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Glossary
Energy standards and regulation

What is ESOS?

Definition

ESOS, the Energy Savings Opportunity Scheme, requires large UK undertakings to measure total energy use and audit significant energy consumption every four years, covering buildings, industrial processes and transport.

Who qualifies

Per GOV.UK, a large undertaking is a UK company that employs 250 or more people, or has an annual turnover above £44 million and a balance sheet total above £38 million. A corporate group qualifies when at least one UK member meets that definition.

Phase 4 dates

  • Qualification date: 31 December 2026
  • Notification of compliance due 5 December 2027, submitted through MESOS
  • Phase 3 participants file an annual action plan progress update by 5 December 2026, signed off by a board level director
  • An ISO 50001 certificate issued after 5 December 2023 and valid on 5 December 2027 can serve as a route to compliance

Measured evidence for action plan progress

Phase 4 assessments must report progress against action plan commitments, which means showing what changed after each measure. Aqueduct holds sub-metered kWh by site, building and feeder, and its baseline comparison separates a measure's effect from weather. A lead assessor can draw on that record, while the assessment and director sign-off stay with the participant.

Questions

ESOS: common questions

ESOS is the UK's mandatory energy audit scheme for large organizations, run by the Environment Agency as scheme administrator. Each phase, a participant measures total energy consumption, identifies significant energy use, has a lead assessor review the findings and notifies compliance. Aqueduct's role is set out on the ESOS compliance page.

ESOS is a four-yearly audit of energy saving opportunities. SECR is an annual disclosure in the company's report, and many large companies fall under both. The same metered consumption can serve each, though SECR reports emissions and ESOS focuses on where savings can be found.

No. GOV.UK states that DECs and Green Deal assessments can no longer be used as alternative routes to compliance. The remaining alternative is a valid ISO 50001 certificate covering the organization's energy use, otherwise a full ESOS assessment with a lead assessor is needed.

Total energy across buildings, industrial processes and transport for a 12-month reference period, plus enough detail to identify significant energy consumption. Aqueduct supplies the buildings and process share as sub-metered kWh by site and system through load disaggregation. Transport fuel comes from the participant's own records.

See Aqueduct on your own facility.

Bring a site, a utility bill or a question. We will show you where the loss is.

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