2012/08/17

The Reliabilty of Nuclear stations compared to Wind Power

Warm seawater forces Conn. nuclear plant shutdown
By Stephen Singer on August 13, 2012
HARTFORD, Conn. (AP) — Connecticut's nuclear power plant shut one of two units on Sunday because seawater used to cool down the plant is too warm.
Unit 2 of Millstone Power Station has occasionally shut for maintenance or other issues, but in its 37-year history it has never gone down due to excessively warm water, spokesman Ken Holt said on Monday.
Water from Long Island Sound is used to cool key components of the plant and is discharged back into the sound. The water cannot be warmer than 75 degrees and following the hottest July on record has been averaging 1.7 degrees above the limit, the Nuclear Regulatory Commission said.
The federal agency issued an "emergency license amendment" last week, allowing Millstone, a subsidiary of Dominion Resources Inc., to use an average temperature of several readings.
"It wasn't enough to prevent us from shutting down," Holt said.
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River temperature forces nuclear plant to 50 percent power


Not even TVA can beat the heat.
On Wednesday, the utility had to bring a third reactor at Browns Ferry Nuclear Plant down to 50 percent power to avoid environmental sanctions because the water in the Tennessee River — where the plant's cooling water is discharged — already was at 90 degrees.
"When the river's ambient temperature reaches 90 degrees, we can't add any heat to it," said TVA's nuclear spokesman Ray Golden.
Similar problems last summer forced the Tennessee Valley Authority to spent $50 million for replacement power, according to Golden. The extra expense translated to something between 50 cents and $1 on most electric bills several months later, officials have said.
To avoid similar heat problems this year, TVA in October began construction on a seventh cooling tower at Browns Ferry, which is near Athens, Ala., and officials expected the $80 million super tower to be complete in June or July.
But weather stormed that plan, too.
"It was delayed because of the impact of the tornadoes, and some spring storms and some heavy rains," Golden said. "It's probably about 98 percent complete, and we hope it will be in service in the next one to two months."

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August 24, 2010 By
90 Degree River Shuts Down Southern Nuclear Plant
Blue Living Ideas

       As a result of the record high temperatures engulfing the South (and much of the planet) the Tennessee Valley Authority has had to shut down its largest nuclear power plant for the 40th day since  July 8th, the TimesFreePress reports. The Tennessee River in Alabama is just much too hot.

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Water shortages hit US power supply
As the United States' extended heat wave and drought threaten to raise global food prices, energy production is also feeling the pressure. Across the nation, power plants are becoming overheated and shutting down or running at lower capacity; drilling operations struggle to get the water they need, and crops that would become biofuel are withering.
While analysts say the US should survive this year without major blackouts, more frequent droughts and increased population size will continue to strain power generation in the future.
Power plants are a hidden casualty of droughts, says Barbara Carney of the National Energy Technology Laboratory (NETL) in Morgantown, West Virginia, because they are completely dependent on water for cooling and make up about half the water usage in the US. That makes them vulnerable in a heat wave. If water levels in the rivers that cool them drop too low, the power plant – already overworked from the heat – won't be able to draw in enough water. In addition, if the cooling water discharged from a plant raises already-hot river temperatures above certain thresholds, environmental regulations require the plant to shut down.
At least four nuclear plants had to shut down in July for these reasons. Nationwide, nuclear generation is at its lowest in a decade, with the plants operating at only 93 per cent of capacity.
Nuclear is the thirstiest power source. According to NETL, the average nuclear plant that generates 12.2 million megawatt hours of electricity requires far more water to cool its turbines than other power plants. Nuclear plants need 2725 litres of water per megawatt hour for cooling. Coal or natural gas plants need, on average, only 1890 and 719 litres respectively to produce the same amount of energy.
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http://www.nytimes.com/2007/05/20/health/20iht-nuke.1.5788480.html?pagewanted=all
Officials at Électricité de France have been preparing for a possible rerun of a ferocious heat wave that struck during 2003, the hottest summer on record in France, when temperatures of some rivers rose sharply and a number of reactors had to curtail output or shut down altogether.
The French company operates 58 reactors - the majority on ecologically sensitive rivers like the Loire.
During the extreme heat of 2003 in France, 17 nuclear reactors operated at reduced capacity or were turned off. Électricité de France was forced to buy power from neighboring countries on the open market, where demand drove the price of a megawatt hour as high as €1,000, or $1,350. Average prices in France during summer months ordinarily are about €95 per megawatt hour.
The heat wave cost Électricité de France an extra €300 million. The state-owned company "swallowed it as a one-off cost of doing business in extreme circumstances," Philippe Huet, an executive vice president at Électricité de France, said.
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So Just like wind, nuclear has to shut down when needed most.

OK so how about wind requiring all that backup running continuously in case the wind drops?

Well, one scram on a nuclear plant will require the generation of 500MW to 1GW of instantly available power (spinning reserve) - you cannot  allow supply interruption (May 2008 outage National Grid).
Wind does not fail instantly everywhere so a gradual decrease in power has to be compensated by conventional. In general, most stations running under warm start conditions will be producing the required power when needed. There is probably no need for spinning reserve as wind backup - the met office seem reasonably accurate predicting a few hours ahead).

lets look at UK National Grid data for a few days:
10th August to 17th Agust 2012 data



Note that the peak delivered is 15GW greater than the lowest delivered. The National Grid may not like this normal situation but the certainly find no difficulty providing the power.

It would therefore seem obvious that at least 15GW of solar and wind could be accomodated. (solar of course would remove some of the daily peak).

From an earlier post here:
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


So what about all those rare earth magnets required in wind turbines and of course there is all that noise from gears being tortured? And wont they make the network more unreliable?

Well not all turbines are created equal

Take a look at:


ENERCON WECs produce clean energy without neodymium
29.04. 2011

ENERCON wind energy converters (WECs) generate electricity in an environmentally friendly way without the use of the controversial element, neodymium. The gearless WEC design on which all WEC types – from the E-33/330 kW to the E-126/7.5 MW – are based includes a separately excited annular generator. The magnetic fields required by the generator to produce electricity are created electrically. By design, and unlike the majority of competing products, ENERCON WECs do without permanent magnets whose production requires neodymium.

Neodymium has made the headlines recently because its extraction partly involves significant environmental damage. China, where neodymium-containing rocks are quarried in mines, is the main supplier of this so-called rare earth element. According to investigations by Germany’s NDR TV station, separation of neodymium from mined rocks results in toxic waste products (Menschen und Schlagzeilen and Panorama television magazines aired on 27 and 28 April). In addition, radioactive uranium and thorium are released by the mining process. These substances find their way into the ground water, heavily contaminating plant and animal life. They are seen as harmful to humans. According to the reports, part of the locals at the neodymium production sites in Baotou in northern China are already seriously ill.

ENERCON feels that these environmental and health aspects support its choice of WEC design. “We are a high-tech company that sets great store by environmental protection,” says ENERCON Managing Director Hans-Dieter Kettwig. “Our choice to rely on separately excited generators was the right one, not only from a technological but also from an environmental point of view.” According to Kettwig, renewable energies need to be viewed in their entirety in order to offer a convincing alternative. Producing clean energy is one thing; however, sustainability in production is just as important.
Helps the network recover:
Staying connected when grid problems occurMost transmission networks and ever more distribution grids require wind energy converters to remain connected to the grid in the event of grid short circuits. Like conventional power plants, wind turbines are not allowed to suddenly disconnect from the grid during voltage dips or overvoltage caused by grid problems. ENERCON wind turbines with the optional ENERCON UVRT feature have this capacity. No matter what type of short circuit occurs, ENERCON wind turbines can ‘ride through’ faults for several seconds, even if they were operating at rated power before the fault. This is also possible if the wind turbine voltage completely breaks down as a result of a power system failure. These outstanding power plant properties have been certified by independent institutes during actual grid fault testing. Flexible setting options offer maximum performance according to the respective grid operator’s specifications or to the project’s framework conditions.
Depending on the selected parameters, the wind turbine can feed in either mainly active or reactive power to maintain grid voltage. If necessary, voltage-dependent reactive current can even be supplied to the grid; this current can be maximum rated current as stipulated by the latest German grid code. If desired or required, fault ride-through is also possible without power feed-in. The ENERCON wind turbine remains in operation during the fault. After the grid problem has been resolved and grid voltage has been restored, the wind turbine can immediately resume power feed-in. Thus the ENERCON Undervoltage Ride-Through feature facilitates adaptable settings in order to meet grid standards (e. g. of the German
Association of Energy and Water Industries) and to maximise the amount of installable wind farm power.






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