Utility Week

14 | DECEMBER 2021 | UTILITY WEEK Electricity Analysis Can we rely on low-carbon sources to restart the grid? A major new project has proven that low-carbon restart is possible – the question is can it become business as usual? A Utility Week insight report, in association with Distributed ReStart, takes stock of the project and the blockers to progress. D uring September and October 2021, a major milestone was reached in energy distribution and the journey to net zero. A•er months of preparation, a small hydroelectric generator was able to energise a completely dead transmission network in the Galloway district of southwest Scotland. In doing so it proved it is possible to restart the transmission network from a distributed energy source – a world first. The trial was the latest stage of a hugely important project being under- taken by National Grid ESO in partner- ship with SP Energy Networks and energy consultancy TNEI. The £10.3 million Ofgem-funded project, known as Distributed ReStart, began in Janu- ary 2019. Its aim is to explore the potential for restoration services to be provided by dis- tributed energy sources (DER) such as wind, hydro, energy storage and other low-carbon energy generators. The current plan in place for a national outage of power takes a top-down approach, reflecting the current highly centralised gen- eration system. But as we move to more dis- tributed power – ESO has pledged to run a decarbonised grid by 2035 – it is essential to test and plan for this very different scenario. Though the probability of a nationwide out- age of services is considered unlikely, the impact should it happen and not be restored quickly, could be catastrophic. The project will run to the end of June 2022 a•er two more trials have been com- pleted. Importantly, the clock is ticking because ESO sees the harnessing of DER as a new component in meeting more stringent restart requirements in a new restoration standard that comes into force in 2026. What has been achieved so far? "We've designed an organisational model for restoration from the distribution networks up to transmission level," explains Peter Chandler, power system manager and lead for Distributed ReStart at National Grid ESO. "The organisational model specifies who instructs, who follows, what happens, the roles and responsibilities and how it all fits together. Basically, a new model for com- mand and control," he says. "We've designed the model and road tested it through a series of desktop exercises that we conducted in the spring. We secured stakeholders from the industry, including representatives from the DNOs [Distribution Network Opera- tors], DERs, transmission companies and the ESO control room, to basically role play themselves." These stakeholders were then taken through a scenario where they had to effec- tively build a distribution power island from black, resulting in an organisational model, which says Chandler they "are comfortable with". The details for this final proposal were published in September. One of the three live trials (all on Scottish Power's networks in Scotland) have been successfully completed but extensive mod- elling has been undertaken on all three of them. "We've proven on paper that it's cred- ible. We're just shoring that up by doing the case study live trials that will provide confi- dence to industry participants that it works." Chandler says that the sticking points to the project are not to do with logistics, but more to do with incentives and contracts and being able to spread the not inconsiderable expense for its implementation across the network, including readying the distribu- tion network and DER for restart – because most would not have been designed for that purpose. He explains: "There's a lot of technical requirements for a restoration service to be able to maintain a small power island – to be able to start several times, control voltage levels, be capable of demand block loading and regulate frequency, inertia and system strength." "When you scale the technicalities down to distribution level, a lot of these smaller DERs cannot provide all those requirements. So our commercial model for DER restoration services is to split up provision into what we've called anchor generator and top-up services. "The anchor generator is the initial self- starting generator. It must have the ability to start from black from its own back-up aux- iliary supplies, be contactable 24/7, be able to create a voltage reference and be able to regulate frequency." The top-up services cover all the other technical requirements needed to create stable power islands. Chandler says the Distributed ReStart designs are technol- ogy agnostic, capable of sustaining storage capabilities such as batteries and flywheels, flexible demand capabilities, as well as con- ventional synchronous generation. "By splitting up the technical require-

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