How do you calculate the payback period for business solar?

Divide your installed cost by the annual net value of avoided electricity purchases and export receipts. In Great Britain, eligible solar installations up to 5 MW can receive export payments under Ofgem's scheme [S1]. Your payback depends on actual daytime consumption, the export contract and project costs; there is no single period for every business. Checked October 2026.

Last checked 16 October 2026

How do you calculate business solar payback?

Use the installed cost divided by annual net cash benefit. For solar photovoltaic (PV) panels, distinguish avoided electricity purchases from money paid into your account. Both can contribute to the business case, but only the export payment or a contracted rent is cash income. Your existing bills and proposed export contract should supply the values used in your own calculation.

The method is: annual value = on-site solar use × avoided import unit rate + exported electricity × export rate minus annual running costs. Simple return on investment (ROI) = annual net value ÷ host capital × 100. Simple payback in years = host capital ÷ annual net value. If net value is zero or negative, this method gives no positive payback. It does not model financing, tax, inflation or the time value of money. Use the green business loan guide to separate a funding proposal from the project payback calculation.

Kilowatts (kW) describe power and kilowatt-hours (kWh) describe energy. Solar peak capacity is often shown as kWp, meaning kilowatts peak. A production estimate must also consider location, orientation and losses; PVGIS, the European Commission’s solar modelling tool, accepts those inputs. [S2] Compare the commercial solar cost guide with the actual scope behind your estimate.

What should a solar payback calculator include?

The following is an illustration, not a quote. Every price, output and operating input in the tables is an assumption, not a surveyed roof or market average. Replace them with a roof-specific model, an itemised quotation and your electricity contracts. The low, mid and high cases describe the proportion of solar used on site.

This is a solar-only calculation: charger power, sessions per day, energy per session and driver charging price are not inputs to these returns. No charging sales are counted. If you add chargers, put their capital, software, maintenance, energy costs and revenue-share percentage into a separate charging model. Otherwise the same solar unit risks being counted as both an avoided purchase and new charging revenue.

Redo the mid case as 27,000 × £0.25 + 18,000 × £0.05 − £750 = £6,900. This excludes standing charges that do not change, and makes no assumption about increased customer spending. Export is counted only once. If you cannot confirm an export payment, run a zero-export-value version alongside the proposed offer.

What could fully funded, part funded and self funded solar return?

Use the funding labels consistently, but read the actual ownership and payment terms. Fully funded means the funding party pays for, owns and operates the equipment. Part funded means shared capital. Self funded means you buy the installation and retain its net value. The numerical arrangements below are hypothetical contracts.

Part funded mid-case arithmetic is £6,900 × 60% = £4,140; £4,140 ÷ £25,000 = 16.6%; £25,000 ÷ £4,140 = 6.0 years, rounded. Self funded mid-case payback is £45,000–£55,000 ÷ £6,900. The fully funded rent is a separate contractual assumption; none of the ownership-case bill reduction is added to it. There is no host-capital payback to calculate when host capital is zero.

A power purchase agreement can instead charge you for the solar electricity used on site. Its net benefit needs that purchase price deducted. Do not apply the ownership table unchanged. Read a power purchase agreement versus buying solar.

How do export rates and daytime use change the answer?

The Smart Export Guarantee (SEG) covers eligible solar installations up to 5 MW in Great Britain. Suppliers set their tariffs and contract terms; Ofgem requires a rate above zero and payments based on metered exports. [S1] The assumed 5p export rate above is therefore a modelling input, not a scheme rate.

In this illustration, shifting 1,000 kWh from export to genuine on-site use adds £200 of annual value: 1,000 × (25p − 5p). That is useful only if the business actually needs that electricity at the time. Match monthly generation estimates with operating hours and interval consumption. A shut warehouse cannot use its weekday consumption profile on a closed weekend. Ask for a low-consumption case before approving roof area.

Which costs and risks could lengthen payback?

Request roof condition, structural checks, access, grid/export work, insurance, maintenance and replacement costs as explicit quotation items. Ask which are included and which remain allowances. Test reduced generation, lower import rates and curtailed exports separately; do not bury all uncertainty in a single optimistic annual total.

Check lease length, roof access, repairs and end-of-term removal with your solicitor. Keep tax relief outside the base calculation until eligibility is established. HMRC designates solar panels as special rate expenditure; check with your accountant rather than treating a deduction as a refund of the installation invoice. [S3] See capital allowances for solar panels.

What should you do next?

Prepare electricity data, a roof plan, your quotation and its generation assumptions. Ask for low, mid and high cases showing both cash receipts and avoided purchases. Read how we work before enquiring.

Piggy Pineapple Ltd operates this referral service. We refer enquiries to installer partners and may be paid a fee. Our owner holds shares in at least one partner. Before sharing your details, we name the proposed partner and disclose any shareholding our owner holds in it. You can get matched with an installer that covers your area.