Commercial solar for factories

Factory and manufacturing buildings usually have the two things solar likes most: a large, structurally sound roof and a wide, unshaded footprint. As a planning rule of thumb, allow about 7 m² of usable roof per kWp installed, so a 250 kWp array needs roughly 1,750 m² of clear roof once you deduct rooflights, plant, walkways and set-backs.

The right size is set by your electricity demand, not by how much roof you have. The aim on a factory is to size the array so that most generation is used on site rather than exported at a lower rate. Typical factory-scale systems fall in these bands:

If your demand is larger, systems scale well beyond this. See the size-specific pages for 50 kW, 100 kW and 250 kW for detailed cost breakdowns.

A factory typically runs a heavy, continuous daytime base load — motors, compressors, extraction, process heat, HVAC and lighting — from early morning through to late afternoon. That profile overlaps closely with solar output, which is why manufacturing sites tend to self-consume a high share of what they generate.

As a realistic guide for a typical site:

• Single daytime shift: often around 60–75% self-consumption.
• Extended or two-shift operation: commonly 75–90%.
• 24/7 running, or with a battery: can reach the upper end of that range.⁴

Self-consumption matters because every kWh you use on site displaces grid electricity at roughly 25–27p/kWh,¹ whereas exported units earn far less under the Smart Export Guarantee — typically single-digit pence.⁶ The economics of a factory are driven by using power, not selling it. For sites with a strong evening or weekend load, a battery can lift self-use further, but for most single-site factories the daytime match is already good enough that a battery is an optimisation rather than a requirement.

A mid-size factory drawing, say, 250,000–500,000 kWh a year at ~26p/kWh¹ is looking at an annual electricity bill in the region of £65,000–£130,000 before standing charges and levies. Solar can take a meaningful slice out of that. The table below is an estimate for a typical site — your figures depend on your load, roof and tariff.

Installed cost per kWp falls as systems get larger, from roughly £1,100–1,300/kWp on a small array down to about £650–750/kWp at 250 kWp.³ Paybacks in the 4–6 year range are common for factories because self-consumption is high, though a conservatively sized system, a lower tariff or roof works can push that out. Over a 25-year panel life, the return on a well-matched system is typically several times the original outlay — but confirm the numbers against your own half-hourly consumption data. If a supplier offers to fund the system, compare owning it outright against a power purchase agreement on our buy vs PPA page.

Two tax points are widely misreported, so it is worth being precise.

VAT. The 0% VAT rate applies to domestic solar only. A commercial solar installation pays the standard 20% VAT.³ A VAT-registered business can normally reclaim that input VAT in the usual way, so it is a cash-flow item rather than a permanent cost — check your position with your accountant.

Capital allowances. Solar PV is treated as special-rate plant and machinery. That means it does not qualify for 100% full expensing (which is for main-rate assets), but it does qualify for the 50% first-year allowance for companies within the charge to Corporation Tax, with the balance written down at the 6% special-rate pool thereafter.² Many businesses instead cover the spend under the Annual Investment Allowance (£1m), which gives 100% relief in year one up to that limit. Which route is best depends on your other capital spending — let your accountant confirm the treatment for your accounts.

Not every commercial roof behaves like a factory. The load shape decides how much value solar delivers, and whether a battery earns its keep:

• Factory: very high, steady daytime demand — excellent match, high self-use, among the fastest paybacks.
• Warehouse (detail): large, unshaded roof and generally good daytime use, though lightly staffed sites may export more.
• Farm (detail): ground-mount is an option alongside roofs, high self-use, plus income diversification.
• School (detail): summer holidays cut self-consumption when generation peaks — export tariffs or a battery become more important.
• Retail (detail): daytime trading hours match generation well.
• Hotel (detail): evening-weighted load, so battery storage usually helps the economics.

Because a factory sits at the favourable end of this spectrum, it is often where a solar investment stacks up soonest. See the commercial solar hub for the full picture.

Factory installs are larger and more technical than a typical rooftop job — structural loading, DNO connection approval for bigger systems, inverter and cabling design, and integration with your existing supply all matter. The single most useful thing you can do is have your installer size the array against your actual half-hourly consumption data rather than an estimate, so self-consumption and payback are grounded in reality.

Insist on MCS certification and ask to see comparable factory references. Our how to choose guide walks through the questions to ask on warranties, DNO approval, monitoring and maintenance.

PlutoHome is a neutral introducer. We match your site with one MCS-certified commercial installer — never a scramble of five sales calls. We do not install, finance or own systems. When you are ready, request a quote and we will connect you with a vetted installer for a proper site-specific assessment.