THE FACTS ABOUT WIND SPEED AND CLIMATE CHANGE

3TIER, Inc. response to “Wind speed trends over the contiguous USA” Sara Pryor and coauthors, (to appear in J. Geophysical Research in August)
Jeff Yin, PhD, Research Scientist; Andrew Wood, PhD, Lead Scientist; Bart Nijssen, PhD, CIO, June 16, 2009 (3Tier Group)

SUMMARY
3TIER Group, which won an American Wind Energy Association 2009 award for commercial achievement and contribution to the wind industry for developing FirstLook, a free Web-based wind and solar energy prospecting tool. The mountain of climatological data that went into creating FirstLook puts 3TIER in a better position than most to evaluate the findings of “Wind speed trends over the contiguous USA,” the paper that recently stirred up so much controversy and comment.

Written by Professor Sara Pryor and her co-researchers, the soon-to-be published Journal of Geophysical Research) paper was a hot topic for its findings that the wind energy industry’s potential capacity may be compromised. Worldwide wind speeds are slowing, the Pryor paper reportedly concluded, and the cause is the very global climate change that wind installations are being built to reverse.

The findings in the Pryor paper come as no surprise to 3TIER. Using its own extensive wind and climate data, 3TIER first presented findings of changes in wind project capacities associated with climate change in 2004. 3TIER’s report simulated a hypothetical wind project in Washington state. It showed a theoretical 1.3% loss of capacity by 2050 and noted the importance of geographic variations in climate change projections.

click to enlarge

A 2008 report from 3TIER in North American Windpower, an industry periodical, described conclusions from 14 different climate simulations that were performed
in support of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). Based on the 3TIER projections, wind speed changes are expected to be modest but large enough to affect existing and future wind project profitability.

The 2008 3TIER study observed a poleward shift in wind speeds, especially during winter, probably associated with the widely documented poleward shift of the jet streams and their storm tracks. It also observed a widely predicted seasonal increase in wind speeds from the Great Lakes to Texas and a seasonal wind speed decrease across the West. The seasonal nature of the changes means U.S. winds will be increased in the winter and decreased during the summer in the North.

3TIER offered 5 important observations on the Pryor paper:
(1) Such studies are vital in advancing the understanding of climate change and its impacts on wind energy. The main value of the Pryor paper, and others that precede it documenting the same phenomena, highlight still-to-be-resolved discrepancies between observation-based and model-based estimates of wind speed trends. The discrepancies illustrate that there are “large uncertainties” in the “nature, source(s) and magnitude” of wind speed observations and trends.

click to enlarge

(2) Further study is needed of longer-term wind station observations, like the decades-long observational records in the Pryor paper, to obtain insight into how much decade-scale variability there is in observed wind speed trends that might be associated with climate system changes.

(3) Wind speed and turbine power output are not the exactly the same. Power depends on a turbine’s power curve. More linear than expected from the cubic relationship between wind speed and power density, wind power may not be as significantly affected by the change in wind speeds created by climate change as would be expected.

(4) Studies, including the Pryor paper, show climate change-created effects on wind speed changes vary regionally. Only location-specific wind studies can inform decisions about wind projects.

(5) The trends and variabilities illuminated in studies like the Pryor paper make diligent assessment of project risk, like those 3TIER has provided for years, even more important.

From 3TIER Group

COMMENTARY
3TIER had some specific observations on the Pryor paper and the media coverage of it. Most of the attention, according to 3TIER, went to the report of an observed decrease in wind speeds since 1973 in the eastern Midwest. The media failed to report the discrepancies between trends predicted from wind speed observations and trends predicted from models and data reanalysis simulations. The 2 kinds of predictions have 2 kinds of drawbacks.

Observed wind speed predictions have inconsistencies from anemometer instrumentation fluctuations and from the effects of nearby buildings and vegetation. The inconsistencies are significant enought that many in the wind industry no longer use the readings.

Simulations, however, have 20-to-200 mile spatial scale approximations in north-south and east-west components. This makes the conclusions drawn less specific.

Discrepancies in the Pryor paper between measures derived from observation and simulation reproduced similar discrepancies in wind speed trend estimates made in studies of Australia and Europe.

Without an explanation of the discrepancies, the conclusions have a limited, challengeable applicability.

click to enlarge

3TIER found 2 very significant “misconceptions” in one major media report on the Pryor paper, from the AP (and probably emblematic of widespread accounts).

(1) The AP reported “a 10 percent change in peak winds would translate into a 30 percent change in how much energy is reaped.” This is a gross oversimplification. It may be true at intermediate wind speeds but most wind sites are selected for above-intermediate speeds. The result is that a 10% change in wind speed would likely translate to not a 30% change but a 10% change in energy output.
(2) The AP implied that decreasing wind speeds are caused by the poles warming more quickly than the rest of the world. This is another gross oversimplification. Most IPCC AR4 simulations showed increased winds with increased greenhouse gas (GhG) accumulations. The GhG accumulation, it is speculated, causes an increased contrast in temperatures in the upper atmosphere. The temperature contrast produces increased storminess and causes a shift in regional surface winds toward the poles. The net impact, therefore, would more likely be an increase in wind speeds in some regions and a decrease in other regions.

3TIER applauded the Pryor paper as a contribution to the understanding of U.S. wind resources but stressed 4 key summary points:
(1) The Pryor paper further emphasizes the need to know more about the effects of climate change to account for its effects on wind in energy policy decision-making.
(2) It is of crucial importance to know why there are discrepancies between observation-based and model-based wind speed trend estimates.
(3) Decisions about wind projects should not be made on general wind speed trend assessments but on location-specific studies.
(4) (This is the shameless 3TIER self-promotion.) 3TIER can provide the necessary information for long-term performance assessments of wind projects.

Wind resources are location specific, not global. (click to enlarge)

QUOTES
- From the 3TIER analysis of the Pryor paper: “In light of these unresolved discrepancies [between observed and simulated wind speed trends], 3TIER strongly agrees with the final sentence of the Pryor et al. paper: “Given the importance of the wind energy industry to meeting Federal and State mandates for increased use of renewable energy supplies and the impact of changing wind regimes on a variety of other industries and physical processes, further research on wind climate variability and evolution is required, as are detailed analyses focusing on reconciling the discrepancies illuminated herein.”

click to enlarge

- From the 3TIER analysis: “Although power production is very sensitive to changes in intermediate wind speeds, where a 10% change in wind speed can indeed result in a 30% change in power production, most wind projects are built at sites where typical wind speeds are above this intermediate, sensitive range. In practice, we find that the annual mean power output for a typical wind power plant has a nearly linear relationship with the annual mean wind speed.”
- From the 3TIER analysis: “…most of the climate change simulations performed for the IPCC AR4 actually produce stronger surface winds in response to increasing greenhouse gases. This is most likely because increasing greenhouse gases produce a larger temperature contrast in the upper atmosphere, which tends to increase storminess and wind speeds near the surface. This increase in storminess also tends to shift the regions of strong surface winds towards the poles, suggesting that there are likely to be some regions that experience increasing wind speeds, while other regions experience decreasing wind speeds.”