The National Grid has to balance the load (demand) with supply - this is a complex balancing act which, whilst it relies on computational power does involve human oversight.
The Operating Margin is the Level of available Megawatts (MWs) above those required to meet forecas demand. The National Grid maintains an Operating margin which they design and trust will ensure security of supply and minimise the costs of balancing. (Learn more here) Costs may go from the average £40 KwHr to £300KwHr
An insufficient Operating Margin will trigger the issue of a Notice of Inadequate System Margin (NISM) warning - this alerts and requires suppliers to the national Grid to review and report availability.
This is an infrequent and unwelcome event because it drives up costs and can in fact lead to the need to close down supplies at short notice - blackout.
Therefore when Reuters reported on September 4th that the UK power supply cushion for Thursday evening looks too tight and another 700 megawatts of generation capacity is needed, they had been alerted by accessing the NISM reports which you can access here.
This was the one referred to by Reuters.
2008-09-04 11:01 From : Power System Manager - National Grid Electricity Control Centre NOTIFICATION OF INADEQUATE SYSTEM MARGIN For the period: from 11:00 hrs to 20:30 hrs on Thursday 04/09/2008 There is insufficient System Margin System margin shortfall 400 MW Maximum Generation Service may be instructed. Trading Points, Control Points and Externally interconnected System Operators are requested to notify National Grid of any additional MW capacity. Suppliers please advise National Grid of any additional Demand Control available The situation will be reviewed again by National Grid at 16:00 hours and an update issued. This Notification of Issue of a GB Transmission System Warning - Inadequate System Margin Notification Issued at 12:00 hrs on 04/09/2008 Issued by Clive Coles National Grid Electricity Control Centre
The immedate problems were caused by shutdowns and a loss of power because of breakdowns over the past two days. Some of the plants that experienced problems included British Energy’s Eggborough power station, Drax and E.ON’s Kingsnorth and Killinghome stations. Times
Expect more this winter. When it really gets cold.
Go to Oil Drum for a discussion on the current and near term position and more wisdom from Chris Vernon who brought our attention to the above.
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