Floating Tidal Power in Scotland Could Challenge Offshore Wind

(3Bl Media) — There was some exciting news in the world of renewable energy made off the coast of Scotland last week. While solar and wind power have been making tremendous inroads around the world, a new player is emerging that could have advantages over both. We’re talking about floating tidal generation. A company called Scotrenewables Tidal Power Ltd., commissioned the SR2000 tidal turbine last December, connecting to the Orkney power grid. Last week, during a grid-connected test, the 2MW turbine produced 18,000 kWh over a 24-hour period. The 500-tonne SR2000 is an integrated turbine-generator. It looks like a ship that rides low in the water, consisting of a floating hull, with two turbines on the lower half of the body that sit just below the surface of the water. Each turbine has a 52-foot diameter rotor. The turbines are designed to stow up against the hull for transportation, and in “survivability mode” during storms and periods of rough seas. Most of the internal components are situated in the hull for ease of maintenance.

According to the company’s website, the technology has been optimized for “fast tidal current regions, such as those of Scotland, Northern France and Canada,” although modifications can be made to suit local conditions elsewhere. 

According to the European Wind Energy Association (EWEA) an onshore wind turbine produces 16,400 kWh per day. Offshore turbines are larger and can produce as much as 36,300 kWh per day. So, while this fledgling first effort is not quite up to the level of the largest offshore wind turbines, it’s already in the same ballpark.

While, like other renewable sources, wave action is variable, the regular arrival of tides coming in and going out make this form of power generation more predictable than wind or sun. Depending on location, a typical tidal installation will produce power for anywhere from 10-18 hours per day. Independent studies cited, claim that the tidal flow resource has the potential for 160 million MWh globally. Because water is more than 800 times denser than air, a tidal turbine does not require as much volume, thus, enormous blades are not needed. Also, wind turbines need to be tall because the wind blows faster at higher altitudes. That is not the case with tidal flows, where the highest velocities are at the surface. This is another advantage of the SR2000 which places the turbines just below the surface.

Atlantis Resources, another British firm, currently sells two different 1.5 MW tidal turbine models. Both have rotors roughly the same size as the SR2000, however these turbines are designed to be mounted in the seabed rather than floating in a hull. The company is developing a portfolio of tidal projects, off the Scottish coast with a combined capacity of over 600 MW. As of March of this year, their MeyGen project was approaching 400 MWh of energy delivered. The capacity factor was reported to be in excess of 40%. Capacity factor is, in essence, the percentage of a turbine’s rated output that is actually achieved, given the variation of flow through the turbine. A capacity factor of 40% is competitive with wind power at this time.

Image courtesy of Scotrenewables