The Buoy is Back: What Data Can Tell Us About Offshore Wind
Scientists analyze data from one of PNNL's offshore buoys
Offshore wind has huge potential to meet the nation’s energy needs. Developing just 1 percent of this potential could power nearly 6.5 million homes.
PNNL is working to accelerate prediction of the power-producing potential of offshore wind at an east coast site using two research buoys. DOE’s Wind Energy Technologies Office commissioned PNNL to procure and deploy two bright-yellow buoys—each worth $1.3 million. The buoys are decked out with advanced scientific instruments designed to measure wind speed at multiple heights, air and sea surface temperature, barometric pressure, relative humidity, wave height and period, and water conductivity. Doppler sensors measure subsurface ocean currents.
After a 19-month deployment off the coast of Virginia Beach, one of the buoys has returned to shore. In collaboration with the State of Virginia, PNNL examined the quality of the data and discovered that stronger winds produced more accurate data—likely as a result of the additional sea spray high winds generate. The increase in spray provides more particles for the LiDAR (Lighting Detection and Ranging) pulse to bounce off of, improving signal strength and return rates. Similarly, researchers found data recovery rates are higher during the warm season and the daytime.
PNNL also found that above 90 meters (295 feet), signal noise affected the integrity of the data. Further analysis revealed that by removing samples with low signal strengths and averaging data across 10-minute intervals, accurate results could be achieved. Additional analysis performed by researchers at Texas Tech University found offshore winds in the U.S. differ from European offshore environments. In the U.S., winds are more sheared, changing velocity and direction more frequently at lower levels in the atmosphere (low-level jets). While low-level jets do not significantly impact the power performance of an offshore wind turbine, their occurrence might lead to inaccurate assessment of the resource as well as increased fatigue loading on wind turbine components.
The data and buoys will help scientists and developers better understand air-sea interactions and their impact on how much wind energy a turbine could capture at particular offshore sites. The data will also help validate the wind predictions derived from computer models, which have thus far relied on extremely limited real-world observational data in U.S. coastal waters.