How to Quote and Run a Commercial Solar PV Installation

What you will learn

• How to use half-hourly meter data and a roof survey to size a commercial solar system accurately before quoting.
• How to build a three-tier quote that captures equipment, labour, and compliance costs as project line items.
• What triggers a G99 DNO application, what documents it requires, and how long approval realistically takes.
• How CDM 2015 applies to commercial solar and what documentation you must have in place before work starts on-site.
• The on-site installation sequence from mounting system to AC connection and fire service labelling.
• How to complete commissioning, issue the MCS certificate, and compile the full project handover pack.

Commercial solar PV is a high-value, multi-stage project type that rewards careful upfront work. A 50kW rooftop array for a warehouse can take 8 to 12 weeks from site survey to commissioning, involves a mandatory G99 application to the Distribution Network Operator (DNO) for most systems, requires structural calculations under Building Regulations, and falls under CDM 2015 as construction work. For the MCS-certified installer managing it, the gap between a well-run job and an expensive one is almost always documentation and sequencing - not the panels themselves. This guide covers the full process from initial feasibility to handover.

Start with Feasibility, Not a Panel Count

The most common quoting error in commercial solar is sizing the system before understanding the site. A customer will often arrive with a roof area in mind and expect a panel count and a price. Starting there leads to mis-sized systems and, worse, quotes that do not reflect what the project actually involves.

Good feasibility work takes two inputs: the site itself and the customer's consumption data.

1. Obtain at least 12 months of half-hourly (HH) meter data from the customer. This is the actual electricity consumption profile for the building - essential for sizing a system that maximises self-consumption and quantifies the financial case accurately.
2. Carry out a roof survey to assess available area, orientation, shading, tilt angle, roof type, and load-bearing condition. Photograph all mounting points and identify any asbestos, fragile roof panels, or access constraints.
3. Check planning status. Most commercial rooftop solar qualifies as permitted development under Class J of the Town and Country Planning (General Permitted Development) (England) Order 2015, with no upper generation limit following the removal of the previous 1MW cap in November 2023. Permitted development does not apply to listed buildings, conservation areas, or National Parks. If the building is protected, factor an 8-week planning application and approximately £234 in application fees into the programme.
4. Identify the local DNO and check grid capacity. For systems with an inverter output above 3.68kW per phase - which covers the majority of commercial installations - a G99 application is required before work begins. Establish this at feasibility stage so it can be built into the project timeline.

How to Build a Quote That Reflects Real Project Costs

A commercial solar quote has more moving parts than a residential one. The key cost components are: panels and inverters, mounting system, DC and AC cabling and protection, generation and export metering, G99 application administration, structural calculations, building control notification, scaffolding or rope-access, and commissioning. Each must be scoped and priced from the outset.

UK commercial solar PV typically costs between £0.75 and £1.05 per watt installed in 2026, depending on system complexity, roof access, and structural requirements. On a 50kW system, that puts the installed cost in the range of £37,500 to £52,500 before any structural reinforcement or battery storage additions.

Structure the quote around three tiers of cost:

Tier 1 - Equipment: Panels (kWp capacity), inverters, mounting system, and DC protection. These are supplier-priced items with defined lead times. Get written supplier prices and confirm availability before quoting - panel lead times and inverter stock can shift significantly between quote and order.

Tier 2 - Labour and access: Installation crew days, scaffolding or rope-access hire, electrical commissioning time, and any sub-contractor trades such as roofing repairs or electrical reinforcement. Commercial installations of 50 to 100kW typically require between 2 and 5 days on-site for the installation itself.

Tier 3 - Compliance costs: Structural calculations, DNO application administration, building control fees, electrical installation certificate, MCS design sign-off, and CDM documentation. These are frequently underquoted by installers who treat them as overhead rather than project line items. They are not overhead - they are deliverables with direct cost.

Managing the G99 Application and DNO Approval

The G99 application is the most commonly underestimated stage in a commercial solar project. Any system with an inverter output exceeding 3.68kW per phase - approximately 11kW on a three-phase connection - requires pre-approval from the local DNO before installation begins. Installing before G99 approval is a breach of grid connection standards and can result in the system being disconnected.

The application must include a single-line diagram (SLD) showing the full electrical design: array capacity in kWp, string count, inverter make and model with rated AC output, DC and AC isolators, protection relay identification, export limiting device if applicable, generation meter, and connection to the DNO network. Each DNO publishes its own application form - do not use one DNO's form for another region's application.

The DNO has up to 65 working days to assess a G99 application. In practice, most straightforward applications in unconstrained grid areas complete within 4 to 12 weeks. In areas with congested networks, approvals can take 3 to 6 months. Submit as early in the sales process as possible - ideally before the customer formally accepts the quote, so the DNO clock is already running.

1. Prepare the full G99 application pack: single-line diagram, system specification, MCS contractor certification details, and the relevant DNO's application form.
2. Submit to the DNO and record the application reference number. Note the submission date and calculate the 65-working-day deadline.
3. Chase the DNO at 30 working days if no acknowledgement has been received. Applications frequently stall on initial review due to missing or incomplete documents.
4. On approval, receive and file the DNO connection agreement. This document must be in place before any on-site work begins.

Where local grid constraints prevent export, a G100 zero-export limitation device allows the project to proceed by capping export to the grid at zero. The system can still operate at full capacity for on-site self-consumption and battery charging - and it avoids the G99 approval queue entirely for sites where grid export is not a priority.

Running the Installation: CDM, Procurement, and On-Site Sequence

Once G99 approval is in hand and the quote is accepted, the project enters the planning and procurement phase. Set a written programme from day one, with named milestones: purchase orders placed, G99 received (if not already), scaffolding erected, installation start, electrical connection complete, commissioning, and building control sign-off.

CDM 2015 applies to all commercial solar installations as construction work. The project must have a named principal designer and a named principal contractor. For larger installations, notify the HSE using an F10 form before work begins on-site. Prepare a construction phase plan covering working-at-height risk, roof access, and emergency procedures. These are legal requirements - not optional.

Equipment procurement: Place purchase orders on panels and inverters as soon as the quote is accepted. Lead times on commercial-grade inverters can run to 4 to 8 weeks. Waiting until the week before installation to order is one of the most common causes of commercial solar project delays and the direct cause of margin loss when programmes slip.

On-site installation sequence:

1. Erect scaffolding or arrange rope-access. Establish a roof exclusion zone and conduct a pre-start safety briefing.
2. Install the mounting system. For flat roofs, ballasted non-penetrating systems preserve the waterproof membrane. For pitched roofs, bracket and rail systems anchor to the rafters through the roof covering.
3. Install panels and connect strings. Verify string voltages before connecting to the inverter.
4. Run and terminate DC cabling. Install DC isolators, surge protection, and the inverter.
5. Run AC cabling from the inverter to the distribution board. Install the generation meter, export meter, and G99-compliant protection relay.
6. Complete all required labelling: DC isolators, AC isolators, generation meter, and fire service emergency shutdown signage at roof level and at the inverter.

Commissioning, MCS Certificate, and Handover

Commissioning is not simply switching the inverter on. It is the formal process that validates system performance, confirms compliance, and produces the documentation the customer needs to register for the Smart Export Guarantee (SEG) and access asset finance.

1. Commission the inverter using the manufacturer's commissioning tool. Record string voltages and currents, inverter output power, and the generation meter opening reading.
2. Complete electrical testing to IEC 62446. This includes insulation resistance testing on DC strings, open-circuit voltage and short-circuit current measurements per string, earth continuity, and polarity verification. Record all results.
3. Submit the Stage 2 G99 notification to the DNO confirming the system has been commissioned in accordance with the approved design.
4. Complete and sign the Electrical Installation Certificate (EIC) to BS 7671 18th Edition, referencing the G99 application number and confirming compliance with Part 7, Section 712.
5. Issue the MCS installation certificate. This is the document the customer requires for SEG registration, most asset finance agreements, and the majority of commercial insurance policies. It cannot be issued retroactively if commissioning is not completed correctly.
6. Compile the full project handover pack: MCS certificate, EIC, DNO connection agreement and Stage 2 notification, inverter commissioning report, structural calculations, O&M manual, monitoring system credentials, and building control sign-off.

Running Commercial Solar Projects in Zigaflow

A commercial solar PV project crosses multiple stages - feasibility, quote, G99 application, procurement, installation, and commissioning - with purchase orders across several equipment suppliers and often sub-contractor coordination alongside. Zigaflow's jobs and project tracking features let you manage the full lifecycle from a single project record. Attach the G99 application, structural calculations, and commissioning documentation directly to the job. Raise purchase orders for panels and inverters against the project record. Track stage payments - typically a deposit on quote acceptance, a progress payment at installation start, and a final invoice on MCS certificate issue. The project view gives a single point of visibility across every stage, so compliance documents, supplier orders, and customer invoices all connect to the same job record throughout the 8-to-12-week delivery window.

Delivering Every Stage, Every Time

Commercial solar PV projects are high-value and involve more compliance than most residential installers expect when they first move into the commercial market. The projects that run profitably share two characteristics: the installer invested real time in feasibility and consumption analysis before pricing, and they treated G99 applications, CDM documentation, and MCS certification as project deliverables with deadlines - not as background paperwork. The 8-to-12-week project lifecycle is predictable and manageable when the G99 is submitted early and equipment is ordered the moment the quote is accepted. Compress either of those steps and the project will compress your margin along with it.

• What Are the Commercial Solar Panel Regulations in the UK?Solar4Good · accessed 2026-07-03
• Commercial Solar PV Compliance UK 2026Commercial Solar Panels Installation · accessed 2026-07-03
• How Long Does Solar Installation Take? (2026 UK Timelines)Synergy PV Renewables · accessed 2026-07-03

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