MHHS Explained: What Half-Hourly Settlement Means for Solar Households

What is MHHS?

Market-wide Half-Hourly Settlement — MHHS for short — is an Ofgem programme that changes the fundamental way your energy bill is calculated. It is one of the most significant reforms to UK energy retail in a generation, though most households will never notice it happening.

Under MHHS, every electricity supplier must settle its accounts with the wholesale market and the network using your actual half-hourly consumption data, rather than estimates based on national averages. If that sounds technical, the plain English version is straightforward: your bill will reflect exactly when you used (and exported) electricity, down to every 30-minute slot, rather than a best guess based on someone who used electricity like you ten years ago.

The programme is being rolled out across all domestic and small business accounts. Mandatory migration began in October 2025 and the full transition must complete by May 2027.

How electricity settlement works today

To understand why MHHS matters, it helps to understand what happens right now when your energy supplier bills you — and why it is less accurate than you might assume.

Most domestic electricity meters, including many first-generation smart meters, are settled using what are called profile classes. These are standardised usage patterns created by the industry that describe when a typical household uses electricity across the day, week, and year.

Your supplier takes your total consumption over a billing period — say, 400 kWh in a month — and distributes it across the half-hours of that month according to your profile class. A household in profile class 1 (typical domestic with no Economy 7) is assumed to use electricity in a particular shape: more in the morning and evening, less overnight, more in winter than summer.

This is an average. It does not reflect your actual household at all. Your supplier does not know whether you charged your EV at 2am or ran your washing machine at 7pm. They know your total units and they apply a standard curve on top.

For the wholesale market, this matters because suppliers must buy electricity in advance for every half-hour slot. If their settlement data does not match when their customers actually used power, they face imbalance charges from the grid. These costs are ultimately passed back to consumers through standing charges and unit rates.

What changes with MHHS

MHHS replaces the profile class approach with settlement based on your actual half-hourly meter data.

Your SMETS2 smart meter already records consumption and export in 30-minute intervals. That data is transmitted to the Data Communications Company (DCC) and on to your supplier. Under MHHS, that granular data becomes the basis for how your supplier balances its books with the wholesale market.

In practical terms:

• Your supplier knows exactly when you used each kWh — not an average of what households like yours do
• Export payments are tied to actual export timestamps — if you exported at 4pm on a Friday, that is what gets settled
• Suppliers have accurate data to design and price time-of-use products — the risk of offering you cheap overnight power is lower because they can see precisely when you take it
• Imbalance costs fall — better data means suppliers buy electricity closer to when their customers actually need it, reducing wasteful balancing

This is the infrastructure change that makes the next generation of smart tariffs commercially viable at scale.

What this means for solar panel owners

If you have solar panels and receive Smart Export Guarantee payments, MHHS makes your export settlement more accurate and more valuable over time.

More accurate export payments. Under the current profile-class system, your SEG payments are calculated against your total export readings rather than a precise half-hourly breakdown. With MHHS, suppliers settle exports at the actual half-hourly level. For fixed-rate SEG tariffs this changes very little — you still receive the same pence per kWh regardless of when you export. But for variable export products, such as Octopus Agile Outgoing or the export component of Octopus Flux, the settlement now precisely matches when your panels generated and exported.

Better alignment with time-varying export rates. Agile Outgoing pays different rates in every half-hour slot — typically 8–12p/kWh on average, but higher during peak demand periods. For this to work correctly, the grid and your supplier need to know that your export happened at, say, 5:30pm rather than distributing it evenly across the day. MHHS provides exactly that granularity.

More innovative export products ahead. Because suppliers can now see your exports at half-hourly resolution, it becomes commercially practical to design products that reward households for exporting at valuable times — peak demand windows, periods of grid stress, or moments when local network capacity is tight. MHHS is the enabler for export products that do not yet exist but are coming.

What this means for battery owners

Battery storage households stand to gain the most from MHHS, because the entire value case for a battery rests on the accuracy of time-of-use billing.

Arbitrage calculations become cleaner. Battery arbitrage — charging on cheap overnight electricity and discharging during expensive peak periods — depends entirely on your supplier accurately measuring when you imported each kWh. Under profile-class settlement, there was always a degree of approximation in how your overnight cheap-rate consumption was attributed. MHHS removes that ambiguity: your 2am charging session is settled at 2am rates, not smeared across the day.

Time-of-use tariff billing improves. Tariffs such as Octopus Go (5.5p/kWh overnight from April 2026), Octopus Cosy (10p/kWh in three off-peak windows), and Flux (tiered import and export rates throughout the day) all depend on half-hourly resolution to bill correctly. MHHS ensures these tariffs are settled accurately across the whole system — not just at your meter, but all the way back through the wholesale market.

Automation tools benefit from cleaner data. Systems like Predbat and inverter-native Agile scheduling optimise battery charge and discharge cycles based on forecast prices. These tools function correctly today, but MHHS means the broader ecosystem — supplier systems, grid balancing, network charging — is all aligned with the same half-hourly framework. Discrepancies between what your inverter sees and what your bill reflects become rarer.

Virtual power plant participation improves. As half-hourly settlement becomes universal, the signals that drive demand flexibility services — Octopus Saving Sessions, grid response programmes — become more accurate and more fairly rewarded. Battery owners who respond to flexibility calls will see those actions reflected correctly in their settlement.

Do you need a new meter?

MHHS requires a SMETS2 smart meter (second-generation smart meter). The good news is that if your smart meter was installed from 2018 onwards, you almost certainly already have one.

SMETS2 meters communicate via the DCC national network. They record consumption and export in half-hourly intervals and transmit this data automatically. You do not need to do anything. Your supplier will migrate you to MHHS settlement without any change to your hardware.

SMETS1 meters (typically installed 2011–2018) operate on a different communications system and were originally linked to individual supplier networks. Many SMETS1 meters are being enrolled into the DCC, which upgrades their effective functionality. However, SMETS1 meters may not reliably provide the half-hourly export data that MHHS requires. If you have a SMETS1 meter, contact your supplier to discuss a free upgrade.

Old-style meters (credit or prepayment meters with no smart functionality) cannot participate in MHHS at all. If you still have one of these, your supplier is required to offer you a smart meter upgrade free of charge as part of the national rollout.

Requesting an upgrade. If you are still on a SMETS1 smart meter or an old-style meter, contact your energy supplier to request a SMETS2 upgrade. This is free and ensures you benefit from MHHS when it reaches your account.

The MHHS timeline

MHHS has been years in development. Here is where the programme stands:

Migration is phased and supplier-led. Your supplier will move your account to MHHS settlement at some point between October 2025 and May 2027. You will not necessarily receive a notification — it happens in the background on your supplier's systems.

Suppliers with larger smart meter estates and more advanced data infrastructure tend to migrate earlier. Smaller suppliers may complete closer to the 2027 deadline.

What you need to do

In most cases: nothing.

MHHS is a wholesale market and supplier-side reform. The migration happens on your supplier's systems. You do not need to change tariff, replace your meter, or take any action to be migrated.

There are, however, a few things worth checking:

1. Confirm you have a SMETS2 meter. If you are unsure, ask your supplier. If you have SMETS1 or an old-style meter, request a free upgrade now rather than waiting. Earlier is better — you will be eligible for better time-of-use tariffs sooner.

2. Check your export metering is working. If you have solar panels and claim SEG payments, log into your supplier's portal and confirm your exports are being recorded. If export data is missing or looks wrong, contact your supplier before MHHS settlement reaches your account.

3. Review your tariff once MHHS is in place. When half-hourly settlement is live on your account, it may be worth exploring whether a variable export or time-of-use tariff suits your usage pattern better than your current deal. Better settlement accuracy means more of the financial benefit flows correctly to you rather than being lost in rounding errors.

4. If you use automation tools, such as Predbat or Home Assistant-based inverter scheduling, no changes are required. These systems operate based on your inverter's data and price forecasts, which are not directly affected by how your supplier settles the wholesale market.

The bigger picture: why MHHS matters for the energy transition

MHHS is not just an accounting reform. It is part of a broader shift in how the UK energy system works.

As more renewable generation connects to the grid, the value of electricity becomes more time-dependent. Solar peaks at midday. Wind peaks unpredictably. Demand peaks in the early evening. The grid operator — National Grid ESO — needs to balance these flows constantly, and the cost of doing so is significant.

A system where every household's consumption is settled on actual half-hourly data, rather than national averages, gives the market far better signals. Suppliers can see when their customers are genuinely flexible. Network operators can see where demand concentrates. Price signals can be more accurately targeted to shift consumption to times when the grid is abundant and cheap.

For solar and battery households, this is straightforwardly good news. Your ability to generate, store, and shift consumption is exactly what the grid needs. The more accurately that flexibility is measured and rewarded, the better the financial case for the investments you have already made.

The dynamic energy pricing products you can access today — Agile, Flux, Intelligent Go — are possible because smart meters exist. MHHS is what makes those products financially sustainable at scale, and what enables the next generation of even more responsive tariffs.

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