Commercial solar panel installation

A commercial solar panel installation is a structural, electrical and regulatory project, not just a roof job. The difference between an install that out-performs its model for 25 years and one that disappoints is in the engineering: a proper half-hourly load model so the system is sized to genuine on-site demand, a structural survey to confirm the roof can carry it, a clean G99 grid connection, and — on a let building — a lease structure that puts the value where it belongs. We handle all of it as a single fixed-price programme.

As a commercial solar panels specialist we install across every building type, from a 50 kWp owner-occupied unit to a multi-megawatt portfolio. What follows is exactly how an installation runs.

What a complete installation includes

Our fixed-price installations are whole-job, not panels-only. Every proposal covers the structural survey, electrical design, panels, mounting and inverters, the G99 grid connection and DNO liaison, scaffolding and access, commissioning and monitoring, and the full handover pack. Where the roof membrane has under 15 years of life left, we will tell you and recommend combining the install with a re-roof in one project rather than paying to strip and refit later — a call most installers never make.

Accredited commercial installers

We hold every certification a UK commercial solar installer should: MCS commercial certification (the basis for Smart Export Guarantee eligibility), NICEIC approved-contractor registration, RECC membership and TrustMark licensing, with ISO 9001, 14001 and 45001 for quality, environment and health and safety. Workmanship is covered by a 10-year insurance-backed warranty, and we share the PVSyst yield model behind every proposal so any third party can check our numbers. Read more about how we work.

Installation on let and leveraged buildings

If your building is let, an installation is also a lease exercise. We coordinate tenant access and notice under the alterations clause, sequence any mortgagee and insurer consent, and address the structural and roof-lifecycle position up front — the detail covered in our owner\'s due-diligence guide. If you would rather commit no capital, a third-party-funded roof lease delivers the same install at zero capex.

What to look for in a commercial solar installer

The gap between a good commercial installer and a domestic outfit taking on its first warehouse roof is wide, and it shows up years later in yield, insurance and warranty claims rather than on install day. For an asset you intend to hold, let or sell, the installer's competence is part of the fabric of the building. Vet it the way you would vet a roofing or M and E contractor, not a supplier of panels.

Start with certification, but read it properly. MCS matters, but the relevant scope is MCS certification for larger systems, not domestic-only registration; ask to see the certificate and the kW ceiling on it. The installing electrician should hold NICEIC (or equivalent, such as NAPIT) approved-contractor status for commercial work. RECC or TrustMark registration adds a consumer-code and dispute layer. None of these individually proves competence on a 300 kWp G99-connected array, so treat them as the entry ticket rather than the decision.

Then look at the things that actually protect the return:

• An IWA (insurance-backed) warranty that survives the installer going out of business. Manufacturer product warranties on tier-1 panels run 25 to 30 years and inverter warranties 10 to 15, but the workmanship warranty is only as good as the company standing behind it, or the insurer standing behind the company.
• A PVSyst yield file, not a headline kWh figure. A serious proposal includes the PVSyst (or equivalent) simulation showing shading losses, soiling, temperature derating and the modelled annual yield around the 950 kWh per kWp UK benchmark. If the number is rounded and unsupported, the whole payback case is unsupported.
• Half-hourly consumption modelling. Self-consumption is the single largest driver of return, so the installer should size the array against your actual half-hourly data, not a rule of thumb. Ask how they arrived at the self-consumption percentage in the proposal and how battery storage would move it.
• Commercial references you can visit, on comparable roofs and comparable sizes, with named clients and dates. Ask what went wrong on those jobs and how it was resolved.

Cross-check the proposal against our cost benchmarks and run your own numbers through the commercial solar calculator before you accept a quote. When you are ready to compare like for like, request a quote that includes the yield file and the DNO position.

The structural and electrical detail

Two disciplines decide whether a commercial installation is safe and insurable: structure and grid. Both need resolving before contracts, not discovered on scaffold.

Structural loading survey. A qualified structural engineer must assess the roof to BS EN 1991 (the Eurocode covering imposed, wind and snow loads) and confirm it can carry the additional dead load of the array plus wind uplift. This is a precondition, not a formality. Older industrial roofs, purlin spacing and existing membrane condition all feed into whether the array can go ahead, be reduced, or needs strengthening. Align the install with the roof's remaining lifecycle: putting a 25-year array on a roof with eight years left is a false economy, because removing and refitting to replace the membrane later can cost as much as the strengthening you skipped.

Ballasted versus fixed. On flat commercial and industrial roofs the array is usually ballasted, held down by weighted trays rather than roof penetrations, which preserves the membrane warranty and avoids new water-ingress paths. Ballast adds load, which loops back to the structural survey. On pitched metal roofs the array is typically fixed with non-penetrative clamps to the standing seam or with sealed fixings. The choice is driven by roof type, wind zone and the membrane warranty conditions, and it should be stated explicitly in the design.

G99 and the DNO. For any array above roughly 50 kW, connection is governed by G99 and needs a formal application to the Distribution Network Operator; smaller systems fall under the lighter G98 route. This is the real programme bottleneck, not the panels. The DNO reviews local network capacity and issues a connection offer, and standard timescales for a G99 offer commonly run several weeks to a few months, longer where reinforcement or export limitation is involved. Apply early, and understand that the offer may cap export or require an export-limitation device. Our guide to planning and grid connection sets out the steps in full.

Commissioning to BS EN 62446. The install is not finished when the last panel is clamped. Commissioning and the handover documentation should follow BS EN 62446, which covers the test regime, string measurements, insulation resistance and the information pack the system owner is entitled to receive. That pack, together with the O and M schedule, is what a buyer's surveyor or a future tenant will ask for, so it forms part of the building's documented value. Where battery storage is added, commissioning also covers the storage system and its interaction with the DNO connection.

Installation on let and occupied buildings

Fitting solar to an empty building is a construction job. Fitting it to a let or trading building is a tenant-relations job with a construction job inside it, and the difference is mostly about access, notice and disruption.

Access and notice. Where a tenant is in occupation under a lease, the landlord's right to enter to carry out works is governed by the lease terms, and the roof may or may not be within the demise. Establish who controls the roof and what notice is required before you plan anything. On a multi-let building this is more involved, because the array often sits on common parts and the benefit and the notice obligations run to several tenants at once. Where the tenant pays the bills under an FRI lease, the split-incentive question also has to be solved commercially before works start; our split-incentive guide covers the routes.

Minimal disruption. The vast majority of a rooftop install happens on the roof, away from the tenant's operations, and can be sequenced around trading hours. Scaffold or a roof hoist, material staging and welfare need a footprint, so agree those locations with the occupier early. Deliveries and crane lifts can usually be booked for early mornings or a weekend to avoid the tenant's peak activity.

Connection outage scheduling. The one point where the tenant will feel the work is the electrical tie-in. Connecting the array to the incoming supply, and any DNO metering change, needs a planned power outage, typically a short window that must be booked with the occupier in writing and, where relevant, coordinated with the DNO. On a building that cannot lose power in trading hours, this is scheduled overnight or on a closed day. Getting this one date agreed early tends to determine the whole programme.

Before committing, work through our owners' due-diligence guide so lease, roof ownership, insurance and access questions are all closed off before the installer mobilises.

Timelines by system size

The figures below are indicative and assume the structural survey is clear and the DNO offer is not held up by network reinforcement. The DNO application usually runs in parallel with design and procurement, so it rarely adds to the on-site time, but it can gate the start date. Grid and planning, not the roof, are the usual causes of delay.

Read the ranges as guidance, not a promise. A clean roof with spare grid capacity moves quickly; an older roof needing strengthening, or a constrained network needing reinforcement, can push the front end out considerably. The way to protect your programme is to start the structural survey and the DNO application first, and to fix the tenant outage window early, rather than treating them as the last items on the list.