NGESO wants industry input on how to manage a fast-growing element of electricity costs: constraint paymenst that arise because the network is limited in how much power can be transferred. These ‘constraint’ costs now represent around 40% of so-called ‘use of system’ charges that are allocated among system users, and they are set to grow as much more renewables is added to the system, often in areas remote from users. NGESO said some spots on the network, “are congested 85% of the time and the original management [regime] is no longer fit for purpose”.

The biggest constraint at the moment is the need for new lines to transfer power from new renewable generation – largely in northern Scotland – to users in England and Wales. This bottleneck was highlighted last week because the Western Link, a major offshore connection between Scotland and England, was out of action and is expected to remain so until the end of March. That raised constraint costs as high as £10M on one day last week.

In the long term, the aim is to install at least four new major connections between Scotland and the England/Wales system, as well as other new major connections on areas where new interconnectors or offshore wind landfall will raise similar issues.  But that will take a decade, as would options such as long duration storage, such as new pumped hydro, for which BEIS is considering a ‘cap and floor’ regime which would mean consumers underwrite projects.

Meanwhile, system operator NGESO has sought aid from the industry on action that could be taken by 2025 and will open a call for expressions of interest on 8 March.

Four year plan

Among the options where NGESO is looking for industry input is ‘intertrips’.  In this measure assets would act something like domestic circuit breakers. In the event of congestion and a surge on the line they would ‘trip off’ to reduce load, forestalling a trip on the line itself and protecting other customers. They would be automatically brought back on line afterwards.

The assets would be paid both for availability of the service and in the event of a trip, potentially providing a new revenue stream for assets that can take part. NGESO said it  wanted to have expressions of interest in the next few months, with a view to running a commercial tender in July-August for delivery from October.

NGESO asked for information from distributed generation operators, although they will not be able to take part in the pathfinder project, because it wants to set the option up as a commercial service including embedded generators in future. Also, in another measure under investigation, it is considering using such generators in a regional constraint management option that would probably be managed in co-operation with distribution system operators (DSOs).

Although the system operator has developed plans for some options, it stressed it was engaging early, not just so the new measures would be ‘co-designed’ with industry but also to be open to other suggestions. The system operator said that among other issues it had to make sure new commercial options would not ‘cannibalise’ other revenue lines for system assets.

Immediate options

Alongside interim solutions, the SO is investigating, with the transmission network owners, five immediate and low-cost technical options that individually make a small impact but cumulatively it said may be “highly beneficial”.

Some rely on the fact that the capacity of each power line is limited because excess power raises the temperature of the cable. Warmer cable stretches and the cable sags and that has to be limited.  However, in most cases the temperature limits are fixed, with considerable margin for safety, and without taking into account varying natural conditions – such as cooling winds – that would allow limits to be adjusted.

Among the options being investigated are:

• ‘Smart valves’ that can ‘redirect’ power to ease an overloaded line.
• Using existing intertrips. 
• ‘Dynamic line ratings’ in which the capacity of the cable is recalculated in real time.
• ‘Hot wire’ in which specific cables are ‘retensioned’ to allow for more sag.  

All have to be investigated to ensure that they do not simply shift the problem to the next line.

More information on the constraint management engagement and pathfinder here

 Further reading

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