As offshore wind power projects gear up in Europe and the U.S., the push for better transmission to ensure steady electricity when winds are weak is gaining momentum.
Earlier this year, 10 companies calling themselves "Friends of the Supergrid" drew up plans to build a massive pan-European offshore grid to connect wind farms across the North Sea. Now a group of America researchers from the University of Delaware and Stony Brook University is making a similar proposal for the U.S. East Coast.
"Solutions that reduce power fluctuations are important if wind is to displace significant amounts of carbon-emitting sources," the researchers said in a study published this month in the Proceedings of the National Academy of Sciences (PNAS).
Indeed, the biggest criticism faced by wind energy is reliability — that winds do not blow all the time and are often slowest during periods of high electricity demand.
The authors found that linking Atlantic Coast offshore wind parks by a huge grid of high-voltage direct current (HVDC) cables under the ocean would substantially smooth out the fluctuations.
This would be especially true if wind power really booms.
"The variability of wind power is not as problematic as is often supposed," the authors said. "However, as wind power becomes a higher proportion of all generation, it will become more difficult for electric system operators to effectively integrate additional fluctuating power output."
Europe boasts roughly 2,000 megawatts of installed offshore wind capacity, with over 800 turbines in nine countries. According to the European Wind Energy Association, a total of 100,000 megawatts of offshore wind is in the planning stages across the continent.
Currently, there are no wind turbines in U.S. waters. But proposals are on the books for five wind developments from Delaware to Massachusetts that would churn out 1,700 megawatts — equivalent to two standard coal plants.
As plans stand now, each wind park would have a separate underwater transmission cable that plugs into the nearest state electric grid.
If baseload power is the goal, a single, federal offshore "Atlantic Transmission Grid" would be a better bet, the authors suggest.
The PNAS study analyzed five years of wind data from 11 meteorological stations along a 2,500-kilometer stretch of the East Coast and estimated electrical output from a hypothetical turbine at each spot. The results revealed ups and downs of the wind, some of which were severe. When the researchers simulated a power line connecting them all, however, the extreme peaks and valleys in the demand curve leveled out. Further, there was never a moment when the wind wasn’t churning out some electricity.
"During the five-year study period, the amount of power shifted up and down but never stopped," the authors said.
HVDC lines are far better at conserving power over long distances than AC transmission. A dip in wind power generation in Delaware could be balanced by better wind gusts in Florida, hundreds of miles away.
Brian Colle, a co-author of the study and associate professor in the School of Marine and Atmospheric Sciences at Stony Brook, said orientation of the turbines is also key. "A north-south transmission geometry fits nicely with the storm track that shifts northward or southward along the U.S. East Coast on a weekly or seasonal time scale," Colle said. "Because then at any one time a high or low pressure system is likely to be producing wind (and thus power) somewhere along the coast."
The hope is that a supergrid could help link into the vast untapped potential of the resource.
Harvesting two-thirds of the wind blowing off the U.S. Northeast could provide all the electricity needed to power states from Massachusetts to North Carolina, according to a 2007 analysis from the University of Delaware. The megawatts likely to come online in the next few years add up to one-tenth of 1 percent of that potential.
Current offshore wind plans in the U.S. would carry a price tag of around $10.5 billion, according to the report. A unified grid would require 350 miles of undersea cables and comprise $1.4 billion of the total upfront costs.
As a fix for intermittency, "transmission is far more economically effective than utility-scale electric storage," the researchers said.
Electric storage is seen as another possible solution to reduce power fluctuations, but most technologies are not yet economically viable.
In Europe, where offshore wind farms could be pumping out at least 70 gigawatts of power in the North Sea by 2030, the cost of a supergrid would would come in at between $27 billion and $40 billion, according to figures from the environmental group Greenpeace. Brussels-based Friends of the Supergrid has not verified the numbers.
Friends of the Supergrid is currently recruiting a chief executive officer and has said it will take two to three years to determine key details, including who would own and govern the supergrid, who would oversee regulation and how the funds would be raised.
In the U.S., there are similar regulatory implications. Currently, electricity generation is largely a state matter. The PNAS study recommends the creation of an independent federal body of private firms, electric utilities and public power authorities "for managing and regulating the bulk power market along the offshore transmission cable."
(Map: Friends of the Supergrid)