As I write this at 8.26 a.m. on the morning of the 8th May, a Friday but a national holiday in the United Kingdom, we are waiting to see how National Grid ESO (Electricity System Operator) will cope with the combination of anticipated low demand for electricity and high solar output from the 12 GW of solar generation capacity connected to the Distribution Network.
Energy from this source reduces Transmission System demand at around midday and after, well before the evening peak, resulting in a novel and somewhat bizarre dual peak to the daily demand, as can be clearly seen in the following chart generated and published by National Grid itself, and describing load over the last seven days.
Figure 1: Transmission System demand for electricity in the United Kingdom, from the earlier morning of Thursday 30 April to 08.22 Friday 8 May. Source: National Grid. Red arrow indicating trough in Transmission System Demand caused by embedded solar generation added by the author.
The operator’s problem is to keep sufficient conventional rotating plant online to provide stabilising inertia, while at the same time making space for generators granted effective must-run status, wind power and solar power, which do not contribute inertia. In addition, with very low load of this nature that inertia must provided in chunks small enough to render manageable their sudden absence, as a result of a power station tripping for example. At 1.2 GW, Sizewell B nuclear power station is rather large for the job.
However, National Grid’s task today is made that much easier by the fact that combined wind generation, on and offshore, is expected to be not much more than 1 GW in total, from a nationwide fleet of about 23 GW. The solar forecast is also lowish, at just over 6 GW in the early afternoon, only fifty percent of the solar fleet’s peak capacity. It will be interesting to discover, as we eventually may, how much of that low output is the result of low winds and cloud cover, and how much has been bought off the system with bilateral trades, and at what cost.
Dr John Constable, GWPF Energy Editor.