Downsides of offshore wind – Installation

Our previous post about wind farm impacts on marine habitat focused on site survey noise. Once the site is surveyed, site preparation – clearing and grading the seafloor is performed, the masts are built and the turbines are installed.

There are three installation strategies for the masts used to mount wind turbines; bottom mounted structures for shallow waters, either on piles driven into the sea bottom (good to 30m or 100ft. depth), or “jack-up” platforms (good to 90m or 300ft.) Deeper waters require floating masts (as pictured). All are intensive construction operations that require powerful (and noisy) service vessels holding everything in place while the structures go up.

Of all of these, pile driving is by far the noisiest, both in terms of installation, and during operation, with transmission of gearbox noise down the mast into the water column and seafloor. Some of the larger masts are 3m (10ft.) in diameter, and up to 120m (400ft.) tall. They are steel, and require a huge “hammer” to slam the bases into the substrate to depths, that sometimes can exceed 40m (130ft.). This is not a formula for quiet.

One of the noise mitigation practices for pile driving are “bubble curtains,” wherein compressors drive air down to the base of the pile, and blow a jacket of bubbles up around the mast, decoupling the banging noise from the surrounding ocean. Pushing air down into the depths takes a lot of energy – directly proportional to the depth. Of course the compressors run on fossil fuel, so not a lot of carbon savings there…

But a number of years back at an acoustics conference, I ran into Mark Worchner, who has come up with another noise attenuation strategy for pile driving using a curtain of “Helmholtz Resonators.” It’s a pretty cool idea, doesn’t require continuous energy input, and is reusable.

After our first offshore wind newsletter we received correspondence from Burt Hamner, President of Windbase Offshore who has adapted “Jack-up” platforms for mounting turbine masts. Jack-ups are a tried-and-true offshore oil industry technology which bears a couple of advantages over pile driving; firstly, the pre-assembly on-shore takes the pile driving-associated noise and concomitant noise mitigation requirements out of the equation. Secondly, because they can be deployed in much deeper water, the “onshore eyesore” is significantly reduced (more on this in a subsequent newsletter).

Seafloor mounted masts are workable on the Atlantic and Gulf of Mexico Outer Continental Shelf (OCS), because of the shallow benthic (depth) profiles available in these places. This is not the case off the Pacific Coast, where the depth drops off pretty fast. This is where floating masts would be the practice. And aside from the vessel traffic, there would not be any extraordinary installation noise.

So the foregoing frames some of the noise liabilities of offshore wind power installation. My next piece will address noise impacts from ongoing operations. Then we’ll move on to non-noise liabilities. As I mentioned when I opened this series, these are all liabilities that need to be honestly addressed.

Since launching this series I have received many passionate, well-articulated (if not entirely correct) responses from many quarters. Apparently people have their eyes on this horizon. We are being asked to change; to move away from fossil fuels and toward something new, and honestly, like leaving any bad relationship, it is a bit scary.

By shedding light on the liabilities of wind power, I hope to ease this transition for us.