Industrial Wind—Power Production Characteristics and Grid Integration
Energy – thermodynamic quantity equivalent to the capacity to do work
Power – the actual performance of work at a measurable rate on a human-defined schedule
Nameplate Capacity – theoretical output of an energy generating machine running at full capacity
Capacity Factor – Percentage of nameplate capacity generated over a period of time
Capacity Value – Reliability of a generator to be available to come on line on demand
The quality of life and economic productivity of the US depend on having reliable, dispatchable electrical power on demand. This is accomplished via the electrical grid—a sophisticated network of generators, transmission infrastructure, and regulating devices that provides power on demand to consumers by precisely balancing generation output with load on a second-by-second basis. If load exceeds generation capacity, voltage drops and blackouts ensue. On the other hand, if generation exceeds load, grid voltage surges, frying sensitive electronics, which are in just about every type of machine these days, from computers and coffeemakers, to industrial equipment. Thus, grid voltage must be maintained within exquisitely tight tolerances, a balancing act performed by regional grid operators such as the Midwest Independent System Operator (MISO) using a series of base load, load-following, and peak-load generators, all available on demand. Historically, the approval of electrical generation methods has had to satisfy six regulatory and economic criteria. They must: 1) produce large amounts of 2) reliable, predictable and 3) dispatchable electricity from 4) compact generating facilities that 5) service one or more elements of grid demand (base load, load following, peak load) at 6) economical rates. A 7th requirement has appeared recently, though not explicitly codified in regulatory language: new generators must emit less or no carbon than existing methods. The latter appears to be the main basis used to justify the recent proliferation of wind farms.
How does industrial wind fit into this picture? The thermodynamics of a wind generator are such that the energy output is proportional to the cube of the wind speed. That means that if the wind speed doubles (or decreases by half), energy output increases (or decreases) by a factor of eight or more. Due to this relationship, modern industrial wind turbines typically do not begin producing electricity until wind speed reaches 7-9 mph, attain their maximum output at 33 mph, and cut out at wind speeds at about 56 mph to avoid structural damage. The same relationship means that output is low until winds are generally above about 20-25 mph, depending on the turbine model, and that small, momentary changes in wind speed result in enormous variations in output. Published data indicate that a typical North American land-based wind turbine produces no energy more than 10% of the time, produces its maximum output about 10-15% of the time, and continuously skitters between these extremes at other times, with an overall annual capacity factor of 25% or less.
Along with its intermittent nature, it is this variability that poses the greatest challenges for grid integration. Sudden increases and decreases in wind speed force grid operators to scramble to bring other compensating generators off- or online with little warning, taxing the grid and causing premature wear to the balancing generators. The problem is exacerbated because the diurnal and seasonal nature of wind velocity doesn’t match electrical demand: peak demand in the Midwest occurs a) generally, during the afternoon and evening, and b) particularly, during hot summer afternoons. Neither period is characterized by appreciable wind velocity, which tends to be greatest during the swing seasons, when temperatures are moderated and demand is lower. In northern Indiana, for example, the average annual wind speeds measured by the NWS at Fort Wayne and South Bend in 2010 were, respectively, 8.4 and 8.2 mph; the highest average values were in February (10.8 and 10.6 mph; March and April were similar), while the lowest were in August (4.6 and 5.9 mph; June and July were similar).
The typical response to this problem is to claim that it will go away with a sufficiently large number of geographically-dispersed wind plants. Unfortunately, studies on some of the largest wind arrays in the world—South Australia, the UK, Germany—do not bear this out, and instead suggest that wind velocities—and thus, turbine output—are broadly and positively correlated over large, continent-sized areas. As a growing number of analyses are showing, integrating the variability and intermittency of industrial wind into a modern electrical grid has serious implications for overall grid efficiency, and thus for reducing both the use of conventional generators and attendant emissions.
Industrial Wind and the Environment—Emissions and Climate
Carbon Dioxide (CO2)—naturally occurring trace atmospheric gas, also produced by combustion and thought to contribute to climate change; also referred to herein as “carbon emissions”
The two most common claims made in media reports viz industrial wind are 1) that “this wind farm will provide “power” for X number of homes”, and 2) that it will reduce carbon dioxide (and other) emissions derived from electricity generation. Indeed, reducing emissions appears to be the sole reason, or at least the one usually put forward, for the recent effort by governments and others to promote wind development. These claims are closely related, and both appear to be exaggerated when scrutinized closely.
It is true that the fuel (wind) is free and that the actual generation of electricity by a wind turbine produces no CO2 or other emissions. However, due to the variable, intermittent, and poorly-matched demand profile of wind, no modern grid could function reliably or maintain stability based on wind as the sole, or even the chief, generator. As an aside, it is important not to conflate industrial, grid-connected wind with small, building-scale wind generators attached to a bank of batteries: the latter does produce a small, though steady, stream of power due to the presence of battery storage. On the other hand, no large-scale storage devices presently exist at the scale of an electrical grid, hence energy must be generated, transmitted, and used instantaneously to maintain stable grid voltage—the balancing act described earlier, as performed by MISO and other operators. There has often been talk of such large-scale storage devices (most recently, “one million electric cars”) being “on the near horizon”, but realistic assessments by numerous experts suggest that such technology is unlikely to be commercially viable for decades. The only storage presently available is hydro, possible at a large scale only in a few, widely scattered regions with suitable hydrology and terrain.
The typical 20-25% annual capacity factors of modern wind turbines means that most of the work on the grid is still being done by conventional, reliable generators—only those generators must now work much harder just to stand still, i.e., to maintain grid stability against the relentlessly variable output of wind generators. This is typically accomplished by cycling natural gas generators—typically less expensive and less efficient open-cycle (OCG) types—or small coal-fired plants up and down over short times frames to “balance” wind output. These generators cannot be shut off due to the capricious nature of the wind resource, lest the grid be destabilized, and they must remain on “spinning reserve” behind the scenes until they are called upon to ramp up again. This is analogous to driving in stop-and-go traffic: obviously, your vehicle’s efficiency is much less. Several studies examining the grid-generation behavior of real grids, in real time, using fine-grained time intervals, show that emissions of carbon (as well as sulfur dioxide, nitrous oxide, mercury, and particulates) are actually greater in this scenario than they would be without any wind in the mix. Still other studies show that much greater emissions reductions of all types can be achieved by simply replacing the dirtiest coal-fired plants with efficient combined-cycle gas generators (CCG) running at full capacity, which produce about half of the carbon output of an older coal-fired plant, and none of the other emissions. The same analogy can be extended to renewable portfolio standards and similar mandates that require utilities to provide a certain percentage of their electricity from renewable sources, chiefly wind. This is like mandating an average speed of 60 mph while driving across the greater LA region: most of the time, the vehicle is stuck in stop and go traffic, so to achieve the average speed, it must suddenly accelerate to 120 mph during breaks in the traffic, before abruptly slowing down for the next traffic jam.
The above results are being confirmed in places commonly held up as examples of wind power success: Denmark, Texas, and California have all seen nominal, if any, reductions in overall carbon emissions from the electrical sector since their wind build outs began, and a careful examination of the data shows that nearly all of the reduction can be attributed to the replacement of coal-fired plants by CCG generators, much of which is being negated by the need to cycle less efficient OCG generators up and down in response to wind variability. This is one of the most under-reported stories by the green-energy-obsessed media.
This gets back to the first claim highlighted above: the “X number of homes powered” implicitly assumes that the wind plant puts out its nameplate capacity 24/7/365. This is not credible, but is accepted by a gullible (and physics-challenged) public and an unquestioning media, driven by a desire for solutions to environmental problems. In reality, conventional generators are reliably providing nearly 100% of the power to those homes.
Industrial Wind and the Environment—Turbine Noise, Shadow Flicker, and Human Health
Decibel “A”-Weighted Scale—Logarithmic scale that quantitatively measures audible noise
Decibel “C”-Weighted Scale—Logarithmic scale used to measure low frequency (inaudible) noise
Shadow Flicker—repetitive strobe effect caused by the shadows cast by a rotating object
Numerous anecdotal reports began to surface in the early to mid 2000’s of various ill effects suffered by persons living close to wind installations. These effects continue to be dismissed as “psycho-somatic” or “Nimby” by wind promoters and most media, but are now starting to be documented and understood by the medical community—and given a label called “Wind Turbine Syndrome”, now summarized in the book of the same name. Today, there are thousands of such adverse-effect reports associated with wind turbines, mostly self reported, along with a small number of systematic studies. Self-reported adverse effects are a standard and accepted part of modern epidemiology, used, for example, by pharmaceutical companies to measure effectiveness and side effects and to develop new warning labels. A key limitation of adverse event reports is that they do not allow the percentage of the population affected by the exposure to be determined.
The reported symptoms are varied—sleep deprivation, irritability, tinnitus, loss of amenity, anxiousness and panic attacks, inability to concentrate, among others—but are similar across affected populations exposed to wind turbines. Most notably, symptoms dissipate when the affected person is removed from the presumed source (wind turbines), a well-known type of epidemiological experiment known as “case crossover”, which is considered one of the most compelling medical indicators of causation.Research suggests that the symptoms are caused by a combination of shadow flicker, low-frequency noise, and/or infrasound that is inaudible to the human ear and is “felt” by the inner ear and body. The wind industry still maintains these effects are spurious or nonexistent, but such assertions don’t pass basic epidemiological scrutiny: when removed from their homes and the proximity to wind turbines, people suffering the characteristic symptoms eventually return to normal, but when returned to their homes, the symptoms resume. The percentage of the population susceptible to “wind turbine syndrome” is unknown, but adverse event reports to date suggest that children may be more susceptible. Infrasound is difficult to measure and quantify, but can be approximated on the decibel “C-weighted” scale (dbC), thus it is frequently overlooked by conventional acoustical studies that typically use the decibel “A-weighted” audible scale (dbA). Several recent peer-reviewed papers in medical journals are beginning to unravel the complex behavior of the inner ear and how infrasound (from any source) affects the body.In any case, the overall mechanism by which wind turbines produce symptoms in some people, at some sites, is incompletely understood. This severely limits the means available to mitigate the issue. Currently, distance appears to be the only reliable method.
Audible turbine noise also poses a serious annoyance in some cases. Wind promoters commonly claim that “turbines are no louder than a refrigerator”. While that may be true at some times and in some places, it is also true that wind developers frequently push local governments to adopt noise standards far greater than a refrigerator, such as the 55 dbA standard in Tippecanoe County. Many neighbors, even at distances of thousands of feet, liken the noise from adjacent turbines to “standing under a jet airplane poised for takeoff but never moving”, “living next to a busy airport”, “the thumping bass sound of disco music”, and similar analogies. Apparently, the broadcasting of noise is highly dependent on the conditions of each specific site. Beyond mere loudness, the rhythmic frequency of turbine noise is significantly different than typical smooth background noise in rural areas, especially at night. This rhythmic quality, along with the persistent duration of audible turbine noise, are often reported to be the most disturbing aspects of living close to wind installations.
Industrial Wind and the Environment—Landscape and Scale
Modern, land-based industrial wind turbines range from 400 to 500 feet tall. The rotors sweep an area larger than a Boeing 747 and travel at speeds up to 200 mph at their tips. Larger models are in development. For comparison, an average cell tower is 150 to 200 feet tall, whereas the tallest building in downtown Fort Wayne is about 375 feet. Total topographic relief in NobleCounty is slightly more than 300 feet, from the lowest to the highest point. In other words, wind turbines would be the largest and most conspicuous structures in the county.
Wind turbines need to be spaced at least ten rotor diameters apart to avoid interference with one another, known as wake turbulence. Under ideal conditions, four to six turbines could be established within a one-square-mile section. Due to variations in terrain, lease rights, and other factors, the spacing within an individual array is commonly greater, and more irregular. The medium-sized wind plant proposed for southern WhitleyCounty, for example, would have ~100 turbines occupying about 13,000 acres (20 square miles), while the proposed Wildcat Wind Farm in parts of four central Indiana counties would have about 262 turbines occupying 62,000 acres (97 square miles). If all of these 2.5-mW turbines generated at a capacity factor of 25%, the Wildcat wind plant would produce electricity equivalent to about 1.4% of Indiana’s total electrical output. By comparison, one large combined cycle gas plant would produce 3-4 times the amount of electricity on less than one square mile. This disparity has led to the term “energy sprawl” to describe the vast amount of landscape taken up by utility-scale renewable energy projects. Indeed, the National Research Council concluded that, if wind turbines were installed along every Appalachian ridgetop and on other optimal east coast upland sites, it would reduce total carbon emissions from the US electrical sector by no more than 1.2 – 3.6%. In contrast, ten nuclear power plants would accomplish the same reduction using less than 40 square miles of land.
Given the vast amount of land required to produce a meaningful amount of electricity by wind, it seems likely that wind installations will increasingly be proposed in proximity to more thickly settled communities, and to natural areas. NobleCounty is such a locality. By virtue of its presence in the Fort Wayne metro area, Noble County is among the top 33% of Indiana counties by population (47,536), being considerably more populated than the western Indiana counties which currently host wind farms (Benton County, at 9.421, and White County, at 25,267). With about 411 square miles of land area, the average population density of NobleCounty is 115 persons per square mile; excluding the incorporated towns, it is 67 persons per square mile. This is far greater than most rural counties in the plains states where many wind projects are being sited.
By some estimates, bird watching is a several million dollar industry in the southern Great Lakes region. Birds and bats provide billions of dollars in free pest control services to farmers, gardeners, and homeowners, and bats in particular are the main defense against nuisance mosquitoes and the advance of West Nile, St Louis encephalitis, and other mosquito-borne diseases. Poorly placed wind installations have been shown to kill hundreds or thousands of birds and bats per year per turbine. NobleCounty contains large amounts of prime bat habitat, including that of the endangered Indiana bat. Cranes, which are the largest North American waterfowl and are especially vulnerable to turbines and transmission lines, are a frequent denizen. With Chain O Lakes State Park (the largest in northern Indiana at 2,700 acres), the ElkhartScenicRiver, and more than 2 dozen other natural areas, NobleCounty is one of Indiana’s key destinations for nature tourism, which is a significant economic force in the county according to the Convention and Visitors Bureau. The county sits on one of the largest groundwater reserves in the southern Great Lakes, which interacts with more than 100 natural lakes and innumerable ponds and wetlands. These waterbodies are, in turn, an integral part of one of the world’s largest migratory bird corridors, the Great Lakes Flyway, and they are a key economic resource for the county.How will these places be perceived if they are allowed to be surrounded by dozens of giant industrial structures?