In September 2026, Statkraft and SSE traded the first swap referencing the ME BESS GB (2h) index. The contract settles against a regulated measure of what GB batteries earn.

On 29 September and 6 October 2026, Modo Energy hosted asset owners, developers, utilities, banks and funds in London to work through how these swaps are built and who would use them. This article covers what was presented. The full slide deck is available to download at the bottom of the article.

A revenue swap lets a battery owner exchange a floating index for a fixed £/MW/year rate. Over the last 12 months, the 2-hour index averaged £69k/MW/year. Across 17 GB 2-hour batteries, an index swap cut median monthly revenue volatility from £22k to £12k/MW/year. The buyer, in turn, gets revenue that rises when wind and solar revenue fall.

Key takeaways

• A swap is a financial overlay used to manage risk, not a route to market. It settles on a notional volume with no availability or dispatch terms. It would sit alongside other contracted revenues.
• The ME BESS GB indices capture 50% more revenue than a day-ahead spread. The 2-hour index averaged £69k/MW/year from September 2025 to August 2026; the day-ahead TB2 spread implied £46k.
• An index swap reduces volatility more than a TB2 swap. Median monthly volatility fell to £12k/MW/year with an index swap, versus £15k with a TB2 swap.
• Battery revenue offsets renewable revenue. A 1,414 MW index swap cut the monthly revenue volatility of a 500 MW AR3 offshore wind farm by 47%.
• Basis risk stays with the asset owner. A battery that underperforms the index ends below the fixed rate.

GB BESS contracting has moved from large Capacity Market contracts to floors to swaps

Each new structure has moved more revenue risk away from the asset owner.

In 2018, most projects were underpinned by a sizeable Capacity Market contract giving long-term secure revenues, with either a lengthy EFR contract or some merchant exposure through an FFR contract. Floors became commonplace around 2021, when the market matured and sites grew to 50 MW. Then, from 2024, physical tolls covered portfolios of ~200 MW or more: the Gresham House and Octopus Energy toll being a prime example. The first battery index swap has been signed in 2026, and these need no physical asset at all.

​​The chart below applies each structure to the same 2-hour asset. Click through the tabs.