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How should organisations measure their energy consumption for ESOS?

To comply with ESOS, businesses are required to calculate their total energy consumption, which can be more complex than it first appears. It’s vital that those affected by ESOS include all of the information that’s required, and calculate their consumption correctly, to ensure that they’re fully compliant.

With this in mind, here are our top tips for measuring your consumption:


  • Your energy consumption must be calculated in a common unit – either an energy unit, like kWh, or energy spend (in pounds sterling). You can use the Government’s conversion factors to help you to do this.
  • Under ESOS, your total energy consumption must include all of the energy you use in your buildings, industrial processes and transport. There are no fuel type exemptions in ESOS, so you must include combustible fuels, heat, renewable energy and electricity.
  • You do not need to include energy that your organisation doesn’t use (and instead supplies to a third party), energy your organisation consumes outside of the UK, or energy consumed during international travel that doesn’t start or end in the UK.
  • You must provide verifiable data on your consumption wherever possible, such as an invoice, meter reading records or stock records for stored fuels.
  • If you can’t provide verifiable data, you will need to explain why in your evidence pack, and you should also provide a reasonable estimate in place of any missing data. There are several ways you could do this, from a pro-rata extrapolation to a benchmarking exercise – talk to your Lead Assessor to determine the best approach.
  • You must calculate your total energy consumption over a period of 12 consecutive months, which must include the qualification date (31st December 2018) and end before the compliance date (5th December 2019). It should be the same 12-month period for all energy supplies.
  • Once you’ve calculated your total energy consumption, you will need to identify assets and activities that account for at least 90% of your total consumption. These are your areas of significant energy consumption. You can then exclude up to 10% of your total energy consumption from your audit – this is your ‘de minimis energy consumption’.


Qualifying organisations must calculate total energy consumption over a reference period of 12 consecutive months. This data must be new and the reference period must include the qualification date of 31 December 2018 and end before the compliance date of 5 December 2019. (If an organisation is unable to collect energy data for the full 12-month period, then it should collect data from as close to 12 months as is reasonably practicable and explain why it has had to do so in its ESOS evidence pack.)

ESOS does include options to make compliance easier in this regard, an organisation could use the average day rate of energy use for one month to estimate the energy used for another month, and extrapolate that data. Or, it could use the annual energy use of one site to estimate how much energy another site is using, particularly if that site is a similar size, age, and build. An auditor should carry out at least one site visit as part of an organisation’s ESOS Phase 2 energy audit. Regulators will look for well-reasoned and documented justifications for the approach that the Lead Assessor took (for example, they will want to know why certain conclusions from site visits might be applicable to any other sites covered in a particular sample).