Offshore wind has been in the news recently — DONG energy is building the largest plant in the world off the coast of Cumbria in the UK, and even the US is finally getting in on the offshore action — but what is it, and why would we want to build wind farms in the ocean rather than on land? Read on for a primer on offshore wind, part of our ongoing series on the future of power.
There are essentially three types of place you can put up a wind farm: on land, in the water, and in between the two (on the coast). They all have advantages and drawbacks, but the things they’re seeking are all the same:
- strong wind
- steady wind
- access to the power grid
Strong wind is all well and good — you need something to push the blades on your generator around — but you also need them to do it constantly if you can. Downtime is expensive and cuts into the bottom line, and sudden strong gusts can actually damage the equipment (which often results, once again, in downtime — if only to protect the generators). The third one is the real kicker: electricity isn’t much good if it can’t be used. Even with storage batteries, like pumped-storage hydroelectrical or molten salt reservoirs, at this point we really prefer to just send power directly to the grid to be used right away. That’s when it’s most cost-effective.
So why, then, would you build a wind farm out at sea? It’s harder to get the electricity to shore to power homes and businesses.
The answer has to do, at least in part, with the terrain.
Ideally, you want your turbine to be in a place where there aren’t any obstructions, so the wind can reach a decent speed and stay there. This website from the Iowa Energy Center explains that, among other things, you want your turbine to be situated:
(1) “upwind at a distance of more than two times the height of [any] obstruction,”
(2) “downwind a minimum distance of 10 times, and preferably 20 times, the height of [any] obstruction,” and
(3) “the wind turbine hub [should be] at least twice the height of [any] obstruction above ground, if the wind turbine is immediately downwind of [an] obstruction.”
Which is all to say that, ideally, you want long stretches of flat space to build your wind turbines on. And if you don’t have flat, then ridgelines are good too.
America — and China, and others — have many good places on land to build wind farms. These have the benefits (in many cases) of being easier to access, easier to build, and easier to link up to the energy grid, simply by virtue of being on land. But not everyone does.
So why not build on the coastlines? These would take advantage of the sea and land breezes that blow inland during the day and back out to sea at night. So-called “near shore” wind turbines — usually built on land or in the water right by the coast — have been built in various locations, but progress is often stalled by NIMBYism.
NIMBYism (short for Not In My Back Yard, if you didn’t know) is what happens when the coastal areas are all taken by humans, and they do crazy things like deciding that wind power is great and all, just so long as it’s somewhere else.
And so there’s offshore wind. Sometimes really offshore.
Offshore wind is great if (a) you don’t have a whole lot of flat places on land to use, and (b) you don’t mind the added expense. As you might have guessed, out at sea, there aren’t a hell of a lot of obstacles, so the wind speeds are both higher and more constant. Plus, without anyone around to see them — the UK’s Wanley Wind Farm is 14km west of Wanley Island, and Rhode Island’s Block Island Wind Farm will be 5km from Block Island, which is roughly 15-20km from literally anything else — you don’t get so much political obstructionism (which could even make your wind project less expensive, depending on who you’d otherwise have to fight).
But how, exactly, do you build a wind farm out at sea?
For a long time the answer has been “attach it to the sea floor” — that’s what DONG is doing at Wanley and in the Thames estuary — but this limits the area you can place turbines to a depth (usually) of 20-80m. A new technology, floating wind turbines, is starting to gain traction, too, with projects like the Scottish Hywind project. The Hywind turbines float, and are moored in place by three ballasted cables, which gives them a great deal of stability even in high waves. A US company, Principle Power, is hoping to use another floating technology called WindFloat off the coast of Oregon.
So is it feasible as the power of the future? It depends on what you mean. The UK, for whom offshore wind is a great solution, already has over 5GW of peak capacity in offshore wind power, with roughly 1.4GW under construction and plans for quite a bit more after that. Which automatically puts it head-and-shoulders over fusion and slow wave reactors because, you know, it exists.
Of course, 6-7GW is a long way from the UK’s 2012 peak consumption of nearly 60GW, as well. In theory, the maximum capacity of offshore wind in UK waters is on the order of 2TW, which is more than enough to power the UK (and much of Europe besides) but, as with all analyses of energy resource potential, it’s a little pie-in-the-sky. It’s wind power, too, which means that there’s a significant difference between peak power and minimum power, raising questions about its stability as a resource (though maybe Tesla’s “powerwall” will change all that). It’s also a little more expensive than land-based wind at present, which is dissuading, well, anyone who can get their electricity by cheaper means.
Nevertheless, it’s a very promising set of technologies that’s being implemented even now, and it seems as though, even if it won’t be the power source for everyone, all the time, it’s likely to stick around as a part of a comprehensive green-energy future — in the right circumstances.
Richard Ford Burley is a writer and doctoral candidate at Boston College, as well as an editor at Ledger, the first academic journal devoted to Bitcoin and other cryptocurrencies. In his spare time he writes about science, skepticism, feminism, and techno-futurism here at This Week In Tomorrow.
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