Concrete example

Embley Energy is developing marine energy technology that uses advanced concrete construction methods for lightness and durability.

Bristol-based Embley Energy is developing marine energy technology that uses advanced concrete construction methods for lightness and durability.

The company hopes to show that its wave-energy converter (WEC) Sperboy can compete with fossil fuels and other renewable energy sources.

The buoy-like Sperboy uses the oscillating water column principle to generate power from wave action.

As the buoy moves up and down on the waves, air is displaced from a chamber within it which then drives turbine-generators situated above.

The team is using laminated concrete composites to lighten the unit and make it more cost-efficient. Also, concrete was chosen because at sea it far outlasts steel or similar materials.

‘The sole aim of the project is to develop a renewable source of energy which is affordable,’ said Embley’s Michael Burrett. ‘The machine is very simple, with only one moving part, the turbines, and they are above the water line. This reduces the cost and, more importantly, enhances reliability and helps maintenance. With the devices as they are we do not envisage having to go back to maintain them at all,’ he said.

‘The concept has been proven. The biggest challenge now is making the device commercially viable and reducing the mass.’

According to Embley, it is the reduction in weight and maintenance that will dramatically reduce the normally prohibitive cost of marine energy generation. The absence of large quantities of invasive products such as oils and lubricants, coupled with minimal impact on seabed ecosystems, also makes the device more environmentally friendly.

Sperboys are to be used in large deepwater arrays containing around 750 devices deployed eight to 12 miles offshore. This will create an offshore windfarm covering an area of nearly six square miles (15 sq km).

The devices, which are expected to have a lifespan of around 50 years, will have an average weight of between 3,500 and 4,500 tonnes and are expected to generate over 250MW.

The cylindrical devices are topped with an average of four turbines. To keep them anchored they will be held in place using three or four diametric tethers attached to subsurface floats moored to the seabed.

The project has already completed tank trials and a pilot unit has been tested.

‘At the moment everything is encouraging,’ said Burrett. ‘The first set of trials show that it does operate and is stable. We will now refine the design and run further tank trials.

‘In the early days people were sceptical it could become commercial, but we have ongoing dialogue with most of the generating companies and are confident that the technology will be taken up if the trials prove successful.’

‘Marine energy has the potential to provide a large proportion of the UK’s electricity needs,’ said Garry Staunton, head of low carbon research at the Carbon Trust, which awarded the project a £150,000 grant. ‘Embley Energy’s innovative use of advanced concrete construction methods is particularly exciting as it has the potential to significantly reduce the cost of wave-generated electricity.’

Staunton said that because onshore wind power is beginning to look very competitive there is much scope for cost reduction. So the Trust needs to look at how much it costs to build Sperboys and how much energy can be got out of them.

‘When we published the Marine Energy Challenge report we estimated that marine power could get below the 7-8p/kWh level for less than £3bn,’ said Staunton.

This level, he added, would suggest it could compete with conventional energy sources.

‘It is by supporting companies such as Embley Energy that we can tap into the massive energy resource the sea offers,’ added Staunton.