IN Brief:
- Centrica Energy has contracted 100MW/400MWh of German battery flexibility from Return under a long term virtual tolling agreement.
- Capacity will come from Return's portfolio of physical German batteries rather than one dedicated storage site.
- Centrica will optimise the portfolio across wholesale and ancillary service markets, allowing additional flexibility to be added as Return expands.
Centrica Energy and Return have signed a long term virtual tolling agreement covering 100MW/400MWh of battery flexibility in Germany, using capacity drawn from a portfolio of physical storage systems rather than one dedicated project.
The capacity will be supplied through Return’s Virtual Flexibility Portfolio, which aggregates batteries owned by the company across Germany. Centrica will use its trading and optimisation systems to commercialise the contracted flexibility in wholesale and ancillary service markets.
A conventional battery toll is generally tied to a named asset whose power and energy are made available to an optimiser under agreed terms. Return’s model instead allocates contracted capability across a wider fleet, allowing eligible capacity to be sourced from several physical batteries as operating conditions change.
Maintenance, temporary outages, state of charge, connection restrictions, and equipment availability can therefore be managed across more than one site, provided the portfolio continues to meet the contractual obligations. The individual batteries remain subject to their own technical and network limits, so aggregation does not remove the physical constraints behind the virtual product.
Centrica will have to coordinate those constraints across wholesale trading and ancillary services. Each battery has a finite quantity of stored energy, a defined power rating, conversion losses, cycling limits, and a permitted operating envelope. Capacity reserved for one service cannot be sold simultaneously into another if both commitments could require delivery at the same time.
The portfolio structure also allows different batteries to be used for different market conditions. Assets with higher power relative to energy capacity may suit fast services, while systems with longer duration may be better placed to exploit sustained wholesale price spreads. Location, network conditions, and service qualification can further influence which site is dispatched.
Centrica has already been expanding its European battery optimisation business through asset specific agreements. Its recent Finnish agreement covers the 125MW/300MWh Karppio battery, while the 99MW/297MWh Hilgermissen project in Germany is covered by a separate tolling arrangement with Zelestra.
The Return deal takes a different form because the contracted 100MW/400MWh is not presented as one four hour battery. The power and energy commitment sits across a virtual portfolio, giving Return scope to allocate flexibility from several systems according to their availability and the rules governing the relevant market.
Return has been developing the same portfolio model with other counterparties. Earlier this month it expanded a virtual flexibility purchase agreement with ENGIE in Germany to 400MW, demonstrating that multiple commercial arrangements can sit over a growing pool of underlying storage assets.
Portfolio contracts can provide storage owners with greater revenue visibility while transferring some trading exposure to specialist optimisers. Battery revenues vary as wholesale spreads, balancing prices, ancillary service requirements, and competing capacity change, making merchant income difficult to forecast over the life of an asset.
An optimiser takes on part of that market complexity in exchange for access to the flexibility. The exact allocation of price risk, availability risk, degradation cost, and upside has not been disclosed for the Centrica agreement, but those elements will determine how the commercial value is divided between the two companies.
Aggregation also increases the importance of data and control systems. Centrica needs timely information on state of charge, available power, site restrictions, outages, and market commitments if it is to dispatch a virtual fleet as one commercial resource. Return must in turn ensure that instructions sent through the portfolio remain within the technical limits of each participating battery.
German network conditions add another constraint. Batteries located in different regions may participate in the same national wholesale market while facing very different local connection conditions. Congestion, curtailment rules, and grid operator requirements can influence whether an otherwise attractive dispatch instruction is physically possible at a particular site.
As more batteries enter service, optimisation is becoming a larger part of project economics. Hardware provides the physical capability to store electricity, but trading systems determine when that capacity charges, discharges, remains idle, or is reserved for another service. A larger virtual fleet gives the optimiser more combinations through which to satisfy those decisions.
The 100MW/400MWh Centrica agreement adds another contracted layer to Return’s German portfolio without tying future growth to a single site. Additional eligible storage can be incorporated as Return expands, allowing the commercial arrangement to scale alongside the physical fleet rather than requiring a new optimisation contract for every battery.
