The hidden costs of ocean power
Sea-based renewable energy can result in hefty environmental costs. Richard A Lovett reports.
Just because it’s renewable, scientists say, ocean power may not be as environmentally benign as it sounds.
In fact, there are situations in which one source of ocean power, tidal energy, can rank worse than coal in its overall carbon emissions, according to Breck Sullivan, a graduate student at the State University of New York, Syracuse, US.
Sullivan recently presented evidence to this effect at the American Geophysical Union’s biannual ocean sciences meeting in Portland, Oregon.
It’s a finding reminiscent of the 1970s environmental rallying cry “TANSTAAFL!”, an acronym of there ain’t no such thing as a free lunch, drawn from a 1966 novel by science fiction writer Robert A. Heinlein. All things come at a price, the idea goes, and there are always tradeoffs.
In the case of tidal power, the fly in the ointment is that the generating equipment must be fabricated, transported to site, maintained, decommissioned, and eventually transported home for disposal or recycled. All of this requires energy, presumably from non-renewable sources. Whether it’s worth it or not depends on the amount of energy produced, compared to the “lifecycle” carbon costs of everything involved in producing it.
In a study of 23 US sites ranging from New York to Alaska, Sullivan found that in some locations, tidal energy production was very much worthwhile. In these places, the lifecycle carbon costs per kilowatt-hour were low — less than a tenth those of natural gas power plants.
In other places, tidal power fared worse than coal.
It’s all about one thing, she says: “Location, location, location.”
Another problem for tidal power is the risk of turbine blades hitting marine animals. Even though the blades aren’t spinning all that rapidly, they could pack a wallop to curious marine mammals, such as seals, porpoises, or orcas.
In order to determine how much harm this could do to such animals, Molly Grear, an engineering graduate student at the University of Washington, Seattle, has been studying skin and blubber from marine mammals washed ashore after they died of natural causes.
“The big data gap is what is marine mammal tissue like,” she says. “How does it stretch? How strong is it?”
Her research also involves compression testing with blocks of tissue — “seeing how it reacts to compression and punches”.
Some of the tests, she adds, require perfectly cut cylinders of blubber — not easy to make. She eventually borrowed a laser cutter from another lab. “[It] worked really well,” she says, “aside from the smell.”
The goal, she explains, is to help understand what types of injuries such animals might receive from turbine blades. Already, she suspects that such impacts would be unlikely to break bones, simply because the turbines aren’t rotating all that fast.
“We’re assuming that this is more of a soft-tissue injury,” she says. Ultimately, she hopes to help figure out the safest way to design such turbines, fine-tuning their designs to the animals most likely to be encountered at any given site.
But tidal isn’t the only form of ocean power to raise TANSTAAFL questions.
Wave power works by using arrays of underwater devices to generate electricity from the tug of passing waves. In the process, it removes energy from the waves themselves, changing what happens when they reach shore.
“The main question is how do wave farms impact the coast,” says Dirk Rijnsdorp of the University of Western Australia.
Possible effects might include reduced wave heights for surfers or changes in wave action that might affect the way sand accretes or erodes on beaches.
“We want to find out how wave farms impact the coast and whether we can develop general guidelines for them, to optimise power output and minimise adverse environmental impacts,” Rijnsdorp says.
So far, his research is preliminary, revealing that the effects will depend in part on the size and design of the wave farm. But in the immediate lee of even a fairly small operation, he says, his calculations show that there is up to a 30% reduction in wave height, with effects persisting as much as a kilometre downrange. “So there might be coastal impacts,” he says.
Wind farms also pose potential marine impacts, even though their turbines are in the air, not the sea. In work conducted in the North Sea, Larissa Schultze, a graduate student at the Institute of Coastal Research at Helmholtz-Zentrum Geesthacht, Germany, found that the pylons that hold these turbines aloft create eddies in ocean currents flowing past them.
The result, she says, is a wake that extends at least 500 metres beyond the pylon. This turbulence can bring up nutrients from below, possibly increasing phytoplankton growth and changing the area’s overall biology.
Unlike other other possible ocean-power impacts, however, this one might not be a bad thing. “There could be more fish,” she says.