Commercial Solar Panel Survey: What's Involved

A commercial solar survey is not a salesperson with a tablet. It is a one-day inspection by a structurally trained, electrically qualified engineer who produces a five-document deliverable: structural assessment, electrical assessment, shading analysis, PVSyst yield model and fixed-price proposal. After the survey there are no provisional sums and no unknowns — what you sign is what you pay. This page lays out the desk feasibility step that comes before any survey, the on-site assessment scope, the asbestos and capacity screens we run, the typical cost (£600-£1,500, refunded against contract) and the realistic five-to-ten working day turnaround on the survey report.

Two stages: desk feasibility (free) and on-site survey (paid)

We split the survey into two distinct stages because most projects can be sensibly priced and screened without a site visit. Stage one — desk feasibility is free and takes 3-5 working days. Stage two — on-site survey is paid (£600-£1,500 typical) and only happens after the indicative quote is accepted in principle. This sequencing means the customer gets enough information to make a yes-or-no decision before any cash is committed.

Stage 1: Desk feasibility (free, 3-5 working days)

The desk feasibility stage takes three inputs from you: 12 months of half-hourly consumption data (HH data), roof drawings or recent satellite imagery showing usable area, and your MPAN (Meter Point Administration Number). All three are normally available within minutes from your supplier and your facilities team.

From those three inputs we model: usable roof area against shading constraints, indicative array size, indicative annual generation in kWh, percentage offset against your consumption profile (your HH data tells us when you actually use power, which dictates how much of the generation can be self-consumed versus exported), indicative capex band based on system size, indicative payback in years against your current p/kWh import rate, DNO region and any obvious capacity constraints (we cross-check your postcode against the DNO heat maps from UK Power Networks, NGED, Northern Powergrid, SSEN, SP Energy Networks, NIE Networks). The output is a written indicative quote — typically 4-6 pages — sent to you within 5 working days.

Critically, the desk feasibility flags any obvious show-stoppers. A pre-2000 industrial building flags asbestos screening as a high probability. A red-zone DNO postcode flags potential network reinforcement charges. A single-phase supply flags the per-phase G98 / G99 constraint that almost certainly forces a three-phase upgrade. Surfacing these at desk stage protects the customer from spending £1,000+ on an on-site survey for a project that has a structural reason not to proceed.

Stage 2: On-site survey (£600-£1,500, one day)

The on-site survey takes one day for most single-building commercial sites and produces five distinct assessments. We attend with one engineer covering structural and electrical scope, two engineers on complex sites with HV connections.

Structural assessment

The structural engineer establishes whether the roof can take the additional load — typically 12-18 kg/m2 for the panel and mounting system, plus wind uplift forces calculated to BS EN 1991-1-4. The assessment covers: roof type identification (standing-seam metal, profiled steel, flat membrane, trapezoidal corrugated, tile, asbestos cement sheeting), sheeting condition (corrosion, fixings, sheet thickness), purlin spacing and condition, age of building and original design loadings if available (Building Control records, structural calculations from the original construction), evidence of any previous strengthening or modifications, signs of water ingress or roof failure.

For modern profiled steel and standing-seam metal roofs (typical for buildings built after 2000), the structural assessment is usually a quick confirmation that the design margin is sufficient. For older buildings, fragile cement sheeting, or anything with corrosion, the engineer specifies the strengthening or replacement works needed. The structural assessment is the primary input to the mounting system selection — see our solar mounting systems page for how mounting type matches roof type.

Electrical assessment

The electrical assessment establishes the existing supply infrastructure and the route by which the new generation will tie in. It covers: meter type and MPAN, available supply capacity (ASC) on the MPAN, single-phase or three-phase, voltage and current rating of the main switchgear, condition of the existing distribution boards, available space for the new inverter and AC switchgear, route from inverter location to point of connection, earthing arrangement (TN-S, TN-C-S, TT), age and condition of the existing wiring.

Critically, the electrical assessment confirms whether the proposed array size fits inside the G98 connect-and-notify regime (under 17 kW per phase, under 100 kW total) or triggers a G99 application (above either threshold). For a project on the boundary the engineer sometimes recommends downsizing to stay within G98 to avoid the longer G99 timeline — a strategic call we make against the financial impact of the smaller array. See G98 application and G99 application for the detail.

Shading analysis

Shading is modelled with two complementary tools. A Solmetric SunEye (a fish-eye lens device that measures sun path obstructions at every point on a roof) gives precise shading data at sample points across the array. Drone photogrammetry covers the full roof footprint and any external shading sources — chimneys, plant rooms, neighbouring buildings, trees, electrical pylons. The shading model is fed into PVSyst to produce a per-string, per-month generation profile. Where shading is significant, we recommend module-level optimisation (SolarEdge optimisers, Tigo TS4) so a shaded module does not drag the whole string down.

Asbestos check (pre-2000 buildings)

Any building built before 2000 is checked for asbestos cement sheeting on the roof. Identification can usually be made visually by an experienced surveyor (corrugated cement sheets with characteristic profile and weathering pattern) and confirmed by sample if there is any doubt. Where asbestos is confirmed, the project either proceeds with full sheet replacement before solar install (typical £15-£60 per square metre, plus disposal — adds 4-8 weeks to programme) or with non-penetrating mounting systems and specialised drilling protocols agreed with an HSE-licensed contractor. We never proceed without a written method statement.

Roof access for crane and scaffolding

The survey also checks the practical access for installation: where can the scaffolding go, can a MEWP (mobile elevating work platform) reach the roof edges, is there space for a crane to lift inverters and panels, where do the scaffold or MEWP delivery lorries park, what hours can we work, are there neighbouring building constraints (overshadowing, oversailing). All of this feeds into the install programme and the install cost.

The five-document survey deliverable

Within 5-10 working days of the site visit you receive a survey pack containing:

• Structural assessment report — load capacity, condition, recommended works, mounting system specification.
• Electrical assessment report — existing supply summary, point of connection, G98 or G99 routing, three-phase upgrade requirement (if any).
• PVSyst yield model — monthly generation in kWh, performance ratio (typically 78-82% for UK commercial), self-consumption ratio against your HH data, financial projection at 4-15p SEG and your import tariff.
• Fixed-price proposal — every line item priced, no provisional sums. Includes panels, inverters, mounting, cabling, switchgear, scaffolding, commissioning, DNO fees and our project management. Valid 90 days.
• Project programme — Gantt chart showing weeks from contract to energisation.

Survey cost and what it buys

The survey fee covers the engineer's time, travel, drone equipment hire where used, and the report generation. Typical 2026 fees: £600-£900 for under 100 kW projects, £900-£1,500 for 100-500 kW, £1,500+ for 500 kW and above or multi-building sites. The fee is normally refunded against the contract price if you proceed inside 90 days — so the effective cost on a signed project is zero. If you decide not to proceed, the survey reports are yours to keep and use as a baseline for any other quote you obtain.

What changes after the survey

The shift from indicative quote to fixed-price proposal is the primary value of the survey. At indicative-quote stage the price has a margin for unknown structural and electrical risk. At survey stage that risk is resolved, the engineer has confirmed every assumption, and the price is locked. Routinely the fixed price comes in lower than the indicative — because at desk stage we tend to over-allow for risk that survey then disproves. Sometimes it comes in higher — typically because asbestos or structural strengthening has been confirmed. Either way the customer is making a decision against fully-quantified information rather than a finger-in-the-air estimate.

When a survey is not necessary

For very small projects (under 30 kW, single-phase, simple modern building, no asbestos risk, healthy DNO postcode) the desk feasibility alone is sometimes sufficient and we can move directly to fixed-price quote without a paid survey. This is the exception not the rule — and we always confirm in writing where we are skipping the on-site stage.

Useful authority links

The HSE governs asbestos handling and remediation: HSE asbestos guidance. MCS competency standards apply to installer accreditation: mcscertified.com. UK Power Networks' network capacity heat map is at ukpowernetworks.co.uk; equivalent maps exist for every DNO.

Related decision pages

For the broader project programme see commercial solar installation timeline. For mounting decisions driven by survey output see solar mounting systems. For the post-install operating phase see solar panel commissioning and commercial solar maintenance contract. For DNO routing decisions see G98 application and G99 application. For sector-specific surveys see factories, warehouses, cold storage, offices. The full hub is commercial solar PV. To start with a quote, head to request a quote.