Last year, I posted an article from Germany about the damage that increased cycling of power plants, due to balancing of renewables on the grid, is having on generation equipment :
http://irishenergyblog.blogspot.ie/2014/10/news-from-germany-and-uk.html
In Eirgrid's Generation Adequacy Report for 2015-2024 published this year, they state that this is in fact the case now in Ireland :
Another aspect of plant availability is that of two shifting, which may result in a change to maintenance patterns. Two shifting is where a generator is taken off overnight or at minimum load times. This will occur more frequently with increased penetration of wind generation, and will result in the requirement for additional maintenance and increased Scheduled Outage Days (SODs)This then represents another cost to be loaded on to people's electricity bills.
Most engineers will tell you that turning on and off a large power plant like this is inefficient and will actually increase emissions. Its a bit like someone continually walking and running. It takes a lot of energy to begin running from a walking position but once you are running it takes less energy. This is because there is momentum behind you. Think of how much energy is required to stop running and to fight the inertia in your body. This is why its better to go running in a park or in the country, having to stop and start in a busy city street is not very efficient. Race tracks are designed like they are to give athletes the best chance. And so it is not very different with a gas or coal generator. But this is now the norm for many of them.
Thurlough Hill is a pumped storage facility in Co, Wicklow. Capacity is 292 mw and there are 4 generators of about 6 feet (2 meters) diameter with a capacity of 292 mw /4 = 73 mw each. So take a coal fired condensing steam turbine alternator in a conventional fossil fuel power station. A medium farm tractor is about 70 kw, a very large one is 100 kw capacity. To power a 73 mw alternator using large tractor engines would need 73,000/100 = 730 such engines. Now mentally consider the torque 73 such engines would exert at optimum revvs. Now consider a condensing steam turbine of 73 mw capacity driving a 73 mw alternator at max output in Ireland. You now add (say) 2,000 mw of wind on a blustery night, with gusts and troughs. Average capacity wind factor is 40% = 800mw varying from 500 mw to 1,000 mw 10 times per hour, a difference of 500 mw. Say out alternator is running at 80% capacity in order to be able to balance wind cumulatively with other such plant = 73 x .8 = 58.4 mw.
ReplyDeleteNow say that this alternator has to cycle between 60% and 100% to balance wind. (10 time per hour)
73 x .6 = 43.8 and 73mw a difference of 73 – 43.8n = 29.2mw = to the power of 29,200 / 100 = 292 large tractor engines. So every 6 minutes the turbine is hit with the torque of 292 large tractor engines some of which will be gradual. Say just one is sudden per hour, a hammer blow with a strength of 292 engines engines. 24 times per day x 7 days per week means that the blades of the steam turbine are hit with a blow = to the power of 292 large tractor engines. That is 168 blows a week and 8760 per year.
It is tearing the toothed blades off and they fly back into the turbine housing destroying the lot. The entire cost is loaded on consumers and wind companies who caused it, get off scot free. In reality the constant cycling forces operators to abandon condensing steam plants during windy weather and go over to less efficient OCGT plant.
https://www.youtube.com/watch?v=gJtv7gkuh1s He is conformation that renewables cannot be made to work on existing grid systems
ReplyDeleteIf you cannot access the link above try to google: "You tube Andrew Dobson Wind farms resonating across the grid @ teac6." Resonance is caused when the inductors current collapses causing an electrical current (like the ignition system of a petrol car). This charges the capacitors which in turn discharge into the induction coils of the inductor. This collapses causing the cycle to repeat, if the frequency is maintained.
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