That Breezy Feeling

There are more three dozen offshore wind farms in the world, many with the potential of producing more than 200 megawatts of electricity. Most are in the United Kingdom and Germany. One is in the United States.

Located a few miles south of Rhode Island, the Block Island Wind Farm is pretty modest. Its five turbines have the nominal capacity of 30 megawatts — enough to power all of Block Island, which has begun decommissioning its diesel generators.

A few weeks ago, I traveled with almost two dozen other journalists to the wind farm to learn more about the project and to see the monster turbines up close.

A group called the New England Science Writers organized our trip (in conjunction with the wind farm’s developers and partners) and included several of the KSJ fellows as well as a smattering of science journalists from the Boston area. We loaded on to a coach bus and trekked about 90 minutes to North Kingstown on the Narragansett Bay where we met our ferry. (Fun fact: across the street at Quonset State Airport is a replica Air Force One 747. It’s quite striking to see it there, completely out of place. Why the website for the plane features George Washington is a bit of a mystery to me.)

The ferry wound its way south through the bay into the Rhode Island Sound. As we plowed through the blue water, a series of speakers gave us the low down on the science of the project, including the environmental impact. (Note: this post is just about my trip and observations rather than a work of independent journalism.)

A few things struck me as especially interesting:

  • The turbine pilings are anchored to the sea floor with nails that are feet across and meters long. Pounding the nails into the bedrock had to be put on hold during the brief period when right wales were in the area, since the sound of driving the nails would interfere with the endangered whales.
  • The thick cable that connects the turbines to each other and delivers electrons back to Block Island prevents commercial fishing in the area — at least with trawlers — but the pilings act as reefs and have been a boon to recreational fishermen.
  • One of the five turbines is outfitted with a tracking station to monitor the movement of previously tagged small birds and bats.

As the speakers delved into details, many of us shifted our gaze to the horizon. Tiny bumps in the distance grew larger and taller as the turbines came into view.

The first turbine stands like a sentry. The rest fade into an oncoming fog.

They hardly seemed special. Turbines are increasingly common along highways or atop mountain ridges. Their slow rotations belie the power being generated where the turbine’s blades meet. If you remember your physics, you’ll recall that electric current can be created by rotating a metal coil in a magnetic field. That’s how those little hand-cranked radios work. Mechanical energy to electrical energy.

Wind turbines (and all other turbines) operate on that same principle — greatly scaled up. Hydroelectric dams use the power of falling water to turn turbines. Steam turbines use the power of rising steam under pressure (heated by coal, natural gas or nuclear radioactive decay) to turn their turbines. Wind turbines use the power of the wind.

At the top of a turbine’s tower sits the generator and other machinery. On most land-based turbines, that includes gear shafts so that the slow turn of the blades is converted to 1,000 RPMs in the generator. Power!

We drifted to within a few hundred feet of the first turbine. My literature outlined the specs. The center of the turbine — the hub — stands 100 meters above the water. Each blade extends 75 meters from there. The end of each blade slices through the air up to 90 meters per second. Those seemed like impressive figures, but I had a hard time making sense of them.

Then we floated to within a few feet of the structure. Suddenly the turbine transformed. No longer was it just a scaled-up version of the machine we see on land. It had suddenly come alive; a lithe giant, powerfully slicing the air overhead with a soft and soothing “woosh.” We were tiny spectators gazing up at this gracefully tall figure, admiring the curves of its blades and smoothness of its tower.

Then, as quickly as it came alive, it reverted back to machine. We moved on to the second tower.

The scale of the turbines was difficult to appreciate until we were directly under them, since there’s nothing to compare them to — just open ocean.

As someone who has never been on the water out of sight of land, I never before appreciated how all sense of proportionality is lost at sea. From sea surface to the tip of the blade at the highest point, these machines stand taller than the Washington Monument. Each turbine stands half a mile apart from their nearest neighbors.

The Block Island turbines feature a number of engineering differences from their land-based cousins. Since they are larger and more remote, servicing the turbines is more challenging. One way to reduce service requirements is to reduce the number of parts and systems. So these turbines forgo the gearing that steps up the rotation and instead uses much larger generators.

People dismissive of wind energy point out that wind turbines generate electricity only when the wind is blowing. That’s true, of course, but far more interesting to me is how the wind turbines know which way to face.

If you look at old wind mills — the kind you might have seen on a family farm decades ago — you’ll notice a tail on the mill. That tail gets pushed by the wind until it is parallel to the wind direction, thus orienting the blades into the air flow, causing them to turn and the mill to do its work.

But modern turbines have no such tail. Instead, the turbines features a gaggle of weather sensors, anemometers and the like. Using those sensors, the turbine turns itself into the wind and twists the blades to achieve maximum efficiency.

Oh, and they also sport helipads. Because of course! (Look at the small yellow platform high up behind the turbine’s hub in the above photo. That’s for helicopters.)

A service vessel pushes against the turbine’s base to make it easier for people to transfer between then. For a sense of scale, look at the top of the yellow platform. Those are big burly guys standing there.

As we motored from turbine to turbine — we toured all five, though they don’t differ in any meaningful way that I can tell — fog rolled in. Sudden and thick, it enveloped us and the turbines, rending them nearly invisible.

The ferry wove through the array of turbines and the scientists resumed their talks. Several points were of particular interest to me:

  • Thanks to the good old conservation of energy, the wind that passes through the turbines and is converted into the rotational energy of the blades (and then the electrical energy of the generators) comes out significantly reduced on the other side. That is, if a 20 mph wind hits the turbine, immediately behind it you have a smaller wind. I don’t know what the precise change is, but let’s say it’s 10 mph. That has potential implications for siting other turbines, as well as environmental considerations. (What might it mean to have less land hitting a beach?) Of course, in the grand scheme, these five turbines have relatively little effect overall, but one can imagine a field of dozens of turbines having an impact on the down-wind weather.
  • It can actually get too windy for the turbines. Think hurricanes. In such an instance, the turbine is programmed to turn sideways to the prevailing winds. I guess there can be too much of a good thing.
  • Wind speed increases (at a decreasing rate) as you rise in altitude, meaning the wind you feel at water level is often much lower than the wind striking the top of the turbine’s blades.
  • Furthermore, winter wind speeds are two- to four-times faster than summer speeds. (Fall and spring speeds are similar to each other and between summer and winter.)

Cost came up, of course. Both in terms of construction of the turbines, but also the cost of the energy produced. It’s more expensive than other forms of electricity, though that accounting could change if externalities of fossil fuels were considered, as could happen with a carbon tax, or if economies of scale make turbine production and installation cheaper.

In any event, we eventually passed the last turbine and turned back toward land. The fog fell behind and the coast of Rhode Island returned to view. On the drive back to Boston, I noted several small land-based turbines. I’ll be honest: they’re not as sexy.

A turbine keeps turning, secreted by the rolling fog.

Leave a Reply

Your email address will not be published. Required fields are marked *