Can we cope with the solar eclipse?

Ian Talbot | 20 Mar 2015 | Comments

The solar eclipse will result in a loss of renewable generation to meet the nation’s energy demands but whilst we are watching this wonderful phenomenon we should have no concerns regarding the lights going out in sympathy with the sunlight.

Solar generation relies on the quality of sunlight as well as the angle of incidence. On a clear sunny day the output of the UK’s 5GW of installed solar generation would drop as the sun becomes obscured by the moon passing in front. However, on cloudy days as is forecast for Friday the light quality is already reduced such that generation is down to 20% of full output and the effect of generation loss is dramatically reduced. Even without this, it will not be a rapid event in electrical system terms because as the seen from the earth, the moon will take about an hour to cover the sun and then another hour to reveal it again. During this time the average output from solar cells distributed across the UK will ramp down and then ramp up again.

It is quite easy for National Grid to prepare for this generation shortfall by scheduling traditional fossil fuelled generation of coal or gas to replace the lost solar generation. With the expected load reduction from people stopping normal activities to view the solar event then it is quite likely that National Grid will have to take relatively little action and the system will ride through the event with minor frequency changes.

To put this in perspective, every day in the UK the working population goes home at approximately the same time and cooks an evening meal. In winter, this results in a regular increase in load of 8GW over a similar duration. Then as we all settle down to watch TV the load drops off again to the background evening load levels. This daily load change is planned and takes place without anyone realising it happens.

Load profile
Typical winter and summer load profiles for England and Wales in 2002

Of far greater difficulty to plan are the short duration load swings that occur in the UK, for example as a result of large numbers of people watching the same TV programme and then all simultaneously turning on millions of kettles to make a drink when it ends. Surges of up to 3GW of load over a five minute period regularly occur on the UK network but are managed through rapid response of Pumped Storage generation and power imports from HVDC connections to other countries.

National Grid will be carefully watching the system to correct for any unexpected changes in voltage or frequency but it will simply be another event in a daily balancing act between load and generation.