Reader Jacob sent me a couple of emails about the mechanics of ramping coal plant up and down to load balance an electricity grid.
I send you two links to articles about “cycling” or “ramping down” coal power stations. I don’t see how they can “cycle” except by keeping the fires burning.
And so the question is if a coal fired power station is “switched off” when demand for coal fired electricity goes down are the furnaces extinguished thus eliminating CO2 emissions or are they kept burning, perhaps at reduced levels? This post poses the question and provides background data to the problem. I’m hoping that informed commenters may provide the answers.
Figure 1 Slide 70 from Professor Bruno Burger’s summary of electricity production in Germany 2013.
Figure 1 illustrates the problem but also shows that the question is rather more complex than originally framed by Jacob. The bulk of Germany’s electricity still comes from nuclear power and coal and it can be seen clearly that hard coal provides most of the dispatchable diurnal load balancing service. Every day hard coal fired power stations are ramped up and down. Are they switched off at night or merely turned down? Notably, Germany uses little natural gas in power generation.
Jacob’s question is more subtle and overprints the diurnal demand pattern. We can see three things happening:
- On many days the solar peak reduces demand for hard coal resulting in a mid day dip on hard coal generation. See for example 6th, 12th, and 13th of June. Is any CO2 emission actually saved during these dips?
- On windy days, see for example the 21st and 26th of June hard coal generation is significantly curtailed. At such times are power stations actually switched off or is the power generated simply spilled?
- On weekends, see for example 15th and 16th June, demand for hard coal generation is effectively zero and demand for brown coal generation is curtailed. Are power stations switched off for the weekend or are they simply turned down in some form of hot standby mode?
This article by John Kemp at Reuters covers many of the issues:
The operational and financial challenges of operating conventional plants in a more flexible mode are enormous.
Large-scale power plants take hours to warm up to operating temperature and synchronise their turbines with the grid.
“(Grid operators) may have to cycle resources on and off more than once a day,” the North American Electric Reliability Corporation explained in a recent report on integrated renewables in California.
“At times this may not be an option because the down time between shutdown and start-up of a resource may be too long, which would prevent the resource from being restarted in time for system peak,” NERC concluded.
While they are warming up, conventional plants waste huge amounts of fuel without producing useful output.
And repeatedly heating up and cooling down the boilers, economisers, pipework, turbines and other components shortens their life-span and requires more expensive maintenance.
On top of all this, cycling power plants must recover their more expensive operating costs as well as the expense of building them, while getting paid for fewer hours of generation each year.
In Germany, combined load and generation adjustments have risen as high as 50 gigawatts in an eight-to-10-hour period – equivalent to more than 60 percent of the country’s peak power consumption.
In response, production from coal plants has been successfully turned down to just 20-60 percent of normal output. The advisory board claims part-loaded coal-fired plants have been able to ramp down by as much as 3 percentage points per minute.
The board’s optimism is spoiled, however, by the financial woes of Germany’s big coal-fired generators. RWE this month announced yet more job cuts and said that 2014 would be a “valley of tears” for conventional power producers.
Rivals E.ON and GDF Suez have also warned of a prolonged crisis in the European power industry.
Enormous renewable generation, subsidised through feed-in tariffs, coupled with low wholesale power prices and the low number of hours in which coal and gas-fired power plants are able to operate mean that revenue is inadequate for conventional generators.
These are issues I covered in Parasitic wind killing its host and by Hugh Sharman in The balancing capacity issue: A ticking time-bomb under the UK’s Energiewende. It is quite clear that FF generators are being heavily penalised by the Energiewende with reduced operating efficiency, increased wear and tear and reduced market share while the opposition receive subsidies to produce electricity that increasingly is not used. All this is done in the name of reducing CO2 emissions and saving Earth’s climate from meltdown. Whilst evidence of meltdown is elusive we also need to ask if the Energiewende and strategies like it else where actually leed to a reduction of CO2 emissions? In Germany it seems likely that the answer is yes. Wind and solar have displaced some FF generation. The question is what portion of that displaced generation represents saved emissions?
I have always felt the best way to tackle both emissions and energy scarcity was to improve energy efficiency at every level of society. The current strategy appears to be taking us in the opposite direction.