ESOS · Reporting and data
ESOS reporting: the report and the carbon data
ESOS reporting produces two things: an ESOS report that the organisation keeps, and a notification of compliance that it submits to the Environment Agency (SI 2014/1643).
Both are measured in energy, not carbon: the Environment Agency’s guidance says in terms that “CO2 is not an energy unit” (§4.1).
This page sets out what an ESOS report contains, what is published, and how its kWh become the tCO2e that SECR and UK SRS ask for.
The ESOS report
What goes in an ESOS report in Phase 4
| Content | What it records | Where |
|---|---|---|
| Energy consumption | Total energy consumption over the reference period, and the areas of significant consumption if identified | Regs 22, 25 |
| Energy intensity ratios | One for each organisational purpose: transport, industrial processes, buildings, any other purpose | Reg 25C |
| Audit findings | The energy audits’ savings opportunities, with estimated savings in kWh | Regs 27, 27A |
| Savings achieved | New in Phase 4: measures implemented in the period, the kWh saved by each, and each measure’s category | Reg 27D |
| Action plan review | New in Phase 4: measures from the last action plan not implemented, and why | Reg 27E |
| Confirmations | That the responsible officer or officers have seen and considered the findings | Regs 30, 31 |
The ESOS report is kept in the evidence pack and shared with group undertakings; it is not uploaded, and the Environment Agency’s checklists set out every item section by section.
What reaches the Environment Agency is the notification of compliance, made through MESOS by 5 December 2027 for Phase 4.
An organisation on the full ISO 50001 route, or with zero energy consumption, produces no ESOS report but still notifies; ESOS Phase 4 covers who is in and when.
Our sister reference site walks the whole Phase 4 route in its ESOS Phase 4 compliance guide.
What becomes public
Phase 4 publishes more than Phase 3
The scheme administrator must publish each action plan and each progress update, and selected fields of each notification set out in Schedule 3 (SI 2026/701).
Phase 4 adds the combined energy saving achieved across all measures to what is published, and keeps the per-measure figures private as commercially sensitive.
The Phase 3 data is on data.gov.uk: action plans, first progress updates and notifications, as at a 5 June 2026 data cut.
Phase 3 data should not be read as a guide to what Phase 4 will publish, because Schedule 3 was rewritten.
| Item | Published? |
|---|---|
| Action plans | Yes |
| Progress updates | Yes |
| Combined kWh savings achieved | Yes |
| Savings per measure | No |
| Action plan review narrative | No |
| Notification details on the full ISO 50001 route | No |
From kWh to tCO2e
ESOS energy data is carbon activity data
The conversion is multiplication: energy in kWh, or litres of fuel, times the DESNZ factor for that energy, divided by 1,000 for tonnes.
The factors are the government’s conversion factors for company reporting, published by DESNZ each June.
The factor year follows the activity: the 2026 methodology paper says the 2026 set is for activity data “entirely or mostly within 2026”.
An ESOS reference period that straddles two years therefore spans two factor sets, and each month’s energy takes its own year’s factor.
Report purchased electricity as Scope 2 on the generated factor; transmission and distribution losses are a separate Scope 3 factor.
The 2026 electricity factor is 26% below 2025’s, partly because DESNZ changed its method; UK emissions factors explains the break.
Mapping purposes to scopes
Four ESOS purposes, three GHG scopes
| ESOS energy | Typical GHG Protocol scope | SECR (unquoted / LLP) | Note |
|---|---|---|---|
| Buildings — grid electricity | Scope 2 | Required | Location-based on the DESNZ factor |
| Buildings and processes — gas and other fuels burned | Scope 1 | Gas required; other fuels not listed | Quoted companies report all fuel combustion |
| Transport — fleet and company cars supplied with fuel | Scope 1 | Required | ESOS and SECR both key on who is supplied with, or buys, the fuel |
| Transport — personal or hire cars on business use | Scope 3 | Required where the company buys the fuel | ESOS includes them; the GHG Protocol treats them as Scope 3 |
| Industrial processes — self-generated electricity | Scope 1 (the fuel) | Via the fuel burned | ESOS counts the incoming fuel, not the electricity generated |
| Any other purpose | Depends on the source | Depends on the source | The catch-all fourth purpose |
The four organisational purposes are transport, industrial processes, buildings, and any other purpose; “buildings, transport and processes” drops the fourth.
The GHG Protocol sorts the same energy by who owns or controls the source, which is why a personal car on business use is ESOS transport energy but Scope 3 in a carbon inventory.
ESOS audit vs SECR
Where ESOS data stops short
ESOS is four-yearly; SECR and UK SRS are annual, so ESOS data covers one year in four.
ESOS counts UK energy only; a quoted company’s SECR figures and UK SRS figures are worldwide.
ESOS lets up to 5% of consumption be de minimis; SECR has no de minimis inside the figures, only the low-energy relief for the whole report.
The ESOS reference period is twelve months including the qualification date; SECR follows the financial year.
So ESOS data is the best-evidenced starting point for a carbon inventory, not a finished one; ESOS and SECR sets out the full comparison.
Annual SECR reporting sits in the directors’ report under SI 2018/1155.
ESOS needs no lead assessor where consumption is less than 40,000 kWh.
SECR’s low-energy relief applies at 40,000 kWh or less, and for unquoted companies only in the UK.
At exactly 40,000 kWh the two give opposite answers.
UK SRS
From ESOS energy to UK SRS emissions
UK SRS S2 asks for gross Scope 1, 2 and 3 emissions under the GHG Protocol, and requires location-based Scope 2, with market-based permitted.
ESOS data can supply the UK part of Scope 1 and 2; overseas operations, a full annual series and Scope 3 have to come from elsewhere.
The FCA’s final rules (PS26/19, 30 September 2026) require listed companies in scope to report against UK SRS on a comply-or-explain basis for accounting periods beginning on or after 1 January 2027.
CP26/5 had proposed making S2 mandatory apart from Scope 3; the final rules adopted comply-or-explain throughout, with a one-year relief for Scope 3.
UK SRS and the FCA covers the listing rules, and UK SRS Scope 3 reporting the part ESOS cannot supply.
Frequently asked
ESOS reporting: questions people ask
What is an ESOS report?
The document that records the outcome of an organisation’s ESOS assessment: its energy consumption and areas of significant consumption, an energy intensity ratio for each organisational purpose, the energy audit findings and savings opportunities, and, in Phase 4, the energy savings achieved during the compliance period and a review of the previous action plan. It is kept in the evidence pack and shared with group undertakings; the notification of compliance is what is submitted.
Is ESOS a carbon reporting scheme?
No. ESOS is measured in energy, in kWh or in energy spend, and the Environment Agency’s guidance says CO2 is not an energy unit. It produces no emissions figure. Its energy data is, though, exactly the activity data that carbon reporting under SECR or UK SRS converts into tonnes of CO2 equivalent.
How do I convert ESOS kWh into tCO2e?
Multiply each energy stream by the matching DESNZ conversion factor for the year the energy was used, then divide by 1,000 to get tonnes. For UK grid electricity in 2026 the location-based factor is 0.13096 kgCO2e per kWh, so 500,000 kWh gives 65.5 tCO2e of Scope 2. Fuels burned on site use the fuel factors and are Scope 1.
What is the difference between an ESOS audit and SECR?
ESOS is a four-yearly energy assessment for large undertakings, notified to the Environment Agency, that identifies savings opportunities. SECR is an annual disclosure in the directors’ report of energy use, emissions, an intensity ratio and efficiency measures, for quoted companies and large unquoted companies and LLPs. The tests for who is in each are different, and so are the intensity ratios: ESOS asks for an energy ratio per organisational purpose, SECR for one emissions ratio.
What does the Environment Agency publish from ESOS?
Each action plan and each progress update, and selected fields of the notification, including in Phase 4 the combined energy savings achieved across all measures. Per-measure savings and the action plan review narrative are not published. The Phase 3 data is on data.gov.uk.
Can ESOS data be used for UK SRS reporting?
As a starting point. UK SRS S2 asks for gross Scope 1, 2 and 3 emissions under the GHG Protocol, with location-based Scope 2 required. ESOS supplies UK energy data for Scope 1 and 2 but is four-yearly, UK-only, allows a de minimis, and says nothing about Scope 3. Listed companies in scope of the FCA’s final rules report against UK SRS on a comply-or-explain basis for accounting periods beginning on or after 1 January 2027.
Sources
Primary sources
Every figure, date and status on this page traces to the instrument’s owner. Secondary commentary is never the source for a number.
- legislation.gov.ukThe Energy Savings Opportunity Scheme Regulations 2014 (SI 2014/1643)
The ESOS report (regs 27A, 27D, 27E), intensity ratios (reg 25C), publication (reg 10, Sch 3).
- legislation.gov.ukSI 2014/1643, regulation 25C — energy intensity ratios
One ratio for each organisational purpose.
- legislation.gov.ukThe ESOS (Amendment) Regulations 2026 (SI 2026/701)
Savings achieved (reg 27D), the action plan review (reg 27E), what is published (Sch 3).
- Environment AgencyHow to comply with ESOS phase 4 (30 July 2026)
§4.1: total consumption in kWh or £ — "CO2 is not an energy unit"; the ESOS report.
- Environment AgencyAppendices A1 and A2: report checklists for participants
The ESOS report checklist, section by section.
- Environment AgencyESOS: find out if you qualify and how to comply
Phase 4 dates, the four organisational purposes.
- Environment Agency, via data.gov.ukEnergy Savings Opportunity Scheme — published data
Phase 3 action plans, progress updates and notifications.
- Department for Energy Security and Net ZeroGovernment conversion factors for company reporting
The factors that turn ESOS kWh into tCO2e.
- Department for Energy Security and Net Zero2026 conversion factors methodology paper, ¶¶1.10, 3.1, Table 9
Year rule; generated factor 0.13096 for Scope 2; T&D losses in Scope 3.
- Greenhouse Gas ProtocolCorporate Accounting and Reporting Standard
Scopes 1 to 3 and organisational boundaries.
- legislation.gov.ukSI 2018/1155 — the SECR Regulations (as made)
The annual disclosure ESOS data most often feeds.
- Department for Business and TradeUK SRS S2, ¶29(a) and ¶¶B30–B31
Gross Scope 1, 2 and 3; location-based Scope 2 required.
- Financial Conduct AuthorityPS26/19: Aligning listed issuers’ sustainability disclosures with international standards
Final rules, 30 September 2026: comply or explain from 1 January 2027 periods.
- Financial Conduct AuthorityCP26/5 — the consultation PS26/19 finalises
Had proposed mandatory S2 excluding Scope 3; the final rules did not adopt that.