By Anton Lang ~
Pretend you are in the market for a new car. The salesman tells you it is the latest technology, brand new, and will do everything your old car did, only much better. Believing what he says, you go ahead and purchase this new car. When you get it home and start using it, you find that your new car starts up okay, but not every time. Once it does start, you then find it will only get you to your destination one time in four, or at best, one time in three. You have no idea when it will stop, or, having just stopped, when it will start up again. True, while it is running, it does all your old car did, only now, you don’t know when it actually will be running for long enough to complete your journey. You ask the salesman about the problem, but he just says that’s the normal operation for this car. Would you be happy with that new car, or if it was explained to you before you purchased it, would you have bought the car in the first place?
We are told that there is a need to close down power plants which have high Carbon Dioxide emissions, more specifically those coal fired power plants. For many decades, almost a Century in fact, these coal fired plants have supplied significantly large amounts of electrical power, and they have supplied that electrical power on the basis it is required for, on a 24 hour basis. Now that we are told they have to be closed down, the main replacement (on a large scale of construction) that they have is Wind Power. However, wind power cannot supply that same huge amount of power on that 24 hour basis. Why it cannot do this is never explained in a manner that the ordinary person can effectively understand.
What I hope to do with this Post is to explain as simply as possible why Wind Power cannot supply electrical power in the same manner as those coal fired plants can, and in doing that, explain why Wind Power can never replace coal fired power.
Across all the eight years I have contributed at this site, I have consistently said that wind power can never replace coal fired power on the same basis of requirement, for the supply of a constant , reliable, and regular 24 hours of electrical power supply, which, let’s face it, is what keeps the Country actually running. The terms used to explain electrical power generation in all its forms are engineering terms, and there is no really simple way to explain it, and so, the general populace, who have no understanding of even the basics of electrical engineering, find it somewhat difficult to understand, because, after all, the electrical power is still being delivered to your home, so it becomes easier to believe that they are all basically the same, just done in a different manner. The main point in contention here is the term Capacity Factor, and here I’ll refer to it from now on by its acronym CF.
Capacity Factor (CF)
It is rarely explained that wind power has a low CF. It is most usually modelled at 38% prior to construction in the planning stage, struggles to actually consistently supply at 30%, and in most Countries that CF can be as low as 20%, and some even lower than that. See now how it becomes a little obscure to understand.
So then, what does that CF term really mean?
CF is the total yearly power actually delivered compared to the maximum power which can theoretically be generated if it was to be running all the time.
Think of it in much the same manner as I explained at the beginning of the Post about the new car. CF means that effectively wind power only delivers for those percentages I mentioned, so it works at around 20% to 30% of the time, but because of the vagaries of the wind, no one really knows when it will be working and when it won’t be working.
Having mentioned this, it is now worthwhile explaining just how both types of plants do actually generate their electrical power, and here, I’ll try and keep it as simple as reasonably possible.
Coal Fired Power
(This image shows two 1000MW units at a plant in Shanghai, China. Click on the image to open it in a new window for a larger image of this plant and note the size of each unit in comparison to the people walking on the floor of this turbine hall)
The electrical power is generated by the Generator. (naturally) A heavy rotating shaft has large electromagnets wrapped around, and along the shaft. As that very heavy rotor rotates at 3000RPM, (3600RPM in the U.S.) it induces electrical power into the Stator, huge fields of wire in a stationary tubular shell, with the rotor rotating inside this shell. The power is then rectified, and via transformers, is then directed out to the grid. To turn that huge weight of the rotor, they use a very large multi stage turbine, which looks a little similar to a jet engine, only vastly more complex. That turbine is made to rotate and drive the generator, and this is done with high temperature steam at a very high pressure. The steam is made by boiling huge amounts of water in a boiler and tubes inside a huge furnace. The furnace is fed by a mixture of coal and air. The coal is crushed to the consistency of fine powder and injected under high pressure into the furnace, along with the air mixture, and this burns at an extremely high temperature which can boil those large volumes of water.
Now, while the generator might not have an overall yearly CF of 100%, an overall coal fired plant might have a CF of between 80% and perhaps as high as 90% with some of the newer technology coal fired power plants. These new tech plants are UltraSuperCritical plants and are now being referred to as HELE plants. (High Efficiency Low Emissions).
However, the generator delivers its maximum rated power while ever coal is fed into the furnace, with the unit up and running. The only time the generator is not turning and delivering power is during scheduled maintenance periods . At all other times it is either turning over slowly, waiting to be called upon to deliver its power, or already running at its maximum. In fact one generating unit at the Stanwell plant near Rockhampton in Queensland, Australia, holds a World record for continuous operation, of 1,073 days running at its maximum and delivering its full rated power, for almost three continuous years, never missing a beat in that whole time. Coal fired plants deliver their power all the time, when these large amounts of power are required. A large new technology Generator can generate 1300MW, and most recently constructed large units in operation are around 1,000MW in size, as shown in the image above. Older technology large scale generators have a maximum power rating from 660MW up to ones of 800MW, and most existing older technology coal fired plants have multiple units of say, 4 units of 660MW for a total power generation of 2640MW. while those newer technology coal fired plants now only need two 1000MW units for similar large amounts of power compared to those older units.
The power is again generated by a generator, only much smaller. It has to be smaller so it can fit inside what is called the Nacelle, which sits on top of the huge tower. The average is usually 2.5MW or 3MW for recent technology generators, some higher, and some older ones lower. The small generator can be direct drive, or as is more usual, it is driven through a gearbox, which again, is a very simplified description of what it really is. The actual driving force for the generator is that large three bladed ‘fan’ device at the front of the large tower, and the wind drives this. Immediately, it becomes obvious what the failing might be for something like this, and that is the vagaries of the wind. Sometimes it blows, and sometimes it doesn’t, and even when the wind speed is too high, the unit is turned off so it doesn’t destroy itself by rotating too fast.
So, with the average sized generator for a wind tower coming in at around at between 2.5MW and 3MW, it’s simple Maths to see that to generate the same Nameplate power as that one 1,000MW unit at a coal fired plant, you will need between 330 (at 3MW) and 400 (at 2.5MW) towers, and if it is a new technology two unit coal fired plant, then multiply those totals by two, so anything up to 800 of those large wind towers. So, as you can see, just to equal the total generating Nameplate of the coal fired plant you now need anything up to 800 of those wind towers.
But that’s not the end of it. Remember I mentioned Capacity Factor and how the variable wind means that they only operate between 20%, and up to possibly 30% of their total power rating, it now means you need to multiple that total number of towers by two and possibly three, keeping in mind that coal fired power averages 80% CF and higher. So now you need anything up to 2,500 or even more of those wind towers just to equal the total power delivery from that one coal fired plant with its two units.
But again, that’s not all of the story. Because the wind is so variable, even though that actual power delivery is around the same, the wind power is such that you never know when it will be delivering power, or not delivering it, while the coal fired plant delivers its maximum power all the time, and all they need do to get that maximum power is to feed in the coal.
So, while a case may be made for equivalent power totals, there really is no comparison. The power delivered from the coal fired plant is reliable, always there, and there when it’s actually needed, while the wind power may be there or it may not be there, unreliable at best, and when it is not delivering, then some plant which actually is reliable has to be called on to deliver power for when it is actually required. Because of that, they will always require backup for those wind plants, and that is something you do not need for coal fired power.
You’ll see articles and hear stories of how wind power is new technology, and can be constructed and utilised to replace coal fired power plants.
As you can plainly see from what I have written here, wind power cannot now, or never will be able to replace the reliability of coal fired plants.
Again, think of it in the manner of the analogy to the car at the top of this Post. It might look the same. It might do everything your old car did, but every time you drove it, you would always be concerned that it might just stop. You’ll never know when. That does not induce confidence.
Two generators at ONE coal fired power plant or up to 2,500 plus wind towers.
Reliable constant regular power or power that is maybe there or maybe not there.
Coal fired power versus wind power is really no contest.
Anton Lang uses the screen name of TonyfromOz, and he writes at this site, PA Pundits International on topics related to electrical power generation, from all sources, concentrating mainly on Renewable Power, and how the two most favoured methods of renewable power generation, Wind Power and all versions of Solar Power, fail comprehensively to deliver levels of power required to replace traditional power generation. His Bio is at this link.