Comparing Manufacturers: Reading Specifications Like for Like

Comparing two solar panels, two heat pumps or two boilers should be a matter of putting the datasheets side by side. In practice it rarely is, because manufacturers do not all quote their figures from the same starting point, under the same test conditions, or with the same caveats. A watt figure on one panel datasheet and a watt figure on another may both be honest and still not be comparable, because the conditions behind them and the certifications claimed alongside them differ.

The way through is to know which numbers on a datasheet are pinned to a common standard and which are chosen by the maker. Certification marks such as IEC 61215 for module performance and IEC 61730 for safety, and heat pump test standards such as EN 14825 and EN 14511, exist precisely so that rival products can be measured on the same bench. This page explains what those standards cover, what they cannot tell you, and how to read two manufacturer datasheets like for like, whether you are comparing solar panel manufacturers, heat pump manufacturers or boiler manufacturers.

Comparing specs across brands is tricky

The first difficulty is that a datasheet mixes two kinds of number: those measured to a shared standard, and those the manufacturer selects and presents. A peak power rating, a seasonal performance figure and a noise level may all appear on one page, yet each is produced differently. Where a standard applies, the figure can be compared across brands. Where it does not, the maker is choosing the conditions, the rounding and the emphasis, and the comparison is no longer like for like.

The second difficulty is that model naming hides differences. Two panels sold under adjacent model names, or two heat pumps in the same family, can carry different certifications, different test bases or different warranty terms, and nothing on the front page signals it. The conflict rulings in this area are real: one product datasheet may cite IEC 61215 while a stablemate cites IEC 61730, and a maker may list IEC 61730 certification on one product and UL 61730 on another. Neither mark is dishonest, but they are not the same claim, and a shopper who treats them as one will compare wrongly.

The third difficulty is the household's own context. Cost remains the main barrier to adopting electric vehicles, heat pumps and solar panels among consumers unlikely to adopt low carbon technologies, according to Ofgem's 2025 tracking research⁶, so price comparisons dominate, and the underlying performance figures get less scrutiny. Official advice is to get various quotes to compare prices of different installers⁷, but quotes present their own figures, chosen by the seller. A parliamentary research briefing on domestic heat pumps likewise notes that reducing the price of electricity relative to gas would make heat pumps more competitive⁸, which is a reminder that the economics a datasheet implies depend on prices outside the manufacturer's control.

For a household aiming at energy independence, this matters directly. The equipment's real contribution, how much of your own power, heat or hot water it produces, depends on figures that are only comparable when the test basis is shared. Our manufacturer certification and approvals page covers the schemes themselves; this one is about reading the numbers.

Standard Test Conditions: the baseline behind every watt figure

Every headline watt figure on a solar panel datasheet is measured under fixed laboratory conditions, so that a module tested in one country can be compared with a module tested in another. The same principle runs through heat pump specification. Heat pumps providing space heating are assessed using EN 14825 test data, used in combination with calculations from BS EN 15316-4-2:2017 to calculate performance⁹, and the calculation method applies a global minimum temperature difference of 5 K throughout⁹. Heat pumps providing water heating only are tested according to EN 16147⁹, with test data to load profile "M" required for hot water only heat pumps⁹.

The point of these fixed conditions is comparability, and the point of knowing them is knowing what the figure is not. A rating measured under standard conditions is a baseline, not a forecast of output on a particular roof in a particular county. The same discipline appears in solar thermal specification: a solar water heating system's primary pump input power should be less than the higher of 50 W or 2% of the peak thermal power of the collector¹⁰, a rule that stops a manufacturer quoting a collector's thermal power while quietly burying a large pump load elsewhere in the system.

For heat pumps, the headline efficiency figure a household will meet is the seasonal performance factor. An SPF of 4.0 means that for every 1 kWh of electricity consumed, the heat pump delivers 4 kWh of heat⁴. That figure is only meaningful because it is built from standardised test data across a season, rather than a single flattering operating point. When two makers quote different efficiency figures, the first question is whether both are quoting the same kind of figure, tested to the same standard, over the same conditions. Our page on product testing and datasheet standards sets out the testing landscape in more detail.

What the IEC 61215 module standard really covers

IEC 61215 is the core design qualification and type approval standard for terrestrial photovoltaic modules. Its purpose is to establish that a module design survives a defined sequence of stresses and still performs within permitted limits, so that a certification to it means something consistent regardless of who made the panel. Independent testing in the UK draws on it directly: Which?'s solar panel testing programme uses tests based on the international standards for photovoltaic modules, EN50380:2003 and IEC61215:2005².

The tests in that programme show what this family of standards is for. Which?'s maximum power tests include power stabilisation with solar radiation exposure of 25 kWh/m2, determination of maximum overall production performance, nominal efficiency, performance decline after sun exposure, power output, power exposure with an external solar radiation exposure of 60 kWh/m2, determination of maximum power generation, electroluminescence, and current leakage due to humidity². Between them, these exercise the things that actually degrade a panel on a roof: sustained exposure, heat, and water ingress.

The standard also reaches beyond ordinary glass modules. IEC 61215-1-5 sets special requirements for testing of flexible, non-glass superstrate photovoltaic modules¹¹, which matters because flexible panels sold for some roofs are a different product category with its own test part, not just a lighter version of a standard module. A household comparing a flexible panel with a conventional one is comparing across two parts of the same standard family, and should check that each carries the certification appropriate to its type.

What IEC 61215 gives a buyer, then, is a floor: evidence that the design passed a defined stress sequence. What it does not give is a ranking. Two certified panels can differ in ways the certification does not measure, which is the subject of the section on limits below.

Which datasheet marks matter beyond IEC 61730

IEC 61730 is the safety standard for photovoltaic modules, and it is the mark to look for alongside IEC 61215 rather than instead of it. Its practical bite is visible in fire safety research. Government research on fire spread over pitched roofs fitted with solar panels found fire spread was much less significant on glass-backed panels, which achieved class A under IEC 61730-2, than on plastic-backed panels, which achieved class C under the same standard³. Two panels can both be certified and still sit at opposite ends of a safety classification, which is exactly the kind of difference a front-page watt figure will never show.

Datasheets also carry marks that are not module standards at all, and a reader who treats every acronym as equivalent will misread them. Some makers list UL 61730 certification where others list IEC 61730, and some list both; these are separate claims issued under different frameworks, and the honest way to compare is to note which mark each product carries and check the certificate itself. The MCS certified product directory is the place to verify what a UK installation actually holds.

For heat pumps, the comparable safety and quality marks exist too. The Heat Pump KEYMARK is a voluntary, independent, third-party certification mark based on European standards, EN 14825 and EN 14511, and owned by CEN/CENELEC¹². Its certification is based on independent third-party testing and is compliant with efficiency requirements as set by Ecodesign¹³. The scheme states its benefits as certified product quality, compliance with EU standards and Ecodesign, increased consumer confidence, increased sales opportunities, and reduced costs for testing, inspection and certification¹³. A KEYMARK certificate tells you the performance figures were verified by a body independent of the maker, which is the strongest position a datasheet figure can be in.

Hail, impact and mechanical load: what the stress tests cover

Mechanical robustness is where datasheet claims and household worries meet, because hail, wind and snow are the stresses owners actually fear. The testing standards address them in defined ways. Panels from MCS-registered brands are made with tempered glass, so they shatter rather than crack, like a car windscreen¹⁴. That construction choice is what stands between a hailstone and a fractured cell, and it is a genuine point of difference between certified products and unverified ones.

The tests behind a certification go further than the glass. Which?'s programme includes electroluminescence imaging and current leakage due to humidity among its contributing tests², which detect the internal damage and water ingress that a storm can cause without leaving a visible mark. Performance decline after sun exposure is measured directly², so the independent picture covers slow degradation as well as sudden impact.

The other half of the mechanical story is the roof, not the panel. Planning guidance requires a check that the roof can support the additional wind, snow and static load imposed by the solar panels, and that it complies with Part A: Structure¹⁵. A panel can pass every impact test and still be the wrong choice for a roof that cannot carry the combined load, and that is a building matter rather than a manufacturer specification. Our solar mounting system manufacturers page covers the equipment that distributes those loads.

For heat pumps the mechanical and acoustic environment is assessed differently. Air source heat pump noise assessments consider existing background noise levels, the characteristics of the noise, noise levels at all operating modes including defrost cycles, the distance between the unit and neighbouring properties, and noise barriers or mitigation measures¹⁶. The MCS noise assessment calculator works to a pass/fail noise limit of 37.0 dB(A) for a two heat pump assessment¹⁷, and supports assessments for one, two or four heat pumps¹⁷. A manufacturer's own noise figure, measured at one operating mode, is not the same thing as an assessment across all operating modes including defrost.

What certification testing cannot tell you

A certification mark is evidence about a design sample under laboratory conditions, and it is important to be clear about what that does not cover.

• It does not certify your installation. An ECO4 innovation measure for solar carries the explicit limitation that "the system is not certified for use in high rise buildings"¹⁸. Certification boundaries are drawn per system and per context, and a mark on a module does not travel with it everywhere.
• It does not guarantee the warranty experience. Which? reports that with cracked panel warranty claims, the cost of labour for replacing the panel and any scaffolding may not be covered, the replacement panel may look different, and some manufacturers require independent testing to prove underperformance¹⁴. A certified panel with a weak claims process is a worse buy than the mark suggests.
• It does not settle which standard applies. MCS provides product certification for heat pumps not exceeding 45 kWth⁵, so larger products fall outside that scheme's scope, and BRE is accredited to EN14511 for air source heat pump testing and can test to EN14825 and EN16147⁵, meaning different labs and different standards coexist legitimately.
• It does not measure your home. Energy Performance Certificate accuracy research compares modelled energy use and internal temperatures with monitored data from large-scale datasets to provide empirical evidence on the accuracy of EPCs and the Standard Assessment Procedure¹⁹. The gap between modelled and real performance is a recognised research question, and a datasheet figure lands in that gap.

Certification also does not tell you how a product behaves in combination with the rest of a system. Solar thermal panels can be installed alongside other renewable or traditional heating systems, though they are not so easy to combine with a combi boiler²⁰. The compatibility question sits outside every individual datasheet.

When a datasheet exceeds the basic certifications

Some products go further than the baseline marks, and it is worth knowing what the extended layers look like, because they change what a comparison means.

The Heat Pump KEYMARK is the clearest example in the heating sector. It verifies the performance, efficiency and quality of heat pumps, ensuring market transparency¹², and a maker seeking it contacts one of the empowered Certification Bodies, with requirements for testing laboratories listed in Annex H of the KEYMARK documents¹³. A KEYMARK figure has been through independent third-party testing¹³, which places it above a self-declared figure in the hierarchy of trust, even when the underlying number looks similar.

Grant and incentive schemes add their own layers, and these are where extended requirements bite hardest. Under the Boiler Upgrade Scheme, the installer must be MCS-certified and the heat pump must be MCS-certified²¹. In Europe, the baseline requirements for heat pumps mean CE marking, compliance with Ecodesign (ErP) regulations, and documented performance data, typically SCOP values, backed by standardised testing and registered in EPREL²¹. Air source heat pumps must also comply with the Microgeneration Certification Scheme Planning Standards, MCS 020, or an equivalent standard, under planning guidance²².

Historic schemes show the same pattern. For the higher Feed-in Tariff band, an Energy Performance Certificate of level D or above had to be issued before the commissioning date of the installation, and the owner had not to be classed as a multi-site generator²³. Ofgem's dispute resolution guidance records consumers who were not told by their installer that the EPC had to be Level D or above and issued before the solar installation was commissioned²⁴. The lesson for reading specifications is that the paperwork around a product, certification, energy assessment, registration, can carry as much financial weight as the performance figures.

Beyond certification, some procurement goes further still. A Welsh local authority solar tender specification requires the contractor to hand over record drawings, test and completion certificates, maintenance instructions, manufacturers' directory and colour product literature, a full description of works, and commissioning certificates at practical completion²⁵. A household buying one panel does not face that regime, but the list is a good picture of what complete product documentation looks like when a serious buyer demands it.

A checklist for comparing datasheets fairly

The comparison itself comes down to discipline: same figure, same standard, same conditions, same caveats. A practical sequence:

1. Identify what each figure measures. Confirm both makers are quoting the same kind of number: peak power against peak power, seasonal performance against seasonal performance, noise against noise at the same operating mode.
2. Check the test standard behind it. Look for the standard named on the datasheet, IEC 61215 for module qualification, IEC 61730 for safety, EN 14825 and EN 14511 for heat pump performance¹², EN 16147 for hot water heat pumps⁹. If the standard is not named, the figure is self-declared.
3. Check who verified it. A figure backed by independent third-party testing, as KEYMARK certification is¹³, carries more weight than one the maker measured alone.
4. Note the safety classification, not just the mark. Two certified panels achieved class A and class C respectively under IEC 61730-2 in fire spread research³, so read the class, not just the acronym.
5. Read the warranty terms next to the performance figures. Labour and scaffolding may not be covered on a panel claim, and some manufacturers require independent testing to prove underperformance¹⁴. Our manufacturer warranties page covers the terms to check.
6. Check the certification's scope. MCS product certification covers heat pumps not exceeding 45 kWth⁵, and some systems are explicitly not certified for high rise buildings¹⁸. A mark outside its scope is no mark at all.
7. Compare the whole system, not the unit. Pump power limits on solar thermal¹⁰, metering requirements, and installation context all sit outside the headline figure.
8. Get several quotes and compare what each seller claims. Official advice is to get various quotes to compare prices of different installers⁷, and the government's check if a heat pump could be suitable for you service compares the cost and carbon emission savings available and what is needed to install a heat pump²⁶.

The impact on your home's energy self sufficiency

Reading specifications well is not an academic skill. It is how a household makes sure the equipment it buys actually delivers the independence it was bought for. A typical home solar system is around 4 kWp¹, and heat pumps and solar photovoltaic panels are now among the key energy efficiency characteristics recorded of new dwellings in official statistics²⁷. The figures on the datasheet are the difference between a system that covers a meaningful share of a home's demand and one that disappoints, and the figures are only trustworthy when compared on a shared basis.

The independence lens also exposes what remains outside the datasheet. A certified panel still depends on the manufacturer's continued existence to honour its warranty, on the installer's competence to fit it, and on the roof's ability to carry it¹⁵. A heat pump's running economics depend on the relative price of electricity and gas, which no maker controls⁸. Certification reduces dependence on a manufacturer's word, but it does not remove dependence on the manufacturer, the scheme or the grid.

The practical position is encouraging. Independent testing exists, certification schemes with third-party verification exist¹³, and official services exist to compare costs and savings before commitment²⁶. A household that checks the standard behind each figure, the body that verified it, and the warranty terms around it is comparing like for like, and that comparison is the foundation of every sound decision about who to buy from. The manufacturers guide covers the brands themselves, and tier 1 and bankability ratings covers the financial-strength ratings used in the solar market.