In recent history, the British electricity sector landscape has changed as more renewables, particularly solar and wind, are connected to the power system. Since 2004, electricity generated from renewables in the UK has increased tenfold, and in 2019 37.1% of total electricity generated was from renewable sources.  These changes have far-reaching implications for the operation of national electricity networks and for ensuring security of supply.

The larger renewable installations are connected to the high voltage transmission network that interconnects the whole of Britain. Smaller ones are connected into the regional lower voltage distribution networks that, typically, transfer power from the transmission network down to each individual electricity users.

The technology used to convert the primary energy source into electricity is very different for renewables such and wind and solar from that used for thermal sources such as fossil fuels and nuclear fission. A common feature of wind and solar generators is the use of power electronic converters. Although the uptake of renewables is in keeping with Britain’s emissions reduction and renewable energy targets, it has the side effect of displacing conventional fossil-fuelled generation and the technical characteristics that these synchronous machines provide to power system operation. As a result, the British Electricity System Operator, National Grid ESO (NGESO), frequently needs to pay conventional power plants to come online and deliver key system services to ensure the security of electricity supply.

Going forward, in April 2019 NGESO announced a target of being able to operate a GB electricity system with zero-carbon generation by 2025. In practice, this means that NGESO aims to operate the system without needing to take actions that would restrict the dispatch of zero-carbon generation in favour of providing balancing services using unabated fossil fuel power plants, avoiding the need to “constrain on” such generators in addition to any that the wholesale electricity market might already be using. In order to achieve this, new service specifications and procurement mechanisms will be required to give NGESO the option of accessing services from zero-carbon technologies rather than coal and gas plants.

Current and emerging system operability concerns in GB cover a broad range of topics. Work recently completed at the University of Strathclyde, outlined in this report, has reviewed: how NGESO currently uses balancing services to manage the power system; possibilities for the future provision of frequency response and reserve; prospects for short circuit current support from power electronic converters; and market changes required to avoid the need for NGESO to constrain on fossil-fuelled generation to support system operability in 2025.