Buoys may best towers in offshore wind assessments

Researchers at Iowa State University are working to evaluate a testing approach that may be able to better predict future success of offshore wind farms. It involves implementing a system of buoy-mounted testing balloons instead of meteorological towers. The altered method could increase energy return on investment and reduce costs spent surveying failed sites.

“For onshore locations, a tower will provide a suitable (testing) platform,” said Eugene Takle, principal investigator on the project and professor of agricultural meteorology at Iowa State. “But for a location, say, 10 miles offshore where water may be 50 to 100 feet deep, a tower is not a good option.”

He says a better option for wind measurement at locations far out in the sea may be a weather balloon tethered to a stationary buoy. He and the university team is making sure to account for the effects movement will have on results from a balloon-attached measurement pack.

Initial insights will come from a deployment near the Iowa State campus.

“We will be flying the balloon near a tower near the ISU campus to measure wind speed, direction and temperature,” said Takle. “Comparison will be made between the tower based measurements and the package suspended from the balloon tether.”

By comparing the two sets of results, Takle says that they can interpret and correct for balloon movement and then apply the same techniques to data from balloons deployed at many heights not possible using towers.

Being able to measure wind at various heights provides more data to evaluate and could encourage the harvesting of energy at higher altitudes, where wind is steadier, more persistent and faster-moving.

According to Iowa’s Alliance for Wind Innovation and Novel Development, the use of a buoy-based, balloon-tethered system for assessing wind energy at proposed sites could reduce the total cost of an offshore wind farm by four percent.

The price of deploying the devices is considerable. Cost for the balloon, helium and measurement package is estimated to range from $30,000 to $40,000 and a moored buoy can cost from $25,000 to $30,000. With a price tag of less than $100,000, however, the system costs less than deploying a tower offshore, which can reach into the millions.

With $600,000 in funding – coming evenly from Anemometry Specialists, Inc. and Iowa’s Alliance for Wind Innovation and Novel Development – the project takes advantage of an industry match provision within the Iowa program meant to encourage partnerships between the state’s research universities and its wind energy industry.

Image: Danish wind turbines near Copenhagen (via Wikimedia Commons)
Front page image:  Wind turbines at the Middelgrunden wind farm off Copenhagen (via Wikimedia Commons)