What is Market-wide Half Hourly Settlement (MHHS)?

MHHS stands for Market-wide Half-Hourly Settlement – an upcoming change in the UK’s energy system. Just so you know, “settlement” is the process of matching the amount of energy we buy for our customers with the amount you actually use.

How is MHHS different to the current system?

At the moment households are “settled” on estimated energy use, based on general energy patterns (not real-time use). Suppliers then forecast how much energy their customers might use, and buy that amount in advance. As you can see, it’s not the most accurate way of doing things. Plus, it doesn’t reward you for using energy at off-peak, or greener, times.

With MHHS, your smart meter records anonymous readings every 30 minutes. This gives suppliers the data they need to buy the right amount of energy for all customers. It’s far more accurate.

Basically, MHHS means suppliers can more accurately match demand with supply.

Differences between MHHS and the current system

Here’s a table to show the differences between the old and new system:

What MHHS means for you

Benefits for customers

• Smart tariff options
  Access to new tariffs that reward you for using energy at cheaper, greener times.
• Supports greener energy
  Makes it easier to use renewable energy and electric vehicles by matching use to off-peak times.
• Lower prices
  Suppliers can buy energy more accurately, meaning fewer costs get passed on to you. But, these savings will be fairly modest for customers on single and two-rate tariffs.

Will I save money with Market-wide Half-Hourly Settlement (MHHS)?

MHHS opens the door to fairer, smarter tariffs that reward you for using energy during cheaper, off-peak times. For example, our new EV tariff offers lower overnight rates of 6.5p/kWh between 12am and 5am. This tariff was designed to use the benefits of MHHS.

By choosing a smart tariff, most people won’t even need to change their habits to start seeing lower bills. But if you're happy to shift some of your energy use – like running appliances in the evening or overnight – you could save even more.

When does Market-wide Half-Hourly Settlement (MHHS) start?

The Market-wide Half-Hourly Settlement (MHHS) programme will start rolling out from September 2025. From late 2025 through to 2027, energy suppliers will gradually switch customers over to the new system. By mid-2027, all households in Britain are expected to be fully moved onto MHHS, helping create a fairer, smarter energy system for everyone.

What happens next

There’s nothing you need to do right now. The switch to MHHS is happening behind the scenes and won’t change anything about your supply. To get ready for MHHS we need to start using half-hourly smart meter data to forecast how much energy we need to buy once the system is live.

It's possible to opt out of half-hourly readings for MHHS – you’ll be able to do this in your online account.

In the future, you might want to explore a smart tariff that rewards off-peak energy use. We’ll let you know when more of these are available, and make sure any future steps are simple and clear. There’s no need to switch tariffs or contact us yet.

What's So Energy doing to help its customers?

At So Energy, we're committed to:

• Making the transition simple and clear for our customers
• Offering smart tariffs that are easy to understand and genuinely help you save
• Using smart meter data responsibly and securely, always with your permission
• Keeping pricing fair and transparent, no matter how you use your energy

We’ll continue to share updates and helpful tips throughout the MHHS changes, and we’ll be here to support you every step of the way.

FAQ: Market-wide Half-Hourly Settlement (MHHS)  

Do I need to have a smart meter for MHHS?

Yes, you need a smart meter to be able to send half-hourly readings. If you opt out, your settlement will stay as it always has been – an estimate. If you don’t have a smart meter yet, we can install one at no extra cost.

Will my bills look different?

No. If you’re not currently on a smart tariff, your bill will still look the same as today. But, if you choose a smart tariff in future, then your bill may look different.

Will my billing cycle change?

No, you’ll still get monthly bills.

Does MHHS mean that I’m better on a fixed or variable tariff?

MHHS itself doesn’t means you have to choose a fixed or variable tariff. It will allow you to choose a new smart tariff where prices can be tailored to fit how you use energy. If you’re happy to shift your energy use to cheaper times, a variable or smart tariff could save you money. If you prefer stable, predictable bills, a fixed tariff might still be right for you.

Might my bill go up?

It’s unlikely. MHHS won’t affect your standing charge or unit rates if you're on a fixed contract. But how and when you use energy could have more of an impact on your bill in future. With smart tariffs becoming more common, using electricity during peak times (like early evening) could cost more, while off-peak use (like overnight) could save you money.

The good news is you’ll have more control over your energy use than ever before.

What happens when a supplier buys more energy than their customers use?

If a supplier overestimates how much energy is needed and buys too much, there’s an imbalance. The extra energy is sold back to the grid, but at a lower price, so the supplier loses money. Plus, they have to pay an imbalance charge. This is why suppliers try to buy energy as accurately as possible, so these costs don’t get passed onto customers.

Who has access to my smart meter data?

Smart meter half-hourly settlement data doesn’t include any of your personal data. It’s anonymous, and is only used by your supplier to report on the overall customer base.

Your supplier will use your smart meter data to suggest money-saving tariffs. This data can also be used by you, when you log on to your account and view your energy-use graph to monitor trends and spot ways to save money. You can control how your data is used using your online account at any time.

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