![]() ![]() Researchers from Cardiff and Liverpool University have previously published reports on how tidal power can negatively impact marine life by altering sedimentation patterns, as well as oxygen and nutrient levels in the water. EDF has previously said it will attempt to mitigate this ecological impact, but general consensus seems to be that more research into the environmental impacts of tidal plants needs to be done for the technology to become a legitimate alternative to conventional energy forms. Numbers of sand-eels and plaice in the area have diminished, though the river has seen the return of sea bass and cuttlefish. Indeed, the barrage has been found to cause a progressive silting in the Rance’s surrounding ecosystem. Thomas Adcock, associate professor in the Department of Engineering Science at Oxford University says there has been ‘major environmental impact’ on the Rance estuary as a result of the station, saying “this would make it very difficult to get permission to do such a barrage again.” “The structure is essentially life unlimited, because you’re constricting the flow and having high speed water around the turbine inflow/outflows, the design needs to be carefully done and maintenance and repairs are needed, but that’s a cost which is pretty trivial over a lifetime of 100 years plus.” Are there any drawbacks? La Rance’s ‘major environmental impact’ “Barrages just trounce free standing turbines,” he says. And when it comes to lifespan, Hart says tidal is leading the way. The design and operating principles are very well understood, having been developed over many decades, so challenges are fairly controllable. That’s a real strength when it comes to renewables, as most other forms are at the whim of nature.” “At Rance you can predict and rely on the energy produced, and know how much you are going to get when, hour by hour, day in day out, with 100% accuracy (neglecting any faults in the turbines). How you would do it now is very similar to the way that Rance does it, though of course technology gets more efficient with time, and tidal barrage is no exception.” “All of these are really good and unusual things for energy production. “Tidal barrage energy is pretty straight forward, incredibly predictable and environmentally carbon zero (or almost so),” says Hart. ![]() As such, some say it has great potential to be a main replacement for fossil fuel sources. In addition, inexhaustible energy can be generated both day and night with minimal influence from weather conditions. Reliant on the movements of the tides, engineers have access to daily, bi-weekly, biannual and even annual cycles on which they can base predictions of energy production. They have to be modified to work with sea water instead of fresh water (seawater being much more corrosive), but that’s just a materials and servicing issue.” Why choose tidal?Ī huge benefit of tidal is that it is predictable. The turbines are or can be very typical water flow turbines, such as those you see in many other applications. “However, once you have the civil works done the rest is pretty cost effective. ![]() “Tidal barrage’s painful expense is the very high cost of initially building the structure,” Hart adds. “I’m not sure how the lifetime economics have worked out overall but seeing as most energy projects have a life of 25-40 years and Rance is still going strong after 50 years plus with no signs of slowing down, it is difficult to think that it’s not paid for itself a few times over.” “Rance being the first barrage of its kind, I think it proves the arguments for tidal” says Professor Phil Hart, director of energy and power at Cranfield University. Since its construction, the plant has produced approximately 27,600GWh of electricity, equivalent to around £3.3bn at today’s prices. While it took around 20 years to pay for itself, the project has now recovered all of its costs through savings made from its energy generation – and the tidal energy produced costs less than nuclear or solar power. Yet the plant also shows the long-term rewards such stations can bring. With an initial building cost of $100m, the station shows the high financial investment needed to develop such operations – the main reason for opponents to claim the energy source is less worthy of exploration than the cheaper alternatives of wind, solar or nuclear. In total, construction time lasted five years. ![]()
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