For most businesses, electricity billing works simply enough: a meter measures how much you use, and a supplier charges you for it. The bill may be complicated, but the principle is straightforward.

For businesses with half-hourly electricity meters, the process is fundamentally different. Your energy consumption is measured every thirty minutes, recorded by a chain of specialist parties, fed into a national settlement process, and then reconciled against what your supplier estimated you would use. Errors can enter at multiple points in that chain, and because the process is largely invisible to the customer, they can persist for years.

This article explains how half-hourly metering and settlement works, why it matters commercially, and what the most common errors look like.

Section 1 - What is half-hourly settlement?

A meter capable of recording half-hourly consumption data logs your electricity use in thirty-minute intervals, producing 48 data readings per day. This data feeds into the national settlement system, and how it does so - and through which parties - depends on whether the site is on the traditional half-hourly settlement model or has migrated to the new arrangements being introduced under the Market-wide Half Hourly Settlement (MHHS) reform.

Historically, businesses with a maximum demand exceeding 100 kilowatts (kW) were required to have half-hourly metering and to settle on a half-hourly basis. This remains the traditional mandatory threshold. Since then, Ofgem's P272 modification extended half-hourly settlement to additional business customers in certain profile classes, and MHHS is now progressively moving the wider market - including smaller commercial and domestic customers - onto half-hourly settlement. The 100 kW threshold is therefore the historic starting point, but it no longer defines the full population of half-hourly settled sites.

It is also worth noting that a meter capable of recording half-hourly data - sometimes described as an advanced meter or AMR meter - is not the same as a meter that is actually settled on a half-hourly basis. As MHHS rolls out, the metering capability and the settlement arrangement are increasingly managed separately.

Section 2 - The parties involved in half-hourly settlement

Unlike a standard commercial meter, a half-hourly settled supply involves several parties beyond your energy supplier. The traditional model - which remains in place for sites not yet migrated under MHHS - involves three specialist roles:

• Metering Services (historically referred to as Meter Operator or MOP) - installs, owns, and maintains the physical meter and associated communications equipment, and is responsible for ensuring the meter is functioning correctly and that data is being transmitted.
• Data Collector (DC) - collects the half-hourly consumption data from the meter and validates it, ensuring readings are complete and plausible before passing them to the Data Aggregator.
• Data Aggregator (DA) - receives validated data from the DC and aggregates it for submission into the national settlement process.

All three roles carry associated fees, which are typically passed through to you as line items on your electricity bill. These fees are set by commercial contract and can vary between providers.

Under MHHS, the traditional DC/DA model is being replaced for migrated supplies by an Advanced Data Service (ADS), which consolidates these data functions under a different structure. Legacy and new arrangements are currently running in parallel as migration progresses. The practical implication for businesses is that the parties handling your consumption data - and the way that data flows into settlement - may differ depending on whether your supply has migrated.

Section 3 - How half-hourly settlement works

The UK electricity market operates on a system of half-hourly trading periods. Generators sell electricity and suppliers buy it, with trades settled every thirty minutes based on actual supply and demand.

Energy suppliers manage their positions across their entire customer portfolio rather than buying electricity specifically for each individual customer. Settlement then reconciles each supplier's portfolio against actual metered consumption. Where there is a difference between what a supplier has bought and what its customers have actually used - known as imbalance - this is settled through the balancing mechanism at a price that can be significantly higher or lower than the contracted rate. Suppliers carry this imbalance exposure, and the degree of forecasting uncertainty across their portfolio can influence the pricing and risk premiums they apply to individual contracts.

For you as the customer, this settlement process can affect your bill in several ways:

• If your consumption profile is difficult to forecast or highly variable, your supplier may apply a higher risk premium to your contract price
• Settlement errors - where your consumption data is incorrect - can result in billing discrepancies that may need to be investigated and corrected
• The accuracy of the data flowing from your meter through to settlement directly affects the accuracy of your bill

MHHS is also changing the settlement timetable as migration progresses, so the specific timings of initial settlement and subsequent reconciliation runs are evolving rather than fixed.

Section 4 - BSUoS and the balancing services charge

One of the less understood charges that can appear on a half-hourly metered electricity bill is the Balancing Services Use of System (BSUoS) charge. BSUoS recovers the costs incurred by the National Energy System Operator (NESO) in balancing supply and demand across the electricity system in real time.

Since April 2023, BSUoS has been recovered from Final Demand through an ex-ante fixed volumetric tariff, rather than the daily variable charge that applied previously. Whether BSUoS appears as a separate pass-through line item on your bill depends on the terms of your specific contract - some suppliers include it within the unit rate, others show it separately.

Understanding how BSUoS is being charged in your contract, and confirming that the tariff rate applied is correct, is a straightforward but often overlooked part of bill validation.

Section 5 - TNUoS: the transmission network charge

Transmission Network Use of System (TNUoS) charges fund the high-voltage national transmission networks across Great Britain. The physical networks have separate owners, and the GB electricity system is operated by NESO. For half-hourly metered sites, TNUoS is a material cost and one that has changed significantly in recent years.

Historically, the residual component of TNUoS for half-hourly demand customers was heavily influenced by consumption during the three highest-demand half-hour periods of the year - the so-called triads. Sophisticated energy managers would reduce consumption during these peak periods to minimise their TNUoS liability.

Following Ofgem's Targeted Charging Review reforms, the residual TNUoS charges for HH demand customers are now recovered through fixed charges based on site characteristics rather than real-time peak avoidance. The opportunity for traditional triad avoidance savings has been significantly reduced, and organisations that have not updated their energy management strategies to reflect this change may be spending management time and money on an approach that no longer delivers the savings it once did.

Section 6 - DUoS: the distribution network charge

Distribution Use of System (DUoS) charges are paid to your local Distribution Network Operator (DNO) for using the local distribution network that delivers electricity from the transmission system to your site. DUoS charges are structured around time-of-use bands - typically red, amber, and green - with higher charges applying during peak demand periods.

For half-hourly metered sites, DUoS charges are calculated using the actual half-hourly consumption data. This means that the timing of your consumption matters commercially - using more electricity during red band periods increases your DUoS costs relative to shifting that consumption to amber or green band periods.

An incorrect DUoS tariff, LLFC (Line Loss Factor Class) or other charging classification being applied to an MPAN can result in incorrect DUoS charges accumulating over time. Because the error applies to every half-hour period of your billing, the cumulative impact on a high-consumption site can be very significant.

Section 7 - Common half-hourly settlement errors

The complexity of the half-hourly settlement chain creates multiple points where errors can enter. The most common:

• Missing or estimated reads - if data transmission from the meter to the Data Collector fails, estimated reads are substituted. Extended periods of estimated data create a growing gap between estimated and actual consumption that eventually requires a large retrospective correction.
• MOP, DC, and DA fee duplication after supplier switches - when you switch energy supplier, the outgoing supplier's MOP, DC, and DA contracts should terminate cleanly. In practice, they sometimes do not, resulting in dual billing - charges from both the old and new providers running simultaneously.
• Incorrect DUoS tariff or charging classification - as described above, an incorrect LLFC or DUoS tariff applied to an MPAN can result in significant cumulative charges, particularly after supplier switches when charging classifications may not transfer correctly.
• BSUoS pass-through errors - where the tariff rate being applied to your account does not match the correct ex-ante fixed volumetric rate for the relevant period, or where BSUoS is being charged in a way that does not match your contract terms.
• Settlement run adjustments - settlement involves multiple reconciliation runs over a period following each trading day. MHHS is changing the settlement timetable as migration progresses, so what constitutes a late or unexpected adjustment is evolving. Unexpected charges on your bill that appear without explanation are worth investigating to confirm whether they are legitimate.
• Meter communication failures - physical meter faults, communications equipment failures, or network issues can interrupt data flow without any visible alert to the customer. The first sign is often an unusually high or low bill.

Section 8 - What this means for your business

If your business has half-hourly metered supplies, the practical implications are:

• Your bill is more complex than a standard commercial electricity bill, with more line items and more parties involved
• Errors are more likely and harder to spot without specialist knowledge
• The costs of errors compound over time because the same mistake applies to every half-hour period
• Retrospective recovery of overcharges is possible, though the recoverable period depends on the type of claim, the contract, and the jurisdiction. As a general guide, energy billing claims can typically go back several years, though this varies - for example, CCL-related claims are typically limited to four years, while water audit recoveries can extend to six years in England. Specialist advice is needed to establish the applicable period in each case.

A forensic audit of half-hourly metered supplies - covering DUoS tariff and charging classification accuracy, Metering Services and data fees, BSUoS pass-through treatment, and settlement data completeness - is the most reliable way to establish whether your current billing is accurate.

For multi-site organisations with several half-hourly metered supplies, the audit covers all meters simultaneously - and systemic errors (such as a DUoS mis-classification applied to all meters on the same network) are frequently found across multiple sites at once.

The bottom line

Half-hourly metering is the right infrastructure for any business with significant electricity consumption. But the settlement process that sits behind it is complex, involves multiple parties, and creates multiple opportunities for billing errors that are invisible without specialist analysis.

Knowing how the system works is the starting point for knowing whether you are paying what you should.