On a commercial roof, the panels are the easy part. The hard questions are about money and evidence. Who pays the electricity bill? Who owns the array? Who gets paid for export? And who can report the carbon?
The answer sits in the lease and the metering, not the modules. This guide covers non-domestic buildings only.
Three streams of value
A rooftop array creates three things worth tracking.
- Avoided import. Every kWh used in the building is a kWh not bought from the grid. Whoever pays the import bill feels that saving.
- Export income. Surplus power goes to the grid. Under the Smart Export Guarantee, SEG Licensees (some licensed suppliers) pay eligible generators in Great Britain up to 5 MW for exported electricity. The supplier sets the rate and contract length, the rate must stay above zero, and payment is based on export meter readings.
- Carbon evidence. Generation and export are measured in kWh. Turning that into a carbon figure needs a conversion factor and a clear owner.
Four common set-ups
Owner-occupier. You own the building, pay the bill and own the array. You keep the avoided import and the export income. This is the simplest case.
Landlord with a tenant PPA. The landlord owns the array and sells on-site power to the tenant under a power purchase agreement. The PPA price usually sits between the export rate and the tenant's grid price. The landlord keeps the PPA revenue and the export. The tenant keeps the difference against their grid price.
Landlord, export income only. The tenant uses the on-site power free and keeps the bill saving. The landlord earns only from export. This avoids selling electricity to the tenant, but it leaves most of the value with the occupier.
Bills included in the rent. The landlord pays the building's electricity. The import saving and the export income both come back to the landlord.
There's more on structuring tenant supply in our guide to solar PPAs for multi-let commercial buildings.
Selling power to a tenant is regulated
Charging a tenant for electricity is supply. Under the Electricity Act 1989 that needs a licence or an exemption. The Class C on-site supply exemption covers self-generated power supplied to consumers on the same site, within set conditions. GOV.UK's licence exemption guidance explains the regime. Ofgem calls the exemption requirements fairly restrictive and complex and recommends legal and technical advice. Take that advice before a PPA is signed.
A worked example (fictional)
Fictional example. Indicative figures only. Not a forecast, a financial promotion, or financial or investment advice.
The figures below come from the default example in NZC Solar Desk: a fictional logistics unit. The numbers are indicative, use the app's own assumptions and are not a forecast.
- A south-facing roof, sized to the load: 101.5 kWp.
- Year-one generation: 99,115 kWh. Of that, 52,890 kWh is used on site and 46,225 kWh is exported.
- Assumed prices: grid import 26p/kWh, PPA 16p/kWh, export 8p/kWh, operation and maintenance £10/kWp a year.
- Under the PPA set-up, the landlord's year-one income after maintenance is £11,145. The tenant's year-one saving against their grid price is £5,289.
Change one assumption, such as the import price, the PPA rate or how much power the tenant uses during daylight, and the split moves. That's the point of the exercise. It shows who is exposed to which number.
Carbon: who reports what
The same kWh can't be claimed twice.
On-site power reduces the occupier's metered grid import, so it usually shows up in the occupier's Scope 2 figures. A PPA can say who holds the evidence. Write that down before either party reports it.
Tenant gas and oil use is the tenant's Scope 1. For a landlord, the same emissions can fall in Scope 3 Category 13, downstream leased assets, under the GHG Protocol.
Export is different. In the fictional example, 46,225 kWh of export at 0.177 kgCO₂e/kWh, the UK electricity factor in the UK Government (DESNZ) conversion factors 2025, comes to about 8.18 tCO₂e. That is reporting evidence. It is not an offset, and it does not reduce the tenant's gas emissions. Replacing the boiler does that.
Use the factor for the year the power was generated. In the UK Government (DESNZ) conversion factors 2026, the same factor is 0.13096 kgCO₂e/kWh, so the same export in 2026 comes to about 6.05 tCO₂e. As the grid gets cleaner, each exported kWh counts for less carbon. More on this in exported solar and carbon claims.
Grid connection comes first
Most commercial arrays connect under EREC G99, which applies above 3.68 kW per phase. G99 needs a formal application and network operator approval before the system runs in parallel with the grid. The simpler G98 route does not cover generation shared between two or more independent customers. Apply before ordering equipment, because the offer may limit export.
About NZC Solar Desk
NZC Solar Desk takes a commercial roof, a load, prices and one of the four set-ups above. It shows an indicative system size and the year-one split between landlord and tenant.
It is a desk tool. It is not an MCS design, a G99 application, a structural check or a financial promotion. Yields are indicative and losses are included. A real project needs a site survey, half-hourly data and professional advice.
NZC Solar is live. PV generation tracking is being integrated into NZC Portal. To see how NZC Portal brings building, energy and carbon records together, book an NZC Portal demo.