Wind speeds are up across the U.S. in Q2 2011

A renewable energy risk analysis released a wind performance map for the second quarter of 2011. The map illustrates wind speeds above seasonal averages for most of the continental U.S. 3TIER’s second quarter map indicates departures from long-term mean wind speeds that range from -20 to 20% and provides an indication of how wind projects should have performed relative to their long-term production average based on their location. This type of analysis lets financiers and owners perform portfolio analysis across regions and quickly view the effects of weather anomalies on both existing and proposed investments.
Looking at wind speeds during the second quarter of 2011, the pattern is 5 to 10% above normal for nearly the entire US. Especially strong positive wind anomalies centered over the southern Mississippi Valley and the southern Rocky Mountains. Some areas within these regions exceeded 25% above normal wind speeds when averaged over all of April, May, and June.
The only areas that experienced wind speeds below average were North Dakota along the Canadian border, isolated areas of California, and along the Carolina coast, and through Florida. These areas saw minor negative anomalies of about 5% with the exception of Florida where wind speeds were up to 15% below normal.
Climate conditions across North America during the second quarter of 2011 were influenced by a weakening of La Niña that occurred this past winter in the tropical Pacific Ocean, leading to neutral El Niño/Southern Oscillation (ENSO) conditions by the end of the quarter. This quarter was also affected by a gradual transition in the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) from a positive state at the start of the quarter to a negative state at the end.
However, the dominant feature of the second quarter across the US was a stronger pressure gradient and thus much higher than normal winds over the south-central part of the country. The unusually strong pressure gradient resulted from three anomalous patterns that developed during the quarter: an upper-level trough over the northwestern United States, associated low surface pressure in the northern Great Plains, and high surface pressure over the Southeast.

The wind performance map was created by comparing output from 3TIER’s continually updated meteorological dataset with wind conditions averaged over the period 1969 to 2008 from the same dataset. Wind speed values were computed using a numerical weather prediction (NWP) model run at a 15 km resolution and adjusted using available observations. The underlying datasets for the company’s wind performance maps provide clients with operational intelligence for every location within a region and are available in nearly all regions worldwide.

3Tier
www.3tier.com

Heated anemometer works in freezing weather

Cup anemometers can generate inaccurate wind-speed values in gusty periods, and should one freeze, its turbine may have to shut down. One solution is an ultrasonic anemometer, like the Ventus UMB 8371 with a 240W heater. This unit provides precise and maintenance-free measurements of wind velocity and direction.  
      Ventus belongs to Lufft’s WS family of professional intelligent sensors (in Booth 106) with digital and analog interfaces. This wind sensor has no mechanical parts as are used with traditional “cups and vanes”. The digital or analog output delivers instantaneous, average, min or max value with flexible measuring rate. The heated Ventus makes it well suited for cold climates. Outputs are available for the NMEA data, ASCII UMB, and binary UMB protocols, along with 4 to 20 mA analog, and soon, SDI12 protocol.

Its official: NREL says sodar data as good as from met towers

Sodar or sonic detection and ranging, is a relatively recent tool for measuring wind speed and direction up to 200-m up. The task was usually relegated to meteorological tower that had to be built and often reached only 80-m up. Portable sodar units simplify the task. Recently, as part of continuing scientific research to understand wind resources, the National Renewable Energy Laboratory (NREL) and sodar developer Second Wind Inc, Somerville, Mass., partnered to characterize the performance of Second Wind’s Triton Sonic Wind Profiler.

The following is an edited version of conclusions reached by NREL authors. Their analysis (http://tinyurl.com/wpenrel) of the wind resource data provided by Second Wind Inc., came from 10-min data samples over a 198-day period. It was collected from an 80-m meteorological tower and a Triton sodar system from a measurement program conducted near an operating wind farm in western Texas. NREL did not participate in the measurement phase of the study. The tower configuration, specs of the locations of the met tower and sodar unit, and the data collection were done by the wind-farm developer with assistance from Second Wind. The collected data were then sent to NREL for analysis.

“Our analysis of the sample Triton data set shows excellent agreement with the tower measurements,” says the NREL report. “Given the 200 m distance between the sodar and the met tower, it would be unreasonable to expect a perfect correlation between the two datasets.” From the data provided, NREL engineers make these observations:

• The operational uptime was greater than 98%, demonstrating sodar’s operational reliability during this 198-day period.

• Triton’s (sodar) measured wind speeds correlated well to the meteorological tower, but were generally slightly lower. The correlation coefficients were greater than 0.983 at both heights (50m and 80m).

• The Triton’s measured wind direction also correlated well to the tower data when the sector containing the wind farm was removed. At 80 m, the correlation coefficient calculated between the Triton and the wind vane was 0.994.

• The wind direction distributions as measured by the Triton and the tower were consistent. A slight rotation of the directions may be attributable to instrument alignment, or may reflect an actual difference in the wind direction over the horizontal distance of 200 m between the meteorological tower and the Triton.

• The percent of valid data (Q >= 90%) measured by the Triton was greater than 95% at 80m and was approximately 81% at 120m.

• Shear exponents calculated from the tower and Triton data were comparable in terms of overall shear as well as daytime and nighttime shear.

• A discrepancy in the average turbulence intensity was measured by the two instruments. At 80m, the Triton measured an average TI of 0.100, while the average 80m TI on the meteorological tower was 0.132.