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Searaser device promises "lowest-cost" offshore power

A new device for harnessing wave energy is promising renewable electricity at a cost to rival fossil fuel sources.

The inventors of the Searaser, an ocean-based pump that drives an onshore hydro-electric turbine, claim it can generate electricity at a rate of 1.5p per kWh – less than a quarter of the cost of other renewable sources and even lower than coal, gas or nuclear.

Dartmouth Wave Energy, the firm behind the device, says the device is so simple to construct and maintain that it will only cost around £200,000 per unit, with a total capital cost of £1.2m per MW.

‘It only has four moving parts so is much better able to stand the rigours of being deployed at sea,’ Dartmouth director Geoff White told The Engineer.

‘It doesn’t need any oil or lubricants because it’s lubricated by water. Maintenance is like that of a navigation buoy ­­– you just need to lift it out of the water once a year and clean it.’

While White acknowledged the figures represent a bold claim, he said they are based on prototype trials and aren’t just a forecast.

‘We have to prove the commercial viability and the numbers may change when we scale up, but all the technology except the pump itself is already proven,’ he said.

Dartmouth hopes the Searaser will eventually produce around 1MW of electricity and has already attracted joint venture investment from green energy company Ecotricity.

Upper float elevated on crest of wave

Upper float elevated on crest of wave

But the device is still in the early stages of development – current output is around 100kW – and long-term testing is needed to see how it will fare in the harsh ocean environment.

Other companies pursuing a similar idea don’t claim to be able to operate anywhere near as cheaply as Dartmouth. Aquamarine Power, for example, expects its Carbon Trust-backed “Oyster” device to eventually generate up to 1MW for 8-9p per kWh, a cost more comparable with that of offshore wind.

The Oyster is much larger than the Searaser and has more a complex design. But its designers have the advantage of more experience and more data to back up their claims, with the first device in operation since last summer and the third generation model already on the drawing board.

There are also many challenges the sector still has to face before becoming commercially viable, according to Stephen Wyatt, head of the Carbon Trust’s Marine Energy Accelerator programme.

‘For example, you’re competing with the oil and gas industries for vessels and divers and you’re restricted in the time you can go out to sea, so it can cost a fortune to change a very cheap component if it goes wrong,’ he said.

Managing the higher water pressure further offshore, getting permission from marine authorities and finding suitable locations close to National Grid connections are other issues to overcome.

Aquamarine’s CEO Martin McAdam, argues firms in the wave sector would benefit more from cooperation than competition at this early stage.

‘There needs to be more shared learning and more honesty in the industry and there has to be a critical look at the performance of different machines,’ he told The Engineer. ‘We need fewer outlandish claims and more companies to share their failures and successes.’




The Searaser concept explained

Hydro energy for the production of electricity is the next most efficient energy source (after nuclear) and has advantages over direct wind systems in being storable and controllable.

Most hydro systems in the western world have been exploited to their full potential, which means that future demand will not be satisfied by hydro unless new hydro energy forms become available.

Moving water to higher ground or to a hilltop facilitates a controllable hydro system similar to the Welsh and Scottish pumped storage systems but utilising renewable energy and not fossil fuels to pump the water up to the head.

Searaser uses wave displacement to lift a float attached to a piston and uses gravity in the wave’s following trough to push the piston back down. It is different from other devices as it is tethered to a weight on the seabed by a single flexible tether, but utilises a double acting piston, thereby producing volumes of pressurised water in both directions of the piston.

Incorporated in the design of the Searaser pump is an adjustable hydraulic column platform which adjusts itself and locks to any height of the tide.

The device has a wave (or swell) pump to pump sea water to a hilltop. It uses the energy of the water in which it floats to pump the stored potential energy.

If high ground is not available or unsuitable for storing the water for the turbines, the pressurised water pumped via an accumulator direct from the waves will be of sufficient pressure to drive the turbine generators near sea level. These are based on land or offshore rigs, or afloat.

Source: Dartmouth Wave Energy

Readers' comments (7)

  • I have watched this industry for some time and I cannot see that they can produce electricity for 1.5p/kWh. When they have a full scale machine operating then they can tell us what the real cost is - This is the same as what happened in wind - companies over promised on delivered cost of energy and then disappeared. I don't often agree with companies who often exaggerate but the McAdam guy from Aquamarine is right when he says that "We need fewer outlandish claims and more companies to share their failures and successes."

    Stephen Harris - thank you for writing on this subject. Watching the start of a new industry is fascinating. Perhaps you could do a follow-up article on why they think they can deliver at such a low cost. People like Stephen Salter (of salter duck fame) abandoned a heaving buoy as the economics don't stack up. None of the leaders in the industry are developing heaving buoys for commercial power. Some companies like OPT are using heaving buoy technology to extend mission lifetimes for US Navy operations (where cost is not a consideration) - rather than delivering commercial power. What have Searaser done that justifies their claims?

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  • It strikes me that people appear to have wnderful notions - using a sine wave and no numbers in a pretty picture. But do they actually have numbers and can explian what will happen in Breaking waves? - when the sine wave ceases to be friendly but applies a saw-tooth impulse to the mechanism? It looks like we'll have more wrecks on the shore than ships provide.
    I agree with Martin Aker's comment.

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  • Gentlemen do not be pessimistic but be patient. Waves generating energy equipment/devices/machines are still very very young, actaully they are babies.
    All encountered problems will be solved one by one and at the end we shall be surpriced as to how easy was and why we did not think of it before.

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  • I am agree with reply of Anthony Chrysostratis. In the beginning there will be lot of difficulties but it can be overcome. In the past for every new experiment there were lot of set backs even for invention of simple lamp, utilisation of RF energy, even flying machine was laughable stock. So surely we should be optimistic for this too.

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  • Designing a wave energy machine to survive on our coasts means designing against the 100 year storm wave. To my knowledge several 100 storm waves have hit the UK coast this last 5 years.
    The engineering costs are driven up hugely by this need and the machine's subsequent mooring strength requirements then add this to deployment costs.
    My advice? Engineer the machine to be simple and reliable, design it to self-sink as the waves increase then re-float by remote or the like.
    Alternative? Try "clean" nuclear! Have a google of Thorium LFTR or try
    A Wave Machine Designer.

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  • The problem with high pressures and a piston is you need close clearances in sliding friction. One of the biggest problems with conventional industrial hydraulic systems is contamination and these are filtered to minimise particulate damage and have a high lubricity fluid. Seawater especially near to shore is loaded with fine sediment which is uneconomical to filter out due to the solids loading and pressure drop. Also the pressure drop due to pipe wall friction will cause significant losses over large distances and the cost of piping capable of resisting high pressures is not insignificant. Long term I believe this device will go the way of many ideas including early windpower and prove just not to provide the required reliability for the power output. Probably do better with a Wells turbine fitted to the oscillating buoy.

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  • Interesting comments! Having been raised on a lighthouse on the west coast of Canada, I feel quite qualified to participate in this forum. Additionally, I have been seriously considering an ocean driven power plant for several years now. Also, I have been engineering things since I was old enough to hold tools.
    My opinions are thus:
    1. Tide harnessing will be less prone to damage than wave harnessing.
    2. The farther north or south latitude you put a tide machine, the better.
    3. If you use a contained liquid in the system (like hydraulic oil in a winch system for example), there will be no problems with contamination.
    4. If the power plants are located in protected bays (which is where power grid access is best obtained anyway), they will be less prone to damage.
    5. All in all, I agree that this technology is viable and it has been much too long in coming. Ocean generated electricity is a no-brainer and is certainly the safest and least environmentally impactful technology I can think of.
    6. Every inventor has its nay-sayers. If they are right, time will prove them to be so and they will get their moment of “I told you so”, but in the mean time, perhaps humility should prevail. What are we afraid of anyway? Failure or success?
    If you wish, you can visit me at

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