A 100 kW commercial solar PV system sits at the borderline between the simpler G98 grid-connection process and the more involved G99 process — and the implications for project timeline and DNO costs are material. This page lays out the real numbers: turnkey cost, panel count, roof space, annual generation, sub-vertical fit, finance comparison and a full worked example. For our canonical service page covering site survey workflow and design detail, see 100 kW solar systems. For broader cost context, see commercial solar costs.
Turnkey cost: £85,000-£110,000 in 2026
A 100 kW commercial PV system delivered turnkey by an MCS-certified installer in 2026 costs £85,000–£110,000, or £850–£1,100 per kW. This sits at the boundary between the sub-100 kW pricing band (£900–£1,200/kW) and the 100–500 kW band (£750–£950/kW), so quotes typically come in 5–10% below the per-kW figure of the smaller 50 kW system. Variation reflects roof access, structural condition, switchgear position relative to the array, three-phase upgrade requirements, and crucially DNO connection complexity (which can swing £25,000+ depending on local network constraints). The pricing covers tier-1 monocrystalline modules, three-phase string or central inverters from Sungrow, Solis, SMA or Fronius, mounting (pitched-rail or flat-roof ballast), DC and AC cabling, G99 paperwork, structural and electrical sign-off, scaffolding, MCS certification, commissioning, and 25-year performance warranties.
Panels and physical specifications
A 100 kW system comprises approximately 185 modules at the standard 2026 540 W large-format commercial panel, or 220–235 modules at the more common 425–450 W rooftop module. Module choice matters at this scale: large-format 540 W panels reduce labour per kW (fewer modules to mount and wire) but require structural capacity for heavier units (~28 kg per panel versus ~22 kg for smaller modules). Smaller modules give more granular MPPT optimisation on shaded roofs but cost slightly more per kW at module level. Array footprint runs 560–640 square metres for south-facing pitched roofs, 640–740 square metres for east-west flat-roof arrays. Inverter sizing typically 90–100 kW (string or central) — three-phase is mandatory at this scale (no single-phase 100 kW exists in the UK market). Multiple inverters in parallel are standard for redundancy and MPPT zoning.
Annual generation: ~92,000 kWh in the UK
A correctly orientated 100 kW system generates approximately 92,000 kWh per year on average across the UK. Regional breakdown: southern England 95,000–100,000 kWh, Midlands 90,000–95,000 kWh, northern England 85,000–90,000 kWh, Scotland 80,000–88,000 kWh. We model conservatively at 92,000 kWh/year (P50, central estimate). A south-facing 30-degree pitched roof with no shading achieves 950–1,050 kWh per kW per year. Flat-roof east-west arrays achieve 870–950 kWh/kWp. We always model both P50 and P90 generation estimates so the project IRR has worst-case downside built in. Shading from rooftop plant, vents and adjacent buildings can cost 5–25% of generation — every site survey we run includes Solmetric SunEye or equivalent shading analysis, and we publish the PVSyst yield model in full as part of every quote.
Annual savings: £16,000-£22,000
Year-one savings on a 100 kW system depend on annual generation (92,000 kWh), self-consumption ratio (typically 70–85% for a site with extended daytime operations), and the gap between import and SEG export tariffs. At a representative 2026 import tariff of 24p/kWh and SEG export of 6p/kWh, a 75% self-consumption ratio delivers: 69,000 kWh self-consumed at 24p = £16,560 avoided import; 23,000 kWh exported at 6p = £1,380 SEG income. Total year-one savings: £17,940. A higher self-consumption ratio (85%, achievable with extended daytime operations or battery storage) lifts that to £19,650. A site with strong daytime demand and a 30p import tariff hits £21,500–£22,800. Larger sites also typically negotiate a SEG export rate above the standard 6p — Octopus Outgoing Fixed and similar tariffs run 8–15p/kWh, lifting export income proportionally.
Worked example: 100 kW manufacturing facility in Leeds
Real-shape project: a 2,800 sqm light manufacturing facility in Leeds, 35 staff, three-phase 400A supply, 7am–6pm operations five days a week, annual demand 165,000 kWh, current import tariff 24p/kWh. We specify a 100 kW south-facing PV array on the unshaded steel-portal roof. Capex: £95,000 turnkey (£950/kW). Generation: 91,000 kWh/year (P50). Self-consumption: 80% (72,800 kWh self-consumed, 18,200 kWh exported). Year-one savings: £17,470 avoided import + £1,090 SEG = £18,560. AIA relief: £95,000 × 25% = £23,750 year-one corporation tax saving. Net effective capex: £71,250. Simple payback: 5.1 years gross, 3.85 years net. 25-year DCF NPV at 7%: £325,000. IRR: 17.8%. Install timeline: contract to commissioning 28 weeks (16 weeks G99 DNO including assessment, 8 weeks lead time on modules and inverters, 2 weeks scaffold and install, 2 weeks commissioning).
G99 grid connection: 6-18 months
A 100 kW system exceeds the G98 threshold (70 kW per phase) so requires G99 grid connection application. The G99 process is materially more involved than G98: submit application with full grid form, single-line diagram, protection settings, inverter datasheets, and load profile; await DNO assessment (typically 12 weeks for first response, 16–24 weeks for connection offer); accept connection terms with deposit; install; submit completion documentation. Application fees start at £1,500 and rise to £30,000+ if network reinforcement is required (a transformer upgrade, new feeder cable, or substation work). We always run an ENA Connections portal constraints check and a DNO pre-application enquiry before quoting — this lets us identify reinforcement risk and price it into the quote rather than discovering it post-contract. For the full G99 timeline, see our G99 FAQ.
Finance comparison: cash, lease, asset finance, PPA
Four financing routes work for 100 kW commercial PV. The numbers below assume £95,000 turnkey capex, £18,000 year-one savings, 4% bill inflation, 25-year asset life.
| Route | Year-one cash | 25-yr NPV @ 7% | IRR | Best for |
|---|---|---|---|---|
| Cash + AIA | -£71,250 (net of £23,750 tax relief) | £325,000 | 17.8% | Profitable Ltd Co with capex headroom |
| Asset finance (7y) | -£0 capex; £15,200/yr finance vs £18,000 savings = +£2,800 | £260,000 | n/a (zero capex) | Cash-flow priority, want ownership end-of-term |
| Operating lease (10y) | -£0 capex; £12,500/yr lease vs £18,000 savings = +£5,500 | £195,000 | n/a | Off-balance-sheet, IFRS 16 small-lease |
| PPA (15y) | -£0 capex; PPA price 18p/kWh vs grid 24p = £4,150 saving | £105,000 | n/a | No corporation tax, planning to relocate |
Cash plus AIA delivers the strongest IRR and NPV. Asset finance is the most popular SME route — zero capex outlay, cash-flow positive from year one, and you own the system at end of term. PPA gives the weakest financial outcome on a 25-year basis but is genuinely zero-risk. See finance options for full route mechanics and commercial solar finance for the side-by-side comparison.
AIA, capital allowances and net effective cost
Solar PV qualifies as plant and machinery for HMRC capital allowances purposes, so 100% Annual Investment Allowance applies up to the £1,000,000 annual cap. A 100 kW system at £95,000 sits comfortably inside that cap. For a profitable UK limited company at the 25% main rate of corporation tax, every £100 of AIA-eligible spend delivers £25 of year-one tax relief. The 100 kW worked example above: AIA claim £95,000 → £23,750 corporation tax saving in year one → net effective capex £71,250. Sole traders and partnerships using the cash basis can also claim 100% AIA on solar PV. Companies with R&D credit interactions need careful sequencing — your accountant should run AIA before R&D enhanced expenditure to avoid wasting reliefs. See capital allowances on solar panels for full mechanics.
Sub-vertical fit: where a 100 kW system makes sense
A 100 kW system fits businesses with annual electricity demand in the 100,000–200,000 kWh range and 560–640 sqm of available unshaded roof or ground space. Common sub-verticals: medium-sized warehouses (1,500–3,500 sqm with daytime picking and despatch), small-to-mid manufacturing facilities with three-shift or two-shift operations, mid-size hotels (60–120 rooms with kitchen, laundry and pool plant), care homes (60–100 beds with 24/7 baseload), supermarkets and convenience store chain locations with refrigeration baseload, leisure centres with pool plant and HVAC, mid-size schools and academy trust schools, distribution centres with battery-charging fleets, food production sites with chiller and freezer baseload, and small-to-mid logistics operations. If your annual demand sits below 75,000 kWh a smaller 50 kW system has better self-consumption economics — see our 50 kW cost guide. If demand exceeds 250,000 kWh, scale up to 200–300 kW.
Choosing an installer for a 100 kW project
For a 100 kW commercial install, four accreditations are non-negotiable in 2026. First, MCS certification on both the installation contractor and the design — required for SEG eligibility. Second, NICEIC, NAPIT or Stroma electrical contractor accreditation for the AC-side installation including HV switchgear if required. Third, IPAF and PASMA tickets on the install team for safe scaffolding and powered access work. Fourth, demonstrated G99 commissioning experience — at this scale you want an installer who has commissioned at least 10 G99 systems in the last 24 months and can name the witness commissioning engineer. Look for itemised quotes (no bundled hidden costs), full PVSyst yield model with shading analysis, four-metric DCF (simple payback, discounted payback, IRR, NPV), and references from at least three commercial installs of similar size in the last 18 months. Every MCS installer in our network hits all four accreditation markers.
Common questions on 100 kW solar systems
How much does a 100 kW commercial solar system cost in the UK in 2026?
A 100 kW turnkey commercial solar PV install in 2026 costs £85,000–£110,000, equivalent to £850–£1,100 per kW. This sits at the boundary between the sub-100 kW pricing band and the 100–500 kW band where economies of scale begin to compress per-kW cost. After 100% Annual Investment Allowance for a profitable UK limited company at the 25% main rate of corporation tax, net effective cost drops to £63,750–£82,500.
How many panels are in a 100 kW solar system?
Approximately 185 panels at the standard 2026 540 W large-format commercial module, or 220–235 panels at 425–450 W rooftop modules. The exact count depends on module choice, roof orientation, structural capacity and shading constraints. Total array footprint runs 560–640 square metres of unshaded roof or ground space.
How much electricity does a 100 kW solar system generate per year?
A correctly orientated 100 kW system in the UK generates approximately 92,000 kWh per year on average. Southern England sites achieve 95,000–100,000 kWh; Midlands 90,000–95,000 kWh; northern England 85,000–90,000 kWh; Scotland 80,000–88,000 kWh. We model conservatively at 92,000 kWh/year (P50) for budget purposes — a south-facing 30-degree pitched roof with no shading achieves 950–1,050 kWh per kW per year (kWh/kWp).
Does a 100 kW solar system need a G99 grid connection?
Yes, in most cases. A 100 kW system exceeds the G98 threshold of 70 kW per phase on a three-phase connection, so it requires G99 grid connection application. G99 is the more involved process — application before install, DNO assessment, possible network reinforcement, with 6–18 month lead times. Application fees start at £1,500 and can reach £30,000+ if reinforcement is needed. We always run a constraints check and ENA Connections portal lookup before quoting.
What is the payback period for a 100 kW solar system?
Simple payback for a 100 kW commercial PV system in 2026 lands at 6–6.5 years on gross capex, or 4.5–5 years on AIA-adjusted net capex. Typical year-one savings: £16,000–£22,000 depending on import tariff, self-consumption and SEG export. After AIA, a £95,000 install nets to £71,250 effective capex. With £19,000 annual savings, simple payback hits 3.75 years on net capex, or 5 years on gross.
How much roof space does a 100 kW solar system need?
A 100 kW commercial array needs approximately 560–640 square metres of unshaded south-facing or east-west roof space using 2026 monocrystalline modules. East-west arrays need 10–15% more area for the same kW because of slightly lower packing density. Pitched roofs at 15–30 degrees south-facing are most efficient; flat roofs use ballasted east-west mounting which packs slightly less densely.
What businesses typically install a 100 kW solar system?
Sub-vertical fit for 100 kW: medium-sized warehouses (1,500–3,500 sqm with daytime operations), small-to-mid manufacturing facilities, mid-size hotels (60–120 rooms), care homes (60–100 beds), supermarkets and convenience store chain stores, leisure centres with pools, mid-size schools and academy trusts, distribution centres, food production sites, and small-to-mid logistics operations. Annual demand for these sites typically sits in the 100,000–200,000 kWh range.