300kW Commercial Solar Systems for UK Businesses

A 300 kW commercial solar install operates at properly industrial scale. Per-kW economics are strong (we typically quote £750-£950 per kW at this scale), procurement leverage on tier-1 panels and inverters is meaningful, and the project supports a full multi-disciplinary delivery team including dedicated structural engineering, witness testing arrangements with the DNO, and a multi-inverter string topology configured for redundancy and fault tolerance. Capex sits comfortably within a single year's AIA headroom for limited companies (£255k against the £1m cap), and the £63,750 of year-one tax relief at the 25% main rate is a decisive component of the IRR calculation.

The 300 kW band is what we recommend for factories with 2-3 shift production, large warehouses (10,000-15,000 sqm), multi-building campuses (school estates, university satellite sites, hospital trust sites, business parks), and food and beverage processing facilities. The common thread: 1,800+ sqm of roof (often spread across multiple buildings), three-phase HV-supplied transformer or 1,200 A+ LV supply, a daytime baseload comfortably above 80 kW, and either substantial corporation tax exposure (let AIA work) or willingness to consider PPA structures (where corporation tax position is limited).

What 300kW looks like physically

A 300 kW system in 2026 uses approximately 555 tier-1 monocrystalline panels at 540-550 Wp each (Trina Vertex, JA Solar Deep Blue, Longi Hi-MO 6 or equivalent). With higher-output 600 Wp modules the count drops to around 500. You need approximately 1,800 sqm of usable, well-oriented roof area free of significant shading. Where a single building does not have 1,800 sqm of usable roof we frequently split the array across two or three roofs on the same site — electrically straightforward at this scale because we run multiple inverters per array and combine on a single AC bus before the point of connection. Total array weight on a flat roof, including ballasted mounting, comes in around 18-22 kg per square metre — substantial enough that we always engage a chartered structural engineer at survey stage and frequently commission full structural calculations, particularly on industrial roofs where as-built drawings may be unreliable. The electrical infrastructure is substantial: typically 4-6 commercial-grade three-phase string inverters (50-100 kW each — Sungrow SG-CX, Solis-S6, Huawei SUN2000-100KTL or SMA Tripower CORE) configured for redundancy, a galvanised-steel mounting system, an MCS-compliant DC and AC switchgear assembly with arc-fault and surge protection on every string, a dedicated PV consumer unit interface with kWh metering for SEG export, half-hourly monitoring with sub-string data, full G99 connection paperwork, and a chartered structural engineer's sign-off plus electrical sign-off witnessed by the DNO.

Cost breakdown for a 300kW install in 2026

Turnkey 2026 pricing for a properly specified 300 kW system runs £225,000-£285,000 plus VAT, working out at roughly £750-£950 per kW. The price band includes 555 tier-1 panels at trade pricing, a multi-inverter string topology for redundancy (typically 4-6 inverters split across the array), an MCS-spec mounting system, all DC and AC cabling (typically 600-900 metres of DC cable plus 150-280 metres of AC cable sized for sub-2% voltage drop end-to-end), surge protection, fire-safe DC isolators on every string, a dedicated PV consumer unit interface with kWh export metering and CT clamps for power quality monitoring, half-hourly monitoring with a dedicated cloud portal, scaffolding and access equipment (typically MEWPs at this scale), structural sign-off, electrical sign-off, full G99 connection paperwork including Type Test certificates and witness testing arrangements with the DNO, 12 months of post-commissioning support, and 24-month performance warranty against modelled yield. We typically engage an O&M provider for ongoing performance monitoring and predictive maintenance from year one — at this scale the cost of an outage is meaningful and proactive monitoring pays back rapidly.

Where a 300 kW project goes over budget tends to be one of four known knowns: an asbestos-cement industrial roof needing licensed removal (£28,000-£75,000 at 1,800 sqm), three-phase headroom upgrade or HV transformer upgrade (£15,000-£60,000 to the DNO), DNO reinforcement charges where local network is constrained (£0-£120,000 depending on area), or roof reinforcement where structural condition cannot carry array weight (£18,000-£70,000). We identify these at survey stage and quote them clearly. We do not bury them in vague site-prep entries.

On AIA: 100% Annual Investment Allowance covers the full capex up to the £1m annual cap. A £255,000 install reduces a profitable limited company's corporation tax bill by £63,750 in year one (at the 25% main rate). That drops the effective net cost to roughly £191,250 before counting energy savings. The Land Remediation Tax Relief recovers an additional 50% of any asbestos-removal element through corporation tax — at 1,800 sqm of asbestos remediation that can return £18,000-£40,000 of additional relief. We coordinate with your accountant on the year-one tax computation and frequently structure the project to maximise AIA stacking against other capex in the same year.

Generation and savings

A typical UK 300 kW system generates 270,000-282,000 kWh in year one. We model this in PVSyst with site-specific Meteonorm 8.2 irradiation data, panel temperature derating, inverter clipping where relevant, and shading losses derived from Lidar-resolution 3D modelling. Self-consumption drives the project economics. A 300 kW system on a multi-shift factory, food processing facility with continuous chiller load, or refrigerated logistics site typically achieves 85-92% self-consumption — exceptional rates that drive payback below 5 years. On a single-shift business, school estate or office portfolio, self-consumption drops to 65-75%. The difference between 75% and 90% on a 300 kW system is roughly £14,500 of additional annual benefit.

At 80% self-consumption with a 24p/kWh blended import price, a 300 kW system avoids around £53,000 of grid energy purchases per year. The remaining 55,000 kWh exports to grid at the SEG rate. At a blended 6p/kWh SEG rate that adds £3,300 of export income, taking total year-one benefit to around £58,000-£72,000. Simple payback on £255,000 capex (or £191,250 net of AIA) lands at 5-5.5 years. 25-year IRR is 15-19% and 25-year NPV at a 7% discount rate is approximately £930k-£1.2m. At this scale we frequently model a second-stage battery storage option — typically 100-200 kWh of LiFePO4 storage configured for self-consumption maximisation and tariff arbitrage — which can lift IRR by a further 1-2 percentage points where the load profile suits it.

DNO grid connection — G99 with substantial DNO study

At 300 kW, full ENA G99 process applies and the DNO will typically require a Connection Application study before issuing an offer letter. Standard DNO turnaround for the offer letter in 2026 runs 9-18 months on uncongested networks, sometimes longer in constrained areas (parts of London, the Midlands and the south-east). The application costs £2,000-£6,000 to file. Around 40% of 300 kW G99 applications get a standard offer with no reinforcement charge; the remainder face contributions ranging from £15,000 to £120,000+ for transformer, switchgear, cable or substation upgrades. Our process: file the G99 application within two weeks of contract signature, run design and procurement in parallel with DNO process, time delivery to site for the week the connection offer is accepted. If reinforcement comes back high we have several options: re-engineer for export limiting, drop nameplate to fit within the local network capacity, opt for self-consumption-only configurations with battery integration to capture the unconsumed generation, or in extreme cases re-route the project to a different metering point on the same site or split across two metering points. We do not commit major capex until the connection offer is formally accepted.

Best-fit sectors for the 300kW band

From our 2025 install book, the 300 kW band overweighted across five sub-verticals. Factories with 2-3 shift production (food processing, drinks production, packaging, light manufacturing, plastics) — high self-consumption rates because production load is well-matched to PV curve. Large warehouses (10,000-15,000 sqm) running general distribution, ambient or temperature-controlled storage with material handling and refrigeration. Multi-building campuses (school estates with 3-5 buildings, university satellite sites, hospital trust sites consolidating PV across estate, business parks). Food and beverage processing where chiller load drives exceptional self-consumption rates often above 90%. Refrigerated logistics and cold storage where PV generation maps almost perfectly to refrigeration baseload. These map cleanly to our coverage of industrial-scale sectors.

Worked example: a Midlands food processing facility, 12,500 sqm production hall and ambient warehouse, 24/7 operation across three shifts, three-phase 1,500 kVA HV-supplied transformer, 2,100 sqm of usable flat membrane roof, 1,180,000 kWh annual consumption with 100 kW continuous baseload (refrigeration plant, lighting, packaging line, compressors). Quoted £258,500 plus VAT for 299.7 kW (555 x 540 Wp Trina Vertex, 6 x Sungrow SG50CX inverters, K2 ballasted east-west mounting at 10 degrees split across two roof areas). Modelled year-one yield 277,500 kWh. Self-consumption modelled at 91% (continuous refrigeration and process load fits PV curve almost perfectly), so 252,500 kWh avoid the grid at 25p/kWh blended (£63,125 saved) and 25,000 kWh export at 6p/kWh SEG (£1,500). Total year-one benefit £64,625. AIA tax relief £64,625. Simple payback 4.0 years, 25-year IRR 21.4%.

Financing a 300kW system

All three financing routes are commercially viable at 300 kW. Cash plus AIA delivers the strongest IRR for any limited company with corporation tax exposure — the £63,750 year-one tax relief shortens payback by around 18 months versus a finance route. Asset finance over 5-7 years (around £4,100-£4,950 per month over six years on £255k capex, with rates improving meaningfully at this scale because risk profile is better) is the route many of our 300 kW customers choose where they prefer to preserve working capital — the monthly finance payment is consistently substantially lower than the monthly bill saving, project is cash-flow positive from month one. Hire purchase preserves AIA; an operating lease forfeits it. PPA structures are highly competitive at 300 kW. A 15-year fixed-rate PPA at 12-15% below current grid retail with end-of-term ownership transfer is straightforward to arrange, and PPA is often the right answer for organisations with limited corporation tax position (charities, schools, multi-tenant industrial estates, low-margin operations, sites loss-making for AIA purposes). PPA also handles tenancy questions cleanly. Where corporation tax exposure is strong, cash with AIA almost always wins on IRR; where it is limited, PPA frequently does. We model all three routes in your finance options assessment, and our grants and funding guide covers any sector-specific schemes that apply.

Next steps

If you want to know whether a 300 kW system makes sense for your specific business, the fastest route is a free desk-based feasibility against your half-hourly meter data — turnaround is five working days for the desk pass, plus a site survey for fixed-price proposal. Request a quote with your address. For broader cost benchmarking across system sizes see our cost guide, browse all our services, or compare adjacent sizes — step down to 200 kW or step up to industrial-scale 1 MW. Common questions are covered on our FAQs page. For policy detail see Ofgem's market guidance on the SEG and grid connection process, and gov.uk's AIA guidance.