100kW Solar System Cost UK 2026

A 100 kW commercial solar PV system costs £85,000–£110,000 turnkey in 2026 — £850–£1,100 per kW — falling to £63,750–£82,500 net once Annual Investment Allowance relief is applied. On our standard scenario it pays back in 3.7 years net of AIA. This page lays out the real numbers line by line: where every pound of that £85,000–£110,000 goes, panel count, roof space, annual generation, annual savings, finance comparison, the G99 grid-connection timeline 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.

Itemised cost breakdown: where the £85,000-£110,000 goes

Every component of a turnkey 100 kW install, with its 2026 cost range and the £/kW it contributes. The component ranges sum to roughly £73,000–£109,000 (£730–£1,090/kW). No real quote stacks the top of every line at once — a typical build lands mid-range on most components, which leaves room inside the £85,000–£110,000 turnkey total for design, project management, contingency and DNO connection fees. A quote sitting at the top of every component line is usually one where access or DNO reinforcement costs have already bitten. Ask any quoting installer for this line-by-line split; bundled "all-in" figures hide where margin sits.

Want these numbers run against your own roof and tariff? Use our commercial solar savings calculator to model capex, annual saving and AIA-adjusted payback for a 100 kW array in under a minute.

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.

Named-brand spec options for a 100 kW array

The four panel families below all appear regularly in UK commercial quotes in 2026. Module count assumes a 100 kW DC array; indicative cost-per-kW is the all-in turnkey figure that module choice tends to land at, not the module list price alone. Any of these panels pairs with any of the four inverter platforms — Sungrow, Solis, SMA and Fronius — that we commission across commercial sites.

Sungrow and Solis dominate the value-engineered three-phase commercial bracket; SMA and Fronius sit at the premium end with longer in-territory warranty support and tighter monitoring. The panel and inverter pairing you choose moves the per-kW figure within the £850–£1,100 band — there is no single "right" choice, only the right trade-off between upfront cost, monitoring depth and warranty terms for your hold period.

Annual generation: ~92,000 kWh in the UK

Every scenario on this page uses one yield assumption: 920 kWh/kWp, giving 92,000 kWh/year from a 100 kW array (P50, central estimate). That is the UK average for a well-orientated commercial array, and it is deliberately the figure we model rather than a best case. Regional spread around it: 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. An unshaded south-facing 30-degree pitched roof in the south sits at the top of that spread, approaching 1,000 kWh/kWp; flat-roof east-west arrays sit 5–10% below the 920 kWh/kWp central figure. If your site is southern and south-facing, treat every payback on this page as slightly conservative. 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: £19,000-£25,000

Year-one savings on a 100 kW system depend on annual generation (92,000 kWh at our standard 920 kWh/kWp), the self-consumption ratio (typically 70–85% for a site with extended daytime operations), and the gap between the import tariff and the SEG export rate. The export rate matters more than most cost guides admit: Octopus Outgoing Fixed has paid 12p/kWh since 1 March 2026, double the 6p smart-export floor that older guides still quote. On a 100 kW array exporting ~23,000 kWh a year, that difference alone is worth roughly £1,400/year and takes about four months off the payback.

At a representative 2026 import tariff of 24p/kWh and the 12p/kWh Octopus Outgoing Fixed export rate, a 75% self-consumption ratio delivers: 69,000 kWh self-consumed at 24p = £16,560 avoided import; 23,000 kWh exported at 12p = £2,760 SEG income. Total year-one savings: £19,320 — the standard scenario used everywhere on this page. The realistic spread across commercial sites:

• Low end (~£18,800): 70% self-consumption, 24p import — 64,400 kWh × 24p = £15,456 plus 27,600 kWh × 12p = £3,312.
• Standard (£19,320): 75% self-consumption, 24p import — the scenario above.
• High end (~£25,100): 85% self-consumption, 30p import — 78,200 kWh × 30p = £23,460 plus 13,800 kWh × 12p = £1,656.

So the honest band is £19,000–£25,000/year. Note which way the export rate cuts: a site with lower self-consumption exports more, and at 12p that exported unit is now worth half an imported one rather than a quarter — which is why the low-end scenario is no longer the disaster it looked like under 6p assumptions. Model your own ratio and tariff with the commercial solar savings calculator.

High self-consumption scenario: £24,000-£26,000/year

The savings climb when a site consumes most of its own generation rather than exporting it. Take the same 100 kW array generating 92,000 kWh/year (920 kWh/kWp), but on a site with strong, sustained daytime demand — a food production unit running chillers, or a two-shift warehouse — achieving an 85% self-consumption ratio against a 30p/kWh import tariff and the 12p/kWh Octopus Outgoing Fixed export rate:

• Self-consumed: 78,200 kWh × 30p = £23,460 avoided import.
• Exported: 13,800 kWh × 12p = £1,656 SEG income.
• Total year-one saving: £25,116 — and that rises every year as grid prices inflate.

Sites that pair the array with a battery, or that simply have heavier midday loads, land in the £24,000–£26,000/year band (80% self-consumption at 30p gives £24,288; a battery lifting self-consumption to 90% gives £25,944). Against a £95,000 turnkey capex that is a simple gross payback of 3.7–3.9 years, or 2.7–2.9 years once AIA relief cuts net capex to £71,250. Note this is a high-tariff scenario — it beats the 3.7-year headline precisely because the import tariff is 30p rather than 24p. Model your own self-consumption ratio and tariff with the commercial solar savings calculator before committing to a system size.

6 factors that change your 100 kW price

Two 100 kW systems on two different sites can be £25,000 apart. These are the six variables that move a quote within — and occasionally beyond — the £85,000–£110,000 band:

1. Roof access & height. Single-storey steel-portal roofs with easy edge access are cheapest; multi-storey, fragile, or restricted-access roofs add scaffolding, mast climbers and labour days.
2. DNO / network reinforcement. The single biggest swing factor. A clean G99 connection is a £1,500 application; a constrained network requiring a transformer or feeder upgrade can add £15,000–£30,000+.
3. Three-phase supply upgrade. Sites without an adequate three-phase supply need a service upgrade before a 100 kW inverter bank can connect — a material added cost and lead time.
4. Mounting type. Pitched-roof rail mounting is the baseline; flat-roof ballasted systems, penetrative fixings on membrane roofs, or ground-mount frames each carry different material and labour costs.
5. Module & inverter choice. Premium panels and SMA/Fronius inverters sit at the top of the per-kW band; value-engineered tier-1 modules with Sungrow/Solis sit at the bottom.
6. Switchgear distance. The cable run from the array to the main switchboard drives DC/AC cabling, containment and voltage-drop mitigation costs — a distribution centre with the board 120 m from the array costs more than one with the board beneath the array.

Worked example: 100 kW manufacturing facility in Leeds

Illustrative worked example — a representative project shape, not a named customer. 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. This example uses the standard scenario exactly, so its figures match the Quick answer above. Capex: £95,000 turnkey (£950/kW). Generation: 92,000 kWh/year (920 kWh/kWp, P50). Self-consumption: 75% (69,000 kWh self-consumed, 23,000 kWh exported). Year-one savings: 69,000 × 24p = £16,560 avoided import + 23,000 × 12p = £2,760 SEG = £19,320. AIA relief: £95,000 × 25% = £23,750 year-one corporation tax saving. Net effective capex: £71,250. Simple payback: £95,000 ÷ £19,320 = 4.9 years gross; £71,250 ÷ £19,320 = 3.7 years net of AIA. 25-year NPV at 7% (4% bill inflation, 0.5%/yr degradation): present value of savings £322,000 less £71,250 net capex = £251,000. IRR: 24.3% on gross capex, 31.5% on net-of-AIA capex. 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).

Sector worked examples: warehouse vs food production

The same 100 kW system performs very differently depending on the demand profile underneath it. These two illustrative sector scenarios show how self-consumption and import tariff drive the return. Both use the same 92,000 kWh generation (920 kWh/kWp) and the same 12p/kWh Octopus Outgoing Fixed export rate — only the demand profile, tariff and capex change.

The gap is driven by the demand profile and the tariff, not the hardware: the food-production site's round-the-clock refrigeration baseload self-consumes more solar at a higher import tariff, which is why its payback beats the warehouse despite £3,000 more capex. Every kWh self-consumed at 30p is worth 2.5× the same kWh exported at 12p — that ratio, not the panel spec, is what moves your payback. Run your own demand profile through the savings calculator to see where your site lands.

G99 grid connection: 6-18 months

A 100 kW system needs a full G99 application. The thresholds, precisely: G98 connect-and-notify covers installations up to 16 A per phase — roughly 11 kW on a three-phase supply — where you install first and notify the DNO afterwards. Type-tested equipment up to 17 kW per phase (around 50 kW three-phase) qualifies for the streamlined G99 fast-track. A 100 kW array is comfortably above both, so the full G99 route applies and the application must be approved before you install. The full G99 process is materially more involved: 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 application guide.

Finance comparison: cash, lease, asset finance, PPA

Four financing routes work for 100 kW commercial PV. All four use the standard scenario: £95,000 turnkey capex, £19,320 year-one savings (92,000 kWh at 75% self-consumption, 24p import, 12p export), 4% bill inflation, 0.5%/yr degradation, 7% discount rate, 25-year asset life. On that basis the present value of 25 years of savings is £322,000, and each route's NPV is that £322,000 less the present value of everything you pay under it.

Route	Year-one cash	25-yr NPV @ 7%	IRR	Best for
Cash + AIA	-£71,250 (net of £23,750 tax relief)	£251,000	24.3% gross capex / 31.5% net of AIA	Profitable Ltd Co with capex headroom
Asset finance (7y)	£0 capex; £15,200/yr finance vs £19,320 savings = +£4,120	£240,000	n/a (zero capex)	Cash-flow priority, want ownership end-of-term
Operating lease (10y)	£0 capex; £12,500/yr lease vs £19,320 savings = +£6,820	£234,000	n/a	Off-balance-sheet, IFRS 16 small-lease
PPA (15y)	£0 capex; PPA price 18p/kWh vs grid 24p = £4,140 saving on 69,000 kWh self-consumed	£69,000	n/a	No corporation tax, planning to relocate

Two caveats on that table, stated rather than buried. The asset-finance row does not credit AIA, even though hire-purchase agreements generally do qualify — claim it and that route closes most of the gap to cash. The lease and PPA rows assume the benefit continues across the full 25-year horizon at market terms after the initial term ends; if it does not, both NPVs fall materially. Under a PPA you also forgo the export income entirely, which costs more now that export pays 12p rather than 6p.

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. One point most cost guides get wrong: solar PV is a special-rate asset, so it does not qualify for Full Expensing. AIA is the route, and at £95,000 a 100 kW system sits far inside the £1m cap so the distinction costs you nothing here. It only bites if total qualifying spend in the year exceeds £1m — above that cap the route for solar is the 50% First-Year Allowance, not Full Expensing. 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.