Half-hourly meter bills, line by line: the eight charges that are most often wrong

Who is on a half-hourly meter

Half-hourly metering is the regime that applies to UK electricity supplies large enough that consumption is recorded in 30-minute intervals (rather than aggregated quarterly or monthly). Historically the threshold for mandatory HH metering was a maximum demand exceeding 100 kW, which captures most medium-sized factories, offices, retail parks and public-sector buildings. Sites with maximum demand above 100 kW were placed on Profile Class 00 — the HH profile class — and metered accordingly.

The Market-wide Half Hourly Settlement programme (MHHS), now in its industry rollout phase, will eventually bring all electricity supplies into half-hourly settlement, but the practical effect on smaller business customers (who will continue to pay the same retail tariff structures) is limited. For this article we are concerned with sites that have always been HH — large business, industrial and public sector — and the eight cost components that make up their bills.

The eight charges in plain English

An HH electricity bill is built from a much richer set of charges than a domestic or small business bill. The eight that appear on virtually every HH bill, and that account for the overwhelming majority of error correction work, are:

1. DUoS (Distribution Use of System) — the charges levied by the regional Distribution Network Operator for getting electricity through the local distribution network. Covers fixed charges, capacity charges, and per-kWh charges that vary by red/amber/green time band.
2. TUoS (Transmission Use of System) — National Grid's charges for the high-voltage transmission network. Largely a per-kW charge applied to the site's measured peak demand during three "Triad" winter peaks (or, post-Triad reform, during the new Demand Residual band).
3. BSUoS (Balancing Services Use of System) — National Grid ESO's charges for keeping the system in second-by-second balance. Reformed in April 2023 to be a fixed daily charge per MWh of demand; previously volatile.
4. MOP (Meter Operator) — the rental and service charge for the half-hourly meter itself. Contracted separately from supply.
5. DC (Data Collector) / DA (Data Aggregator) — charges for collecting half-hourly meter data from the MOP and aggregating it into a settlement-ready volume. Two services, two line items, although they are increasingly bundled.
6. Available Capacity — a fixed monthly charge based on the kVA capacity reserved at the substation, regardless of actual use.
7. Excess Capacity — a penal charge applied when the site exceeds its agreed available capacity.
8. Reactive Power — charged when the site's power factor falls below 0.95 lagging or has a leading reactive component, both of which load the network unproductively.

Available capacity vs excess capacity

This is where we recover the most cash. Available capacity (sometimes called "agreed supply capacity" or ASC) is set in the connection agreement at the time the site was first connected, often decades ago. It is expressed in kVA and the customer pays a fixed monthly charge per kVA whether they use it or not. Many sites are paying for capacity they no longer need — sometimes 30–60% more than current operations require — because no-one has revisited the figure since the original electrically-thirsty equipment was removed or the lighting was converted to LED.

The reverse problem is excess capacity. If maximum demand exceeds available capacity in any half-hour, the DNO charges an excess capacity rate that is typically three to five times the standard available capacity rate. Sites that have grown into and through their original capacity allocation can pay tens of thousands of pounds a year in excess charges before anyone in finance notices — because excess capacity often hides in the broader DUoS line and looks, at first glance, like ordinary distribution cost.

The fix in either direction is a formal capacity review:

1. Pull 12 months of half-hourly demand data and identify the actual peak in kVA.
2. Compare to available capacity. If there is consistent headroom of 25% or more, apply to the DNO to reduce the available capacity. The charge cut takes effect from the next billing period.
3. If excess is regularly being incurred, apply to increase available capacity, accepting a higher base charge to eliminate the higher excess charge. The maths usually works in favour of the increase.

DNOs vary in how willing they are to reduce capacity and at what notice. Most will, but some require evidence of demand patterns over a sustained period.

MOP, DC and DA explained

The metering and data services that feed an HH bill are a separate contractual stack from the supply contract itself. They are often arranged via the supplier ("bundled MOP/DC/DA") or directly with specialist providers.

• MOP (Meter Operator): physically owns and maintains the meter. Typical UK MOPs include Lowri Beck, SMS, Calvin Capital, Stark, MeterPlus.
• DC (Data Collector): pulls the half-hourly readings from the meter (typically over GSM) and validates them.
• DA (Data Aggregator): aggregates the validated reads from one or many DCs and submits the settlement-grade volume figure to Elexon for industry settlement.

The bundled cost typically lies between £180 and £550 per meter per year. Customers with multiple HH meters and bundled supplier arrangements often pay above the open-market MOP/DC/DA rate. Tendering MOP/DC/DA separately from supply is one of the few procurement levers that almost always pays for itself within twelve months on a portfolio of more than ten HH meters.

Reactive power and power factor

Real power (kW) does work. Reactive power (kVAr) is the magnetising current required by inductive loads — motors, transformers, fluorescent lighting ballasts. The vector sum is apparent power (kVA), which is what the network has to deliver. The ratio kW / kVA is the power factor. Anything below 0.95 lagging means the network is supplying disproportionately more apparent power than the work being done, and DUoS charges include a reactive power component to discourage it.

Sites with old motor stock, large inductive loads or older fluorescent lighting are the most exposed. The fix is power factor correction (PFC) capacitor banks installed at the main switchboard, which feed the reactive component locally and stop the network having to supply it. Capital cost varies — £15,000 to £40,000 for a typical mid-sized industrial unit — and payback against eliminated reactive charges is usually 18–36 months.

An audit-stage warning: bills sometimes show leading reactive power as well as lagging. Leading reactive arises from over-correction — too many capacitors for the inductive load, especially overnight or when production is off. The DUoS regime charges for leading reactive in some regions, and a PFC bank installed without contactor switching can quietly create the problem the customer thought they were paying to solve.

Where errors typically come from

From our portfolio audit work the recurring error patterns are:

1. Available capacity set above current demand. The single largest recoverable item on most HH portfolios.
2. Triad / TNUoS mis-allocation. Sites whose Triad-period demand has fallen because of operational changes (shift patterns, load shedding, generator running) but whose TUoS bill still reflects the historical figure.
3. BSUoS estimated, not reconciled. Pre-April-2023 BSUoS was famously volatile and many bills used estimated figures that were never reconciled with actual outturn. Reconciliations more than 12 months old are sometimes still recoverable, depending on supplier policy.
4. DC/DA double-billing. When MOP/DC/DA is bundled with supply, occasionally the same service is also being separately invoiced under a legacy contract. Easy to overlook on a complex multi-site bill.
5. Reactive power penalty without PFC review. The customer pays the penalty for years rather than once paying for the correction kit.
6. Estimated half-hourly volumes. Even on HH meters, communications failures occasionally lead to estimated rather than actual reads. If the estimate runs high, the customer over-pays until the read is reconciled.
7. Wrong DUoS band classification. Sites can be assigned to the wrong DUoS time-of-use band on the original connection. Reclassification is administratively involved but worth it where it applies.
8. Climate Change Levy errors, where applicable — separately covered in our CCL guide.

How to audit your own HH bill in seven moves

1. Pull 12 months of bills and 12 months of half-hourly demand data. Both should be exportable from the supplier portal.
2. Tabulate the eight line items above for each month. Look for anomalies — line items that vary unexpectedly, or that step-change at a particular date.
3. Calculate measured peak kVA and compare to available capacity. Compute the percentage utilisation. Below 70% is a strong reduce-capacity candidate.
4. Identify any month with an excess capacity charge. Sum the annual excess and compare to the cost of an upward capacity adjustment.
5. Calculate effective power factor each month from kWh and kVArh totals. Below 0.95 lagging triggers a reactive review.
6. Compare MOP/DC/DA cost per meter to current open-market rates. £180–£550 is typical; significantly above suggests a tender opportunity.
7. Check for any line items that have stayed flat to two decimal places for more than six months — those are usually estimated rather than actual.

If a portfolio audit on this scale is more than your team has time for, that is precisely the engagement we run. Our pricing is published on our business energy page. We disclose any commission earned on procurement before contract signature, and audit work is fee-based rather than commission-based.