Next Generation Energy is managed and written entirely by Seed editors and expert guest bloggers. Read more about them The week's question asks about the likelihood of embracing tidal power, a form of hydropower that converts the energy of tides into electricity. Basically, we're talking wind turbines located where there's strong tidal flow. Sounds clean, and heck, I sure do like the ocean... but uh, I just don't see this becoming a major contender in our alternative energy future.
Okay, so yeah, tides are more predictable than wind and solar sources. They're pretty much inexhaustible, meaning tidal power is completely renewable, and the conversion of potential energy into electricity is also more efficient than with solar or fossil fuel plants. There are two commercial sized operations in La Rance, France and Nova Scotia, Canada, but here at home, we've got none. Thing is, only about 20 locations have good inlets and a large enough tidal range to produce energy economically.
There are plenty of reasons I don't buy tidal power hook, line, and sinker starting with density. Water is about 800 times denser than air, so tidal turbines have to be much sturdier than wind--meaning they're heavy and more expensive to build. Those that are directional also don't capture flow efficiently and they're complicated to maintain because they must be below the mean low water level and require a robust mounting system to prevent turbulence and high-pressure waves nearby. And there's the added trouble that
tidal barrages can change the tidal level in the basin, increase turbidity in the water, and affect navigation and recreation.
And here's my principle concern... See as it happens, I'm a fan of marine life--from the majestic sea cucumber to the northern right whale. And turbines may be hazardous to all sorts of ocean dwelling critters. According to the Gulf of Maine Times:
Fish passage studies using tagged fish have shown a mortality rate of 40 percent, plus or minus 30 per cent. It is difficult to know what impact, if any, handling the fish to tag them had on their ability to survive passage through the turbine system. While pressure differentials are killing fish, it is unclear if the mortality rate is greater or less than would be expected in a traditional hydro installation. Nova Scotia Power has made improvements to the original fish way designed by Fisheries and Oceans Canada. As the turbine operates on the ebb tide, the fish-way is only needed during the generation cycle.
Needless to say, you won't find me endorsing this potential next gen idea anytime soon until more research is done on turbines ecological impacts. But it's not just about protecting charismatic species at sea...in an arguably more practical consideration, the payoff from investment--at least right now--isn't all that worthwhile due to high initial costs.
So when it comes to 'offbeat ideas' for energy, I'm more excited about some other realistic possibilities not far down the pipeline.
Environment
Comments
There are other ways of capturing tidal energy besides underwater windmills. An auger or horizontal turbine (think roof-top vents) would be easier to maintain and less disruptive. A buoy that turns a generator as it rises could also harness tidal energy and doesn't require a channelled tidal flow. The amount of energy is absolutely incredible, we just need to figure out how to harness it safely.
Posted by: mfagan | September 23, 2008 10:56 AM
I think there's much more promise in capturing energy from wave motion than from tidal flow. There are many more places where it could be used and no underwater turbines need be involved. Much more likely and promising than Venter's energy bug, IMHO.
Posted by: chezjake | September 23, 2008 11:43 AM
Nothing is going to get "sucked into" the blades - the blades aren't sucking, they're pushing. The flow rate through the turbine must be lower than the flow rate outside the turbine - that's where the captured energy comes from. And even if this were a problem, the ratio of the volume affected to the total volume of habitat is minuscule, unless you're operating in a very unique habitat.
Tidal (or current) flow generation is potentially a great idea if you have the right geography for it.
Posted by: Dunc | September 23, 2008 11:44 AM
Windmills do not work that way! Good night!
Posted by: Joe V. | September 23, 2008 12:06 PM
Dunc: the blades are not sucking or pushing-- To get any energy out they have to be pushed by the flow. Still, if there is flow, there has to be an outlet and inlet
Also, if they are anything like the big-diameter wind turbine things in the picture, friction and turbulence will eat up all the energy.
Damping the motion of a bouy with generators seems interesting.
Posted by: Dave X | September 23, 2008 12:26 PM
Dunc,
Thanks for catching that. I've clarified my concern a bit above. I'd like to see more research on ecological effects because it seems that the largest disadvantage of tidal power is potential impacts on plants and animals.
Joe V.,
The comparison to wind turbines can be found at the Department of Energy's site.
Posted by: Sheril R. Kirshenbaum | September 23, 2008 12:31 PM
chezjake,
Venter's not the only one working on an energy bug. And knowing some folks involved, I suspect this possibility will become a reality... sooner than you think ;)
Posted by: Sheril R. Kirshenbaum | September 23, 2008 12:37 PM
Miss sheril,
Now you know I hate to get on my Roomie's bad side - so please accept this with your usual grace. I hear your concerns, and you and I are probably going to be some of the hardest pushers for proper review of the siting of these things as they go forward. That said, I am wondering if you may be . . . . a bit too strident in your concerns.
First, there is at least one local scale generation project going on in your old stomping grounds. Granted, lighting up one supermarket a short distance away isn't much to crow about, but it is a start.
Second, looking at the photos of the turbines in question, I really have to wonder how much damage they will do to fish or other marine life. Most fish that migrate with tidal currents have good sensory systems, and I can certainly see the bigger ones avoiding the whole thing altogether. The small ones, the bait fish, well they may get chopped up, but given their large population size and high fecundity, they may well adapt to over come this issue as well. I suspect plankton will just flow around the whole thing, as they do any underwater obstruction.
So, before we dismiss this alternative outright, let's use this installation to gather some good data.. After all, science may hold a really fascinating answer, if we just do the work.
Posted by: Philip H. | September 23, 2008 12:40 PM
Philip,
As if you could never get on my bad side...
I've heard some mixed reviews on those projects going on in my old stomping grounds from the folks involved. But what's your take on the more practical hurdle of location? According to DOE, in the US, there are few sites where tidal energy could be produced economically.
Posted by: Sheril R. Kirshenbaum | September 23, 2008 12:49 PM
Miss Sheril,
My take, in these energy desperate times, is we install where we can generate real energy, and we use all the weapons in the arsenal - wind, wave, tide, sun. To do less is heresy.
Posted by: Philip H. | September 23, 2008 2:04 PM
I don't think Sheril need worry too much. The main impediment to scaling up these schemes is demonstrating that the lifetimes of the expensive hardware will be long enough for the things to be economically viable. That basically means many years, -perhaps a decade or two of data on the early small scale installations will be needed before investors will commit the big bucks needed for a major scaleup. That should give plenty of time -if used properly, to figure out what sort of impacts (and mitigations of impacts) these things will have.
Posted by: bigTom | September 23, 2008 4:09 PM
Phil, I think the kill concern is from pressure differentials... not sure how severe those are in an incompressible fluid, but they would propagate better.
Noise pollution is also something to be concerned with.
Anyways, if we manage to avoid shutting down ocean circulation, there is massive amounts of quite reliable energy in currents.
I'm also fascinated with the idea of using fixed piezoelectric devices to harness the pressure changes generated by passing waves or tidal movements. I have no idea how practical that idea is though, though they wouldn't rely on flow per-se.
Posted by: travc | September 24, 2008 2:08 AM
That's what I meant - whether you regard the blades as pushing against the current or the current pushing against the blades is simply a matter of which way round you want to view Newton's First Law.
Posted by: Dunc | September 24, 2008 4:34 AM
Of course, there is also the possibility of positive impacts - for example, I don't imagine anyone will be dredging or drift-netting anywhere near these things, so a tidal power installation has the potential to become a de-facto marine reserve. More research? Always!
Hello? There's a whole world out here you know... Here in Scotland, we have excellent tidal resources and a well-established marine engineering industry. We're now at the stage of dealing with the practicalities of deployment.
Posted by: Dunc | September 24, 2008 4:43 AM
I concur with Philip here. We cannot afford to leave any stone unturned in our efforts to extricate ourselves from the death grip oil has on us. Personally, I believe that every kilowatt of energy we can squeeze out of non-fossil fuel sources needs to be undertaken. If less than ideal methods for obtaining that energy are pursued, we pursue them anyways and then let the engineering and technology play catchup. In the meantime, at least we have something out there doing the job.
Now, I'm not saying that we need to rip the environment apart in the process, but if we can undertake these processes with minimal disturbances to the environs, we must do it.
As I mentioned over at the Intersection, there are other wave energy capture solutions such as the Anaconda (bulge wave) which are being developed and studied. These, as far as I can tell, raise even less questions about environmental impact.
Posted by: TomJoe | September 24, 2008 10:51 AM
Speaking of wave power, it's no longer just being developed, it's being commercially deployed:
http://planetark.com/dailynewsstory.cfm/newsid/50342/story.htm
Posted by: Carlos | September 24, 2008 1:07 PM
Amen to the 'silver shotgun' approach. A benefit of not looking for a single solution is that we can actually build a few facilities and see how they are working (and gauge environmental impacts and other unforeseen consequences) before trying to build them everywhere possible.
Yeah, we need to move fast... 10 years on small scale pilot plants is no good. But we don't need to simultaneous start building 100s of identical installations either.
Posted by: travc | September 28, 2008 8:47 AM