"At a recent meeting, I heard a politician say that he didn't want his city to buy electricity from wind energy because 'Wind energy creates just as many greenhouse gas emissions as coal'. This can't be true, can it?"
- Becky from Chicago
This is an odd, although not surprising question. Generating electricity from wind energy has several questions that communities have to answer, mostly those communities where the wind turbines produce the electricity. Low level noise from the rotating turbines can disturb neighboring residences, turning blades can cause issues with migrating birds, and installing the turbines in the middle of farmland (although a great financial benefit to farmers) can cause disruption with new roads and infrastructure to build and maintain the turbines.
The claim made by the politician stems from one of two additional issues, or perceived issues depending on your point of view: the need for reserve energy should the wind stop blowing, and the lifetime energy intensity of building, operating, and decommissioning the turbines. I will deal with the latter question first.
According to a 1990 study by the Solar Energy Research Institute, an at-the-time, state-of-the-art coal power plant generated 1,041 metric tons of CO2 per GWhe (giga-watt hours of electricity generated), mostly coming from the burning of the fossil fuel (96.8%), with the remainder coming from ongoing operation and maintenance (2.7%) and initial construction (0.5%). As a comparison, a natural gas turbine electricity generating plant, according to a 2000 report by the Energy Center of Wisconsin, has a lifetime CO2 emissions of 464 metric tons per GWhe. In 2009, an Australian research team looking to improve upon previous studies that underestimated the embodied energy (and therefore emissions) associated with constructing wind turbines, calculated that the life cycle emissions for a wind turbine fell in the range of about 8-10 metric tons per GWhe. Admittedly, the study did not focus on quantifying the decommissioning of the plant for the case of the study, but even at a level equivalent to construction, wind power appears to reduce electricity-related CO2 emissions by 98% relative to late 20th century technology for electricity generation from coal and by 95.5% relative to modern natural gas generation.
Since the embodied energy theory does not make sense, that leaves the case of reserves.
This will require a (hopefully) straightforward analogy to explain the difference between the two types of reserves: spinning and non-spinning reserves. As the name implies, spinning reserves are already in motion, ready to go, and non-spinning reserves stay dormant until called into action. Like any machine, a generator producing electricity has a level at which it likes to run to efficiently produce electricity. Above or below that level, the unit still works, but produces less energy output per level of input. Also, when starting a generator "cold", it takes significantly more energy to get running than during normal operation.
Since the human body acts as a machine as well, the best analogy I can come up with relates electricity generation to a relay team. Each team member contributes to the overall goal of completing the distance in the best time possible. Consider electricity generated by coal, nuclear, natural gas, and wind as the four relay team members. Nuclear has strong efficiencies, but must get going as soon as it has warmed up and must run at a constant rate...a good lead runner. Coal should run next, as its plants also run large and requires a relatively constant load. Wind runs in the third leg of the relay, and when running at peak form, it generates a significant amount of electricity very efficiently and puts the team in great position to finish. Currently, natural gas runs as the anchor because it can get up to speed quickly and increase speed if necessary to bring the team to the finish line.
The problem with wind comes from variability...it does not always produce as forecasted, and on some rare days, does not show up at all. Reserves, in the electricity generation realm, help to cover for this in one of two ways. Spinning reserves increase the output of other generation already online. In the analogy, this takes the form of other runners running faster (and less efficiently) to make up for a dip in wind's contribution. Non-spinning reserves act like a substitute runner who takes wind's place in the event at the last minute. They do not get optimal time to warmup, and cannot perform at their best, but fill in as best they can.
A 2011 study by a team of researchers from Argonne National Labs, the University of Illinois and the Georgia Institute of Technology looked at the implication to emissions reduction from the need for fossil-fuel-based generation to be brought on during times when wind forecasts failed to meet expectations. They found two interesting results. First, the amount of "base load" wind (meaning the amount of possible wind generation available as a percentage of total generation) heavily influenced the type of reserves available, and therefore, the total emissions. When new wind generation reached a high level of base load, it allowed nuclear plants (which normally run full out) to act as spinning reserve and enabled more natural gas plants to transition to non-spinning reserve. Under lower levels of wind base load (or none at all), nuclear and natural gas run at capacity leaving inefficient coal plants to provide most of the spinning and non-spinning reserves. In the relay race, under the low base-load scenario, the variability of wind gets covered by the coal leg running faster but less efficient, and if wind cannot run at all, it gets replaced by a less efficient coal runner, reducing the overall efficiency of the team. When wind has a larger base load, the nuclear and natural gas team members have more capacity to cover for wind, thus enabling better overall team performance, even when wind cannot perform. The second observation answers the question fully: under every possible scenario, the presence of wind generation reduced the overall emissions of the electricity generation relative to a "no wind" baseline.
Every new technology displaces an established way of life or business practice. Those that profit from the status quo will always find reason to question the validity of the new technology's supposed performance. This skepticism provides a healthy check against getting "ripped off" by new ideas that do not really deliver. In this case, relative to carbon emissions, the new technology completely betters the old. Additionally, as wind generation increases penetration, we will find more efficient ways to handle the variability, and will reduce the risk of variability through the citing of generation facilities in a wider area of service. As the grid becomes "smarter", this area of service can expand to include large areas of the country, thereby decreasing the risk further.
Thanks for the question.
Enjoy the journey!
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