The Effect of Variable Generators, aka "Renewable Energy" on the Efficiency Of Fossil Fuel Plants.
Last edited Sat Mar 28, 2020, 02:00 PM - Edit history (1)
In other news, another big problem for humanity is still climate change.
The paper I'll discuss in this post is this one: An Analysis of Thermal Plant Flexibility Using a National Generator Performance Database (Rossol et al., Environ. Sci. Technol. 2019, 53, 13486?13494)
One of the coauthors is Paul Denholm whose 2005 paper on the subject of compressed air energy storage (CAES) to convert the useless wind energy systems into base load power, certainly stimulated a lot of thought on my part, although initially I was interested and amused by the paper since it relied on the combustion of dangerous natural gas to "store" energy.
(Emissions and Energy Efficiency Assessment of Baseload Wind Energy Systems, Denholm et al., Environ. Sci. Technol. 2005, 39, 6, 1903-1911) To be fair, under these conditions, this idea was less noxious than other types of dangerous natural gas plants, but it was still reliant on the combustion of a dangerous fossil fuel to back up a so called "renewable energy" facility. In any case, the point is moot. Fifteen years later, the number of dangerous natural gas enhanced compressed air energy storage systems that have converted wind energy into baseload energy is essentially zero. In the week of January 16, 2005, the week during which Denholm's interesting paper was published, the concentration of the dangerous fossil fuel waste carbon dioxide in the planetary atmosphere was 378.13 ppm. In the week of March 16, 2020 it was 414.28. None of the endless prattling on about so called "renewable energy" in the intervening years has prevented the increase by more than 35 ppm in the concentration of dangerous fossil waste carbon dioxide.
That's a fact. Facts matter.
Even if the wind industry is useless in addressing climate change, everything that has been written about it is not. As I said, Denholm's paper certainly stimulated a lot of thought on my part, and to the extent that we attempt to store energy, compressed gases including, but not limited to compressed air, seems to offer several thermodynamic and environmental advantages, particularly if future generations attempt to clean up the mess with which we have left them in our contempt for them.
(The contempt for young people I hear expressed here, on a liberal website distresses me to no end, particularly because the Millennials I know are all very impressive people.)
The use of compressed gases for energy storage is certainly a superior option to all that potentially environmentally odious crap that's written about batteries. So thank you, Paul Denholm, for stimulating me to consider this idea!
It has seemed obvious to me that when you shut down a dangerous fossil fuel plant because so called "renewable energy" happens to be available because the wind is blowing and/or the sun is shining, that you decrease that dangerous fossil fuel plants energy efficiency, simply since these plants require heat to operate. If they cool, they need to be reheated. The result, I have argued based on this obvious assertion is to limit any advantage that inherently variable energy might provide with respect to climate. Moreover, the need to have a redundant system whose cost recoveries are limited, making them more expensive to exist, raises the costs of overall energy despite all the delusional crap we hear about how "the costs" of wind energy and solar energy are going down, down, down. There is a reason that the most expensive electricity in the OECD is in Germany and Denmark. That is because while the momentary production of solar driven electricity and wind electricity appears to be cheap, it drives up the costs of reliable energy. Fifteen years after Denholm's paper the back up for the trivial and useless solar and wind industry is dangerous fossil fuels, dangerous fossil fuels being the fastest growing source of energy on this dying planet.
The wind and solar energy facilities have not arrested this rise, the are not addressing it, and they won't address it.
Anyway, the paper cited at the opening of this post details where one can get data to support what I have regarded as the assertion that I have considered obvious that adding variable (and random and notoriously unreliable) energy to the grid reduces the thermodynamic and economic efficiency of the required back up systems.
From the introduction to the text:
...A key element of integration studies is understanding the capability of fossil-fueled thermal generators to turn off and on and vary output over multiple time scales.(5,8) This is partly because increased penetration of VG resources results in increased variability of net energy demand (i.e., normal demand minus the contribution of VG). As VG is added to the grid, thermal plants will produce less energy, reducing fossil fuel use and emissions. However, these plants operate at different efficiencies when operated at part load, and increased VG penetration results in greater thermal plant output variability.(3,6) The ability of thermal plants to respond to increased variability, and the impact of this variability on costs and emissions, is often a key element of VG integration studies, so it is important that the operational characteristics of power plants are well represented...
...In this work, we use historical data from the U.S. Environmental Protection Agency’s (EPA) Clean Air Markets (CAM) Division that captures about 71% of the U.S. thermal generation fleet (excluding nuclear) to demonstrate that most plants spend a large fraction of their operation at part load, including traditional baseload generators...
A note: Nuclear energy - which is the only environmentally and economically sustainable form of energy in my often stated opinion - can be excluded because it is everything that so called "renewable energy" is not, that is that it is reliable and dependable and is continuously available and because, as Denholm claimed in 2005, it's carbon cost is extremely low, as close to zero as one can get. (His figure was 10-25 g CO2/kwh for nuclear, compared to 67-104 gCO2/kwh for compressed air storage of wind energy over a 50 hour period.) (Op cit., Denholm, 2005, Table 1, page 1909.) Thermal Rankine cycle nuclear plants are not shut down because the wind is blowing and the sun is shining: It would be exceedingly stupid and damaging to the environment to do so. They do not require expensive redundancies to be base load. This said, I have convinced myself that an intelligent race - that may not be us in this generation - would build combined cycle nuclear plants which inherently involve (in the nuclear case) compressed gases, inasmuch as the Brayton component involves compressed gas. To the extent that the use of compressed air can play a role in these types of operations, the passage of air will allow for the removal of dangerous pollutants, including carbon dioxide, but not limited to it: Sulfates, higher nitrogen oxides, and ozone may removed. In the latter case, if the removal involves exposure of air to a high radiation field - desirable in my view - the ozone destruction may be accompanied by the destruction of dangerous organohalides, and other inorganic halides such as SF6 and NF3, and the very risky ozone depleting side product of agriculture, nitrous oxide.
Now let's turn to the energy efficiency discussed in the paper.
The hand waving fool Amory Lovins, in a delusional but regrettably famous paper filled with poorly referenced assertions that were rather Trumpian inasmuch as they just sprung out of his head and were not backed by any serious research, Energy Strategy: The Road Not Taken?, claimed in 1976 that energy efficiency and so called renewable energy would save the world. This is despite the fact that in the 19th century (1865) a fellow named Jevons stated "Jevons Paradox" which asserted that increases in energy efficiency increased the use of energy. The energy efficiency of this planet, as a whole has been rising throughout the 21st century, and indeed, for much of the latter part of the 20th century. In the year 1971, according to the 1995 edition of the World Energy Outlook published by the International Energy Agency, World Energy Consumption was around 5000 Million Tons Oil Equivalent (cf page 18, 1995 World Energy Outlook) which translates to about 210 exajoules in SI units. In 2018, according to the 2019 World Energy Outlook, energy consumption on the planet has risen to 599.34 exajoules.
The data suggests that Jevons was right. The data suggests that Lovins was and is a fool.
It turns out that to the extent the other leg of his waving 1976 ravings, the claim that so called "renewable energy" would save the world is also self defeating. Because of rants of uneducated anti-nukes of which Lovins is only one example, the use of nuclear energy has been arrested since 1990, and has remained fairly constant, roughly between 28-29 exajoules per year, which is still considerably more than all of the world's solar and wind plants combined produced in 2018, after decades of wild cheering, 12.26 exajoules.
2019 Edition of the World Energy Outlook Table 1.1 Page 38] (I have converted MTOE in the original table to the SI unit exajoules in this text.)
As the paper shows, the presence of variable energy on the grid which is still backed up by dangerous fossil fuels decreases the efficiency (as well as the economics) of these redundant yet necessary plants.
Mind you, in the graphics from the paper, I am about to show here, there has been unwarranted kindness to these efficiency figures.
The interested reader (if there are such readers) is invited to check out the flow chart for data treatment found in the Supplementary Data, which is open sourced, figure S1 showing that the data involved with shut down and restart of the dangerous fossil fuel plants has been removed, even though this data is very real, and is very much involved with emissions and efficiency, since all of this energy is wasted and provides no value to humanity.
In these graphics from the paper please be aware of the units which are units of heat divided by units of electrical energy generated, formally, but not in the described axes, dimensionless numbers. This means that the higher values on the y axis reflect lower efficiency. These are for some sample plants in the EPA CEM data set:
The caption:
The caption:
In the case of these two plants, they clearly show the degradation of efficiency at low load.
The paper does not draw overweening conclusions, it is more of a procedure paper suggesting how to analyze data and does refer to the results of evaluating the data.
The paper may be accessed with a subscription or by access to a good university library, although right now these libraries - in my area at least - are closed, consistent perhaps, with our national celebration of ignorance. More frightening to me than anything connected with Covid-19 is the possibility that we are entering a dark age, like all dark ages, dependent on ignorance.
The authors are from the National Renewable Energy Laboratory, NREL, in Golden Colorado. Although I am personally appalled by the belief that so called "renewable energy" could or should save the world, I have great respect for the scientific integrity of the authors.
I hope, during this weekend that you will find the excitement and pleasure that we probably have neglected to feel in our previously hurried world, the mere joy of being alive.
