Commercial solar feasibility study

What a feasibility study is for

A commercial solar feasibility study is the piece of work that turns "we have a big roof and high bills" into a decision you can take to a board, a landlord or a finance provider. It should tell you how big a system the site can take, how much electricity it will generate, how much of that you will use, what it will save, what it will cost and what could get in the way.

A good study is honest about the negatives. Some roofs are too old, some supplies are too small, some buildings use most of their power at night. Finding that out before you commit is the whole point. A study that only ever says yes is a sales brochure, not a feasibility study.

It also sits at the front of a sequence. The study tells you whether to proceed, the roof survey and structural survey confirm the building can carry the system, the G99 application secures the grid connection, and only then does an installer finalise the design and price.

Desktop assessment versus on-site survey

Feasibility work usually starts at a desk and ends on the roof. Both stages have a place, and it helps to know what each can and cannot tell you.

A desktop check is quick and cheap to produce, but it is only as good as the assumptions behind it. If it has not looked at your actual consumption, the savings figure is a guess. The on-site or virtual stage is where most of the real risks are found.

What goes into the study

Your energy use

The single biggest driver of payback is how much of the generated electricity you use on site rather than export. That depends on when you use power, not just how much. Annual totals from bills give a starting point; half-hourly data shows the shape of your demand through the day, the week and the year. Our page on energy data analysis explains what the study looks for.

The roof or land

Usable area, orientation, pitch, shading, covering type, age and condition all affect how many panels fit and how well they perform. A typical UK rooftop array produces roughly 800 to 1,050 kWh per kWp per year, higher in southern England and lower in northern England and Scotland. East-west layouts on flat roofs produce less per kWp but fit more panels, which can mean more generation overall. If the roof is unsuitable, the study should look at alternatives such as ground-mounted arrays or solar carports.

The electrical supply and grid

The study needs to know your supply capacity, the rating of the main switchboard, where panels would connect and whether the local network can accept the output. Anything above the small G98 limit needs approval from your Distribution Network Operator under G99, and the answer can shape the whole project.

The outputs you should expect

A useful feasibility study gives you these, in plain numbers with the assumptions written down:

1. Proposed system size in kWp, with a draft layout showing which roof areas are used and why others are excluded.
2. Yield model: expected annual generation in kWh, ideally month by month, with the orientation, pitch, shading and degradation assumptions stated.
3. Self-consumption and export split: how much of the generation you are expected to use on site, based on your demand profile.
4. Savings: the value of on-site use at your own unit rate, plus export income where a Smart Export Guarantee tariff or other export arrangement applies.
5. Indicative cost and payback: an installed cost range, a simple payback period and, where useful, a longer-term view over the panel warranty period.
6. Grid position: whether G98 or G99 applies, whether export limitation is likely to be needed, and any known network constraints.
7. Risks and unknowns: roof condition, structural questions, asbestos, planning, landlord consent, long cable runs, access costs.
8. Next steps: what has to happen, in what order, before a firm quote can be given.

If any of those are missing, ask why. The commercial solar survey checklist is a useful prompt list.

A worked example (illustrative)

Take a 100 kWp rooftop system at an illustrative £900 per kWp, so about £90,000 excluding VAT. At 900 kWh per kWp it generates about 90,000 kWh a year. If 80% is used on site at an illustrative 24p per kWh, that saves about £17,280. The other 20% exported at an illustrative 5p per kWh brings in about £900. That is roughly £18,180 a year before maintenance, giving a simple payback of about 5 years before any tax relief.

Change one assumption and the answer moves. If the building is empty at weekends and only 55% is used on site, the annual benefit drops noticeably and the payback stretches. That is why a study built on your real consumption is worth far more than one built on averages. Our solar payback guide walks through the sensitivities, and the commercial solar cost page explains what moves the price per kWp.

Risks a good study flags early

• A roof near the end of its life. Panels last 25 to 30 years. If the covering needs replacing in ten, it is usually cheaper to re-roof first than to lift and refit the array later.
• Structural capacity. Older portal frames and lightweight purlins may not have spare capacity for the added load.
• Asbestos. Fibre cement roofs on older buildings often contain asbestos, and the duty to manage asbestos means a survey is usually needed before any work.
• Grid constraints. A network that cannot take your export may mean an export limit, a smaller system or a reinforcement cost.
• Ownership and consent. Tenants need landlord consent, and lease length matters for payback.
• Planning. Most non-domestic rooftop solar in England falls under permitted development, but listed buildings, conservation areas and some flat roof arrangements need checking.

How the free survey covers feasibility

When you request a survey, we review your enquiry and call you to understand the site. If it looks suitable, we arrange a free survey with one MCS certified installer matched to the site, either in person or virtually. Your details go to that one installer only. The installer's surveyor looks at the roof, the electrical intake and your consumption, and produces a proposal that should cover the outputs listed above. There is no obligation to proceed, and you can use the findings to compare other options. You can read more on what the survey includes.

What to have ready

• Twelve months of electricity bills, or half-hourly data if you have it
• The MPAN from your bill and your agreed supply capacity if you are on a half-hourly contract
• Any roof drawings, the age of the roof and details of past repairs
• Whether you own the building or lease it, and the remaining lease term
• Any asbestos register for the premises

If you are ready to start, use the form below to request a free survey.