Commercial Solar Installation Process UK 2026

The UK commercial solar installation process is a 10-stage sequential pipeline taking 10-64 weeks total depending on system size and DNO connection complexity. This page walks through every stage with deliverables, durations, costs, and decision points — so UK business owners and finance directors know exactly what to expect and when to make commitment decisions. For elapsed-time detail see installation timeline; for end-to-end buyer guidance see commercial solar buyer\'s guide.

The complete 10-stage commercial solar installation process

Stage 1: Desk feasibility (5 working days, free)

The process starts with a free desk-based feasibility. You submit basic project information (postcode, building type, annual electricity spend, roof drawings if available). Within 1 working day we acknowledge and confirm any additional information needed. Within 5 working days we deliver the desk feasibility report covering: PVSyst yield model with P50/P90 estimates, indicative capex range with itemised cost breakdown, AIA-adjusted net effective cost calculated against your corporation tax position, 4-route finance comparison (cash + AIA, asset finance, operating lease, PPA), DNO constraints check via ENA Connections portal, and sector-specific load profile modelling. The feasibility is generic enough for any qualified installer to deliver. You make a go/no-go decision based on this output. Approximately 60% of desk feasibilities proceed to Stage 2; 40% don\'t (either economics don\'t pencil or timing changes) — either way, zero cost to you.

Stage 2: Site survey (2-4 hours, free for sub-100 kW)

Once you approve the desk feasibility we schedule a site survey within 7 working days. The survey takes 2-4 hours on site and covers: full roof inspection (mounting points, condition, asbestos status, structural capacity), electrical survey (switchgear capacity, supply phase configuration, metering, earthing), shading assessment with Solmetric SunEye or equivalent equipment, drone roof scan if useful, structural engineer\'s review if structural concerns flagged in desk feasibility. Site survey is free for sub-100 kW SME projects; for 100+ kW projects we charge £400-£1,200 site survey fee (fully refundable against the project if you proceed with us; payable if you decide not to proceed). The fee covers structural engineer time, drone survey, and senior installer time on site.

Stage 3: Fixed-price quote (10 working days)

Within 10 working days of the site survey we deliver the fixed-price quote. The quote document is typically 12-25 pages and includes: 12-item itemised cost breakdown (modules, inverters, mounting, DC + AC cabling, switchgear, scaffolding, DNO fees, MCS certification, structural sign-off, commissioning, PM, contingency), updated PVSyst yield model with site-specific shading and inverter clipping factored in, updated 4-metric DCF (simple payback, discounted payback, IRR, 25-year NPV), finance route comparison with named lender + indicative monthly payment if asset finance route preferred, project timeline week-by-week from contract to commissioning, named project manager + named site supervisor + named commissioning engineer, insurance certificates (£5m+ public liability + £5m+ professional indemnity), and reference list with 3-5 similar-scale UK installs contactable directly. Quotes are fixed-price, valid 30 days, with milestone payment terms (30/30/30/10).

Stage 4: Contract signature (same day, 30% deposit)

Once you decide to proceed, contract signature happens within 1 working day. The contract documents include: signed quote + scope of works + technical specification, milestone payment schedule (typically 30% on contract / 30% on materials delivery / 30% on installation completion / 10% retention to commissioning + 30-day defects period), defined timeline with named PM + site supervisor + commissioning engineer + escalation contact, change-order pricing schedule (rates per type of change), insurance certificates, warranties (manufacturer module + inverter + installer workmanship), and IPAF + PASMA + MCS + NICEIC accreditation evidence. Don\'t accept "as required" change-order pricing — change orders should be priced against agreed rate card. Retainage at 10% held until 30 days post-commissioning.

Stage 5: DNO application (4-8 weeks G98 or 16-24 weeks G99)

DNO grid connection application begins immediately after contract signature. G98 (sub-70 kW per phase, typically sub-100 kW systems): "Connect and Notify" process — install first, notify DNO afterward within 28 days. Application fee £350-£500. DNO acknowledgement typically 4-8 weeks. See G98 process. G99 (above 70 kW per phase, typically 100+ kW systems): formal approval required BEFORE installation. Application package includes grid form, single-line diagram, protection settings, inverter datasheets, load profile. DNO assessment 12 weeks for first response, 16-24 weeks for connection offer. Application fee £1,500-£35,000+ depending on reinforcement requirements. See G99 process. For sites at risk of expensive reinforcement, G100 export limitation can keep the system fully self-consuming and bypass reinforcement.

Stage 6: Procurement (4-12 weeks supply lead)

Materials procurement runs in parallel with DNO application. Lead times vary by brand and quantity: Tier-1 modules (JinkoSolar, Longi, Trina, JA Solar, REC) — typically 4-8 weeks supply lead in 2026 for commercial-volume orders. String inverters (Sungrow, SMA, Solis, Fronius) — 4-6 weeks. Central inverters (Sungrow SG250HX, SMA Sunny Tripower CORE2, Huawei SUN2000-HC) — 8-12 weeks. Mounting systems (K2 Systems, Schletter, Esdec, S-5!) — 2-4 weeks. Switchgear and metering — 4-8 weeks. The 30% materials-delivery payment milestone triggers at the start of procurement. Materials are delivered to a secure compound near site (often the installer\'s yard) until installation week.

Stage 7: Scaffolding + site prep (1-3 days)

Scaffolding erection happens 1-2 weeks before installation start. For commercial buildings: IPAF + PASMA-certified scaffolding companies erect edge-protected scaffolding around the install area. Tower scaffolds for pitched roofs; cherry-picker access for industrial flat roofs; mobile elevating work platforms (MEWPs) for ground-floor commercial. Typically 1 day for sub-100 kW projects, 3+ days for 500 kW+ industrial scale. Materials delivered to site at the same time. Site induction conducted for all install crew + scaffolding team. CDM (Construction Design Management) regulations comply for any project where install duration exceeds 5 days.

Stage 8: Panel installation (2-15 days depending on size)

On-site installation is the most visible stage but typically the shortest in elapsed time. Sub-50 kW SME: 1-2 days install. 50-100 kW: 2-4 days. 100-250 kW: 4-7 days. 250-500 kW: 7-12 days. 500 kW+: 10-20 days. The install sequence: (a) mounting system attached to roof — clip-fix to standing seam, through-fix to purlins, or ballasted blocks for flat roofs; (b) modules mounted and inter-connected with DC cabling; (c) DC cabling routed to inverter location; (d) inverter mounted (plant room or wall-mount near main panel); (e) AC cabling from inverter to main electrical panel; (f) generation meter and DNO interface metering installed. Throughout install your operations continue normally — no power-down until Stage 9 commissioning.

Stage 9: Electrical commissioning (1-3 days)

Electrical commissioning is the critical sign-off stage. Sequence: (1) DC string testing — IV curve measurement, insulation resistance, polarity check on every string. (2) AC commissioning — voltage, frequency, phase rotation, anti-islanding test. (3) Inverter parameter setup — country code (UK), grid code (G98 or G99), protection settings (under-voltage, over-voltage, under-frequency, over-frequency, vector shift, ROCOF). All settings signed off by commissioning engineer. (4) Generation meter setup — verified accuracy, registered with SEG provider. (5) Planned power-down — typically 2-4 hours scheduled outside trading hours (Tuesday/Wednesday mornings most common). During this window the building loads transfer to a UPS or accept short interruption. We work with your operations team to schedule for minimum disruption.

Stage 10: DNO witness test + handover documentation (1-2 days)

The final stage. For G99 systems, the DNO sends an engineer to witness commissioning + verify protection settings — typically a 2-4 hour formal sign-off process. G98 systems skip this — the install is "notified" to the DNO via paperwork without witness attendance. After witness sign-off, the handover documentation pack is prepared and delivered to you. The pack contains: as-built drawings (single-line diagram, layout, structural), datasheets (modules, inverters, mounting, switchgear), warranties (manufacturer + installer workmanship + insurance-backed policy numbers), commissioning certificates (MCS, NICEIC, IPAF), PVSyst yield model with shading analysis, monitoring system credentials, maintenance manual, end-of-life decommissioning guidance. Don\'t sign off the 10% retention payment until you have the handover pack in hand and have reviewed it. See commissioning detail.

What about post-install operations?

Post-Stage 10, ongoing operations require modest attention. Monitoring: cloud-based dashboard tracks generation in real-time with alerts for underperformance, string failures, inverter offline events. Annual maintenance contract: £1,000-£2,500/year covering visual inspection, electrical test, performance monitoring, inverter health check. Skip the maintenance contract and you typically lose installer workmanship warranty. Cleaning: annual cleaning recommended for urban or coastal sites; every 2-3 years for rural sites. £500-£2,500 depending on access. Year 12-15 inverter replacement: the one major maintenance event during 25-year system life. £15-25k for typical 100 kW string inverter replacement. SEG payment management: SEG provider statements show export income; verify meter readings flow correctly. See maintenance contracts + monitoring options.

Decision points throughout the process

You make 4 separate go/no-go decisions across the process. Decision 1 (after Stage 1 desk feasibility): do the headline economics work for our business? ~60% proceed. Decision 2 (after Stage 3 fixed quote): is the specific commercial proposition acceptable? ~85% proceed at this point. Decision 3 (during Stage 5 DNO process): if reinforcement risk emerges, do we accept the additional cost or pivot to G100 export limitation? ~5% projects face this decision. Decision 4 (at Stage 10 handover): are we satisfied to sign off the 10% retention and close the project? ~98% sign off without issue. Throughout the process you have a named project manager as your single point of contact — escalation routes defined upfront in the contract.

What can go wrong in the commercial solar installation process

Honest assessment of the 5 most common issues that can surface during a UK commercial solar installation. (1) DNO reinforcement triggers (G99 only): 25-40% probability on constrained networks. Adds £20k-£100k+ cost + 8-16 weeks timeline. Mitigation: G100 export limitation often bypasses reinforcement entirely. (2) Asbestos discovery (pre-2000 buildings): Asbestos cement roofing surfacing during structural survey. Requires re-roof first (£40-£100/sqm). Increasingly identified at Stage 2 site survey rather than during installation. (3) Structural sign-off required (older buildings): Structural engineer\'s assessment reveals roof can\'t accept full system load. May require lightweight mounting (aluminium not steel) or reduced system size. £600-£1,500 structural fee. (4) Supply lead delays: Module or inverter lead times occasionally extend (Chinese New Year factory shutdowns, Suez Canal disruptions historically). Add 4-8 weeks contingency. (5) Permission denials: Listed Building Consent or conservation area refusals on visible roof elevations. ~15% refusal rate on heritage sites. Mitigation: pre-application planning consultation.

Recommended next step

If you\'re ready to start the commercial solar installation process for your UK business, the right first step is Stage 1 — submit our quote form for a free desk-based feasibility within 5 working days. No upfront cost, no obligation. From there, the process unfolds at your pace with clear go/no-go decision points before any commitment. Most UK SME projects complete the full 10-stage process in 10-16 weeks; mid-market 100-500 kW projects in 24-36 weeks; industrial 500 kW+ projects in 36-64 weeks.