Alectrona
Commercial guideA credible carbon claim rests on metered self-consumption rather than a modelled estimate. The kWh your array generates and you actually use on site is auditable evidence that lowers reported Scope 2 emissions and feeds public-sector social-value and Carbon Reduction Plan bids.
OrientationThis is an orientation, not formal advice. SECR, the GHG Protocol, the Social Value Model and Carbon Reduction Plan requirements carry thresholds and weightings that are revised over time. Confirm the current position with the relevant body, your accountants and your bid team before relying on any figure here.
A solar array does more than cut a bill. For a large organisation it produces data that has to stand up in a carbon report and, increasingly, in a bid. The question a finance or sustainability lead should ask is not how much carbon a supplier claims the system saves, but whether the claim can be evidenced when an auditor or an evaluator pushes on it.
The answer comes down to metering. A credible carbon claim rests on the kWh your array generates and you actually consume on site, recorded by a meter, not inferred from a design model. That metered self-consumption is the auditable basis that SECR disclosures, ESG questionnaires and public-sector Carbon Reduction Plans are built to accept. What follows is a plain-English orientation to how on-site solar lowers the carbon you report, where the no-double-counting line sits, and how the same evidence scores in social-value and Carbon Reduction Plan bids. It is a guide, not formal advice; your accountants and bid team confirm the specifics for your organisation.
The difference between a defensible carbon claim and a challengeable one is the meter. A modelled figure says what the array should produce; a metered figure records what it actually generated and what you actually consumed on site. Reporting frameworks, auditors and tender evaluators expect the second.
A generation meter, and ideally import and export metering alongside it, lets you evidence the kWh that were genuinely used on site rather than estimated from a design assumption. That self-consumed figure is the auditable basis SECR disclosures, ESG questionnaires and public-sector Carbon Reduction Plans are built to accept. An estimate is weaker and can be questioned; metered self-consumption stands up. The practical implication is that the metering setup is not an afterthought, it is the part of the project that makes the reporting claim real, which is why we specify it as part of the system rather than leaving it to chance.
The page turns on one distinction: a modelled figure says what the array should produce; a metered figure records what it actually generated and what you actually consumed on site. Reporting frameworks, auditors and tender evaluators expect the second.
A design figure that says what the array should produce, inferred from a design assumption rather than recorded.
The kWh your array generates and you actually consume on site, recorded by a meter as auditable evidence.
On-site solar has no direct emissions, so it is not itself a line in your inventory. What it does is reduce the grid electricity you purchase, and purchased electricity is the heart of Scope 2 under the Greenhouse Gas (GHG) Protocol. Every kWh you self-consume is a kWh you do not import, so the Scope 2 figure you report falls.
The Protocol asks you to report Scope 2 two ways, and self-consumed solar reduces both. On a location-based basis, your grid power is valued at the published grid-average carbon factor (the UK government's DESNZ conversion factors), so less import means a lower number. On a market-based basis, the self-generated portion you consume carries no separate purchase, so it sits at a zero factor for that electricity. One caution matters here. Only the portion you self-consume reduces your own emissions; electricity you export cannot be claimed as your carbon benefit beyond having reduced import. And if the certificates (REGOs) attached to your generation are sold or transferred, those same certificates cannot also be claimed against your own emissions. Claiming both is double counting, so retaining the certificates for the self-consumed share keeps the market-based claim clean.
SECR, Streamlined Energy and Carbon Reporting, is the UK's mandatory minimum for large companies. Qualification turns on tests such as turnover, balance-sheet total and employee numbers, and quoted companies are caught regardless of size. Those thresholds are set in the regulations and revised over time, so your accountants confirm whether you are in scope rather than a fixed figure quoted here. If you are large enough to be weighing a commercial array, there is a fair chance one applies.
Where it does, SECR asks for your energy use, your Scope 1 and Scope 2 emissions, at least one intensity ratio, the methodology and a narrative of the energy-efficiency action taken in the year. On-site solar shows up twice in that disclosure: as a reduced Scope 2 figure, and as a named decarbonisation action in the narrative. The same metered evidence also feeds the voluntary and expanding regimes around SECR, such as TCFD-aligned disclosures, CDP and science-based targets, and the ESG sections of tender questionnaires. One well-specified generation-metering setup serves carbon reporting, social-value bids and ESG disclosure at the same time, which is the efficiency of getting the metering right once.
If you bid for public contracts, on-site solar is direct, evidenced material against two distinct mechanisms, and it helps to keep them apart.
One scope point matters. These central-government rules did not formally bind local authorities, many of which use the privately maintained National TOMs framework or their own social-value scheme instead. National TOMs is a voluntary measurement system that assigns a financial proxy value to each measure, including carbon reduction, and it favours genuine on-site reduction over offset claims. Frameworks and thresholds move, so check which one the specific contracting authority uses, and confirm the current position with that body before relying on a weighting or threshold here.
A carbon claim is only as strong as the file you can produce when someone asks to see it. For on-site solar feeding a SECR disclosure or a bid, the evidence pack is a short, specific set of records rather than a single headline number, and assembling it at handover is far easier than reconstructing it a year later under audit.
The core records are the half-hourly or interval data that shows generation against site demand, so the self-consumed share can be derived rather than assumed; the import and export figures from the supply meter, which reconcile against your electricity invoices; and the calculation note that states which emission factors were applied and for which reporting period. Where a market-based Scope 2 claim is made on the self-consumed share, the REGO position for that generation belongs in the file too, with a clear statement that the certificates were retained and not sold. The Energy Savings Opportunity Scheme (ESOS) and SECR both reward an auditable trail, and our ESOS and SECR guide sets out how the two regimes intersect. The data itself comes off the metering described in the half-hourly metering guide. We hand over the generation data and the methodology behind it; your accountants and assurance provider turn that into the disclosed figure.
A reported reduction is generation in kWh multiplied by an emission factor, so the credibility of the number rests on using the right factor for the right purpose and naming it. The figures are not invented for the report; they come from published government data and the GHG Protocol's two-method structure.
For a location-based Scope 2 figure, UK organisations apply the annual greenhouse gas conversion factors published by the Department for Energy Security and Net Zero (DESNZ), formerly issued by BEIS. These are revised each year, so a multi-year trend has to be read with the factor that applied in each reporting year rather than back-applying a single value. For a market-based figure, the relevant factor reflects your actual contracts: a supply backed by retained REGOs on the self-consumed solar share carries no separate purchased emissions for that electricity. The sections that follow set out which factor row to use and where the annual average stops being the right answer. One honesty point sits underneath all of this. We model expected generation from a PV*SOL yield study at the design stage, but a modelled estimate is a forecast, not the reported number. Once the array is running, the metered output replaces the model, and it is the metered figure that goes into the disclosure. Confirm with your accountants which factor set and reporting boundary apply to your organisation before any number is published.
The public-sector mechanisms are explicit, but the same metered evidence increasingly decides private-sector contracts too, and a sustainability lead should expect to use one evidence pack across both. Large customers are pushing their own Net Zero commitments down through their supply chains, and a credible on-site reduction is a direct answer to that pressure.
This shows up in several forms. CDP, the disclosure system many large buyers run their suppliers through, scores the strength and evidence of emissions data, and metered on-site generation is stronger material than a purchased-offset narrative. Suppliers reporting against science-based targets, validated through the Science Based Targets initiative (SBTi), need genuine reductions in their own footprint rather than claims that net off elsewhere, and self-consumed solar is exactly that kind of reduction. Customer ESG questionnaires and prequalification frameworks ask for the same Scope 1 and Scope 2 data that SECR asks for. The practical consequence is a competitive edge: an organisation that can evidence a real Scope 2 reduction is better placed in a tender than a competitor that cannot. The pattern is sector-specific, so the case made to a public buyer differs from the one made to a corporate customer; our public-sector and councils sector page covers the procurement angle, and the feasibility study is where the modelled generation that underpins any of these claims first gets quantified.
Two refinements come up once the basic Scope 2 claim is understood, and both affect how much you can honestly report. The first is storage. Because only self-consumed electricity reduces your own emissions, anything you would otherwise export at midday earns no carbon benefit to you beyond having cut import. Battery storage can lift the self-consumed share by holding midday surplus for evening or early-morning demand, which raises the reported Scope 2 reduction rather than letting it spill to export. Whether storage earns that place is a modelling question against your own load shape, not a default, and the commercial finance hub is where the economics of adding storage are weighed.
The second is Scope 3. The Carbon Reduction Plan required for in-scope central-government contracts asks for a defined subset of Scope 3 alongside Scope 1 and Scope 2, and corporate buyers increasingly ask suppliers to report their value-chain emissions. On-site solar acts directly on Scope 2, the electricity you purchase, so it does not by itself clear a Scope 3 obligation. It is honest to present it as a Scope 2 measure that strengthens the overall plan, rather than as a fix for value-chain emissions. The embodied carbon of the panels and mounting system is itself a Scope 3 item for you and is reported by responsible manufacturers in an environmental product declaration, which is worth requesting where embodied-carbon reporting matters to the buyer. Treat all of this as orientation and confirm the current scope boundaries and thresholds with your bid team and the contracting authority before relying on them.
The single most misused input in a carbon claim is the grid factor itself, because the UK government greenhouse gas conversion factor set published each year by DESNZ contains more than one electricity figure and they answer different questions. The headline number most people reach for is the grid electricity generation factor, the average emissions per kWh consumed across the UK grid. Sitting alongside it are a transmission and distribution losses factor, which accounts for the energy lost moving electricity from the power station to your meter, and separate well-to-tank figures covering the upstream emissions of producing the fuel before it is burned. A saving stated against generation alone is not wrong, but it is not the same as one stated against generation plus transmission and distribution losses, and a careful report says which it used.
On-site solar is relevant to the losses question precisely because it generates where it is consumed. Electricity your array produces and you use behind the meter never travels the transmission network, so it avoids the losses that imported grid power carries. That is a genuine, defensible part of the saving, and it has to be claimed deliberately against the right published sub-factor rather than folded in silently. We name the exact factor row, the publication year and whether the figure is generation-only or generation-plus-losses on any number we hand you, because that is what lets a reporting accountant trace it back to source.
The DESNZ conversion factors give one number for the whole year, an annual average. That is the correct basis for a Scope 2 carbon report and it is what an ESOS or SECR submission expects. It is not, however, how the grid actually behaves through a day. The carbon intensity of Great Britain's electricity swings widely between a windy night and a still evening peak, and the National Energy System Operator, formerly National Grid ESO, publishes a near real-time and forecast carbon intensity that exposes that variation directly.
This matters for solar because the two views can tell different stories about the same array. Solar generates in the middle of the day, and the marginal grid carbon it displaces at that moment is not identical to the flat annual average. For an annual carbon report the averaged DESNZ factor remains the right and auditable choice, and we use it. The real-time data is a useful sense-check and a planning input, particularly if you are pairing the array with a battery and want to understand when a stored unit displaces the dirtiest grid power, and it is not a substitute for the dated annual factor in a formal disclosure. We keep the two apart and are explicit about which one any figure rests on, rather than borrowing the more flattering number from whichever view suits.
An honest carbon account does not stop at the avoided-grid figure, because the modules, inverters, mounting and cabling carry their own manufacturing emissions before the array has produced a single kWh. The standard way to weigh both sides of that ledger is the energy payback time and the associated carbon payback, the period over which the clean generation offsets what went into making and installing the system. For UK-deployed crystalline-silicon systems that payback is a matter of a few years against an asset life of 25 to 30, after which the array runs well into net-positive territory.
We do not invent an embodied-carbon figure for your system. A credible number comes from the manufacturer's own life-cycle data or an Environmental Product Declaration for the chosen module, verified to EN 15804, the standard that governs construction-product EPDs. Where a module range carries a published EPD we cite it; where it does not, we say so rather than fill the gap with a generic figure. The embodied carbon is real, it is modest against the lifetime saving, and it is paid back early, and the net-positive claim is only as good as the source behind the embodied figure. That declaration is itself a Scope 3 item for you, which is worth requesting where a buyer asks for embodied-carbon reporting.
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We model the array in bankable-grade software, size it around your daytime load, and set out generation, savings and payback across three funding routes.
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Kept performing, year on year
Indirectly, yes. On-site solar has no direct emissions, so it is not a line in your inventory by itself. It reduces Scope 2 because every kWh you self-consume is a kWh of grid electricity you do not buy, and purchased electricity is the core of Scope 2 under the GHG Protocol. Importing less lowers the figure you report, on both the location-based and market-based methods. The reduction applies only to the share you consume on site, not to any electricity you export.
Because a credible carbon claim rests on what was actually generated and consumed, not on what a design model predicted. A generation meter, with import and export metering alongside it, evidences the self-consumed kWh that SECR, ESG questionnaires and public-sector Carbon Reduction Plans expect. An estimate is weaker and can be challenged by an auditor or evaluator. Metered self-consumption is the auditable basis that stands up, which is why we specify the metering as part of the system.
No, not as your own emissions reduction beyond having reduced your import. Only the self-consumed portion of generation lowers your Scope 2. Exported electricity benefits whoever uses it, and if the certificates (REGOs) attached to your generation are sold or transferred, those same certificates cannot also be claimed against your emissions. Claiming both is double counting. Retaining the certificates for the self-consumed share keeps a market-based claim clean.
In two separate ways. For in-scope central-government procurement, social value carries a minimum 10% weighting at award, and on-site solar is evidenced material against the climate-change theme, assessed at the level of the specific contract. Separately, for individual contracts above a value threshold, bidders must publish a Carbon Reduction Plan committing to Net Zero by 2050; that is a pass or fail condition, and solar lowers the Scope 2 baseline it reports. Local authorities often use the National TOMs framework instead, so check which the authority uses.
No. We design and build the array, specify the metering and give you the metered self-consumption and the carbon methodology behind it. Your accountants prepare the SECR disclosure, your bid team prepares the social-value or Carbon Reduction Plan submission, and your sustainability advisers confirm how the figure lands in your ESG reporting. We provide the engineering evidence; the reporting and the claims stay with the parties accountable for them. Frameworks and thresholds change, so confirm the current position with the relevant body.
Because an honest tonnage is the output of a calculation rather than a number to be guessed. The saving is your array's generation in kWh multiplied by the carbon factor of the electricity it displaces, and both inputs are specific to your site and the reporting year. We use the grid factor from the official UK government greenhouse gas conversion factors published by DESNZ, and we name the exact row, the publication year and whether the figure is generation-only or generation plus transmission and distribution losses. Using a published, dated factor is what makes the saving auditable rather than a sales assumption.
Because the grid is getting cleaner. As more low-carbon generation comes online, the carbon factor per kWh of grid electricity falls, and the official factors are revised down to match. Your saving is generation times that factor, so the same kWh displaces less carbon each year. The array's output stays broadly steady, declining only slowly with normal module degradation, but the carbon value of each unit it produces declines faster. A defensible projection shows that decline rather than holding today's factor flat and overstating the later years.
There is no fixed figure, because the generation and import or export metering needed to evidence a carbon claim is specified as part of the wider array, and the cost depends on the system size, the metering arrangement and your site. We do not quote a price online for that reason; the figure is established by survey for your project. The metering is a small element of the overall capital cost rather than a separate reporting fee, and we do not charge to prepare your SECR or social-value submission, since those stay with your accountants and bid team. Our commercial solar cost guide explains how the survey-led price is built up.
Metered generation data begins accumulating from the moment the system is commissioned and energised, so usable carbon evidence exists from day one of operation. A full reporting year matters more than the start date, because SECR and most ESG frameworks disclose against a financial year, and a complete twelve-month dataset captures the seasonal swing between summer and winter generation. If a bid deadline falls before a full year has run, the modelled PV*SOL forecast can support the intent while the metered record builds behind it. We confirm the commissioning timeline and the data handover for your project during design.
Last updated August 2026
A guide can only take you so far. The figure you get is modelled from your own half-hourly load and a system sized from the on-site drone survey. No obligation, and systems this size sit outside the domestic MCS scheme, so the assurance is the engineering stack.