Tidal Power on the Cheap?

STROMNESS, U.K. -- ScotRenewables isn't aiming to build the most efficient tidal turbine in the world. It wants to build the easiest one to repair.

The startup, located on the Orkney Islands, way north of Scotland, has raised £6.2 million to build a working prototype of a floating tidal turbine that it says will be cheaper to install and maintain than others being tested now. The 8-meter-long prototype, ideally, will go into the water at the European Marine Energy Centre (EMEC) Tidal Test Site that sits just down the road from ScotRenewables in 2010. Commercial versions of the turbine will measure up to 40 meters long and weigh 250 tons, but generate 1.2 megawatts of power.

"That's quite impressive when you compare it to others," said CEO Barry Johnston. "We want to be competitive with offshore wind." 

Rather than anchor a permanent turbine on the ocean floor, ScotRenewables will build a floating turbine that is slack moored with chains to an anchor on the sea floor. The body of the turbine – a long 40-meter tube of metal with a point at the end – will face directly into the tide. Below, two turbines attached to fins will convert the power of the tides into electricity. Johnston showed me a 1-meter prototype ScotRenewables is experimenting with in the wave tank it built. It looks like a model rocket with two fins with propellers attached to the ends of the fins.

Tidal is the potentially most predictable, reliable form of renewable energy. With a tide table and computer, power providers can calculate the power output of a turbine decades in advance. You can't do that with intermittent, variable sources like wind, solar or wave. Unfortunately, harnessing tidal power is quite difficult. Some of the prototypes that have been tested in recent years are quickly mangled by rushing tides.

Pulling those turbines up from the sea bed and taking them into the shop consumes time and money. Taking the ScotRenewables turbine in for repairs should be easy: maintenance workers would just have to take a boat out, unhook it, and put another in its place while the first is being detangled.

Tidal power is also 50 percent stronger at the surface than at the seabed so these turbines should be capable of generating more power, he said. Other companies have tried to create surface tidal turbines before. The difficulty has been keeping the turbine pointed in the direction of the tide. Some get washed away. Other times, the creators build large superstructures around the turbine, which costs money.

ScotRenewables says it will come up with control mechanisms and advanced hydrodynamics (i.e., aerodynamics in water) to keep the turbines pointed in the right direction. While speaking to Johnston, I looked at the desk of one of the company's engineers. It contained several books on aeronautical engineering.

The 40-meter body of the turbine can also be made by a conventional manufacturing processes, which further cuts costs.

"You can roll them out cheap," he said.

Scotland is betting heavily on wind and wave power. The notoriously harsh waves and currents of the Pentland Firth, a channel which separates the main body of the U.K. with the Orkneys that is often referred to as the Saudi Arabia of Marine Energy by locals. By 2020, Scotland wants to get half of its power from renewable sources, including large hydroelectric dams. Hydroelectric constitutes about 11 percent of the country's power now and 9 percent comes from wind and other renewables. A large portion of the new renewable sources of power will come from wind, tidal and wave (see Trawling for $500M in Ocean Power and Tide Turning for Ocean Power?)

Marine energy could provide up to 35 terawatt hours of power to the U.K. by 2020 and 84 terawatt hours of power by 2050, according to Edwina Cook, business development officer at EMEC. The U.K. in 2004 consumed 340 terawatt hours of power.

"We have nothing between us and Canada," she said. That gives the waves, which are propelled by winds, loads of energy."  

The EMEC has created tidal and wave testing centers for companies to build and validate prototypes. (The Pelamis – that sea snake looking wave power device – was tested at EMEC before commercial rollouts in Portugal.) The government has also passed exceptionally large credits for power providers that put tidal and wave power on the grid. (Prototypes participating in the EMEC test beds are actually connected to the grid and selling small amounts of power.) The hope is that the program will create jobs, exports and green energy. Offshore, the Dublin-based Open Hydro Power is already testing a large tidal device that looks like a big rotating fan.

Talking about the prototype and commercial power production, however, is easier said than done. ScotRenewables did not like the software simulation tools it found when it first set out. Some software focused on tidal changes; others focused on waves. To build an effective surface tidal turbine, Johnston realized that the company had to take into account both tidal and wave power. Thus, it had to build its own tools, which cost several thousands.

It also built its own wave tank. It was easier than trying to book time at an EMEC wave tank. The company now hopes to lease time on the tank to other wave companies to generate revenue. And, because ships to deploy tidal and wave devices are in short supply, it is contemplating buying or building its own multi-purpose vessel.


Source: http://www.greentechmedia.com/articles/tidal-power-on-the-cheap-5686.html