Atlantis emerges out of a high tide

Four years after connecting a low-kilowattage tidal-current turbine to a grid in Australia, Singapore-based Atlantis Resources is preparing to launch an evolved, one-megawatt model that will set a new standard for 'water- to-wire' efficiency

BRISTOL: The latest incarnation in a line of pioneering tidal turbines developed over the past decade by marine-power technologist Atlantis Resources is girding its loins to go into the water early next year, with the Singapore-based company currently discussing a maiden commercial deployment for a one-megawatt (MW) model of its Solon-K device.

Two deep-water locations - one in the southern hemisphere and one in the northern hemisphere - are being weighed up, according to Atlantis chief executive officer Tim Cornelius, as a first site for the turbine. The Solon-K turbine, a horizontal- axis unit, is designed for water depths of 25-50 metres.

Though the Solon-K is Atlantis' showpiece technology concept, it is in fact only the most recent evolutionary step in a design that has emerged after 10 years' research and development along parallel project tracks. Before Solon, there was Nereus, an aquafoil-driven turbine designed with shallow waters, rivers and hydro tail-race deployments in mind. Pre-dating both these units was the Aquanator, a small-scale, tidal-power device successfully connected to grid as early as 2006. "With the launch of the Solon-K, we will have the full evolution," states Cornelius. "We started with the five- kilowatt [kW] Aquanator, then built up scale step by step until we reached 150kW [at which point it was rebranded the Nereus], and now we've tested the 500kW Solon and are getting ready with the 1MW version." The technologies used - the names of which are taken, like the company's, from ancient Greek history and mythology - have undergone some of the most thorough-going verification programmes witnessed so far by the marine renewables sector, capped by extensive, dynamic tow-testing to check the Solon's energy-generation rates and operational fitness.

Star performance

Following tow-testing operations - where the turbine is pulled though open sea by two ocean-going tugs - a 150kW Nereus I turbine was installed and grid-connected in May 2008 at San Remo, Australia.

After this, a fine-tuned 400kW Nereus II was put through its paces offshore in July 2008, which was overseen by international engineering consultancy Black & Veatch (B&W). Meanwhile, a 20-tonne, 500kW Solon tow-tested off Singapore over five days last August - again under the watchful eye of B&W - has since returned even more encouraging results. Featuring a proprietary 'swept-back' blade design and a specially engineered, power take-off system derived from engineering lessons learned developing Nereus, the Solon turbine produced more than 500kW in eight knots (4.12 metres per second) of water flow during testing. This figure represents an over 50% 'throat efficiency', marking it out as the pace-setter among tidal turbines for efficiency in an open-sea environment. The Solon can be outfitted with a cowling - the cylindrical casing that houses the turbine blades - as well as without, so that it can be adapted for either offshore or deep-river environments. "We were hugely excited by Solon's performance during testing and, more importantly, the close correlation of the actual performance to the expected performance predicted by Atlantis' theoretical model, which we have invested in heavily over the past 12 months," says Cornelius. "This is the result of 10 years' hard work, and the investment is testament to our rigorous engineering discipline and application of cutting-edge technology in the design process." In March, the Solon went into Tasmania's Bell Bay for further trials focusing on a new bi-directional blade developed for the device.

The development of the Atlantis tidal turbines, underlines Cornelius, has been "quite unusual, as we have built and tested 10 prototypes at real scale, as well as carrying out world-first tow-testing of the largest Nereus and Solon". He adds: "There has been a lot of money and time spent understanding not only the technology, but also the environment - which is crucial because it is very environment-specific where each turbine will be deployed." The twin-track development of the Nereus and Solon turbines was a conscious, strategic tactic by the company. By hatching two distinct designs, part of Atlantis' unique selling point is that it can offer "the right turbine for the right micro-location within any particular tidal-current resource, connecting them in the optimum configuration to maximise project returns". Atlantis continues to consider christening a 2MW version of Solon, but Cornelius cautions against putting too fine a point on the megawattage rating. "It is very important to think about what speed you rate your turbine. Theoretically, you could have a turbine rated at 1.2MW in [currents of] 2.5 metres per second [m/s] that can produce well in excess of 2.5MW in eight knots [4,1m/s] of flow," he says. "However, from our perspective, it is more about extracting the optimum wattage from any given site because we are trying to work to a utility model, so we need robust internal rates of return for our investors and the project owners. Without giving away any trade secrets, we are aiming at units that will be 1-1.5MW-rated in 2.5m/s." Following the signing of a memorandum of understanding with Hong Kong's CLP Group last December, Atlantis' total electricity-generating project pipeline stands at more than 800MW, with sites under investigation ranging from Asia-Pacific, Australia, the UK and North America.

With untapped renewable marine energy estimated to be able to meet 15% of the total current power needs of both the US and the UK - and, by Atlantis' calculations, some 180 terawatt hours per year of economically exploitable resources available worldwide - the race is on to put commercial industrial-scale tidal arrays in the water.

"There are quite a number of very large companies now entering the tidal space that each have their own research and development schemes and are testing turbines of significant scale, and this is the most exciting prospect for us," states Cornelius. "There is nothing better for the advocacy and credibility of [tidal-turbine technology] than seeing the major, diversified engineering companies coming into the sector," he underlines. "This is positive for the entire industry."