Due to inadequate network capacity, renewable energy is being wasted, adding to energy bills and increasing carbon emissions. From October 2021 to September 2022, National Grid ESO spent £2bn switching off renewables to manage constraints on the transmission system.(1) ESO forecasts that constraint costs will rise above £3 billion by 2030 – assuming planned infrastructure is built on time.(2) ESO analysis commissioned by the Government shows that a 3-year delay would increase constraint costs even more, to around £8bn in the late 2020s. This would add £80 a year to the average household electricity bill. 

Energy storage can reduce these costs. In international contexts like Germany and Australia, batteries are already being used to tackle constraints, reduce energy bills and cut carbon emissions. But the UK has not yet grasped opportunities to harness clean tech to cut bills. 

The Cost-Effective Solution 

In this paper, four leading energy storage companies set out policy solutions that can cut constraint costs. If implemented, these will allow ESO to use low carbon technology to increase flows of renewable power across constrained boundaries, saving consumers money. We set out cost-effective options to ease constraints before the end of the decade, bringing down energy bills while bolstering energy security by using renewable electricity more efficiently. 

Ahead of transmission network reinforcement forecast from 2027 into the 2030s, battery storage is the only available option to reduce emissions and system costs from constraints. In January 2024, National Grid ESO initiated the Constraints Collaboration Project to explore opportunities for new services that can unlock the value of battery storage to alleviate constraints. 

Eku, Zenobē, Field and Kona have all proposed aligned solutions. We have each identified that ESO has an opportunity to implement enhancements to the current intertrip scheme, known as the Constraint Management Intertrip Service (CMIS), and to use flexible capacity to increase utilisation of available network capacity. In this paper we summarise these solutions, illustrating how ESO can – if they upgrade their ageing technical systems – use batteries to rapidly reduce the public cost of constraints.  

Four businesses, shared solutions 

Two key options for using storage to alleviate constraints have been identified: (1) enhancing intertrip services; and (2) using storage to increase network capacity. 

Enhanced intertrip schemes: An intertrip automatically disconnects generation or demand from the electricity system in the event of a fault, preventing overloads, maintaining stability or managing voltage. The ESO is already using batteries with Constraint Management Pathfinder contracts to alleviate constraints using intertrip schemes. To expand this, we recommend enhancing intertrip schemes using batteries for constraint management by: 

• Increasing the size of the intertrip capacity procured via the Constraint Management Pathfinder in line with increasingly large infeed losses seen from energising increasingly larger low carbon energy infrastructure (e.g., Hinckley Point C). 
• Procuring more inertia, response and reserve to enable the electricity system to withstand a larger instantaneous loss, allowing an even larger capacity via the intertrip service. 
• Applying the intertrip to all storage behind constraints, providing more operational capacity and choice, and only arming batteries when exporting. 

Using storage to increase network capacity: During thermal constraints in Scotland, the ESO does not use maximum boundary transfer capabilities due to a need to keep reserve capacity, or headroom, on the network. Otherwise, an unexpected fault on one of the boundary circuits could suddenly increase power flows across the remaining circuits, pushing them beyond safe limits. To enable the ESO to maximise use of network capacity, we recommend: 

• Using batteries as a shock absorber to import power during wind gusts and exporting power during wind lulls, all during a continuous period of constraint, enabling the ESO to keep less reserve capacity at constraint boundaries and increasing power flows across them.  
• Pairing storage systems across constraint boundaries to manage imbalances between constrained and unconstrained zones (mimicking virtual power flow solutions already in use on international transmission networks); enabling the ESO to increase the pre-fault power flow across the boundary by accessing the short-term circuit rating of the smallest circuit; and unlocking up to 40% more transmission capacity.  
• Installing a battery on the demand side of the constraint, directly connected via an intertrip similar to the generation on the other side of the constraint, enabling the ESO to reduce the transmission line’s rating from 10 minutes to three minutes on specific boundaries by injecting active and reactive power.  

• Using battery storage systems as a demand initiation service (with frequency management managed by a paired battery outside the constraint to reduce Control Room post fault actions).  This would operate as a pre-fault service with a battery on standby ready to charge, initiated for a transmission fault (as for intertrips). This service would not be limited in its duration pre-fault and would remain on standby for very long periods, providing enhanced ratings at the boundary as a function of its effectiveness against contingent faults. 

We believe there is a strong case for a market trial of these solutions with the intention to expand their use as experience increases. If the scheme is designed to enable stacking, then it can be delivered at lowest cost and utilise existing assets, as well as those coming online. This will enable parties to come forward to provide these solutions – just as they have with fault-current, voltage, inertia and other ancillary services.