By Elisabeth Jeffries on Aug 22, 2014

Plat-O, built and developed by tidal technology company Sustainable Marine Energy (SME), is a holding structure suitable for a whole range of different types of turbines. Following successive test campaigns in IFREMER in France and in the Ocean Systems Test Laboratory in Cranfield University, the structure will be submerged in Yarmouth, Isle of Wight. It will hold two 50 kilowatt tidal turbines manufactured by German engineering company Schottel.

According to SME managing director Jason Hayman, its unique design, positioned in the middle of the water column, could allow tidal project developers to halve many of their costs. “It avoids heavy lifting, and there is no need for DP (dynamic positioning) vessels from the oil and gas industry. This has a significant impact on costs ancillary to the turbine itself,” he says. The original platform takes the shape of the letter W and could be used by many turbine developers in the industry using different configurations. Hayman claims that installation, operations and maintenance, support structure costs and the costs of fixing the device to the seabed are all reduced.

Relatively low material use for the holding device, as well as its design for the middle of the water column, account for the heavy reduction in costs compared to individual project developers using their own platform. “The anchoring method is cables, which are cheaper,” says Hayman, “they allow the use of a taut mooring system, because if the structure is beneath the waves, they always stay tight.”

Dr Florent Trarieux, who run the Ocean Systems Test Laboratory in Cranfield University, is responsible for the tank testing programme. Trarieux points out the disadvantages of working either at the surface or on the seabed: “On the surface, you have to sustain the harshest environments there, the nastiest weather. Waves are a terrible thing to contravene using, say a floating platform. It’s costly. If you’re on the seabed, the current is not that strong and so you lose energy. Sediments blow around and that is not good for the blades,” he says.

Optimal positioning?

By contrast, the team has aimed to optimise the position of the platform and turbine to avoid having to deal with these concerns. “We wanted to position the turbine in the right place in the water column and find the fastest flow possible without going to the surface,” says Jason Hayman.

Commenting on Plat-O, Professor AbuBakr Bahaj, head of the Energy and Climate Change division at Southampton University, said the idea of a low impact platform of this kind for multiple types of turbine had been around for years but had so far remained a dream. Professor Bahaj previously had the chair in sustainable energy at the university.

“If these work well, it will be fantastic for the technology,” he said. “Platforms like these, which minimise civil works and the other structures to put turbines in the sea will be useful to cut down cost and minimise environmental impacts - such as the intervention with the seabed that is normally necessary when piles are put in to support single/twin turbines and so on,” he points out.

However, he indicates its particular characteristics could mean compromising on depth. “A rigorous testing regime is needed to assess their appropriateness and commercial viability,” he suggests.

Initial trials

According to Hayman, initial trials will be completed at Yarmouth in 2014, following which Plat-O will move to a grid-connected site in 2015. A commercial demonstration is expected by the end of 2015, with the first delivery of a commercial platform due in 2016. Further developments are likely thereafter. “Like a lot of technology developers we will probably have to do our own array project first, and planning for that is under way,” he says.

The company aims to take a gradual approach to scaling up the project. “Our commercial model is 200 kilowatts for each platform. This can be done incrementally, so that the cost of the array is more manageable. We can put in five 200 kilowatt turbines rather than five single megawatt turbines. This is more cost-effective and less risky. Later on, the turbines can get bigger,” says Hayman.

The company indicates a number of other benefits from the platform. These include housing of power electronics and control systems with access at the surface, load reduction on tidal turbine drive trains and scalability. It is suitable for small-scale and utility-scale projects. SME also suggests the platform has a lower footprint than competing systems, can be anchored in any type of seabed, and is tolerant of uneven terrain.

SME is involved in one of the UK’s most environmentally-aware council plans. The Isle of Wight’s Strategic Partnership wants the island to be self-sufficient in electricity from renewables by 2020. Based on a theoretical mixture of wind, tidal stream and energy from waste, the installed capacity would need to be 170 MW.

At the time of writing it was announced that the East Cowes-based company was awarded grants by the IoW Council’s Solent Offshore Renewable Energy Consortium (SOREC) and Future Solent’s Green Growth Fund (FS GGF) for the development its PLAT-O tidal turbine platform.

Sustainable Marine Energy will receive up to £50,000 from the Solent Offshore Renewable Energy Consortium, and up to £100,000 from Future Solent, which the company will match with equal investment to provide up to 10 jobs working on its tidal energy system.