2 December 2025

RIIO - ET3 and increasing costs

Following on from our previous article about rising TNuOS costs, we look at the reasons behind energy price rises, and which other items on your bill are likely to increase in the near future.



What is RIIO – ET3?

RIIO: “Revenue = Incentives + Innovation + Outputs” is Ofgem’s regulatory framework for setting how much network operators can recover from users while delivering value, efficiency and innovation. The current RIIO-2 period ends 31 March 2026, and RIIO-ET3 (also called RIIO-3) will run from 1 April 2026 through 31 March 2031. 

What changes are being made?

RIIO-ET3 introduces a number of significant changes in how network costs are recovered and how risk and incentive mechanisms operate. The key proposals include:


  1. TNUoS (Transmission Network Use of System)
    Under RIIO-ET3, TNUoS charges will be higher, reflecting the scale of investment required to upgrade the grid. Our 
    recent article looked in detail at these charges.
  2. BSUoS (Balancing Services Use of System)
    While BSuOS is not a transmission-specific charge, balancing and system operation costs will increasingly feed through to users as the system becomes more complex. These costs may grow due to higher levels of intermittent generation and greater need for flexibility and system balancing. 
  3. NRAB (Nuclear RAB or Network Revenue Adjustment / RAB-style levies)
    This new charge (
    that we discussed in detail here) is designed to help fund the UK’s growing nuclear energy fleet.
  4. Other structural changes, uncertainty & incentive mechanisms
  • A “stepped” Totex Incentive Mechanism (TIM) approach: overspends/underspends will be shared differently in different bands (e.g. 25 % sharing on first 5 %, lower sharing on next bands)
  • Greater use of uncertainty mechanisms, UIOLI (Use-It-Or-Lose-It) allowances, and new load reopener windows to allow costs to be adjusted mid-period if demand or connection needs differ from estimations.



Because RIIO-ET3 is still in draft and under consultation, many of these mechanisms remain subject to change with the proposals set to be confirmed in December 2025.


Why are these changes being made?

The changes in RIIO-ET3 stem from the need to dramatically increase investment in electricity transmission to support net zero and decarbonisation. Ofgem and the government now have statutory net zero and economic growth duties, pushing for faster decarbonisation while trying to shoulder as little of the financial burden as possible.

Older frameworks (such as in RIIO-2) are judged too rigid to handle uncertainty, volatility, and the scale of change required. The new design aims to allocate risk more flexibly and provide transmission companies with greater investment to deliver the grid upgrades needed. 

What impact will it have on my business?

You are likely to face higher non-commodity costs in your energy bills. TNUoS charges will increase meaningfully, especially for customers with high peak demand or connections in constrained areas. BSuOS and balancing costs may also escalate as the system becomes more dynamic. Over time, the introduction of RAB-style cost recovery could further add to existing fixed network charges. Depending on your size, flexibility and demand profile, your business might see a notable rise in transmission and system charges in the 2026–2031 period.


If you would like to discuss exactly how these changes could impact your business, contact our expert advisors at SeeMore Energy to see how we can help you manage your energy costs.

by Craig Watson 27 March 2026
With consumer spending declining and OFGEM raising their price cap, you would be forgiven for seeing February as a month where negative news was at the forefront, but in the energy markets, this was not the case.
by Craig Watson 27 March 2026
In a year that began with falling energy prices, there were recurring catalysts that led to prices climbing steadily higher. Geopolitical uncertainty and the perennial threat of escalating conflicts meant fear would maintain a constant presence in the wholesale markets. We will look back at the key energy stories from 2024, and how the energy markets are likely to shape up in 2025. Quarter 1  The year began with cautious optimism as the UK’s gas reserve levels were healthy and prices for the Summer’24 season were in freefall. In February, prices pulled back to their lowest levels since 2021, and for the first time in a while, we identified that there was greater potential for upside risk than for further downward price movement: “ there now (exists) an asymmetrical element of risk should the market encounter a supply-side problem of significance. ” During February we had advised customers on flexible contracts that this was an ideal time for making purchases. March would see prices begin to ascend again as international conflict would create problems with LNG imports, and we would highlight the geopolitical risks as an area for concern moving forwards: “ fears remain and there are potential negative catalysts that could lead to prices rising further, with the main factors to watch out for being based on geopolitical unrest. “ For a business that purchases their energy in advance, this quarter was the optimal time for purchasing during 2024. In February, electricity prices for Winter’25 were down to 7.75p/Kwh, and as low as 6.05p/Kwh for Summer’25. Winter’25 ended the year with prices above 11.1p/Kwh, with Summer’25 prices exceeding 9p/Kwh. For a company that uses 500,000Kwh of electricity per month, the difference between buying at the February low point compared to today’s prices would represent a yearly saving of over £200,000.
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