Energy 101: How do wind turbines work?
San Luis Obispo County could one day see large collections of behemoth floating turbines spinning off its shores as the federal government explores the ocean’s potential as a source of wind energy generation.
The idea of possibly hundreds of turbines as tall as 700 feet has attracted interest from several companies, while the U.S. Navy considers whether the industry is compatible with its operations off the coast.
Many questions remain to be resolved before anything is built, but there’s one in particular of interest to anyone who lives along the North Coast or enjoys visiting there: Just how visible would an offshore wind farm likely be here?
What do we know about the proposed turbines?
The effort to explore building wind turbines off the California coast is being managed by the U.S. Bureau of Ocean Energy Management.
Three possible locations in federal waters have been identified to date: two off SLO County and one off Humboldt County.
One area off Morro Bay — located in waters closer to San Simeon — begins 24 miles offshore, while another off Diablo Canyon nuclear power plant begins 22 miles offshore.
To put that distance in perspective, the turbines would be located about four to five times farther away than structures like the oil platforms in the Santa Barbara Channel.
In 2018, the agency issued a Call for Information and Nominations to “confirm interest in potential offshore wind leasing and development,” according to John Romero, BOEM’s Pacific region public affairs officer.
Though two companies — Trident Wind (now part of Castle Wind, a joint venture with EnBW) and the Redwood Coast Energy Authority — included some possible details in unsolicited lease requests submitted previously to BOEM, at this point in the process it’s not exactly clear how many turbines might be installed and how tall they would be if a wind farm is cleared for either of the current locations.
Romero said that BOEM has not recommended any exact project specifications. Instead, it’s having interested companies provide a general description of what they are “thinking in the way of a possible future project. An actual project plan comes to BOEM for review only after a lease is issued.”
A cursory look at BOEM’s website shows that most of the nominations from the 14 interested companies describe the energy generation potential of possible projects but do not suggest specific numbers, models or heights of turbines.
What matters when it comes to the visual impact of offshore turbines?
Bob Sullivan, a self-described “visual resource scientist” from the U.S. Department of Energy’s Argonne National Laboratory, has extensively studied the visual impact of renewable energy sources like wind turbines.
Sullivan said it could be difficult to characterize what people gazing out from the coast will see without a more formal analysis, but we can get a general idea of what an offshore wind farm might look like here.
When asked what influences the visibility of turbines, Sullivan says he’s identified at least 20 factors.
Some of the obvious ones are the distance, size, color and height of the turbines, along with the elevation of the observer looking out to sea.
Sullivan pointed out a statement on Castle Wind’s FAQ site that says “400-feet-tall structures will not be visible by an observer at the sea level at distances greater than 23.4 nautical miles.”
This detail — originating from a Coast Guard document that describes aids to marine navigation like buoys and beacons — assumes a person looking at those structures has their feet planted firmly at sea level and that an object of that height is obscured by the curvature of the earth.
There’s a good chance, however, that turbines will exceed that height, making them more visible.
As Sullivan notes and Vox described in a recent May article, the industry continues to produce larger and more powerful turbines in order to more effectively harness available wind and create extra energy.
For instance, General Electric is currently developing the Halaide-X, which it describes as the “most powerful offshore wind turbine in the world to date.” The gigantic 12-megawatt turbine will stand at 853 feet from base to tip of blade — about four-fifths the height of the Eiffel Tower.
Also, not everyone taking in the ocean view from the SLO County coastline will be at sea level.
Hearst Castle views could be affected
One widely visited location that definitely offers higher-elevation views is Hearst Castle, which sits at 1,600 feet.
Any potential change to the view visitors see from the iconic Castle is already on the mind of Stephen Hearst, the vice president and general manager of Hearst’s Western Properties.
“They walk to the window and say, ‘You’ve got to be kidding!’” he said in an October Tribune story, referring to how visitors’ experiences could change. “It’s the view … one of the most valuable attributes of the Castle. I don’t think impairing it is in the best interests of the state or the Central Coast.”
Sullivan agreed that that an offshore wind farm would be more visible to viewers at higher vantage points.
But he noted that distance also is a major factor in how turbines will appear to people on land, adding that there is “going to be very large difference between 15 miles and 30.”
At closer distances, he said an observer’s eyes are most likely to be drawn to the turbines’ motion: “People need to keep in mind turbines have moving blades, and movement is pretty conspicuous.”
His own research — including his role as lead author of a study published in a 2013 issue of the journal Environmental Practice and partially funded by BOEM — suggests moving blades are not easily visible beyond a distance of about 25 miles, but Sullivan said it doesn’t mean offshore wind turbines will be invisible at longer distances.
Describing turbines that could be shorter than those proposed here, he said, “I have seen them out to 27 miles at sea, on land I have seen them beyond 35, and have verified that they can be seen beyond 40 miles.”
But, at those extremely long distances, the turbines appear tiny, and unless someone is “really scrutinizing the horizon,” they are very unlikely to see them, he said.
Sullivan also noted that “people tend to focus on visibility during the day,” when actually the turbines’ lighting at night can be just as or more noticeable.
Turbines typically have two sets of lights: at the top of the tower to caution local air traffic and closer to the base for marine navigation. The top lights are more visible at longer distances.
Sullivan also said that how noticeable the lights from an offshore wind farm appear depends on “whether the horizon has a lot of existing lights or not.” That’s not likely too much of a factor with these proposals.
In any case, he said, a formal viewshed analysis will be essential to determining just how visible any particular offshore wind project might be, because there are “a lot of factors beyond just the simple issue of geometry.”
For its part, Castle Wind LLC has already taken some initial steps to study this impact, as described in its nomination for BOEM.
The developer contracted DNV GL, an independent renewable energy consultant, to simulate the expected views from Hearst Castle under typical visibility conditions using information recorded by the Morro Bay Harbormaster’s Office.
Based on the results, Castle Wind has concluded that “the proposed project site will rarely be visible from onshore locations such as Hearst Castle and the Piedras Blancas Light Station, given the site’s distance from shore and the area’s typical weather conditions.”
Whether that’s true won’t be determined until more precise turbine sizes and distances offshore can be analyzed.