The Combined Business Case for Solar + EV Charging
Separately, solar and workplace charging are both decent investments. Designed together they are a materially better one — here is the arithmetic, line by line.
Line one: capex synergy
A solar project and a charging project share most of their expensive plumbing: supply capacity assessment, DNO applications, switchgear and distribution upgrades, groundworks and cable routes, design and project management. Procured as one project, the shared lines are paid once. Measured against quoting the two separately, combined projects routinely save 10–20% of total capital — £8,000–£25,000 on a typical SME scheme — before any operational benefit is counted.
Line two: self-consumption transformed
The weakness of commercial solar on a five-day business is the surplus: 20–40% of generation exported at 4–12p/kWh. EV charging is the perfect counterparty because it is large, flexible, daytime-schedulable load. Smart charging shifts vehicle energy into the generation curve, lifting self-consumption to 90%+ on most sites — converting export-rate electricity into full-displacement-rate electricity. On a 100kW array that conversion alone is worth £3,000–£7,000 a year.
Line three: the cheapest vehicle fuel available
Fleet energy in 2026 comes at three prices: public rapid charging at 60–85p/kWh, depot grid charging at 24–30p, and on-site solar at a lifetime cost of roughly 5–8p. A single electric van doing 20,000 miles a year uses about 6,000kWh; fuelling it on solar instead of public networks saves £3,500–£4,500 annually, per van. Fleet operators discover that the array stops being an energy project and becomes a fuel hedge with a 25-year term — the depot guide scales this from four vans to forty trucks.
Line four: grants and tax
The Workplace Charging Scheme contributes £350 per socket (up to 40 sockets) on the charging side. The solar side carries no grant but better-than-grant tax treatment: the Annual Investment Allowance delivers a 100% year-one deduction on qualifying plant up to £1 million, worth up to 25% of project cost to a profitable company. Chargepoint equipment likewise qualifies for first-year treatment. Stack the WCS, the AIA and the capex synergy and a £65,000 headline project can carry an effective net cost in the high £40,000s.
Line five: the soft lines that turn out hard
Staff charging is now a recruitment and retention line in sectors competing for drivers and engineers. Fleet decarbonisation reporting — Scope 1 falling as vehicles electrify, Scope 2 controlled by on-site generation — increasingly features in tender prequalification, especially for businesses supplying larger firms with CSRD-shaped obligations. And canopy or rooftop hardware is visible commitment: the rare ESG line item that customers can see from the car park. None of these appear in the payback calculation; all of them show up in board approval speed.
A worked example to argue with
Regional services business, 35 staff, 8 electric vans by 2027. Installed: 80kW rooftop solar plus six 22kW dual-socket chargers — £92,000 combined, less £4,200 WCS (12 sockets), net £87,800 before tax relief (~£21,900 at 25%). Energy: array yields 70,000 kWh; building load takes 38,000, smart-scheduled van charging absorbs 26,000, export 6,000. Annual value: building displacement £9,900, van fuel versus the public-charging alternative £14,300, export £400 — £24,600 a year. Net-of-relief payback: about 2.7 years. Your numbers will differ; the structure of the argument won't. Get the version built from your data via the quote form, and see how the engineering delivers it.
What combination buys you
Business case questions
What payback should we expect on a combined system?
Four to six years is typical for well-sized combined projects in 2026, calculated on net cost after the WCS grant and year-one tax relief. High-mileage fleets shorten it: every 10,000 electric miles charged on-site instead of on public networks saves £2,000–£4,000 a year at current public charging prices.
Does the EV charging element qualify for capital allowances too?
Yes. Chargepoint equipment has benefited from first-year allowance treatment, and the Annual Investment Allowance covers qualifying plant and machinery — most combined projects fully expense both elements in year one within the £1m AIA cap. Confirm treatment with your accountant against the current Finance Act position at the time you commit.
How do you count the value of charging on solar versus grid?
Three prices matter: lifetime solar cost (~5–8p/kWh), your grid rate (24–30p typical commercial), and public charging (60–85p/kWh on rapid networks in 2026). Every kWh moved from public charging to on-site solar saves 55p or more; even grid-powered depot charging beats public networks by half. The model values each kWh at the rate it actually displaces — that discipline is what makes the case bankable.
Is it better to phase: solar first, chargers later?
Sometimes — phasing suits sites whose fleet transition is more than three years out. But design the phase-one electrical infrastructure for the end state: duct routes, board capacity, DNO application sized for the full picture. Retrofitting capacity costs two to three times what provisioning it does. The wrong answer is two unconnected projects that each pay full price for groundworks and grid work.