Hundreds of electricity meters connected to Britain’s transmission system are sending power-flow data in the wrong direction, potentially adding up to £100 million a year to grid operating costs.
NESO documents reveal more than 800 metering points have inconsistent polarity, meaning generation can appear as electricity consumption – and demand can appear as power being produced.
The Times reports at least 818 installations are affected, including connections serving all 45 UK offshore wind farms alongside unidentified onshore sites.
The problem does not mean household meters have been installed backwards or customers are being directly charged for electricity they have not used.
It affects operational meters feeding live information into NESO’s Supervisory Control and Data Acquisition system, which control-room engineers use to monitor the network and balance supply with demand.
Incorrect readings can reduce visibility of what is happening across the transmission system and force operators to spend more time checking data before taking decisions.
NESO’s own documents warn the errors can damage situational awareness, make grid operation less efficient and increase balancing costs passed through to consumers.
They also identify a potential risk of breaching electricity security standards, alongside possible settlement errors between NESO and energy companies.
The issue stems partly from the absence of a single enforceable industry standard defining whether power flowing through different types of equipment should be recorded as positive or negative.
Generators, transmission owners and offshore transmission operators, have therefore used different conventions when supplying data to NESO.
NESO said the electricity system remains safe and interim measures allow engineers to identify and correct misleading signals before they affect operational decisions.
However, the permanent solution currently being developed would initially standardise new or modified meters rather than automatically correct every existing installation.
Grid Code modification GC0182 would create a common polarity convention for generators while linked changes would extend the requirement to transmission and offshore network owners.
NESO published voluntary guidance in April but said the convention is not yet enforceable and there is no confirmed date for approval.
The cost of correcting existing meters has reportedly been estimated at between £4.5 million and £44 million, significantly below the potential annual operating cost attributed to inaccurate data.
The revelation adds to scrutiny of NESO’s ability to monitor an increasingly decentralised electricity system as offshore wind, batteries and smaller generators expand.
NESO’s documents state that incorrect polarity can lead to “deteriorating accuracy” in grid management and reduce the reliability of information available to engineers operating the system in real time.
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