Although tidal energy is a micro-niche market over-shadowed by wind and solar, global giant Siemens has recently upped its stake from 45 to 90 percent in tidal energy pioneer, Marine Current Turbines (MCT). Currently, the small, 25-employee, UK-based company has only one grid-connected prototype, which may not appear very auspicious.
MCT's unique advantage
But Siemens isn't new to offshore energy. Over the last 18 years, the company has worked on several offshore wind farms, and MCT's primary attraction, according to Siemen's CFO Michael Axmann, is predictability. While solar and wind projects constantly battle intermittency, MCT's sun and moon controlled tidal cycles are much more stable and potentially very profitable. "Power output could be calculated for centuries in advance," said Axmann confidently. Axmann told Technology Review that tidal power's predictability "...increases the value of the energy produced, and makes the business case more reliable for the investor and operator." He also anticipates that by 2020, marine turbines will deliver power at a cost that's competitive with today's offshore wind farms - in spite of the challenges involved in engineering for underwater operations. Siemens has also obtained MCT's patented technology: a turbine, known as SeaGen, which came online in 2008 and is already an accredited UK power station. As the most powerful tidal turbine in the world - with the capacity to deliver about 10 MWh per tide - it has already delivered 3 Gw of power to 1500 nearby homes and businesses in Strangford Narrows, Northern Ireland.
How does MCT benefit? Like many startups, it's still unprofitable and its technology is still too costly, given that its proprietary turbine is virtually handmade. Most investors have opted for cheaper green-tech, sucking all the funding out of the sector. With Siemens' deep pockets and energy industry influence, that disadvantage will disappear as the company harnesses economies of scale. Watch a short demo of multiple turbines envisioned for a future project:
Siemens and many other global companies are finally commercializing technologies that were developed decades ago but never fully funded, or even ignored.
The original idea for the SeaGen turbine began in a different world and time: southern Sudan in the late 1970s. MCT founder Peter Fraenkel, a British mechanical engineer working with an overseas aid group, was trying to help farmers harness the flow of the Nile River for crop irrigation to reduce the use of expensive diesel fuel. Walking along the Nile, Fraenkel realized that he should exploit the power of the river. "Why not turn windmills upside down and put them in the water?" he'd asked himself - and then proceeded to engineer the answer.
Using an inexpensive catamaran raft with short vertical axis rotors attached beneath, a workable device was built that pumped up to 50 cubic meters of water a
day and ran for nearly two years until the Sudanese civil war aborted the project. After this small success in the Sudan and the 70's painful OPEC oil shock, Fraenkel started thinking on a much grander scale: harnessing coastal tides to generate electricity for the UK. Unfortunately, he had to sit out a decade of low oil prices. Fraenkel told DailyTech, "In the 1970s, the big snag was the market for that technology consisted of people with no money. Now (after fresh oil shocks) it's clear governments are gagging for new renewable energy technology." The U.K. is now providing substantial support for tidal and wave power, according to Earthtechling. Last year, the UK offered ?20 million for marine energy development, and increased the tariff rate for stream tidal generators from 2 to 5 credits per megawatt-hour (MWh). The government thinks that tidal power can potentially meet 15-20 percent of the UK's energy needs, while supplying nearly 15 billion to the U.K. economy by 2050.
Cost-driven design choices
The current at Strangford races at 10kts, and is 25m deep. When Fraenkel designed SeaGen to withstand those strong forces, he created several patented features which also reduced costs while improving performance. The most important: dual rotors mounted at the outer ends of wings supported by a deeply embedded, tubular steel, monopile. At Strangford Narrows, the monopile makes the structure capable of withstanding the drag from the strong spring tide - the equivalent to a wind turbine surviving wind speeds of 250mph. It also allows the rotors to be moved up and down, submerging the rotors relatively high in the water column, where most of the energy is found. A kayaker demonstrates the strong currents racing past the monopile and submerged turbines:
The rotor design, developed using a modified wind turbine computer model, is a patented 180-degree axial blade that automatically controls steady and reliable power generation during incoming and outgoing tides. Also, the separated twin 16m rotors are always clear of the pile wake when they are downstream. The configuration also makes maintenance easier and less expensive. Since the
entire rotor and power system can be physically raised up the pile and above the water, routine repairs can be made from a small boat. This is important because tidal energy's strong currents make divers or remotely piloted vehicles nearly impossible. Early on, when one of SeaGen's rotor blades broke, it was easily raised out of the water and quickly replaced. Such was not the case for Verdant Power, another tidal energy startup, which after submersing its turbines on the bottom of New York City's East River in late 2006, had powerful currents smash several rotor blades. Each damaged turbine had to be hauled up out of the river before the rotor could be replaced. Tidal turbines also have a competitive advantage over wave energy systems. The company reports that the once-in-50-year storm forces a degree of over-engineering which isn't required for its tidal stream devices. As a result, this not only lowers costs, but the prospects for seeing more rapid technology development seem to be assured. Some great turbine beauty shots.