Generating electricity from the sea

Posted by Mat McDermott, EarthTechling

Waves may not be that predictable, even though technology and forecasting has improved (from World War II, when wave forecasting began in earnest, thanks to the requirements of the D-Day landing, up through the sophisticated models used by sports organizations like Surfline today), but the tides are thoroughly predictable.

We have very accurate charts detailing high and low tides, know how they shift each day, how much above the average high or below the average low they will be. This means making electricity from the ocean a thoroughly enticing idea, even if it’s one that hasn’t really been acted on.

Broadening things slightly, exploiting tidal power to do useful work is something humans have been doing for literally millennia. The Romans may have used water wheels powered by man-made tidal pools to grind grain. Skip ahead quite a ways: It wasn’t until the mid-1960s that the first large-scale tidal power plant was developed.

waves-at-dawn-australia

Photo: Jan Smith

Let’s leave the long history aside and look to the recent past, today, and the future: What’s going on with wave power and tidal power right now, and will this ever have anything but a niche or very geographically-specific role in a low-carbon future?

Making electricity from the forces of the ocean can be split into broad categories, tidal power (which taps the very predictable action of the tides, primarily being a function of the relationship between the Earth and the Moon, though influenced by geography, shoreline, and wind) and wave power (which are generated by wind, influenced strongly by geography, as well as, in terms of breaking waves, by tides).

We’ll get into this is more detail, but wave power generally uses some sort of mechanical device that is moved by the waves well outside the surf zone to generate electricity — there have been many different designs to do this; tidal power either uses some device placed in the steam of the moving tide to generate electricity, or some sort of dam-like arrangement to channel or contain the water and then turn a turbine.

You sometimes here the term ocean power used, but in general this is being used as a synonym with wave power (devices marketed as ocean power are relying on waves to make electricity), or as a catch-all term for both wave power and tidal power technologies. I’ll use it here in the latter sense.

Let’s deal with wave power first. It’s the flashier of the two variations of ocean power, although it’s also the least proven one at scale, and probably the one with the lesser potential — even if its developers would have you believe otherwise.

There have been all sorts of interesting looking (and sounding) devices developed to make electricity from waves: The Anaconda, the Limpet, the Oyster, the Pelamis Wave Energy Converter, the Power Buoy, the SeaRaser, the Wave Dragon.

The individual configurations of these devices vary, but you can sort of tell by their names what’s going on. The Anaconda is a large snake-like device that’s tethered underwater, generating electricity as it moves. The Oyster is a big clam-shell looking device that gets moved back and forth by the movement of water.

The Power Buoy moves up and down on the surface the water, the movement generating electricity. The SeaRaser does what its awful pun on a name implies: In one operating mode it can pump sea water up a nearby hill for storage until electricity is needed, generated by letting it flow back down hill, in a pumped storage arrangement; it can also generate (less) power by just powering a turbine at sea level.

Over the past several years many prototypes of these, pilot projects, and even small commercial versions have been deployed. But none have frankly amounted to much of anything.

* Mat McDermott, EarthTechling