The last weekend in June, overnight on Sunday 28th, saw another record low power demand on the national transmission system.

In early estimates the System Operator was expecting 15.3GW on the national transmission system, and even four hours ahead it was predicting 14.4GW.  In the end, more wind on Sunday morning (which meant small wind plants met more demand) and less demand than expected brought the transmission load down to 13.4GW. Local generation – on-site and on the low voltage (distribution) system – act to reduce the demand visible at transmission level.

NGESO said it would “learn lessons from the unprecedented low demand situation”.

The actual usage of the transmission system was higher, because in addition to GB demand there was considerable export across the interconnectors with Europe. That was a mixed blessing for the system operator.

Exports help raise overall demand (when demand is too low, NGESO has to carefully manage the types of plant on the system to maintain inertia). It was largely the favourable interconnector exports that meant NGESO did not call for offers in its new ODFM products. However, in this case the high export level compared to demand could have created instability.

To manage the system, NGESO traded power across the interconnector to reduce the export level by 1GW to 2.3GW. By paying pumped storage hydro plants to increase their demand (pumping water) it raised system demand at 17GW. By also constraining off 3.5GW of wind it had the ‘footroom’ to add 3GW of biomass and CCGT plant to the 2.5GW already brought on by the market, so that system characteristics could be maintained.