100kW system
100kW Commercial Solar
A 100kWp system is the natural first step up from a domestic-scale install. It's large enough for real economies of scale and serious tax relief. However, it stays small enough that most single buildings can host it without a grid-reinforcement fight.
At 100kWp, per-kWp pricing already drops well below small commercial and domestic rates. You get enough scale to unlock commercial-grade equipment and labour rates. Meanwhile, you avoid the grid-connection and structural studies that larger systems require.
This size also marks a real shift in how the industry treats a system. MCS's installation standard for solar PV, MIS 3002, applies only up to 50kWp. A 100kW system sits above that threshold, so it isn't a routine MCS job like a house install. As a result, you should specify, commission and warranty it as a genuine commercial project, not a scaled-up domestic one.
On tax treatment, a 100kWp system's total cost normally sits well inside the £1 million Annual Investment Allowance limit. Assuming your business hasn't used that allowance elsewhere in the year, the whole cost qualifies for a 100% first-year deduction. That deduction applies against your taxable profits. However, that's not the same relief as 'Full Expensing'.
Solar is special-rate expenditure under HMRC's rules. That means the Annual Investment Allowance applies first — or, above it, the 50% special rate first-year allowance. It is not the 100% main-rate 'Full Expensing' regime often quoted online. Since that distinction changes your real, after-tax payback, it's exactly what we model before you commit.
Sources & further reading
Frequently asked questions
Is a 100kW system just a bigger version of a domestic install?
No. MCS's solar PV installation standard (MIS 3002) applies only up to 50kWp, so a 100kW system falls outside that framework. It needs commercial-grade design, structural sign-off and commissioning documentation — an experienced commercial installer, not a scaled-up domestic quote.
Will the Annual Investment Allowance cover the whole cost?
Usually, yes — a 100kWp system's cost normally sits well inside the £1 million annual AIA limit. The exception is if your business has already used the allowance on other capital spend that year, in which case the balance falls to the 50% special rate first-year allowance instead. We model this against your actual tax position.
Further reading
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Read more →Talk to us about a 100kw 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.