Skip to content
Commercial Solar Finance UK · Independent
Cost Guide · 100kW

How much does a 100kW commercial solar system cost in 2026?

A 100kWp commercial solar installation is the most common SME-scale UK project — large enough to use scale efficiencies on bill-of-materials and labour, small enough that AIA headroom typically applies for the full project, and large enough that the FYA/special-rate-pool route also delivers materially. Most 100kWp projects sit in the £85k–£110k turnkey bracket in 2026.

Capex range

£85,000–£110,000

£/kWp

£850–£1,100

Annual yield

95 MWh

Payback (post-FYA)

3.5–4.5 years

Cost breakdown — where the money goes on a 100kW project

L01 · 52–55%

Hardware (modules, inverters, mounting)

£48k–£60k

Higher per-Wp than larger projects due to lower volume — typically £0.50–£0.65/Wp on hardware vs £0.45/Wp on 500kW+ projects.

L02 · 15–18%

Installation labour (M&E, roof access)

£14k–£20k

Heavily dependent on roof condition. New industrial units run lower; aged roofs requiring scaffold can push to upper end.

L03 · 9–13%

Soft costs (DNO, structural, design)

£8k–£14k

DNO charges typically modest at 100kWp (under G99 threshold for connection studies). Structural surveys £3k–£8k.

L04 · 3–5%

Commissioning & certification

£3k–£5k

G98 commissioning for sub-100kWp; G99 for above. MCS certification £2k–£3k where SEG export tariff is wanted.

L05 · 13–18%

Margin and contingency

£12k–£20k

Installer margin plus 5% project contingency. Smaller projects often carry higher margin percentage to absorb fixed overhead.

Worked example: 100kW commercial solar at central pricing

Capex (central)

£95,000

Year-1 corp tax saved

£11,875 corp tax saved (50% FYA × 25%)

Year-1 electricity saving

£20k (95MWh × ~21p blended self-consumption + export)

Year-1 net cash

-£63k (after capex, FYA, savings)

25-year lifetime IRR

12–17%

Simple payback

4.5–6 years

Run your own numbers in our interactive calculator →

Best fit

Profitable trading SMEs with stable daytime demand on a single site. Companies with AIA headroom available for the period (full 100% relief in year one — typically stronger than FYA route at this scale).

Best for

A 100kW system suits SME industrial unit, single-shift manufacturer, smaller distribution warehouse, professional services occupying a single mid-sized commercial unit.

Not suitable

Loss-making businesses without trading subsidiaries, very short remaining lease tenure (under 5 years), buildings with very poor roof condition where structural reinforcement materially shifts the bottom line.

Other system sizes

200kW system cost

£800–£1,000 per kWp

500kW system cost

£720–£900 per kWp

1MW system cost

£700–£900 per kWp

100kW cost FAQs

Is 100kW the right starting size for my SME?
Right size depends on demand profile, not premise size. A daytime-heavy operation (production manufacturer, retail open 9–6) consuming 200,000+ kWh/year typically uses 80%+ of a 100kWp system's output directly, producing strong economics. A 9–5 office consuming 50,000–100,000 kWh/year may find 30–60kWp better-sized — adding capacity above demand reduces self-consumption percentage and dilutes IRR.
Should I claim AIA or 50% FYA on a 100kW project?
For a £95,000 project, both are available — AIA if you have remaining headroom in your £1m AIA cap for the period, FYA if not. AIA delivers 100% year-one relief: £23,750 tax saving at 25%. FYA delivers 50% year-one (£11,875) plus the residual 50% via the special-rate pool over time. AIA wins on year-one cash; lifetime values converge for profitable businesses. Talk to your accountant first — the AIA position depends on your wider capex for the period.
Why does £/kWp go up at smaller sizes?
Fixed costs (design, scaffolding mobilisation, commissioning, DNO process) don't scale linearly with system size. A 30kWp project might bear £15k in soft and fixed costs; a 100kWp project bears £18k for similar work. The fixed overhead amortises across more capacity at larger sizes. Below 50kWp, £/kWp typically runs £950–£1,200; at 100kWp it falls to £850–£1,100; at 500kWp+ to £700–£850.
How long does a 100kW project take from order to commissioning?
Typical lead time 12–18 weeks for straightforward 100kWp projects: 4–6 weeks for design, structural, and DNO; 6–8 weeks for procurement; 1–2 weeks installation; 1–2 weeks commissioning. Sites with structural concerns or DNO complications can push 20–30 weeks. Year-end FYA capture requires order placement by November to safely hit a 31 March commissioning.

Get a comparable 100kW cost benchmark for your specific site

Send postcode, roof area, and annual electricity consumption. We return an indicative capex range plus the after-tax model across all six finance structures, sized for 100kW.

Request a finance review