Market-wide half-hourly settlement for large users

Market-wide half-hourly settlement, usually shortened to MHHS, is a reform of the rules that settle the Great Britain electricity market. It moves every meter, including homes and small businesses, onto settlement based on its own consumption in each half hour, in place of the older approach of estimating a smaller site's usage from a standard profile. For a large electricity user the direct effect is small, because a site with a maximum demand of 100 kW or more is already settled half hour by half hour, a threshold set out in Elexon's half-hourly settlement rules. What MHHS changes for a large user is mostly indirect.

What is market-wide half-hourly settlement?

Settlement is how the electricity each site uses is accounted for and paid for between suppliers and the rest of the market. The Great Britain market runs in half-hour blocks, so a day holds 48 settlement periods, the resolution the market is settled at under the rules that Elexon administers through the Balancing and Settlement Code. Until MHHS, only larger meters were settled on readings taken every half hour. Smaller non-domestic sites and homes were settled on an estimated shape, a standard profile fitted to the meter's periodic readings, rather than on what the site actually drew in each period.

MHHS removes that estimation and settles every meter on its own half-hourly consumption, so the energy a supplier is charged for matches when its customers actually used it. Ofgem took the decision to implement the reform on 20 April 2021, and assessed the net benefit to consumers at between £1,559m and £4,509m over 2021 to 2045, in its decision and full business case. Elexon, the body responsible for delivering the reform through the MHHS Programme, switched its central systems on for MHHS on 22 September 2025. Meters began moving onto half-hourly settlement in November 2025, over an 18-month window ending on 7 May 2027, the dates set out in Elexon's MHHS programme pages.

Is my site already half-hourly settled?

Almost certainly, if it is a sizeable commercial or industrial site. A connection whose maximum demand reaches 100 kW or more has to be metered and settled half-hourly, under Elexon's half-hourly settlement rules, so the large sites a feasibility study is usually run on already produce a reading for every half hour of the year. Many sites a little below that level were moved onto half-hourly settlement in earlier reforms as well.

For these sites MHHS does not change the way their own energy is settled, because they are already on the basis that MHHS is extending to everyone else. Their half-hourly file is the same record a feasibility study already relies on, described in how to read half-hourly electricity data. The effects that do reach a large user come from elsewhere.

What does MHHS change for a large electricity user?

The reform reaches a large user through its effect on the rest of the market rather than through its own meter.

Suppliers receive a sharper signal of their own costs. Once every meter is settled on its real half-hourly shape, a supplier is charged for exactly when its customers draw power, so the cost of serving a flat overnight load and a spiky weekday-peak load is no longer averaged into a single standard shape. Ofgem expects this to prompt suppliers to offer more time-of-use tariffs and flexibility products, among the innovations Ofgem anticipated in the decision. A large user that already shifts load can be paid more precisely for doing so.

Smaller sites in a portfolio move onto half-hourly data. An organisation holding many sites often has a mix: large sites already on half-hourly meters, and smaller shops, offices or depots still settled on an estimated profile. As MHHS migrates those smaller meters, each one begins producing an actual half-hourly record. For a portfolio owner that is new visibility of demand across sites that previously showed only a periodic total, which is the same data a feasibility study needs, and which makes those sites readable in a portfolio screen.

The settlement systems behind the meter change. New central systems and data roles sit behind the reform, and the migration of each meter is handled by its supplier and agents. For a large user this is largely administrative and needs no action beyond the normal course of a supply contract.

Does MHHS change the case for solar and batteries?

MHHS does not change the part of that case that matters most. The value of on-site solar and a battery on a large site comes from the site's own half-hourly demand and the tariff it is on: the import it avoids at expensive times, the distribution charges it brings down by drawing less at peak, and the solar it uses on site rather than exporting. Those figures come from the site's existing half-hourly data, which MHHS does not alter for a site already settled this way. A feasibility study run today uses that file whether or not the reform has reached the wider market.

The reform does reach that case indirectly: more time-of-use tariffs across the market sharpen the price difference between periods, which is the gap a battery charges and discharges against, and is the same gap behind the separate P415 route to wholesale value. More time-of-use pricing improves the return on storage, though whether a battery is worth installing still rests on the site's own demand and tariff. The size and payback still follow from the site's own numbers, worked out as in how to size a commercial battery and commercial solar and battery payback.

Lupa models solar and storage against a site's own half-hourly file and electricity invoice, and the platform sets out the bill savings and the right size of system from that site's real demand, on the half-hourly basis MHHS is bringing to the rest of the market.