The heat is on - and so is the wind

The best way to solve arguments concerning the performance of offshore wind turbines is with actual data. Opponents of Cape Wind - the nation's first fully permitted offshore wind farm have long argued that the turbines would be still during the hot summer months when demand for electricity is at its greatest.

Real-time data from a meteorological tower mounted at the site of the proposed project tells a very different story. (GW)

Offshore wind energy potential boosted during heat wave, data shows

Climate Central
KnoxNews
July 30, 2011

When summer temperatures climb in New England, some people head to Cape Cod, where cool air blowing off the Atlantic Ocean often helps lower temperatures to more comfortable levels. But that characteristic sea breeze offers more than an escape during the hottest days; it also means offshore wind power can chip in when electricity demand is at its peak.

Last week, for example, when high temperatures roasted cities across the Northeast, winds were blowing hard and steady at the Cape Wind site in Nantucket Sound. If the proposed 130 wind turbines had already been installed, they would have been running nearly at full capacity, at the same time electricity demand was reaching record levels.

“Last week had the two highest electrical demand days of 2011,” says Mark Rodgers, Cape Wind’s Communications Director, “and we observed that the winds were very strong on Thursday and also above average on Friday.”

When a heat wave settles in, like it did last week across much of the country, it’s a given that people turn to their air conditioners for relief. Running so many air conditioners all day and through the night, however, requires a lot of electricity. In fact, electricity demand is usually highest during a heat wave, and often spikes in the late afternoon when the sun’s scorching heat is at its worst.

Last week was no different. In New England, the managers of the electrical grid, the Independent System Operator of New England (ISO-NE), reported two of its highest electricity demand days on record. On Thursday and Friday, July 21 and 22, when temperatures across Connecticut, Rhode Island, and Massachusetts, climbed well above 90°F and, in some cases, above 100°F, electricity demand was more than 25 percent greater than on a typical summer day.

According to Rodgers, information from a data tower built at the Cape Wind site showed the turbines would have been running at their full capacity on Thursday, collectively generating 420 megawatts of electricity, and also would have run well above average on Friday.

Climate science research shows that heat waves are becoming more likely in the Northeast and other parts of the country as the overall climate warms, which means that the electrical grid may see more sharp spikes in demand. In Boston, for example, the average number of days each year with temperatures above 90 degrees is expected to double by the middle of this century.

The Cape Wind project is the first offshore wind farm to receive both federal and state approval, but so far construction of the turbines has been stalled by opposition from local communities, who have protested the wind farm’s location. The ongoing debate over Cape Wind’s development continues to be thoroughly reported by WCAI’s Sean Corcoran as well as Climatide's Heather Goldstone.

Nantucket Sound isn’t the only patch of the Northeast coastline where the winds tend to pick up during a heat wave. According to recent research from Stony Brook University, there is a distinct trend of windy weather that develops in the summer between New Jersey and New York harbor, and extending northeastward up to Cape Cod.

According to meteorology professor Brian Colle, the wind can be enhanced by 20 to 30 percent along this stretch of coast during the warmest months.

“It’s more than just standing at the beach and having the wind blowing on your face; it’s more than a sea breeze,” says Colle. Even though the air over the land heats up quickly during the summer, he explains, the air over the water can stay as much as 20°F cooler. That temperature difference sets up a difference in air pressure, and sends the cooler ocean air blowing towards the land.

A data tower at the Cape Wind site in Nantucket Sound shows that the hottest days tend to be accompanied by higher winds. Credit: Cape Wind.

Colle says that this enhanced airflow tends to be most dramatic between six to 20 miles offshore. This distance coincides with the proposed sites for several offshore wind farms along the Northeast coast, including ones in Delaware, New Jersey, and New York.

The warm weather isn’t beneficial for all wind farms, however. On land, wind tends to be weaker than average during heat waves. In the past, this has been a point of criticism for wind energy projects, because the hottest weather also tends to be the time when electricity is needed most.

For example, during an intense July 2006 heat wave in California, wind farms were producing electricity at less than ten percent of their maximum capacity, and some days these dipped as low as four percent.

“People sometimes say that when you really need the power, during the hot 'dog days of July and August,' the wind isn’t there,” says Rodgers. For land-based wind turbines, he says there is some merit to the criticism.

On the other hand, he says, data that Cape Wind has collected from Nantucket Sound during the past eight years shows that the same conditions don’t apply to their site. The days of highest electricity demand in New England were days when Cape Wind would have been running above 70 percent of its maximum capacity. During regular wind conditions, Cape Wind claims it will run at about 48 percent capacity, and overall, its average capacity (including times with little to no wind) is expected to be around 21 percent of its maximum rating.

The wind may not be enhanced to that same degree at all of the potential locations for wind farms along the Northeast coastline, but according to Colle, other power companies have picked up on the trend and are now trying to find out where hot weather might influence offshore wind power the most.