Solar Car Park Feasibility Study: What to Expect

What a solar car park feasibility study includes

A full solar car park feasibility study covers seven workstreams: (1) site measurement and shading analysis; (2) structural assessment of the ground and existing infrastructure; (3) DNO grid capacity check; (4) planning risk assessment; (5) PV yield modelling (hourly, 25-year); (6) financial modelling (capex, opex, NPV, IRR, payback); (7) carbon and MEES compliance benefit quantification. A credible study takes 2–3 weeks and costs £1,500–£4,000 depending on site complexity. Many specialists (including us) absorb the feasibility cost in the project if instructed to proceed.

Site assessment — what the surveyor measures

The surveyor visits site to record: car park dimensions and orientation (satellite imagery alone misses overhangs, columns, height restrictions); shading obstacles (trees, buildings, lighting columns) plotted against solar path; ground condition indicators (cracking, made-ground evidence, drainage gradients); DNO meter and switchgear position (relevant for AC export cabling route); existing services (manholes, telecoms ducting, fuel interceptors in column footprint zones); and access constraints for construction (clearance for 60-tonne crane, temporary fencing zones). If roof integration is also in scope, the surveyor assesses roof load capacity and access points.

Irradiance and yield modelling

Yield modelling uses hourly irradiance data from Solargis or PVGIS for the specific lat/long at 10-arc-second resolution, combined with the surveyor's shading model and the chosen panel tilt/orientation. Output: a P50 (median expected) and P90 (conservative, 90% probability of exceeding) yield figure in kWh/year for year 1 and degradation-adjusted year 10 and year 25 figures. Bifacial rear-face gains are modelled separately at the site-specific albedo value (tarmac: 0.10–0.15; concrete: 0.20–0.30). The yield model is the single most important input to the financial model — challenge any study that uses a generic 'UK average' rather than site-specific hourly data.

Financial modelling: capex, savings, payback, NPV

The financial model should output: (1) total capex (turnkey including planning, design, structure, panels, inverters, installation, MCS certification); (2) opex (O&M, monitoring, insurance, inverter replacement reserve); (3) annual generation savings (kWh × tariff, escalated at 4–6% per year); (4) DNO export revenue if export is metered; (5) OZEV WCS grant recovery; (6) AIA corporation tax saving in year 1 (25% × eligible capex); (7) PSDS grant if applicable; (8) simple payback in years; (9) net present value (NPV) at a corporate discount rate of 8–12%; (10) internal rate of return (IRR) for comparison with alternative capital uses. Insist on sensitivity tables: payback under ±20% electricity price scenarios and ±10% capex variance.

Planning risk assessment in the feasibility report

The planning risk section should assess: Local Development Plan policies relevant to the site (most UK LDPs now have explicit renewable energy policies); listed building or conservation area constraints; ecology screening (bat roosts above car park, great crested newt on adjacent greenfield); archaeological potential (brownfield sites in sensitive areas); visual impact on neighbouring receptors; noise and glare during construction; and likely planning conditions (landscaping, lighting colour temperature, EV charger numbers). The output should be a RAG-rated planning risk score with a recommended submission strategy (householder vs full, EIA requirement, pre-application consultation advisability).

What to do with your feasibility study report

Use the feasibility report to: build the internal business case (the NPV and IRR slides translate directly into capital committee or board approval documents); shortlist installers (share the yield and capex assumptions and ask installers to price against them — this benchmarks their numbers accurately); negotiate PSDS or Salix funding applications (feasibility outputs are required attachments in most grant submissions); instruct a planning consultant if the risk assessment flags medium/high planning risk; and brief your energy consultant on the tariff and export assumptions (incorrect tariff escalation assumptions are the most common feasibility modelling error we see). A well-structured feasibility report is worth ten times its cost in clarity and time saved in subsequent project stages.