Weather Model Optimizes Offshore Wind Farm Placement

 
A team of engineers from Stanford University have used a sophisticated weather model to plan the optimal placement of four interconnected wind farms planned for the east coast of the United States.

“It is the first time anyone has used high-resolution meteorological data to plan the placement of offshore wind grid,” said senior author Mark Z. Jacobson, a professor of civil and environmental engineering. “And this sophistication has provided a deeper level of understanding to the grid plan.”

The region in question accounts for 34 percent of the country’s electrical demand and creates 35 percent of the country’s carbon dioxide emissions. Optimizing the placement of a renewable energy source such as wind farms is the natural next step.

But why bother? What optimization is there to do?

Wind doesn’t blow consistently all the time. There are times when it drops off, and, in those instances, there is suddenly no electricity being generated. So, what happens when there’s that lack of wind during a hot summer day when everyone wants their air conditioning working?

For the east coast of America, this is especially tricky, as a meteorological phenomenon known as the Bermuda High — a high-pressure center that affects winds along the entire east coast — brings with it a dearth of storms and strong winds.

“In some areas, like Massachusetts, the Bermuda High boosts sea breezes,” said Mike Dvorak, the lead author of the study and a recent PhD graduate in civil and environmental engineering at Stanford. “But south of Long Island, NY, where one offshore grid has been proposed, the Bermuda High has the opposite effect and often hinders sea breezes.”

“Until recently, large scale wind resource assessments have neglected the aspect of time. We matched peak productivity with peak demand at specific times of day and year,” said Dvorak. “Our analysis matches production to demand.”

How they did it

The engineers started out with 12 energetic potential locations along the eastern coast of the US and then narrowed that number down to the four in play at the moment. The four sites are outlined in red in the image above, and the farms planned for those locations would each have approximately 100 turbines delivering an individual maximum capacity of 500 megawatts, making for an interconnected grid of 2000 megawatts. That’s approximately the same yearly capacity of one and a half conventional coal-fired power plants.

“Two thousand megawatts and four farms are somewhat arbitrary figures. The sizes and locations could be adjusted for economic, environmental, and policy considerations,” said Jacobson.

“An offshore grid as an extension of the onshore grid in this region will improve reliability, while reducing congestion and energy price differences between areas,” said Dvorak.

Technical challenges

“The farms had to be in waters less than 50 meters deep to allow use of bottom-mounted turbines and near urban load centers like Boston and New York,” said Jacobson. “And, we wanted to smooth power output, ease hourly ramp rates and reduce hours of zero power.”

So, the engineers decided on an interconnected grid of offshore farms.

“The goal is to even out the peaks and valleys in production,” said Dvorak. “In our model, expensive no-power events — moments when individual winds farms are producing zero electricity — were reduced by more than half from nine percent to four by connecting the farms together.”

Over the space of a year, the interconnected grid was able to yield a 48 percent capacity factor, meaning that it could reliably produce close to 1000 megawatts on average across the whole of the year.

“Generally, with wind farms, anything over 35 percent average capacity is considered excellent,” said Jacobson.

Source: Stanford University
Map: Mike Dvorak, Stanford School of Engineering