National Grid expects embedded solar PV to increase by 150MW a month over 2017, which would take UK installed capacity towards 13.5GW. Meanwhile the system operator has spelt out the scale of the challenge it now faces in keeping the system balanced in summer as well as winter.
National Grid’s Summer Outlook report says summer minimum demand continues to fall as generators connected to the distribution system, over which it has limited visibility, continue to rise.
National Grid will therefore pay other generators to stop pushing power onto the transmission system over summer. It must do that to keep frequency stable at 50Hz. Too much power drives frequency upwards, too little creates a drop in frequency. Once it hits a pre-set threshold, actions are taken to keep it in check. Otherwise the system could potentially fail, leading to power cuts.
Dynamic frequency response is one way of keeping the system balanced. Automated fast-acting assets, such as batteries or fridges or electro furnaces, can be aggregated to respond in either direction. National Grid has other forms of frequency response at its disposal but may decide to wrap them all into a single ‘pre-fault’ service in order to maximise fast types of frequency response when trigger points are reached.
Get your RoCoF
However, National Grid has also recognised the need to deal more proactively with system inertia issues. Along with generators, technology firms and aggregators, it is involved in trials of technology that would enable it to react not just at set trigger points, but to the speed of frequency change. Those trials, around rate of change of frequency (RoCoF) should also give National Grid a clearer understanding of how regional variances can lead to different knock-on effects throughout the system.
Turn up, tune in, drop off
This summer, National Grid is likely to procure most demand turn up (DTU) during June and July, when it predicts demand will be lowest due to long daylight hours increasing solar generation.
Demand turn up pays companies to increase power consumption or turn off their on-site generation and instead draw power from the grid, helping to reduce system frequency.
While National Grid has already procured 138.6MW of DTU via a fixed tender in February, it will likely buy several times more capacity via flexible tenders run fortnightly during spring and summer. Providers in the flexible tenders can name their own price. If it is cheaper for National Grid to take that price than to use other balancing options, those companies are called upon to deliver.
Given solar was creating challenges for the system operator as early as March this year, it looks set to be an interesting service in terms of how providers play their hands within ongoing tenders.
National Grid confirmed late last year that it would look to broadly double the 300MW of DTU it procured in 2016.
See the full summer outlook here.
Developments within demand turn up and frequency response will be covered at The Energyst’s DSR Event in London, 7 September. Register for a ticket here.