I’m not convinced that wind power is the greatest thing since sliced bread. I’m not too convinced that wind deserves the subsidies it receives. However, there are things being said against wind that are completely unfair. Since I both know better and have a blog, why not call some people out?
Out there in the aether that is the internet, is a person named Richard S. Courtney who argues against wind by completely misrepresenting how bulk power systems (i.e. the grid) currently operate. As early as 2006, he published a paper titled, “Wind Farms Provide Negligible Useful Electricity.” It’s quite a claim. In it there are two sections, numbers 8 & 9, in which he horribly mangles the current state of things. Fortunately the sections are short and easy to dissect.
Section 8 is Thermal Power Stations.
Conventional (i.e. thermal) power stations fission a material or burn a fuel to obtain heat that is used to boil water and superheat the resulting steam which is fed to the steam turbines (some power stations – e.g. combined cycle gas turbine: CCGT – also use gas turbines in combination with steam turbines). The turbines drive turbogenerators that make electricity.
The first paragraph, aside from leaving out simple-cycle gas turbines, is unobjectionable.
A thermal power station takes days to start producing electricity from a cold start.20 Time is needed to boil the water, to superheat the steam, to warm all the components of the power station, and to spin the turbogenerators up to operating speed.
For steam plants, that’s approximately true. That’s not at all true for gas turbines or combined-cycle plants.
And if if it tells you anything else, the source listed for citation #20 is http://www.worley.com.au/v5/page.aspx?id=166, which no longer works.
Each thermal power station is designed to provide an output of electricity. It can only
provide very little more or very little less than this output (i.e. a power station has a “low
turndown ratio”).21
Citation #21 is Flynn P & Kumar A, ‘Site visit to Alholmens 240 MW power plant, Pietarsaari, Finland’ University of Alberta, September 2005. As the title suggests, the source is about a site visit to a lone power plant in Finland that happens to burn various non-traditional fuels such as wood waste. The source goes on to say, and I quote, “[a]t Alholmens it has a 35% turndown ratio (ratio of minimum sustainable operating level to design operating level).”
In other words, Courtney is extrapolating to every thermal plant from a single data point that actually says the opposite of what he’s claiming.
In practice, it’s typical for fossil fuel fired steam plants to have a turndown ratio of 20 to 40%. Admittedly, however, gas turbines & nuclear power plants (at least those in the US) have a turndown ratio of about 100%. Combined-cycle plants fall somewhere in between.
Moving on to the next section.
Sec. 9 - Electricity demand matching22
Electricity is wanted from a grid supply all the time but the demand for electricity varies from hour to hour, day to day, and month to month. The electricity grid has to match the supply of electricity to the demand for it at all times.
Going well so far..
This is difficult because thermal power stations cannot be switched on and off as demand varies, and only small variation to the output of each power station is possible.
That derailed quickly.
Gas turbines can be switched on and off as demand varies. Fossil fuel fired Steam turbines have can, and typically do, handle very large variations in output. The grid uses both technologies because they complement each other in this way. Courtney is taking the negatives from the separate technologies and applying them to all the thermal systems.
The problem of matching electricity supply to varying demand is overcome by operating
thermal power stations in three modes called
· ‘base load’,
· ‘generation’ and
· ‘spinning standby’ as backup capacity.
Some power stations operate all the time providing electricity to the grid, and they are said to provide the ‘base load’.
Other power stations also operate all the time but do not provide electricity all the time. They burn (or fission) their fuel to boil water and superheat the resulting steam which is fed to the steam turbines that are thus kept hot and spinning all the time. Of course, they emit all the emissions from use of their fuel all the time. But some of this time they dump heat from their cooling towers instead of generating electricity, and they are then said to be operating ‘spinning standby’.
One or more power stations can be switched from spinning standby to provide electricity to match an increase to demand for electricity. It is said to be operating ‘generation’ when it is providing electricity.
This is a relatively fair description. Although my experience says that it’s pretty rare for plants to be in ’spinning standby’ without also generating. Since steam plants can generate over a broad range, they can operate at 50% and still provide what is elsewhere referred to as ’spinning reserves.’ This basic premise carries over to show how his paragraph is similarly misinformed.
The wording about emissions also bothers me. Literally all he’s saying is that burned fuel releases emissions. However he seems to be implying that plants on spinning standby burn every bit as much fuel as those operating as base load.
Power stations are switched between spinning standby and generation as demand for electricity changes. Thus the grid operator manages the system to match supply with demand for electricity by switching power stations between ‘generation’ and ‘spinning standby’. And the small available variation in output from each power station is used to avoid large step changes in the supply when this switching is conducted. But operating a power station at less than its optimum output severely reduces its efficiency so it has little reduction to its fuel consumption and emissions although it supplies less electricity.23
If you carefully consider the last sentence quoted above in the context of the rest of Courtney’s work, you’ll realize that he is actually contradicting himself. Think about it. Earlier he says, “only small variation to the output of each power station is possible.” But now he’s saying that being at less than “optimum output” reduces its efficiency “severely” resulting in “little reduction” to fuel use & emissions. If a small variation (10% would be my assumption) to output causes a severe (I’d guess a 50% change) efficiency loss, then fuel use & emissions can only increase. As I’ll show in a later post, output can achieve large variations with small efficiency changes leading to very large reductions in fuel consumption & emissions.
For all of these statements by Courtney in Sec. 9 about how things are run, and how that affects carbon emissions, there appears to be 2 sources. The citations page though shows that they are, in fact, the same source, a 2002 Platts article that I cannot access from Platts. However, a copy seems to exist here in Appendix I. The source agrees that the grid needs to be balanced between load and generation. That’s about all. It says nothing about carbon emissions nor fuel consumption. And it says this about backups:
Some of this spare capacity would be on ‘hot standby’, i.e. connected to the network and operating at part load to ensure a stability of connection as in the case of steam plant, or available for instant start-up and connection as is the case for hydro and gas-turbine plant.
Courtney provided 3 sources. Only 2 could I find, and both of them contradicted what he said. Sadly some people seem to trust Courtney.