How to Compare Commercial Solar Quotes in Spain

Commercial solar quotations cannot be compared as received. Three proposals for the same building will differ in capacity, equipment, what they include, what they assume and how they calculate savings, and those differences can outweigh the price gap between them. Comparison begins by normalising every bid onto the same scope and the same assumptions, and only then looking at the numbers.

Done in the other order, the exercise selects for whichever supplier was most willing to leave things out and most optimistic about what the system would earn. Neither is a quality worth buying.

This article sets out a method: what to require from every bidder, how to check a generation model, how to test a savings claim, how to price the exclusions back in, and how to weigh the result.

Why the cheapest quotation may not be the lowest-cost project

Price differences between bidders frequently reflect differences in scope rather than differences in margin.

Items that can be absent from a low quotation include engineering and the signed technical project, structural verification, access equipment, electrical upgrade work, distributor charges, legalisation and registration, and monitoring beyond a basic inverter portal. None of these disappear because they were omitted. They are paid later, usually by the customer, often at short notice and without competitive tension.

A second source of difference is capacity. A supplier proposing a smaller system will quote a smaller number, and whether that is better depends entirely on whether the business could have used more generation productively. Total price answers no question on its own.

A third is optimism. A proposal claiming a shorter payback has usually made different assumptions, not built a different system. Assumptions are free to make and expensive to rely on.

How many quotes to obtain

Three is a workable number for most commercial projects. It gives enough variation to reveal where the differences lie without creating a comparison exercise larger than the decision justifies.

More important than the count is that every bidder works from the same brief. Send each the same consumption data, the same drawings, the same site information and the same list of questions, and require responses in a common format. Bids prepared from different information are not comparable however carefully they are read afterwards.

Where the capacity is genuinely open, ask each bidder to quote their recommended capacity and to justify it from the consumption data. Where capacity has already been established through a feasibility exercise, specify it and require deviations to be argued.

The comparison process

Establish the scope you are buying. Write down what a complete project includes for your site before reading any quotation. This becomes the reference against which each bid is measured.

Require the minimum information set. Set out below. Chase anything missing before comparing, and treat persistent gaps as information in themselves.

Normalise the scope. For each quotation, list what it excludes, price those items and add them in. The comparison is between normalised totals, not headline prices.

Check each generation model. Verify the inputs rather than accepting the output.

Test each savings calculation. Rebuild it with your own assumptions and see how much of the claimed benefit survives.

Compare on normalised figures. Only now does cost per kWp become meaningful.

Weigh the non-financial factors. Contractual terms, delivery risk, support arrangements and the quality of the evidence behind each bid.

Decide on the whole picture. Not on payback, and not on price.

Minimum information checklist

Require every quotation to state:

• Panel capacity in kWp and inverter installed capacity in kW, given separately
• Exact panel and inverter manufacturer and model numbers, with quantities
• Usable roof or installation area assumed, and how it was established
• Modelled annual generation, with the tool, version, radiation database, all inputs and the date the model was run
• The consumption data used, its source, date range and interval resolution
• Self-consumed, exported and curtailed electricity as separate figures
• Self-consumption rate and solar coverage rate, both stated
• Valuation of self-consumed electricity by tariff period, and of surplus separately
• Capital cost excluding and including IVA
• Annual operating and maintenance costs
• Degradation and inverter replacement assumptions
• Payback, and the underlying cash flows
• Whether structural verification is included and in what form
• Full electrical scope
• Full administrative scope
• A written exclusions list
• Programme, with the elements outside the installer's control identified
• Payment terms tied to defined milestones
• Warranty terms, distinguishing product, performance, inverter and workmanship cover

A quotation that cannot supply this is not a quotation for a commercial project. It is a price.

The comparison table

Build one table with every bid in a column. Fill it from the quotations, not from what the covering letter says.

Two rows deserve emphasis. Panel capacity in kWp and installed capacity in kW are different quantities, and under Real Decreto 244/2019 the legal measure for photovoltaic installations is the maximum capacity of the inverter or the sum of the maximum inverter capacities. A proposal that gives only one figure is concealing the other. Self-consumption rate and solar coverage rate move in opposite directions as capacity changes, so a single percentage without a label tells you nothing.

Why different capacities cannot be compared on price

A quotation for 120 kWp at €96,000 and one for 200 kWp at €150,000 are not competing offers at €800 and €750 per kWp. They are proposals to build different things.

The larger system generates more. It also self-consumes a lower proportion of what it generates, because additional capacity increasingly lands on hours when demand is already met. The correct question is whether the incremental 80 kWp earns enough, after the extra capital, to justify itself.

Calculate the incremental figures directly: additional cost, additional annual benefit, and the payback on the difference. That comparison frequently shows that the extra capacity is the weakest part of the larger proposal even where the whole-system payback looks acceptable.

Cost per kWp, and when it means anything

Cost per kWp is the right unit for comparing normalised bids and a misleading one before normalisation.

It becomes useful once every quotation includes the same scope: the same structural work, the same electrical work, the same access equipment, the same administrative handling, the same monitoring. At that point the figure genuinely compares value.

It misleads where scopes differ. A bid at €680 per kWp that excludes structural verification, access equipment and legalisation is not cheaper than one at €790 per kWp that includes them. It is a smaller purchase. Roof works, electrical upgrades, distributor charges and equipment quality all move the figure without any change in what the business ends up owning.

Normalise first. Then divide.

Checking the generation model

Do not accept an annual generation figure. Require the inputs that produced it, and check them.

PVGIS, maintained by the European Commission's Joint Research Centre, is a common and reasonable basis for this work and provides hourly time series suitable for overlay analysis. Whichever tool is used, the model should be reproducible: another party given the same inputs should obtain the same output.

Different layouts, orientations and equipment can legitimately produce different outputs for the same building, so a difference between bids is not by itself an error. Where two bids propose broadly equivalent designs and their generation figures differ materially, compare the coordinates, the capacity used, the layout, the shading treatment, the loss assumptions and the radiation dataset until the source of the difference is identified.

Why annual generation is not enough

A generation figure describes what the system produces. It says nothing about what the business receives.

Value depends on the overlap between generation and demand, on the tariff periods the displaced electricity occupies, and on what happens to whatever is not used on site. Two identical systems on two businesses with the same annual consumption can produce materially different returns because their operating patterns differ.

Require every quotation to show the overlay: the consumption data used, its date range and interval resolution, the hour-by-hour comparison against modelled generation, and the resulting split between self-consumed, exported and curtailed electricity. Then require self-consumed electricity to be valued against the tariff periods it displaces, and surplus to be valued separately under whichever arrangement applies.

A proposal that jumps from annual generation to annual savings has skipped the only part of the analysis that establishes the answer.

Six ways savings get inflated

Each of these is a modelling choice, and each moves the result in the same direction.

Applying the full retail price to every generated kWh. Only self-consumed electricity avoids an import at the prevailing price. Applying that price to total generation overstates the benefit by the whole value of the surplus gap.

Treating exported energy as equal in value to self-consumed energy. Surplus is valued under simplified compensation or through sale under producer arrangements, and in either case differently from avoided import cost. Under a zero-export configuration it is worth nothing at all.

Asserting a self-consumption rate rather than demonstrating it. Any material self-consumption claim should be shown from the interval data. A high figure can be entirely credible for a seven-day operation or a site with continuous base load, and equally implausible for a five-day office. The test is the evidence, not the number.

Guaranteed electricity price escalation. Compound annual increases across a twenty-five year horizon do most of the work in a cumulative savings figure. Ask what the result looks like at zero real escalation.

Including unawarded grants. A capital cost with a grant already deducted, before any award, describes a project that may not exist on those terms.

Ignoring degradation, maintenance or inverter replacement. Output declines. Maintenance costs money. Inverters may require repair or replacement within a twenty-five year model. A projection omitting all three is not a projection.

Rebuild each bid's savings figure with your own assumptions applied consistently across all three. The ranking often changes.

Comparing equipment

Require exact manufacturer and model numbers. "High-efficiency tier-one modules" is not a specification.

No panel brand is categorically the right choice. What matters is that the specification is stated, that the warranty terms are read rather than summarised, and that the equipment can be supported for the life of the asset.

Warranty terms are not interchangeable

Four distinct things are commonly described as "the warranty", and they cover different risks.

Product warranty covers defects in the module or inverter itself. The remedy is whatever the written warranty defines, which may be repair, replacement, a credit, a refund or another stated remedy, and it is not automatically the supply of a new unit.

Performance warranty covers output falling below a stated percentage of rated capacity at defined years. It is a guarantee about degradation, not about defects.

Inverter warranty runs on its own terms and duration, usually shorter than the module warranties and often extendable at a cost.

Installer workmanship cover addresses the installation itself: mounting, fixings, cabling, waterproofing and commissioning. It comes from the installer, not the manufacturer, and it depends on the installer still trading.

A twenty-five year manufacturer warranty does not mean twenty-five years of cover for the installation. Manufacturer warranties commonly do not include labour, access equipment, crane hire, diagnostic time or lost generation, and they do not cover business interruption unless their terms expressly say so. On a high-bay warehouse, access equipment to replace a single faulty module can cost more than the module. Ask who pays for that in each of the four cases.

Ask also what happens if the manufacturer ceases trading, and what happens if the installer does.

Mounting, fixings and environment

The mounting system determines how the array survives twenty-five years on a Spanish roof.

Compare the mounting manufacturer and system, the fixing method, and whether the roof is penetrated or the array ballasted. Penetrations require a stated waterproofing method and a position on how they interact with any existing roof warranty. Ballasted systems require the resulting load to be within the structure's capacity, which returns to the structural question.

Corrosion class matters and is site-specific. Coastal locations, sites near industrial processes and agricultural buildings with ammonia exposure all place higher demands on materials than an inland urban roof. Ask which corrosion category the mounting system is specified to and why that category suits the site.

Wind loading calculations should exist for the proposed configuration, particularly for ballasted arrays on exposed flat roofs.

Structural scope

This is the exclusion with the largest potential consequence.

Establish for each bid whether structural verification is included, and in what form. A visual roof inspection by an experienced installer is a useful observation and it is not a structural calculation. A calculation by a qualified professional establishes the structural position, and it may also be required as supporting documentation for the design or for parts of the administrative process, depending on the project and the applicable regional requirements.

Then check what happens if the verification finds a problem. Many quotations exclude reinforcement works entirely, which is reasonable provided the exclusion is explicit and the business understands it is carrying that risk.

Ask what the quotation assumes about roof condition and remaining service life, and what it assumes about asbestos-containing materials. Older Spanish industrial roofs may contain fibre cement with asbestos, which changes the mounting approach, the cost and the programme, and brings health and safety obligations. A bid silent on asbestos has assumed there is none.

Electrical scope

Compare these line by line, since they are where scopes diverge most.

Without an existing or survey-derived single-line diagram, the electrical position has not been adequately assessed. Long cable runs in large industrial buildings are a significant cost and a common source of variation between quotations.

Administrative scope

Establish who does each of these and whether it is priced.

Administrative routes are not uniform across Spain. Requirements are set nationally, regionally and municipally, and a quotation describing a generic "handling of permits" has not established what applies at this site. Ask each bidder to name the specific procedures.

Note also that the installer does not control distributor or municipal timescales. A bid promising a fixed date for grid connection is promising something outside its control, and the contract should reflect where that risk actually sits.

Exclusions checklist

Ask each bidder to confirm, in writing, whether each of the following is included or excluded:

• Structural verification by a qualified professional
• Structural reinforcement, if required
• Asbestos survey and any resulting works
• Roof repair or replacement, if the survey finds it necessary
• Access equipment, scaffolding and lifting
• Switchboard modification or replacement
• Transformer works
• Cabling, containment and civil works along the full route
• Earthing works
• Metering equipment
• Anti-export controller and its documentation
• Distributor charges and any network reinforcement
• Economic guarantee funding
• Electrical project signed by a qualified technician
• Municipal procedure and ICIO
• Regional legalisation and registration
• Inspection by an authorised control body, where required
• Producer registration and market representation set-up, where applicable
• Monitoring hardware, platform and ongoing subscription
• Commissioning documentation and handover pack
• Ongoing maintenance beyond any initial period
• Removal of waste and existing equipment
• Fire safety alterations arising from the array layout

Price each exclusion and add it back before comparing. Where a bidder cannot price an item, that is a risk the business is being asked to carry.

Programme and disruption

Compare the delivery plan as well as the price.

Ask how site access will be managed, what lifting or crane operations are required, what working hours are proposed, and whether any shutdown of production or trading is needed. For a facility running continuously, a proposal requiring a two-day outage has a cost that does not appear in the quotation.

Establish equipment lead times and whether the price is held if they slip. Establish the weather assumptions and what happens to the programme if they fail.

Then separate the programme into elements the installer controls and elements it does not. Design, procurement, construction and commissioning are within its control. Distributor processes, municipal decisions and regional legalisation are not. A contract should allocate delay risk accordingly rather than pretending the installer governs the whole timeline.

Operations and maintenance

Compare what happens after commissioning, since quotations vary widely in how much they say about it.

Cleaning assumptions in particular should match the environment. A dusty agricultural building, a coastal hotel and an urban office roof do not need the same regime, and a proposal applying the same allowance to all three has not thought about it.

Contract and payment terms

Payment should follow demonstrable progress. Milestones worth defining separately include deposit, equipment delivery to site, installation completion, commissioning, legalisation, energisation, and a final payment or retention.

The distinction between these matters. An installation can be physically complete and not legalised, or legalised and not yet energised, or energised and not yet receiving value for surplus. A payment schedule that treats "installation complete" as the end of the project pays for something short of the deliverable.

Deposit and retention percentages vary by supplier, project size and contract, and there is no standard figure. What matters is that the schedule is weighted towards outcomes the business can verify, and that meaningful value remains outstanding until the documentation is delivered.

Also settle what happens if measured output falls materially below the proposal. Establish whether the installer offers any performance undertaking, what it covers, how underperformance is measured, over what period and against which baseline, and what the remedy is. Many commercial quotations offer nothing here, which is a legitimate commercial position and should be visible rather than assumed either way.

Installer due diligence

Verify the following for each bidder rather than relying on presentation:

Authorised installer status appropriate to the work. Requirements differ for low-voltage and high-voltage work, and the status held should cover what this project involves. Ask for the registration and check it.

Insurance. Professional indemnity and public liability, with current certificates showing the cover levels and the period. Check the cover is proportionate to the project value and to the consequences of a roof failure.

Commercial references. Completed installations of comparable size, on comparable buildings, ideally in the same autonomous community so the administrative experience is relevant. Ask to speak to two of them.

Trading identity and finances. CIF, registered address, trading history and, for a significant contract, filed accounts. A twenty-five year asset backed by a warranty from a company two years old carries a different risk from one backed by an established business.

Subcontracting. Who actually carries out the electrical work, the structural assessment, the access work and the administrative handling. Subcontracting is normal. Undisclosed subcontracting is not.

Responsibility. Who is contractually responsible for the design, for the construction and for the legalisation. Where these sit with different parties, establish who the business holds to account if the system underperforms or the legalisation stalls.

Worked comparison: three illustrative quotations

The following uses clearly illustrative figures for one business, and every input is stated. These are not market averages.

The site. Industrial unit, annual consumption 480,000 kWh, operating Monday to Saturday, roof capable of accommodating up to 300 kWp. The same consumption data was supplied to all three bidders.

Surplus arrangement. All three proposals exceed 100 kW of inverter installed capacity, so simplified compensation is not available to any of them. Surplus is therefore sold under producer and market arrangements in every case. The €0.045 per kWh figure below is a gross sale value, with market representation and settlement administration shown separately as an annual cost. Producer registration and representation set-up are treated as part of the administrative scope and normalised across all three bids.

Assumptions applied uniformly during normalisation. Self-consumed electricity valued at €0.155 per kWh weighted across tariff periods. Surplus at €0.045 per kWh gross. Maintenance at €12.50 per kWp per year. Degradation 0.5 per cent annually. Figures exclude IVA.

As quoted

As presented, Quote A is the cheapest per kWp and Quote B claims the best payback. Quote C is the most expensive per kWp and quotes the longest payback, because it is the only bid whose figures have not been flattered.

After normalisation

Excluded items priced and added, generation models checked against site inputs, and savings recalculated on the uniform assumptions above.

Incremental analysis

Reading the result

There is no single winner here, and the figures are close enough that the decision turns on factors outside the payback column.

Quote A has the lowest normalised capital requirement at €148,500 and the shortest normalised payback at 4.6 years. It also has the weakest evidence: no interval overlay, no stated self-consumption rate, and a yield claim of 1,550 kWh per kWp that the site inputs did not support. Its quoted 3.1 year payback was built on assumptions nobody could inspect, and its two-year workmanship cover is the shortest of the three. A business choosing Quote A is buying the lowest capital requirement and accepting that several of the numbers behind it were never demonstrated.

Quote C costs €11,500 more in normalised capital and returns €2,204 more each year, an incremental payback of 5.2 years on the difference. Its payback is fractionally longer than Quote A's, at 4.7 years against 4.6. What it offers instead is a proposal whose figures survived checking: the overlay was provided, the 74 per cent self-consumption rate was demonstrated from the interval data rather than asserted, the electrical scope was surveyed rather than allowed for, and the workmanship cover runs to five years. A business choosing Quote C is paying a modest premium for evidence and contractual cover.

Quote B produces the highest annual benefit of the three, at €39,298, and it is the strongest option in absolute terms for a business that wants to maximise the money saved. Its 85 per cent self-consumption claim did not survive the overlay: at 260 kWp on this consumption profile the rate falls to around 62 per cent, and most of the additional generation becomes surplus at roughly a quarter of the value of self-consumed electricity. The incremental step from Quote C to Quote B costs €44,400 and returns €5,128 a year, a payback of 8.7 years on that increment against 4.7 years for the base system. The capacity is not wasted, but it works considerably harder for considerably less.

The choice therefore depends on the buyer:

• A business with constrained capital has a genuine case for Quote A, provided it accepts the evidential gap and prices the risk of the unverified assumptions.
• A business with low risk tolerance, or one that will struggle to manage exclusions and administrative work itself, has a genuine case for Quote C, at a small cost in return.
• A business with cheap capital, a long ownership horizon and no better internal use for €44,400 has a genuine case for Quote B, provided the decision is taken with the 8.7 year incremental payback visible rather than hidden inside a 5.2 year whole-system figure.

What the exercise establishes is not which bid wins. It is that the ranking as presented, with A cheapest and B claiming the best payback, bore little relation to the ranking on evidence, and that the only way to see this was to normalise every bid onto the same scope and the same assumptions.

Weighted evaluation matrix

Financial comparison is necessary and insufficient. The following weightings are illustrative and should be adjusted to reflect the buyer's own priorities. A business with constrained capital will weight financial factors higher; one with a critical production process will weight delivery and disruption higher.

Score each bid on each factor, apply the weights and total. The exercise is less about the final number than about forcing a considered view on every factor rather than an impression driven by price.

Warning signs

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

Generation figure with no inputs. An unreproducible model is an assertion.

No interval overlay. The proposal has skipped the analysis that determines the answer.

Self-consumption rate asserted rather than demonstrated. Whatever the figure, ask to see it derived from the interval data.

One system size only. No optimisation was performed.

Payback under three years. Possible, and worth interrogating closely for the assumptions that produced it.

No exclusions list. Everything was either included or quietly assumed, and the reader cannot tell which.

Grants deducted before award. A project that may not exist on those terms.

Structural position described but not calculated. A visual impression presented as an engineering conclusion.

Fixed grid connection date. A promise about something the installer does not control.

A deadline attached to the price. Equipment price movements and finance offers do carry real dates. Ask for written evidence of the deadline and an explanation of what changes commercially if it passes, and treat an unevidenced deadline as pressure rather than information.

Questions to send every bidder

Send these as a numbered list and require numbered answers, so responses can be compared directly.

1. State panel capacity in kWp and inverter installed capacity in kW separately.
2. Give exact panel and inverter manufacturer, model numbers and quantities.
3. Provide the full generation model inputs: coordinates, azimuth, tilt, mounting configuration, shading treatment, loss assumption, radiation database, tool, version and date run.
4. State the consumption data used, its source, date range and interval resolution.
5. Provide the interval overlay showing self-consumed, exported and curtailed electricity.
6. State the self-consumption rate and the solar coverage rate, and show how each was derived.
7. State how self-consumed electricity was valued by tariff period, and how surplus was valued.
8. State whether the surplus value quoted is gross or net of representation and settlement costs.
9. State degradation, maintenance and inverter replacement assumptions.
10. State whether any grant is assumed and whether it has been awarded.
11. Confirm in writing whether each item on the exclusions checklist is included or excluded.
12. Confirm whether structural verification is included, by whom and in what form.
13. State what the quotation assumes about asbestos and roof condition.
14. Confirm the electrical scope item by item, and whether the single-line diagram has been reviewed.
15. Name the specific municipal, regional and distributor procedures applicable, and who handles each.
16. State warranty terms separately for panel product, panel performance, inverter and workmanship, giving the defined remedy in each case and confirming whether labour and access equipment are covered.
17. State the programme, identifying which elements are outside your control.
18. State payment milestones and any retention.
19. State any performance undertaking, how it is measured, over what period and what the remedy is.
20. Provide insurance certificates and authorised installer registration.
21. Provide two references from comparable commercial projects.

Pre-signing checklist

• Every quotation normalised onto the same scope, with exclusions priced and added
• Generation models checked against site inputs and reproducible
• Savings recalculated on your own uniform assumptions
• Self-consumed, exported and curtailed electricity shown separately for the preferred bid
• Surplus valuation confirmed as gross or net, with representation costs identified either way
• Incremental return calculated where the preferred bid is larger than the alternatives
• Structural verification arranged, whether inside or outside the contract
• Asbestos position established
• Electrical scope confirmed against the single-line diagram
• Administrative route named specifically, with an owner for each step
• Warranty terms read in full, not summarised, including the defined remedy in each
• Payment milestones tied to legalisation and energisation, not just installation
• Delay risk allocated between installer-controlled and external processes
• Insurance and installer registration verified
• References taken
• Ownership of monitoring data and platform access agreed
• Handover documentation list agreed in the contract

Frequently asked questions

How many commercial solar quotes should a business get? Three is workable for most projects. More important than the number is that every bidder receives the same brief, the same consumption data and the same questions, so the responses are comparable.

What should a commercial solar quotation include? Panel capacity in kWp and inverter capacity in kW separately, exact equipment models, the full generation model inputs, the consumption data used, the interval overlay with self-consumed and exported electricity separated, structural and electrical scope, administrative scope, a written exclusions list, programme, payment milestones and warranty terms.

How do you compare quotes for different system sizes? Normalise the scope first, then compare on cost per kWp and on return. Where one bid is larger, calculate the incremental cost and incremental annual benefit of the additional capacity separately, since it usually performs worse than the system average.

Is cost per kWp a useful measure? Yes, after scope normalisation. Before it, the figure compares different purchases and misleads, since exclusions, roof works, electrical upgrades, grid work and equipment quality all move it.

How should I check an annual generation estimate? Require the inputs, not the output: coordinates, azimuth, tilt, mounting configuration, shading treatment, loss assumption, radiation database, tool, version and the date the model was run. Another party with the same inputs should reproduce the figure.

What is a realistic self-consumption estimate? It depends entirely on the overlap between generation and demand at that site. A high rate can be entirely credible for a seven-day operation or a site with continuous base load, and implausible for a five-day office. Whatever the figure, require it to be demonstrated from the interval data.

Which costs are commonly excluded? Structural verification and reinforcement, asbestos survey, access equipment, switchboard and electrical upgrade work, distributor charges, municipal procedure and ICIO, regional legalisation, inspection where required, producer registration and market representation where applicable, and monitoring beyond a basic inverter portal.

Does a long panel warranty protect the business? Not by itself. Product warranty, performance warranty, inverter warranty and installer workmanship cover are four different things, and the remedy under each depends on its written terms. Manufacturer warranties commonly exclude labour, access equipment and lost generation, so the cost of replacing a module on a high roof may fall to the business.

Should structural calculations be included? Either included in the contract or arranged separately before design is fixed. A visual roof inspection is not a structural calculation, and a calculation by a qualified professional is what establishes the structural position and may be needed as supporting documentation later.

Who handles permissions and grid connection? It varies by bid and should be stated explicitly. Ask each bidder to name the specific municipal, regional and distributor procedures applicable and to confirm who submits each. The installer does not control distributor or municipal timescales.

How should grants and tax savings be treated? Model the project without them first. A grant should only be deducted from the capital cost once awarded in writing, and tax treatment depends on the ownership and financing structure and should be confirmed with the business's own advisers.

What payment terms are reasonable? Terms tied to verifiable milestones: deposit, delivery, installation, commissioning, legalisation, energisation and a final payment. Percentages vary and there is no standard figure, but meaningful value should remain outstanding until the documentation is delivered.

What if output is below the proposal? Establish before signing whether any performance undertaking exists, what it covers, how underperformance is measured, over what period and what the remedy is. Many commercial quotations offer none, which should be visible rather than assumed.

Should I choose on payback? No. Payback ignores everything after the payback point and rests on assumptions that differ between bids. Compare on normalised return alongside technical, contractual and delivery factors, and be explicit about whether the priority is the lowest capital requirement, the strongest evidence or the highest absolute saving.

Reviewed 19 August 2026. All figures in the worked comparison are illustrative and internally consistent, not market averages. Regulatory routes and equipment terms change, and both should be confirmed for the specific project.

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