Commercial Solar Installation Process

What to Expect: Commercial Solar Installation from Start to Finish

Commercial solar installation is a coordinated process involving surveyors, electrical engineers, structural engineers, DNO representatives and local planning authorities. When it runs well, a business goes from first enquiry to generating its own electricity in 10–14 weeks. Understanding each stage helps you plan around it, avoid delays and hold your installer to account.

This guide covers every step of the process — from desktop feasibility through to SEG registration and long-term monitoring — based on how MCS-certified commercial installers work across England, Scotland and Wales.

Stage 1: Initial Enquiry and Desktop Feasibility

Every commercial solar project begins with a desktop review. Your installer will look at satellite imagery of your roof, check your grid connection capacity on the DNO's public map, review your electricity bills, and produce an indicative system size, cost range and financial model within 24–48 hours.

At this stage, the key questions are: Is your roof structurally suitable? Is there grid capacity to connect your proposed system? Does the financial case stack up given your consumption profile? For most commercial premises, the answer to all three is yes — but identifying exceptions early saves everyone's time.

• ✓Roof/ground area: minimum 200 m² for a commercially viable system
• ✓Roof age: if less than 10 years remain on roof life, re-roof before solar installation
• ✓Orientation: south-facing is ideal; east–west splits work well; north-facing is not viable
• ✓Grid capacity: DNO map check confirms available export headroom without reinforcement
• ✓Consumption profile: daytime electricity use above 50% maximises self-consumption ROI

Stage 2: Full Site Survey

The site survey is the most critical pre-installation step. A structural engineer assesses your roof's load-bearing capacity and fixing options. The lead electrician reviews your main distribution board, available three-phase capacity and meter location. A shading analysis — using tools like Solargis or on-site measurements — confirms there are no significant obstructions that would reduce generation.

For flat-roofed industrial buildings, the surveyor will specify mounting type — ballasted frames (no roof penetration) or mechanically fixed rail systems — based on roof membrane type, parapet height and local wind load data. For pitched roofs, rafter spacing and tile type determine fixing method.

Stage 3: System Design and Proposal

After the survey, your installer's design team produces a full system design: panel layout diagram, string configuration, inverter selection, single-line electrical diagram, generation estimate and 25-year financial model. This is the document you use to compare quotes and make your investment decision.

Key design elements to check on your proposal:

• ✓Panel brand and specification — tier-1 manufacturers (JA Solar, LONGi, REC, Jinko) carry stronger warranties
• ✓Inverter type — string inverters (lower cost) vs. microinverters/optimisers (better performance under partial shading)
• ✓Performance ratio — should be 78–82% for a well-designed UK commercial system
• ✓Generation estimate — verify against PVGIS online tool using your postcode and system orientation
• ✓DNO connection route — G98 (self-notification for systems up to 50 kW) or G99 (formal application above 50 kW)
• ✓Financial model assumptions — electricity rate, export rate, annual degradation, inflation rate

Stage 4: Planning Permission

The majority of commercial solar installations in England and Wales qualify as permitted development under Class A or Class J of the Town and Country Planning (General Permitted Development) Order. However, permitted development rights are removed for: listed buildings, buildings in conservation areas, sites subject to Article 4 directions, and ground-mounted systems above certain sizes.

In Scotland, the rules differ slightly under the equivalent Scottish planning framework. Your installer will confirm permitted development status in writing before proceeding. Where planning permission is required, expect 8–12 weeks for determination. Pre-application discussions with the local planning authority can significantly reduce this.

Stage 5: DNO Application — G98 and G99 Explained

Connecting a solar system to the grid requires notification or formal application to your local Distribution Network Operator (DNO). The process depends on system size:

For G99 applications, your installer submits a Protection and Control Requirements document, single-line diagram, site plan, and technical specifications. The DNO may require specific protection relay settings (ROCOF, vector shift, over/under-voltage and frequency) before approving connection. Your installer handles this entire process.

Stage 6: Equipment Procurement

Once planning is confirmed (if required) and G99 approval is received, your installer orders equipment. Lead times for tier-1 solar panels and commercial string inverters are typically 2–4 weeks from UK distributors. Mounting systems and switchgear are usually available within 1–2 weeks.

Your installer will schedule delivery to coincide with scaffolding erection and installation start. For large systems (100 kWp+), deliveries are typically staged to avoid large quantities of equipment sitting on site.

Stage 7: On-Site Installation

On-site installation typically takes 3–10 days for systems between 30–200 kWp, depending on roof access complexity, wiring routes and inverter configuration. The installation crew follows a structured sequence:

Stage 8: Commissioning and MCS Certification

Commissioning is performed by a qualified electrical engineer — typically the lead installation engineer or an independent commissioning specialist for large systems. The commissioning process confirms the system is safe, correctly configured and generating at expected levels.

Commissioning checks include: inverter protection relay settings (ROCOF, vector shift, over/under-voltage, over/under-frequency), anti-islanding function test, earth fault monitoring, insulation resistance of all DC circuits, and comparison of measured output against expected generation using real-time irradiance data.

On completion, your installer issues:

• ✓MCS certificate — required for SEG registration and proof of quality installation
• ✓Electrical Installation Certificate (EIC) — BS 7671 compliance document
• ✓DNO commissioning notification — confirms the system has been correctly connected
• ✓Operation and maintenance manual — system overview, fault codes, emergency procedures
• ✓Monitoring platform credentials — access to real-time generation data

Stage 9: SEG Registration and Export Income

The Smart Export Guarantee (SEG) requires Ofgem-licensed energy suppliers with 150,000+ customers to pay for surplus electricity exported to the grid. Registration requires your MCS certificate, an export meter reading and your MPAN (Meter Point Administration Number).

Current SEG tariffs (2025/26) vary by supplier:

Post-Installation: Monitoring and Maintenance

Modern commercial solar systems include remote monitoring via cloud platforms (SolarEdge, SMA Sunny Portal, Growatt ShineServer, Solis Cloud). Your O&M dashboard shows real-time generation, string-level performance data, and fault alerts. Most systems require minimal maintenance — typically an annual inspection and cleaning cycle.

Annual O&M contracts for commercial systems range from £500 for 50 kWp to £3,500 for 500 kWp+. They typically include: annual panel cleaning, inverter health check, thermal imaging scan (identifies failing cells and poor connections), performance report vs. predicted generation, and 4-hour on-site response SLA for faults.

Frequently Asked Questions