exists for the moment you decide you want a fixed price from a real survey, and using it is your call. A calculator you can use anonymously is also one whose numbers do not need to flatter you into a sales funnel.

Three things. First, stress-test it: re-run with your actual unit rate from your bill and an honest on-site use figure for your operating hours. Second, read the worked example nearest your size so you understand each line of the result. Third, if payback lands inside your investment horizon, request a desk feasibility through the quote form — it converts the estimate into a fixed-price proposal from your half-hourly meter data, and tells you plainly if your site does not suit solar.