What Does a Commercial Solar Feasibility Study Include?

A commercial solar feasibility study is a technical and economic assessment that establishes whether a specific installation can be built at a specific site, under what conditions, at what cost and with what return. A credible study covers five areas: the physical site, the electrical infrastructure, the energy analysis, the regulatory route and the financial case. It states its assumptions, identifies what remains unresolved, and reaches a conclusion that a business can act on.

What separates it from a sales proposal is not length or presentation. It is that the calculations are reproducible, the exclusions are stated, and the conclusion can be negative.

This article sets out what should be inside one, what the written report should contain, and how to tell a feasibility study from a quotation with a cover page.

Three levels of assessment

These are frequently conflated, and each answers a different question.

A screening exercise can be done in an afternoon and is genuinely useful for triage across a portfolio of sites. It cannot support a capital decision, because it has not established that the roof can carry the array or that the connection can accept the output.

A feasibility study supports the decision. The engineering design implements it. Problems arise when a screening is presented as a feasibility study, or when a business is asked to commit capital on the strength of one.

What a feasibility study is not

Real Decreto 244/2019 does not impose a general national requirement for a document carrying that generic name before a self-consumption installation proceeds. That said, equivalent technical and economic evidence is frequently required in practice: grant programmes commonly ask for a technical report and a justification of the investment, regional procedures may call for supporting documentation of their own, public and corporate procurement exercises often specify one, and lenders and funders typically require a study before committing finance. The absence of a national mandate is not the same as the absence of a requirement for your particular project.

This matters because the documentation that is required for permitting and legalisation is a separate set of deliverables. Depending on the installation, that can include an electrical project signed by a qualified technician, installation certificates, structural justification, health and safety documentation, and the submissions required by the municipality, the autonomous community and the distribution company. A feasibility study does not replace any of these, and a study that presents itself as satisfying a permitting requirement is describing something it is not.

The relationship runs the other way. A good feasibility study establishes which of those documents will be needed, who produces them, and what they are likely to cost and take.

Information the business must provide

A study is only as good as its inputs, and most of the important ones come from the business rather than from the site visit.

Electricity data. The CUPS reference for every relevant supply point, twelve months of bills, and the access tariff and contracted capacity in each period. Bills establish what the business pays. They do not establish when it consumes.

Interval consumption data. Obtained through Datadis using the CUPS, or through the distributor's own portal, or by authorising the assessor to retrieve it. The curve available may be hourly or quarter-hourly depending on the meter, the supply and the distributor's records, and the depth of history varies by supply point. Whatever is obtained, the study should state its resolution, its date range and any gaps.

Operating pattern. Working hours, shift arrangements, weekend and holiday operation, seasonal variation and any annual shutdown. A three-week August closure changes the answer and will not be visible from a roof.

Future loads. Fleet charging, heat pumps, additional process equipment, expansion or contraction. These belong in the model where they rest on committed plans with dates and specifications, and should be modelled separately where they do not.

Drawings. Site plans, roof plans, sections and, where available, the original construction documentation. Roof construction type and approximate age.

Ownership or lease position. Whether the business owns the building, and if not, the remaining lease term, the landlord's position and any restrictions on alterations. A twenty-five year asset on a four-year lease is a different proposition.

Existing electrical documentation. Single-line diagrams, switchboard schedules, transformer details, the most recent inspection certificates and any records of previous electrical work.

Where any of this is unavailable, the study should say so and state what was assumed in its place.

The site assessment

The site visit establishes what is physically possible, and it produces findings rather than impressions. It is normally a non-intrusive visual inspection unless testing, sampling or opening-up work has been included in the agreed scope, which should be settled before the visit rather than after it.

Usable area. Not total roof area. Deductions apply for perimeter and edge zones, separation between arrays, rooflights and smoke vents, existing plant and its maintenance access, walkways, and areas permanently shaded.

Orientation and shading. The roof's azimuth and pitch, and every near-shading source: roof plant, parapets, adjacent buildings, chimneys, trees, neighbouring structures. Near shading is site-specific and is not captured by modelled horizon data.

Roof condition and remaining service life. The membrane, sheeting, fixings, flashings and drainage. Where the roof has substantially less remaining life than the proposed installation, the study should say so plainly and price the consequence.

Structural capacity. Whether the structure can carry the additional dead load, wind uplift and any ballast, taking account of the existing loading and the building's design basis.

Rooflights, plant and access routes. Locations, dimensions and any that must remain clear or accessible.

Fire and maintenance access. Routes, separation distances and any requirements arising from the building's fire strategy or from the applicable technical building code provisions.

Asbestos-containing materials. Fibre cement sheeting in older Spanish industrial buildings may contain asbestos. Where its presence is suspected, this determines whether a conventional fixing approach is available at all. Where work may expose workers to asbestos, Real Decreto 396/2006 requires a work plan to be prepared and approved by the competent labour authority before work begins, subject to the regulation's scope and exceptions.

Working at height and construction access. Vehicle access, hardstanding, crane or lifting positions, scaffolding or mobile platform requirements, delivery routes and any operational restrictions on when work can proceed.

The limits of visual inspection

This is the section that most distinguishes a serious study from a confident one.

At preliminary feasibility stage, a site visit is normally a non-intrusive visual inspection by a competent person unless testing or opening-up work is included in the agreed scope. It is not a structural calculation, an asbestos survey, a geotechnical investigation or an intrusive examination of a roof build-up. A feasibility report should state explicitly which of these remain outstanding, and it should not present a visual impression as a structural conclusion.

Specifically, the report should record whether a structural engineer's assessment is still required and on what basis, whether an asbestos survey by a qualified surveyor is needed before any fixing work, whether ground investigation is required for a ground-mounted or carport option, and whether any part of the roof needs opening up to confirm its construction.

A study that says "the roof appears adequate" has not assessed the roof. A study that says "the roof appears adequate; structural verification by a qualified engineer is required before design, estimated at X and Y weeks, with a risk that reinforcement is needed" has done its job.

The electrical assessment

The electrical infrastructure can limit system size before the roof does, yet this part of a study is sometimes skipped.

Connection voltage. Whether the supply connects at low voltage or medium voltage determines the equipment, the metering, the protection and the procedures. It is a different project in each case.

Transformer and switchboard capacity. The existing transformer rating and loading, the main switchboard's capacity and available ways, and whether generation can be connected without upgrading either.

Proposed connection point. Where the installation ties in, why that point was chosen, and what work is required to make it available.

Protection and metering. The protection required for the proposed configuration, the metering arrangement, and whether existing equipment is suitable or must be replaced.

Cable routes. The physical path from inverters to the connection point, distances, containment requirements and any obstacles. In large industrial buildings this can be a significant cost line and it is regularly omitted from early estimates.

Earthing. The existing earthing arrangement and whether the proposed installation is compatible with it.

Export limitation. Whether the design is with surplus or without surplus, and where an anti-export system is proposed, what equipment and control arrangement it requires.

Distributor constraints. Available capacity at the connection point, any known network limitations, and what the distributor process is likely to involve for the proposed configuration.

Without an existing or survey-derived single-line diagram, the electrical position has not been adequately assessed.

The energy analysis

This is the modelling work that establishes what the system would actually deliver.

The consumption side starts with the interval data, examined for seasonal variation, weekday and weekend patterns, shutdowns, data gaps and any load that runs continuously. Consumption should be allocated across the six tariff periods, since generation displacing P1 energy is worth considerably more than the same generation displacing P6.

The weekend position deserves specific attention. Saturdays, Sundays and national holidays fall entirely within P6 in every season, so for a five-day operation weekend generation arrives when demand is lowest and displaces the cheapest electricity of the week.

The generation side requires modelling for the specific coordinates and roof configuration, using PVGIS or an equivalent tool. The report should record which tool and which version produced the figures, the radiation database selected, the date the model was run, and all inputs including azimuth, tilt, mounting configuration and the system loss assumption. A generation estimate that cannot be reproduced cannot be checked.

The two series are then overlaid, hour by hour, at several system sizes and layouts. For each option the study should report modelled annual generation, electricity self-consumed, surplus exported, energy curtailed where applicable, the self-consumption rate and the solar coverage rate. Those last two move in opposite directions as capacity changes and both should be stated, since a single percentage is ambiguous.

Presenting one system size only means no optimisation has taken place.

The regulatory and planning review

Spanish self-consumption is governed nationally by Real Decreto 244/2019, but the practical route for a specific project depends on the configuration, the capacity, the connection and the location. There is no single national permitting path that applies everywhere.

The review should establish:

Configuration. Whether the installation operates with surplus or without surplus, and the consequences of that choice. Installations without surplus are exempt from grid access and connection permits, which materially affects the programme.

Access and connection requirements. Whether the project falls within an exemption or requires a formal process with the distribution company, and what that is likely to involve.

Autonomous community procedures. Registration and legalisation are administered regionally and the requirements differ between communities. The study should identify the applicable regional route by name rather than describing a generic process.

Municipal planning and works requirements. Licence or prior communication procedures, the construction tax, and any local conditions. These are set by each town hall and must be checked for the specific municipality.

Environmental or land-use constraints. Relevant where a ground-mounted option is under consideration, or where the building or its setting carries any protection.

Capacity above 100 kW. Installations above 100 kW cannot use the simplified compensation mechanism, so surplus must be handled through sale under producer arrangements, through an anti-export configuration or by increasing on-site consumption. The study should state which route it has assumed and what obligations follow.

The output should be a named route with an indicative sequence and duration, not a paragraph saying that permissions will be required.

The financial assessment

The financial section should be reproducible by someone who did not write it.

Installed cost and exclusions. The estimated capital cost, broken down sufficiently to be checked, with an explicit list of what is excluded. Access equipment, structural reinforcement, electrical upgrade work and distributor charges are the items most often left out.

Operating and maintenance costs. An annual allowance appropriate to the site. A coastal hotel, a dusty agricultural building and an urban office roof do not need the same regime.

Inverter replacement. Timing and cost, included within the modelled period.

Degradation. An annual output decline applied to generation, with the rate stated.

Value of self-consumption and exports. Two separate figures, derived from the tariff period analysis and from the applicable surplus arrangement. A single blended price applied to total generation invalidates the result.

Simple payback. Useful as a first filter and insufficient on its own.

NPV and IRR. The measures appropriate to a capital decision, with the discount rate stated and justified against the business's actual cost of capital rather than a convention.

Financing. Where debt is contemplated, the study should distinguish project return from equity return and be explicit about which it is presenting.

VAT, grants and tax treatment. VAT applies at the general rate to commercial installations and is normally recoverable subject to the usual rules, so it is generally a cash-flow matter rather than a cost. Grants should not be deducted from the capital cost before they have been awarded, and any tax treatment assumed should be flagged for confirmation with the business's own advisers.

Scenarios rather than a forecast

A single projection implies a precision that does not exist. The study should present low, central and high cases, varying the inputs that genuinely move the answer: installed cost, self-consumption rate, the value of displaced electricity, the value of surplus and the operating cost.

Electricity prices should be modelled in real terms with sensitivity tested rather than escalated at a compound rate for twenty-five years. Where a case only works under an optimistic price assumption, that should be visible rather than buried.

The spread between the low and high cases is itself information, though it must be read carefully. A narrow spread suggests a robust answer only if the principal uncertainties have actually been included in the scenarios; a narrow spread produced by varying trivial inputs tells you nothing. A wide spread shows that the outcome is sensitive to assumptions which warrant further investigation before capital is committed. In either case, check which inputs were varied and by how much before drawing a conclusion from the range.

The risks and assumptions register

Every unresolved issue in the study belongs in a register, and the register is often the most useful page in the report.

Each entry should record four things: the assumption that has been made, its financial or programme impact if the assumption proves wrong, who is responsible for resolving it, and by when.

A register with no entries is not a sign of a clean project. It is a sign that the study did not look.

What the written report should contain

The exclusions section is the one worth reading first. It tells you what the study is not claiming.

The four possible conclusions

A study that can only reach one conclusion is not an assessment.

Feasible. The project can proceed on the terms described, with the identified return, and the remaining work is design and procurement.

Feasible subject to conditions. The project works provided specified items are resolved. Each condition should be named, with its potential impact and its owner.

Not currently feasible. The physical, electrical, regulatory or financial position does not support the project as considered. The report should say why, and whether anything would change the answer.

Insufficient information to decide. The data needed was not available. The report should state what is missing and how to obtain it, rather than proceeding on assumptions and presenting the result as a conclusion.

Why "subject to structural confirmation" is different

A conditional recommendation and an unconditional one carry different risk, and the distinction is often lost in the executive summary.

"Feasible" means the assessor has established that the project works. "Feasible subject to structural confirmation" means the assessor has established everything except whether the building can carry the installation, and that question could still return an answer requiring reinforcement, a reduced array or, occasionally, abandonment.

Both conclusions can be perfectly appropriate at feasibility stage. Structural verification costs money and it is reasonable to defer it until the rest of the case is established. What is not reasonable is to present a conditional finding as an unconditional one, or to allow a condition to disappear between the body of the report and its summary.

Before approving capital, read the conditions and confirm that each has an owner and a date.

Warning signs

Any of these indicates a document that is doing something other than assessing feasibility.

No site visit. Aerial imagery does not show roof condition, plant, structure, switchboard capacity or access.

Annual bills used without interval data. Bills show totals. The entire question is timing.

Roof capacity assumed. If the report contains no structural discussion and no recommendation for verification, the load-bearing question has been skipped.

No electrical single-line review. The connection is usually the binding constraint and it cannot be assessed from outside the building.

No export or grid assessment. Available capacity at the connection point can cap the project regardless of everything else.

One system size only. A single option means no optimisation was performed, and the size was probably set by the roof or by the supplier's preferred package.

Grants treated as guaranteed. A capital cost with an unawarded grant already deducted describes a project that may not exist.

No sensitivity analysis. A single payback figure implies certainty that the underlying inputs do not support.

No assumptions or exclusions section. Everything was either established or quietly assumed, and the reader cannot tell which.

Produced as a sales proposal. A document whose conclusion could only ever have been "proceed" is a proposal, whatever it is titled.

Independence and conflicts of interest

An installer can produce a thorough, competent feasibility study, and many do. Installers have direct experience of what actually gets built, what distributors accept and what roofs turn out to contain, which an independent consultant without site history may lack.

The point is not that installer studies are unreliable. It is that the commercial incentive is real and should be recognised rather than ignored. An organisation whose revenue depends on the project proceeding has an interest in a positive conclusion and, more subtly, in a larger system.

Two practical safeguards. First, require that the calculations be reproducible: the generation model with its inputs, the consumption overlay, the financial model with its assumptions visible. A study you can check is a study whose incentives matter less. Second, on larger projects, consider paying for an independent study and tendering the construction separately, so that the assessment and the sale are not the same transaction.

Where an installer's study is used, it is reasonable to ask directly whether the study is chargeable, whether it is refundable against a contract, and whether the business owns the output and may share it with other bidders.

What a free study usually covers

Free assessments are common and genuinely useful within their limits.

A free study will typically establish approximate usable roof area from imagery and a short visit, an indicative system size, a modelled generation figure, an estimated saving based on the electricity bill, an indicative price and a headline payback. For a business deciding whether solar is worth investigating at all, that is proportionate.

What it commonly leaves unresolved is the structural position, the presence of asbestos, the switchboard and connection capacity, the interval consumption analysis, the tariff period weighting, the distributor process, the regional and municipal route, sensitivity analysis and the exclusions. Those are exactly the items that determine whether the headline figure survives contact with the project.

The sensible sequence is to use a free assessment for triage and a paid, scoped study for the decision. Treating a free assessment as a feasibility study is where projects acquire their surprises.

Frequently asked questions

What is a commercial solar feasibility study? A technical and economic assessment establishing whether a solar installation can be built at a specific site, at what cost, with what return, and what conditions remain unresolved. It covers the site, the electrical infrastructure, the energy analysis, the regulatory route and the financial case.

Is a feasibility study legally required in Spain? Real Decreto 244/2019 does not impose a general national requirement for a document carrying that generic name. Equivalent technical and economic evidence is often required in practice by grant programmes, regional procedures, procurement exercises and lenders. The technical documentation required for permitting and legalisation is separate, and a feasibility study does not substitute for it.

How does a feasibility study differ from a quotation? A quotation prices a proposed installation. A feasibility study assesses whether that installation is viable, tests more than one option, states its assumptions and exclusions, and can conclude that the project should not proceed.

What information does a business need to provide? CUPS references and bills, interval consumption data, operating hours and shutdown periods, planned future loads, site and roof drawings, ownership or lease details, and existing electrical documentation.

Does a feasibility study include a structural survey? Not usually. A site visit is normally a non-intrusive visual inspection unless testing or opening-up work forms part of the agreed scope. The report should state explicitly whether structural verification by a qualified engineer, an asbestos survey or intrusive inspection is still required, and what each could change.

Should a feasibility study consider more than one system size? Yes. Comparing several capacities is how the optimum is identified, since self-consumption rate falls and coverage rate rises as capacity grows. A single option means no optimisation took place.

Can an installer produce an impartial feasibility study? An installer can produce a competent one, and often has useful practical experience. The commercial incentive should be acknowledged, the calculations should be reproducible, and on larger projects an independent study with separately tendered construction is worth considering.

What does "feasible subject to conditions" mean? That the project works provided specified items are resolved, typically structural verification, asbestos, or available connection capacity. Each condition should be named with its potential impact, an owner and a deadline, and it should not disappear from the summary.

Reviewed 19 August 2026. Regulatory routes for self-consumption installations differ by autonomous community and municipality, and should be confirmed for the specific site before a programme or budget is fixed.

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