Given the variable nature of wind power, the wind capacity credit expresses how much conventional power generation can be avoided or replaced by a certain level of wind power.
Only 476MW out of a total of 4,617MW or about 10% can be relied upon in the event that a conventional generator fails :
When it comes to keeping the lights on there is no room for the hyperbole and feel good talk that permeates much of the debate around renewables in the media and in the chambers of the Irish parliament.
The spare generating capacity above electricity demand is called the capacity margin. It has halved from 3,199MW in 2016 to 1,793MW in 2018. Two gas powered generators have closed down in 2018 and Moneypoint coal power station has suffered an outage.
Generators shut down
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Output MW
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Aghada AD1 (gas fired steam turbine)
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258MW
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Marina (open cycle gas turbine)
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95MW
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Moneypoint (coal)
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855MW
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1,208MW
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In recent days, it was gas power, the UK interconnector and "other" generators (presumably peat and oil) that ensured the lights stayed on in the absence of Moneypoint and the above units. Renewables (mostly wind energy) varied between 7% and 27% so could not be depended on. Back up power stations are still essential in a grid with large amounts of renewables.
You can also see the importance of the interconnector with the UK (EWIC). Can the UK guarantee they will have spare capacity to export electricity to Ireland ? The black line below shows the profile for coal power in the UK in recent days. As you can see, they too were having problems with their coal units.
Scotland too is in a precarious position and will likely be reliant on imports from the UK over the winter period :
At the time of writing the Torness 2 and Hunterston 3 and 4 reactors were down, leaving Scotland with only 612 MW of nuclear capacity and only 3,900 MW of dispatchable capacity to service over 4,000 MW of demand. However, all three reactors are scheduled to restart by mid-December, and any shortfalls that might occur in the meantime could probably be covered by imports from England [Euan Mearns]
If we get a very cold winter, and there are indications that a cold one is coming, the already strained grid could come under a lot of pressure as demand increases. Couple this with more generator outages, and we could be in for some big problems. This is where the demand side of the equation would become crucial - essentially disconnecting large energy users from the grid who would have to rely on their own generation i.e. diesel generators or combined heat and power.
Essentially, a return to the pre grid times of the early 1900s, when there was a large and inefficient diesel generator in most big towns in Ireland.
Our esteemed new Minister of the DCCAE will undoubtedly conjure up a fine dialogue to obscure the issue. The alternative is to take the datacentres off grid (demand shedding) and run them on sustainable energy diesel gennies . . .
ReplyDeleteBecause electricity most be supplied continuously without interruption, the traditional way to measure the contribution of individual generating plant was capacity credit (firm capacity in the US). This "the amount of other capacity which can be shut down and replaced by the one being measured without endangering supply". When wind and solar arrived on the scene, capacity credit was conveniently dropped and replaced by load factor (capacity factor in the US). This is "the actual electricity generated expressed as a percentage of the rated capacity of the plant being measured". The remuneration of wind and solar plant is based on load factor.
ReplyDeleteThe credit capacity of Irish and UK wind varies and have never been measured officially. Dutch engineers Keys LaPair and Dr Fred Udo studied Irish wind and arrived at 4% capacity credit, I studied it and found it to be 1.6%. As wind capacity increases its capacity credit falls. The ESB said it tends to zero.
Right now on the 3rd October, 2018 at 22.40 hours, Eirgrid's Dashboard shows wind to be at 59% of demand. However, observable wind speeds should be yielding much more. As the evening progressed, demand dropped off and as it did wind dropped off in the ratio of 59 MW of wind to 41MW conventional generation. This proved that at least 41% of generation must be conventional and that there never can be a 100% wind system.The EWIC is in the same category as wind. Total non synchronous generation must be kept below 60%.
A very obvious question for Eirgrid, is how they can rely of renewables having a 10% capacity credit on a calm night? For many months in 2018 there was no wind at all, and there can be no solar at night. More likely they are averaging over one year. If they are, then they consider all the wind and solar to only be worth 10% of its capacity. In other words, not matter how much of it we have installed, only 10% of it can be relied on on average. Eirgrid have not taken account of the fact that capacity credit declines with increased wind installation. With 3,400 MW of wind installed at a cost of 1.7 million Euros per MW, it's a very expensive 10% indeed. Eirgrid are careful to tell some of the truth, bit not the whole truth. Government does not want to hear the whole truth.
Wind generation can have no capacity credit as you cannot switch on a wind turbine.When the wind is not blowing and a thermal plant crashes. During a nationwide frosty period . Not one megawatt of wind generated electricity will be generated."Eirgrid average everything" you can average yourself out of business.Averages are developed from historic/past data. The future, given the high level of unpredictability and chaotic nature of the data , is very unlikely to replicate the past. Wind cannot have any capacity credit.
ReplyDeleteTo add to the above post on averaging. If it were completely calm on Monday, there would be no wind generation. If there were 35 MPH winds on Tuesday, turbines would have to be shut down for safety (@33 MPH and less). The average wind would be 25 MPH, but the total generation would be Zero.
ReplyDeleteIf you were running a local supermarket with 14 staff. Your would arrange them in scheduled rosters between 8am to 9pm opening hours. If a local factory closed and government ordered you to employ 8 new staff from that factory paying you a subsidy = to half their wages, a key issue would be whether you could schedule their hours or whether the previous factory could schedule them? If you did not have full control of their rosters, they could arrived in at 10 pm for a night shift which did not exist. On average they would be a benefit, in reality they would not be much use and they would cost too much.
There is a similarity between wind farming and non intensive farming. Neither can ever pay if the capital to buy the farm is borrowed. There is not enough income and there are no official barriers to entry. If the farm is inherited or the wind farm is acquired free, then there is a small profit to be made. Only the normal day to day running inputs are counted as costs. The running costs of a wind farm can be covered by a load factor of about 19%. Both scenarios include state subsidies.
ReplyDeleteAll private Irish and foreign investment is running away with a golden handshakes from utility companies. They will hide their wind farm purchase costs among all the other capital costs in their portfolio. Then they make a profit with no interest or principle to pay off. The consumer of fossil fuel electricity is unwittingly carrying a non performing wind sector.
That leaves Greencoat. They take in investments, they can pay a dividend because they have no interest or capital costs to pay off. Unlike utility companies, they have no other revenue stream, so in 10 to 20 years there will be nothing. Investors will never get their capital sum back, where will the money to build new wind farm some from?
As for the real farmer, there will still be the land assets, building assets and stock.
When this problem was put to a representative of the Irish Energy regulator on radio recently, she replied "battery storage". She was referring to her belief that wind's intermittency would be overcome by huge batteries.
ReplyDeleteThe Irish Government (with a Green Party minister) for energy, banned traditional electric light bulbs. Re-chargeable batteries for torches, radios, tools and a wide range of hand held appliances have been around for decades. Why was no government effort made to phase them out and eventually ban non-rechargeable batteries? Where are the chemicals going at the end of life? What is the environmental impact? It does not seem to bother anyone at all.