250kW system
250kW Commercial Solar
At 250kWp, per-kWp cost keeps falling as system size increases. However, the grid connection stops being an afterthought at this size. DNO capacity and the G99 application process become a real part of the feasibility question.
Per-kWp cost keeps falling as scale increases. A 250kWp system typically installs meaningfully cheaper per kWp than a 100kWp one. That's because fixed costs — scaffolding, cabling runs, commissioning, project management — spread over more panels.
What changes at this size is the grid. Connecting a system this size usually falls under Engineering Recommendation G99. That means a formal application to the local Distribution Network Operator.
Depending on how much headroom already exists at the substation, that can also trigger a capacity study. The study may flag reinforcement costs before you commit. That's a question worth answering at feasibility stage, not after you've ordered kit.
The tax position follows the same principle as the 100kW band. Solar is special-rate expenditure. That means the Annual Investment Allowance — 100% relief, up to £1m a year — is normally what shelters the cost. That's not the same as the 100% 'Full Expensing' regime. Full Expensing only applies to main-rate plant and machinery.
At 250kWp, total spend still sits comfortably below the £1m AIA ceiling for most buyers. As a result, the relief is usually available in full. The exception is if something else in your capital programme that year competes for the same allowance.
Sources & further reading
Frequently asked questions
Do we need to apply to the grid operator for a system this size?
Almost always, yes. A 250kWp system typically connects under Engineering Recommendation G99, which means a formal application to your Distribution Network Operator and, in some cases, a capacity study. We check DNO headroom as part of feasibility, before any capital commitment.
We let part of the building to tenants — does that complicate things?
It changes who benefits, not whether solar works. Landlord/tenant and service-charge structuring (or an on-site PPA) is exactly what our sectors work on commercial and office buildings covers — see /sectors/commercial-offices/.
Further reading
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Read more →Talk to us about a 250kw system
An initial consultation is free and carries no obligation. Tell us about your building or estate, and we'll model the real numbers for your specific site. Because every roof and load profile differs, we skip the generic range entirely.