Originally posted on MasterResource by Jon Boone, September 15, 2010
SCIENCE IS THE DISINTERESTED SEARCH FOR THE OBJECTIVE TRUTH ABOUT THE MATERIAL WORLD.
This post in our series looks at how the integration of wind variability affects thermal activity on the grid, favors flexible natural gas generators, and influences economic dispatch and the spot market. It also examines how estimates of carbon emissions are derived and summarizes the limitations of statistically based knowledge. It concludes with a discussion of what Energy Information Administration (EIA) actually says about the causes of carbon emission reductions in the country over the last three years
It is true, as AWEA notes, that any wind production must displace some existing generation, but only in terms of electricity–not any of the underlying energy forms transposed into electricity. It is rather due to the stricture that supply match perfectly with demand at all times (and this is another oversimplification of a complicated situation).
Just as the grid must reduce supply in precise increments to keep pace with specific reductions in demand—or increase supply in just the right increments to keep pace with increasing demand, the grid must respond to increased wind penetration, which, to a grid operator, looks much like a reduction in demand. Since wind plants are continuously generating between zero and 100% of their rated capacity in flux, providing who-knows-what for any future time, conventional generation must infill any reduction in wind energy at the precise increment of that reduction and, conversely, it must be withdrawn in increments that match any wind increases.
If wind generation were merely intermittent and unpredictable while producing at a steady rate, it might achieve some of its claims about backing down coal. However, wind’s relentless variability imposes daunting challenges for integration. Clever engineering schemes can mask the problem, but not without imposing increased costs and thermal activity.
Any fossil fuel saved when it is sporadically displaced by wind is often consumed in even greater volume as it is called upon to compensate for wind’s relentless skittering—the phenomenon described by Bentek. Wind existentially reduces the efficiency of these compensatory plants, raising the heat rate penalties of older, less efficient coal plants such that they may be forced to emit 40% more CO2 than when operating efficiently. Even efficient penalties of 2% can increase emissions up to 16%.[1] Depending upon the fossil-fired plant involved and the circumstances, a reduction in output in response to the addition of wind “can cause a very small reduction in the efficiency of that fossil-fueled power plant,” as AWEA claims. But over time, these inefficiencies accumulate. But where is the evidence for any of this activity in the real world, aside from the Bentek study?
Evidently, AWEA understands and agrees with Bentek’s recommendation that its product would do much better paired with “more flexible, less polluting natural gas units.” The association knows nuclear plants are not designed for load balancing purposes and that cycling coal-fired boilers in a wind following role is just as problematic, as AWEA obliquely conceded.
Yet as Australian engineer, Peter Lang, has shown, even the best possible thermal entanglement with wind, comprised of both open and combined cycle natural gas systems, can save only 15% more CO2 than can be achieved by the natural gas systems alone, without any wind. However, the direct and indirect costs of replacing coal with such a tandem would insure that all grid-connected Americans would see their utility bills skyrocket, given wind’s capital costs, which, on per kWh production basis, are on a par with nuclear’s.[2]
Inefficient use of natural gas systems with wind, such as responsive open cycle units normally used only at peak demand, would save no carbon dioxide emissions. And as Canadian Kent Hawkins shows, modeling a combination of coal and natural gas for wind balancing results in more carbon emissions than would be the case without any wind, despite wind’s huge capital costs. Moreover, as Lang has said, “ So wind cannot contribute to reducing capital investment in generating plants. Wind is simply an additional capital investment.” And one that seems entirely unnecessary if the goal is reduced CO2 emissions.
Any valid attempt to measure the effects of wind integration must account for all the variables at play, including what generation wind displaces, what generation is used to follow and balance its volatility, the cycling rates and heat rates, type of fuels, even voltage regulation systems, among other things. All of these back end factors must be tallied and weighed against any initial carbon savings claimed for wind at the front end. Here’s how energy expert Tom Hewson, in an article for POWER magazine, summarized the havoc wind’s presence plays on economic dispatch:
“…new wind generation will displace highest incremental cost generation on the regional powerpool margin. This marginal generator constantly changes throughout the day due to continuing load fluctuations. This constantly changing market makes it extremely difficult to predict what resources would be displaced throughout a given year. Without use of a regional dispatch model in combination with the project generation profile, wind developer consultants
make simplifying and often flawed assumptions. These assumptions often center on the displaced generation being either coal-fired generation or a weighted average regional blend of fossil fuel generation. Given that higher cost gas and oil can be on the margin, a weight average fossil fuel average that better reflects the dominant baseload generation resources (more heavily coal based) result in even overestimating displaced emission characteristics for their selected historical period.”[3]
One should add that not only does the marginal UNIT change, but so does that unit’s operating characteristics (i.e., ramping heat rate) and the need to match actual wind speed data and (via performance of its turbines) wind output.[4]
Given the inherent complexity, it is problematic to speculate about how wind volatility either lowers price or improves reliability on the spot market, as AWEA stoutly affirms that it does. Regional transmission operators are obliged to obtain the lowest cost set of suppliers to achieve high reliability, often deploying “redispatch” rebundling of the power mix to solve impromptu predicaments.
Consequently, spot market prices are contingent on many conditions within a series of priorities, some of them temporal, some functional, some related to scheduling. For most regions, about 90% of the spot market supply is purchased in a day-ahead auction in which wind rarely participates since it cannot assure firm delivery 24 hours in advance (and would be liable for financial penalties). Instead, it usually participates in the real-time, at-the-moment market, which historically accounts for only 10% of the overall spot market. In this situation, if wind can deliver, conventional generators may back down and still receive the agreed marginal price set from the day before while saving fuel—a good deal for particularly natural gas generators in many areas of the country.
However, in areas like Texas, where there is no day-ahead spot market, wind is responsible for eroding natural gas prices, as the Wall Street Journal reported last March. Suffice it to say, as Lisa Linowes once did:
“Since the price paid for 90% of the generation is established twenty-four hours in advance of the power day, any low-cost participation from wind will have only a marginal impact on prices limited to those resources operating within the real-time market.”[5]
Government projections, particularly those from the National Renewable Energy Lab, that show wind can provide a substantial percentage of electricity in the United States while substantially reducing CO2 emissions are uncontaminated by reality; they have no more credibility than college football polls. Simulations based upon even hourly dispatch models without considering the gustiness of the wind and the corresponding heat rate penalties yield incomplete, if not duplicitous, information about a complex process—while assumptions about wind’s ability to replace generation one-to-one are cartoonish misrepresentations of reality.
The NREL projections do not even try to account for the impact of thermal cycling events in response to wind volatility. Politically correct but untested testimonials from independent grid operators are equally problematic.
Measurement of greenhouse gas emissions is imprecise and statistical. Power plants are apparently not equipped with monitoring sensors; consequently, emission data is not based on direct observation. Rather, it is derived by plugging in numbers according to a formula, factoring information about fuel type and operating hours, estimating a plant’s thermal efficiency, and then leavening all that with a coefficient that calculates the pounds of CO2 produced by particular fossil fuels.
It is unlikely that these averages are computed at time frames less than a day, which greatly disguises the effects of minute-to-minute wind flux. In short, reported numbers are typically formed from indirect model calculations, which themselves are fraught with a series of estimates.
Any statistician familiar with the problem of “averages” knows the difficulty of using them to explain complex phenomena. Wind behavior is different than the rather straight on performance of conventional generation. As stated earlier, trying to describe wind activity with snapshots at any given time masks its volatility, making it seem steady and sober, deceptively giving the impression that the energy yield from wind is the same as that from conventional sources.
For the purpose of more accurately accounting for the way wind volatility distorts the general formula in use for calculating emissions production, given the present limitations for direct measurement, load dispatch analyses at, say, 15-minute intervals, should be the preferred modeling tool, italicized here to emphasize that models are merely a means of examining reality, not reality itself. They would allow a much better look at the way routine wind flux affects the overall thermal activity within the grid.
WHAT THE USEIA DATA REALLY SHOW
No one with knowledge about how CO2 emission data is estimated should say they represent objective reality, as AWEA does, for the possibility of plus or minus error is non trivial. With this in mind, let’s look more closely at what the EIA has actually said about wind and carbon emissions, in context. Here’s what Robert Bryce had reported in his Wall Street Journal article: “The U.S. Energy Information Administration (EIA) has estimated the potential savings from a nationwide 25% renewable electricity standard…. Best-case scenario: about 306 million tons less CO2 by 2030. Given that the agency expects annual U.S. carbon emissions to be about 6.2 billion tons in 2030, that expected reduction will only equal about 4.9% of emissions nationwide.” There is a worst-case scenario: all that wind will produce virtually no reductions, a conclusion of the National Academy of Science.[6]
Bryce also reported that the NREL believes that if 20% of the electricity in the eastern U.S. came from wind, “the likely reduction in carbon emissions would be less than 200 million tons per year,” not even a drop in the bucket, as we will see.
Here’s what the EIA national generation mix data for 2007 and 2008 reveals:
- US electricity demand in 2008 fell 0.9% from the previous year. Peak summer demand fell 3.8%. Coal generation declined 1.5%; natural gas, 1.5%; nuclear, 0.3%. CO2 emissions fell 2.5%–”largely due to decreased fuels consumption,” explained the USEIA commentary.
- During this period, wind generation increased 60.7 percent, from 34.5 million MWh in 2007 to 55.4 million MWh in 2008.
- The overall improvement in the average natural gas capacity factor since 2003 reflects both the increased reliance on combined cycle generation to meet energy requirements and further efficiency gains in combined cycle generation technology, leading to lower CO2 emissions.
- Sulfur dioxide (SO2) emissions fell 13.4 percent, from 9.0 to 7.8 million metric tons, between 2007 and 2008. This amounts to the largest year-over-year decline since 1995, almost entirely due to the improvement in natural gas plant efficiency. The large reductions in SO2 in 2008 resulted in part from a decline in fuel consumption but mostly from the installation of emissions reduction equipment in response to the Environmental Protection Agency’s Clean Air Interstate Rule.
- “Estimated carbon dioxide emissions by U.S. electric generators and combined heat and power facilities fell 2.5 percent from 2007 to 2008 (from 2,540 million metric tons to 2,477 million metric tons), largely due to a fall in fuel consumption at electric power plants.” (Italics added)
The substantial increase in installed wind clearly had little to do with reductions in CO2 and other greenhouse gasses. Rather, according to the USEIA, they were almost entirely due to reductions in demand, with corresponding reductions in generation. There were additional reductions of CO2 emissions attributed to increased use of more efficient CCGT units. Significant CO2 reductions at a national level in 2008 cannot be tied to wind, even indirectly. And, most likely, no CO2 reductions can be ineluctably credited to wind activity.
According to the EIA, the total U.S. electricity-related emissions of greenhouse gases in 2008 were 2,499.8 mmt of carbon dioxide equivalent (CO2e), or about 35% of total US greenhouse gas emissions. In 2009, it experienced a decline of 205 mmt, the largest in recent times. Moreover, this 4% drop in the carbon intensity of the electric power sector, was
primarily due to fuel switching as the price of coal rose 6.8 percent from 2008 to 2009 while the comparable price of natural gas fell 48 percent on a per Btu basis. The carbon content of natural gas is about 45 percent lower than the carbon content of coal and modern natural gas generation plants that can compete to supply base load electricity often use significantly less energy input to produce a kilowatt-hour of electricity than a typical coal-fired generation plant. For both of these reasons, increased use of natural gas in place of coal caused the sector’s carbon intensity to decrease. (bold added)
In discussing 2009 CO2 reductions, the EIA does state wind was responsible for avoiding 39 mmt. This was 19% of the total claimed CO2 emissions drop for the year—205 mmt— which also factored reduced demand and improved nuclear (26 mmt) and natural gas (82mmt) efficiency. However, since the total CO2 emissions tied to electricity production for the year was 2295 mmt, the 39 mmt from wind contributed only 0.016% of the total—a thimbleful, despite the presence of over 35000MW of installed wind capacity. And even this may have substantially overstated the case for wind, given the margin for error inherent in the EIA’s emission savings projection from wind.
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The following provides links to the other posts in this series as they are published:
Part I – Windpower on the Firing Line
Part II – Getting to the Facts on Emissions Reductions
Part III – (This post)
Part IV – Where’s the Empirical Proof?
ENDNOTES
[1] When coal-fired turbines are frequently and rapidly ramped up and down to compensate for wind variation, “the unit emission of CO2 per kWh increases …to cope with load. This can easily be 2% or more…depending on the degree of r1amp-down. On a coal-fired boiler, a 2% reduction in efficiency increases the unit emissions from 950 grams per kWh to nearly 1,100 grams per kWh, a change of 150 grams per kWh….”—a 16% increase in emissions.” David White, Reduction in Carbon Dioxide Emissions: Estimating the Potential Contribution from Wind Power, December 2004, page 16, Renewable Energy Foundation http://www.ref.org.uk/Files/david.white.wind.co2.saving.12.04.pdf
[2] William Tucker, Obama’s Nuclear Power Breakthrough, The Wall Street Journal, February 26, 2010: http://online.wsj.com/article/SB10001424052748703787304575075413484405770.html
[3] Tom Hewson, “Calculating Wind Power’s Environmental Benefits.”Power Engineering. July 2009: http://www.evainc.com/Publications/windpowerbenefit.pdf
[4] Tom Tanton, personal email dated August 21, 2010, and, personal email, dated August 27, 2010.
[5] See Russell Gold, Natural Gas Tilts at Windmills in Power Feud, The Wall Street Journal, March 2, 2010. See also John Chandley, How RTOs Establish Spot Market Prices (and How This Helps to Keep the Lights On), PJM Interconnection, September 27, 2007: http://www.pjm.com/~/media/documents/reports/spot-market-prices-j-chandley.ashx. See also Ross Baldick, Single Clearing Price in Electricity Markets, University of Texas at Austin, February 18, 2009: http://works.bepress.com/cgi/viewcontent.cgi?article=1156&context=cramton.. Quote taken from Lisa Linowes’ essay, WindAction, March, 2010: http://www.windaction.org/faqs/26050. Special thanks to Tom Stacy for providing the Chandley article.
[6] The NAS worst-case scenario—1.2% reductions. “Wind power will offset emissions of carbon dioxide by 1.2-4.5% from the levels of emissions that would otherwise occur from electricity generation.”
