On the morning of March 20 up to some 35,000MW of solar energy in Europe (depending on local weather conditions) is set to gradually fade and then gradually be reinjected over a 2-hour period as a solar eclipse takes place over the Atlantic Ocean and across continental Europe and North Africa.
For the first time such an event has the potential to impact Europe’s power system – leading the European transmission system operators association (ENTSO-E) to develop a plan to mitigate the impact and maintain security of supply at a level comparable to that of a standard operating day.
Eclipse affects Europe’s PV
In 2015 the installed capacity of PV in the synchronous area of continental Europe is expected to reach 90GW. In order to assess the effects of the eclipse, ENTSO-E estimates the PV level in each country to find that under clear sky conditions, a maximum drop of 34GW could occur at 9:41 (UTC) or 10:41 (CET). On a minute-to-minute basis the power gradient may exceed -400MW/minute and +700MW/minute – this higher gradient occurring when the PV infeed returns and requiring a reduction in the load following reserves.
Germany, with a 50% infeed reduction and Italy with 21% reduction are found to be the countries most affected, indicating that the risk of line overloading should especially focus on this region. Other countries strongly affected are France, Spain and Belgium.
ENTSO-E says that while not all the TSOs will be affected by the eclipse on the same scale, all will see the same impact on the frequency. Thus, some countries that are not affected by PV variations can support the other TSOs by providing them reserves. The main challenge for the TSOs will be to coordinate the use of the reserves in order to balance the power in real time without creating overloads on the grid. To this end continuous online coordination is being put in place between control rooms across Europe ahead of, and during the eclipse to better coordinate the scheduled remedial actions.
Day-ahead forecasting of PV
Among the recommendations is that as the infeed from PV is highly dependent on cloud coverage, day-ahead forecast of PV will be particularly important for March 20 and careful preparation and coordination of solar forecasts are necessary.
TSOs are also recommended to estimate and increase the amount of control reserves they will need to follow the gradient of PV variations (mainly frequency restoration reserve). TSOs expecting difficulties in balancing their control areas with their own reserves should ensure the use of reserves from other TSOs.
Great Britain’s grid expected to cope with eclipse effects
In the Great Britain synchronous area the loss of PV infeed during the eclipse and its return after maximum obscuration is calculated to occur at a maximum rate of just below 50MW/min. However, the change in residual demand due to the halting of normal activities by people to observe the eclipse dominates the PV effect and acting in the opposite direction, serves to ameliorate the situation. Thus, the rates of change of residual demand will be slightly less than those experienced during the previous eclipse in 1999, for which National Grid Transmission System coped well. The system is also expected to cope well with the March 20 eclipse.
In their conclusions ENTSO-E comment that TSOs are taking all necessary measures to mitigate the risks. However, the solar eclipse is a perfect illustration that maintaining system security with more and more volatile and dispersed generation is becoming increasingly challenging.