How wind energy is integrated on the grid

A recent trade publication article by Ken Silverstein reported that U.S. utility system operators are concerned about the variability of wind generation and how it may affect system operations.

In light of some of the misleading claims expressed in the article, it is important to remember that large amounts of wind energy are already being reliably and cost-effectively integrated with the grid in the U.S. and around the world. In 2010, the Texas grid obtained 7.8% of its electricity from wind energy, with wind energy providing more than 25% of the grid’s electricity at one point. Over 15% of the electricity produced in Iowa now comes from wind energy. Similarly, European countries like Germany, Spain, Portugal, Denmark, and Ireland now obtain more than 10% of their electricity from wind energy, with wind providing more than 45% of Spain’s electricity at one point.

How is this possible? A large part of the answer is that grid operators are already very good at dealing with variability and uncertainty on the power system. Factories turning large electrical equipment on and off and millions of people changing their use of air conditioning and electric heating as the weather changes cause large and often unpredictable changes in the demand for electricity. Similarly, large changes in electrical supply occur fairly frequently when large conventional power plants experience sudden outages due to mechanical or electrical failures and must go offline instantaneously. The loss of a large power plant can happen at any time, forcing grid operators to have 1000 Megawatts (enough to power a large city) or more of reserve generation standing by 24/7, ready to activate at a moment’s notice if needed.


While the casual observer does not see what is going on behind the scenes to keep the lights on, it is actually a very sophisticated balancing act. Grid operators often deal with these changes by changing the output of power plants, in many cases hydroelectric dams or natural gas power plants that can store their fuel behind a dam or in a pipeline. In other cases the grid operator may purchase or sell power to a neighboring region, or it may use demand response resources–large electricity users like factories that have agreed to change their electricity use in exchange for payment.


In contrast to the large, abrupt, and often unpredictable changes in electricity demand and in conventional generator output, wind output changes tend to be gradual and predictable. When wind turbines are spread over large areas, it typically takes an hour or more for a significant change in wind output to occur, as demonstrated in the table below showing the amount of variability in wind output over certain time intervals. In addition, wind energy forecasters can now predict what wind output will be hours and days in advance with a high level of accuracy and confidence, thanks to the use of advanced computers, weather models, and trained meteorologists.






Wind Penetration Studied

1 minute

5 minute

1 hour

Texas 2008

15,000 MW

6.5 MW

30 MW

328 MW

California 2007

2,100 MW, plus 330 MW solar

0.1 MW

0.3 MW

15 MW

7,500 MW, plus 1,900 MW solar

1.6 MW

7 MW

48 MW

12,500 MW, plus 2,600 MW solar

3.3 MW

14.2 MW

129 MW

New York 2005

3,300 MW

1.8 MW

52 MW


It is also important to keep in mind that much of the variability of wind energy is canceled out by opposite changes in supply and demand caused by other sources of variability. Just as the odds are very high that the additional demand caused by me turning my lights on will be offset by someone else turning their TV off, many increases in wind output will be offset by people turning appliances on and vice versa. In fact, one of the main reasons we built a power grid in the first place over 100 years ago was so that different sources of variability could cancel each other out.


The fact that changes in wind output are slower and predictable has important implications for the cost and emissions associated with integrating wind. Slower changes can be dealt with through the use of non-spinning reserves–power plants that are not operating but are standing by ready to provide power within 30 minutes or so. Since non-spinning reserves are not operating, there is no fuel use associated with them standing by, ready to operate. As a result, there is little to no emissions impact from having these reserves, and the cost of these non-spinning reserves is typically a few percent of the cost of the fast-response and higher-emitting spinning reserves that are needed to accommodate sudden changes like the loss of a large fossil or nuclear power plant.


The emissions concern has already been thoroughly debunked. Mr. Silverstein’s article’s main source for the emissions myth is a report by the group Bentek that was paid for by the Independent Petroleum Association of Mountain States (IPAMS), a fossil fuel industry lobby group. It is disappointing to see that this myth is continuing to receive attention after this report was thoroughly debunked as fossil industry-funded junk even before it was publicly released almost a year ago.


As one would expect, the fossil industry report’s analysis was riddled with problems. Most importantly, U.S. Department of Energy data directly and conclusively contradicts the study’s claims by showing that emissions of all pollutants declined precipitously and in lockstep as wind was being added to the grid in Colorado and Texas. The fossil industry report’s conclusions are derived from a number of flawed assumptions, such as assuming that all variability on the power system is driven by wind energy and extrapolating an estimate for normal wind plant behavior by cherry-picking a few hours of data that showed the highest wind variability.


In contrast, detailed, peer-reviewed power system studies show that any emissions increase is very small–a fraction of the emissions savings created by wind displacing fossil generation in the first place–and that in most cases the emissions savings of wind are even larger than expected due to wind energy’s disproportionate displacement of dirtier and less flexible coal generation in favor of more flexible gas generation. In fact, as Mr. Silverstein’s article notes, it appears that this transition to gas is already beginning to happen, making the article’s concerns about coal cycling unfounded.


Wind energy integration can be made even easier if our grid operating procedures are updated. Many of the rules that govern grid operations were enacted decades ago when the fuel mix was dominated by coal, gas, nuclear, and hydroelectric, and these operating procedures haven’t kept pace as technology has improved and as the fuel mix has changed. As the Federal Energy Regulatory Commission (FERC) recently noted in a proposed rulemaking on this topic, many of these obsolete grid operating practices constitute discrimination against renewable resources that are trying to get on the grid.


Relatively simple reforms like better coordinating regional grid operations, dispatching generators at faster time intervals, creating ancillary services markets that will incentive flexible resources like demand response to provide their services, increasing the use of demand response resources, and better integrating wind forecasting into grid operations can greatly reduce grid operating costs and facilitate wind integration. As FERC noted, many of these reforms yield major benefits for consumers even in the absence of wind energy by simply making the grid more efficient, so grid operators should be implementing them anyway.


Texas serves as a powerful example of how wind is being reliably and cost-effectively integrated. As mentioned above, the Texas grid obtained 7.8% of its electricity from wind energy in 2010. The chart below shows that reliability on the Texas grid, as measured using the industry standard CPS1 score, has increased significantly as wind has been added in large quantities over the last several years. Just over a month ago, wind vividly demonstrated its important contribution to grid reliability by keeping the lights on for millions of Texans while over 50 coal and natural gas plants experienced unexpected outages due to unusually cold weather.


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