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. The Smart Export Guarantee covers Great Britain only; in Northern Ireland suppliers set their own export tariffs (Power NI pays 11.88p per kWh from 1 October 2026 to 30 September 2027).

Often not, but the planning route depends on size and nation. In England, solar on a building that is not a house or a block of flats falls under Class J of Part 14 of Schedule 2 to the General Permitted Development Order 2015. Up to 50 kW it is permitted development subject to conditions: it must not protrude more than 0.2 metres from a pitched roof or sit more than one metre above a flat roof, must stay a metre from the roof edge, and listed buildings are excluded. Above 50 kW the council’s prior approval on design and external appearance, including glare, is needed. Wales uses Part 43 Class A of its own order and Scotland Class 6J; check the current order for your nation. 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. Small systems up to 16 amps per phase connect under the simpler G98 notify-after-install route; almost every commercial rooftop system is larger and needs the DNO’s approval under G99 before it can connect, and on constrained parts of the network the DNO may limit export or require reinforcement — occasionally at material cost. No network operator publishes a typical timescale for business connections, so ask for the DNO’s position on your site before relying on any date. In Northern Ireland the single network operator, NIE Networks, runs its own G98/NI and G99/NI process.

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 any calculator to differ from 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.

Rarely, for an ordinary company. As of November 2026 we know of no open UK-wide grant for business rooftop solar: the Industrial Energy Transformation Fund closed in April 2024 with no successor, Invest NI’s Energy Efficiency Capital Grant is paused, Power NI’s NISEP-funded grant for business solar PV has closed for applications for 2026/27, and Business Energy Scotland’s interest-free SME Loan is not accepting new solar PV applications. The meaningful support is fiscal: the Annual Investment Allowance deducts up to £1 million of qualifying spend a year, and qualifying solar plant is kept out of business-rates valuations in England, Scotland and Wales until 2035 (in Northern Ireland, generating plant up to 50 kW is not rateable). Most businesses pay for solar from their own funds, with asset finance or a loan, or through a PPA; the funding comparison sets out what to expect from grants in each nation and how the other routes compare. 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 when you want us to reply by email about your result, 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. If a figure looks wrong, send us a correction.

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, send your numbers through the quote form and we reply by email; an installer you choose can then turn the estimate into a fixed-price proposal from your half-hourly meter data.