If your building has a maximum demand of 100kW or above at any point, you are legally required to have a Half Hourly (HH) meter. This is a regulatory requirement under the electricity settlement rules that govern how energy is traded in Great Britain.
A Half Hourly meter records your electricity consumption in 30 minute intervals, 24 hours a day. That is 48 data points every single day, transmitted automatically to your supplier. This determines precisely how you are charged, not on an estimated basis, but on your actual verifiable usage profile.
The settlement process for electricity in GB allocates energy consumed across the grid between suppliers, generators and trading parties. Below 100kW maximum demand, sites are profiled against a standard load estimate. Above 100kW, actual half hourly data is used.
Under the Market wide Half Hourly Settlement programme every electricity supply is moving to settlement on actual Half Hourly data, not just sites above 100kW. The migration is under way and completes across 2026 and 2027. The practical effect is that data quality and metering arrangements now matter for every site, not only the largest.
For HH meter customers, Distribution Use of System charges are applied in three bands: Red, Amber and Green. Red band periods typically run 4pm to 7pm on weekdays between November and February. Red band rates remain significantly higher than Green band rates, although the DCP228 change narrowed the differential from April 2018. The difference still creates a direct financial incentive to shift consumption away from peak periods.
TNUoS demand charges are split into two distinct components, and understanding the difference is now more important than ever. The first, and by far the largest, is the residual (TDR) charge, a fixed standing charge applied per site per day based on your meter type, connection voltage and agreed capacity band. This charge cannot be reduced through behavioural changes or load shifting. It is simply unavoidable. From April 2026, these residual charges are rising sharply. The average year on year increase in the residual charge is approximately 63%, rising from £15.72/MWh in 2025/26 to £25.68/MWh in 2026/27, under the new RIIO-3 price control period.
The second component is the locational demand (Triad) charge, which remains relevant for Half Hourly metered sites and is still based on consumption during the three half hour periods of peak system demand between November and February. However, its significance has diminished considerably. The average HH Triad tariff for 2026/27 is £2.79/kW, and critically, no Triad charge applies at all for sites in northern England and Scotland (Zones 1 to 7). For eligible sites in southern GB, some saving potential through Triad avoidance remains, but the opportunity is far smaller than it once was, and the fixed residual charge now dominates the overall TNUoS cost. For most businesses, the focus should shift from Triad avoidance to managing capacity band classification and understanding how your agreed supply capacity affects your standing charge exposure.
If you have a Half Hourly meter and your bills have never been formally audited, ask us to look. The complexity that makes HH billing error prone is the same complexity that creates recovery opportunities when errors are found.