Short Term Operating Reserve (STOR)

STOR helps National Grid to manage a shortfall in supply by either providing additional electricity generation from spare plant capacity or back-up diesel generators or by reducing electricity demand. At least 90% of STOR provision comes from increasing generation whilst the remaining 10% comes from demand-side reductions.

STOR services are used by National Grid when there is a shortfall in electricity supply resulting in what is known as a grid ‘event’. This usually means the frequency has deviated from 50 Hertz by greater than 0.2Hz. For example, if an interconnector to France failed. Whilst Frequency Response services provide an immediate response (0-30 minutes) STOR services can help National Grid to meet demand in the mid-term (20 minutes – 2 hours +) while larger, more permanent generators can be brought on line – or back on line in the event of a failure.