Tidal power generation interests utilities as the most reliable of alternative energy categories. Occurring twice a day come rain or shine, the tides are consistent and completely predictable. Currently, the largest tidal power plant in the world is France’s 240 MW Rance plant, which was completed in 1967.
If either of the proposed tidal power projects in the pipeline gets final approval, the Rance plant’s days of being the biggest fish in the pond will be numbered. South Korea is planning a project more than five times larger than the Rance plant, rated for 1.34 gigawatts, in the Incheon Bay. Pending regulatory approval, the $3.4 billion project could be underway by the second half of next year with completion scheduled for 2017. The Incheon project employs a barrage, or an ocean dam, which traps water in a basin and uses turbines to make electricity from the water level differences created by the tides.
It’s possible that another tidal power project, the U.K.’s proposed Severn Barrage, could generate over five times as much energy as Incheon, depending on final decision on the plant’s power generating capacity. The government is considering five different proposals for the barrage, ranging in generating capacity from 1.05 to 8.6 GW. There are three alternate concepts as well. The largest version of the project would build up to 10 miles of dams and sluice gates across the Severn Estuary, a topic of debate for almost 30 years.
Ironically, both the Incheon and Severn tidal projects face significant environmental opposition, not for emissions but for flooding and other concerns. Much like river dams, these tidal barrages can cause some unintended environmental consequences, making them unpopular with environmentalists. For one thing, the barrages disrupt the flow of water from the tides as well as the exchange of water from the basins. This changes the composition of the water which alters the surrounding wetlands and impacts the wildlife that lives there.
Underwater turbines that operate like those found in wind farms don’t get the same kind of environmental opposition, but the technology is still being developed. These turbines use ocean currents to generate electricity without needing a barrage, but being submerged in saltwater provides issues that are still unsolved. Still, there are several projects competing to be the first online and/or the largest of the tidal current plants. Each of the projects is rated at 200 MW with two proposed for Scotland and one in New Zealand.