The UK Storm of 28th October and the National Grid

The storm of 2013-10-28 managed to isolate a UK nuclear station from the National Grid leading to headlines such as:

Dungeness nuclear power station shuts down following hurricane-strength winds

St Jude’s UK storm forces the Dungeness B reactor in Kent to shut down for up to a week

The isolation from the grid means that essential systems controlling the reactor only have diesel generator backup and so for safety the reactor is shut down.

 

Just How is the loss of 1GW handled by the grid - the two plots that follow use data generated every 5 minutes (the dotted curves use the scale on the right of the plots all vertical scales are in MW):

 

 

 

Note that the bulk of the transient is compensated by pumped storage during the 1st 5 minutes (actually responds within 12 seconds) Hydro and coal and gas (CCGT) are also ramped up and pumped storage is reduced.  However at this time in the morning demand is rapidly increasing and coal and gas output cannot provide further rapid increase an so pumped supply is again increased,

 



 The plot shows data at 5 minute intervals so the immediacy of the Pumped storage is not visible.

 

 

It is also worth noting that the rarely used OCGT (inefficient gas) is brought online in case it is needed (only 50MW is utilised - past OCGT has provided up to 400MW).

 

So this aging reactor of approximately 1GW switching off is handled adequately by the system. In particular the instant response pumped storage.

 

The proposed Nuclear plant at Hinkley Point C will use 2 * 1.6GW reactors Losing one of these will equire spinning reserve (as provided by pumped storage and spinning turbines of other thermal stations)

 

Pumped storage:

 Each of Dinorwig's six generating units can produce 288MW of electricity, offering a combined station output of 1728MW.

Ffestiniog's four 90MW units have a combined generating capacity of 360MW.

 

I.e. a total of around 2GW. This will handle one of Hinkley's reactors but not both.

 

Efficiency of power plant operating below capacity, start up times etc.

First a combined cycle gas turbine - not known for its efficiency at less than 100% of rated output.

http://www.gepower.com/prod_serv/products/tech_docs/en/downloads/ger3574g.pdf
Fast starting and loading is characteristic of STAG combined-cycle generation systems. This enables them to operate in mid-range, with daily start peaking service as well as baseload.

Typically, STAG systems can achieve full load within one hour during a hot start and within approximately three hours for a cold start.

Multi-shaft STAG systems allow the gas turbines to start independently of the steam cycle and provide about 65% of the plant capability within 15–25 minutes, depending on the size of the gas turbine, for hot, warm, and cold starts, as illustrated in Figure 36.Single-shaft STAG systems are started and loaded to full capacity in about the same time period as the multi-shaft STAG systems. The startup sequence and load profile for the single-shaft systems differ because the gas and steam turbines are started as a single integrated unit and not as two separate units. Single-shaft STAG startup is illustrated in Figure 37.

Now one designed for variable output

http://www.gepower.com/prod_serv/products/aero_turbines/en/downloads/lms100_brochure.pdf
The LMS100 is the Right Solution:
Outstanding full- and part-power efficiency
Low hot-day lapse rate
High availability – aero modular maintenance
Low maintenance cost
Designed for cycling applications
No cost penalty for starts and stops
Load-following capability
10 Minutes to full power
Improves average efficiency in cycling
Potential for spinning reserve credits
Reduced start-up emissions
Synchronous condenser capability

From the House Of Lords.

http://www.parliament.the-stationery-office.co.uk/pa/ld200708/ldselect/ldeconaf/195/19507.htm

101. The first cost imposed by intermittency is that more plant has to be held in reserve to cope with short-term fluctuations in output. At present, National Grid, which operates the electricity system,[34] keeps a number of power stations running at less than their full capacity, providing about 1 GW of spinning reserve—that is capacity which can automatically respond to any shortfall in generation within seconds (Q 293).[35] The company also contracts with other stations to start generation quickly and has arrangements with industrial consumers to reduce their demand at short notice, in order to restore the level of spinning reserves as soon as possible after they are used. The company holds about 2.5 GW of this standing reserve (Q 293); 70% of this comes from generation, and 30% from industrial consumers (p 144).

102. As the amount of wind generation rises, the potential short-term change in wind output will also increase, and National Grid will have to hold more reserve to cope with this increase. The company told us that if renewables provided 40% of electricity generation—the share the company believes would be needed to meet the EU's 2020 energy target—its total short-term reserve requirements would jump to between 7 and 10 GW. Most of this would be standing rather than spinning reserves. This would add £500 million to £1 billion to the annual cost of these reserves—known as balancing costs—which are now around £300 million a year (Q 293). This is equivalent to around 0.3 to 0.7 pence per kWh of renewable output.

103. Estimates of balancing costs vary widely. The government has commissioned research from the consultancy SKM,[36] which estimated that if renewables provided 34% of electricity by 2020, with 27.1% from wind power, the extra cost of short-term balancing would be about 1.4 p/kWh of wind output[37] (Q 481). This equates to a total cost of £1.4 billion, well above that assumed by National Grid. Several pieces of evidence cited a 2006 report by the UK Energy Research Centre (UKERC),[38] which had estimated the balancing costs with up to 20% of intermittent renewable output in Great Britain at 0.2-0.3 pence per kWh. Although the share of renewables in the SKM study was less than double that of UKERC, the balancing costs per unit were more than five times higher. In part, this may reflect higher fuel costs since the studies surveyed by UKERC were performed; but it will also reflect the greater challenges of dealing with larger shares of intermittent renewable generation.

So the costs of up to 20% wind is between £0.002 and £0.014 per kWh

The UK cost per kWh is approx £0.11

added 2011-11-24

National grids reserves

From wiki
There is generally about 1.5 GW of so called spinning reserve
NG pays to have up to 8.5 GW of additional capacity available to start immediately but not running, referred to as warming or hot standby, that is ready to be used at short notice which could take half an hour to 2 hours to bring on line
A similar amount of power stations (8–10 GW by capacity) are operable from a cold start in about 12 hours for coal burning stations, and 2 hours for gas fired stations


Short term and instantaneous load and generation response mechanisms

The national grid is organized, and power stations distributed, in such a way as to cope with sudden, unforeseen and dramatic changes in either load or generation. It is designed to cope with the simultaneous or nearly simultaneous failure of 2 × 660 MW sets
Spinning Reserve National Grid pays to keep a number of large power station generators partly loaded.
Pumped Storage Pumped storage as in Dinorwig Power Station is also used in addition to spinning reserve to keep the system in balance.

Frequency Service For large perturbations, which can exceed the capability of spinning reserve, NG (National Grid plc) who operate the national grid and control the operations of power stations (but does not own them) has a number of partners who are known as NG Frequency Service, National Grid Reserve Service or reserve service participants. These are large power users such as steel works, cold stores, etc. who are happy to enter into a contract to be paid to be automatically disconnected from power supplies whenever grid frequency starts to fall.
Standing Reserve  Operating closely with NG Frequency Response is the National Grid Reserve Service now called STOR or Short Term Operating Reserve.[9] NG Standing Reserve participants are small diesel engine owners, and Open Cycle gas turbine generator owners, who are paid to start up and connect to the grid within 20 minutes from the time Frequency Response customers are called to disconnect. These participants must be reliable and able to stay on and run for an hour or so, with a repetition rate of 20 hours.

National Grid has about 500 MW of diesel generators on contract, and 150 MW of gas turbines with about 2,000 MW of disconnect-able load.[9]

Sources of intermittency on the UK National Grid The largest source of intermittency on the UK National Grid is the power stations; in fact, the single largest source is Sizewell B nuclear power station. Whenever Sizewell B is operating the entire 1.3 GW output is liable to stop at any time without warning. Its capacity is 2.16% of the national grid maximum demand, making it the single largest power source and therefore the largest source of intermittency. Despite this issue, NG readily copes with it using the methods outlined above including the use of diesel engines. An industry-wide rate of unplanned scrams (shutdowns) of 0.6 per 7000 hours critical means that such a shut-down without warning is expected to happen about once every year and a half.[11] However, no matter how low the rate of unplanned scrams, this is largely irrelevant - what matters is the fact that it can and does happen, and measures have to be in place to deal with it.

In 2008 both Sizewell and Longannet power stations both stopped unexpectedly within minutes of each other, in fact causing widespread power failures, as substations were tripped off using prearranged under-frequency relays.[12]

Reports of May 2008 outage
National grid http://www.nationalgrid.com/NR/rdonlyres/E19B4740-C056-4795-A567-91725ECF799B/32165/PublicFrequencyDeviationReport.pdf

Ofgem
http://www.ofgem.gov.uk/Markets/WhlMkts/CustandIndustry/DemSideWG/Documents1/National_Grid_-_System_Events_of_27_May_for_DSWG_16_July.pdf