According to worldwide data, wave energy presents a bigger resource than tidal power which requires certain niche locations. Further, it has an edge over wind or solar energy as waves can be seen forming at a distance. So why is it taking so long to get into the water and start commercial generation?
A developer’s view
Chris Ridgewell of Helsinki, Finland-based AW Energy, the firm behind the WaveRoller device admitted that “there’s a lot of cynicism” to overcome, not helped by developers taking shortcuts in order to get into the water: “There’s been a number of stories of companies trying to gain an advantage by being first into the market, spending huge amounts of investor’s money and not getting the predicted results. It’s the wrong way round: once you have a large device it’s very difficult to go back and start sorting out the problems,” he said. While it’s not the only issue the nascent industry has to overcome, it remains a significant issue: by contrast AW Energy “has been focused on methodically solving the challenges”, scaling-up over a period of 14 years before getting to its fourth – and latest – deployment.
However, he believes there is also a practical point to address: the best place to look to harvest the energy may not be the most obvious. Therefore the WaveRoller isn’t placed on the surface where dynamic conditions add to the challenges, but looks to the invisible ‘belt’ of water as it moves across the seafloor for its yield.
Shaped like a rudder laying on its side, the idea came from a discovery back in the 90s by well-known diver Rauno Koivusaari: on trying to prop open a wreck’s hatch cover he found the subsurface wave force was strong enough to shatter wood. The WaveRoller uses this same hydraulic action to push a generator into giving between 500kW and 1000kW from a single panel.
This, of course, applies to moderate conditions. As Chris Ridgewell pointed out: “The biggest challenge for wave power is the occasional, very high load, extreme event.” In other words, how do you build a device that will cope with waves with enough power to reach up to 30m on the surface and still be able to harvest the energy from 1m waves?”
The answer lay close at hand: “We realised that we could use the seabed as a tool: a lot of the extremes are just filtered out by it.” Further, while deeper-water waves can travel in almost any direction, this ‘friction’ from the seabed causes them to turn towards the shore and allows the device to capture a larger proportion of the energy. His colleague, Markus Berg added: “We’ve picked the position carefully: 10m to 20m water depth where the wave surge is most powerful.”
Its underwater site lends a couple of distinct advantages. “On the surface you can’t get away from the extreme loads, but the WaveRoller panel is just pushed over to lie down flat so the energy flows over the top,” said Mr Ridgewell, It also avoids cable fatigue issues and finding mooring chains sturdy enough to handle the 50-year freak events while not hampering day-to-day efficiency.
Its nearshore location also means the export cables should be fairly short – around a kilometre - and the connection points can be economised: “A lot of the cable connectors come from the deepwater offshore industry with its high pressures, but because we are in shallow water we don’t need to take on those issues. Likewise we don’t need to mate the connectors underwater either, this can be done on the surface and simply sunk into position,” he explained.
“It means saving a lot of money,” added Mr Berg: “I reckon that the plug alone costs less than a tenth of the usual EUR100,000-plus amount.
Manufacturing costs have also been minimised as far as possible: although the main panel is bespoke, the ‘rudder’ similarities mean that a lot of the other elements exist ‘off-the-shelf’ said Mr Berg – and further, rudder components are sized to meet the huge torque presented by a ship heading into oblique waves. “The technology is already out there: the hydraulics and actuators, all this can be already found in other parts of the marine industry, its crossover technology.”
As others have noted, access is one of the big issues so the WaveRoller can easily be floated up to the surface for maintenance or towed into dock. The method retains stability: air is pumped into the internal tanks and it rises up, one edge at a time so that control is retained over the stability. “It’s a fairly straightforward process and we don’t need a big heavy lift vessel to come in... we can make use of the smaller, local vessels of the kind that offshore wind is leaving behind,” said Mr Ridgewell.
Despite the excitement of deploying the company’s fourth device (like the third, it’s for Portuguese waters) with a panel measuring 8m by 12m, he added “the devil is in the detail”, not only can very small components play havoc it’s also important to show that various codes and standards are met. “This means building a numerical simulation, then validating the numbers based on real sea deployments – to do that with a small team has been a big challenge.”
Could it survive not just sea but market pressures? Mr Ridgewell believes so: “Even with our current technology the levelised cost of energy from a WaveRoller array would undercut the cost of wind at its current price.”
A research organisation’s view
Wave’s development ‘tardiness’ is also, somewhat counter-intuitively, a result of the plethora of opportunities it provides.
“Where do you think the optimum place to extract the energy is, is it the crest of the wave as it crashes, is it the long wavelengths you find out at sea, or is it down below? You have to make a decision early on,” explained Simon Cheeseman of the UK’s Offshore Renewable Energy (ORE) Catapult.
He pointed out that, for example, while Aquamarine’s ‘oyster’ worked in breaking waves to good effect, Pelamis rode the offshore waves to generate energy, whilst point absorber devices bob about in a variety of water depths: “We have a vast range of different designs, it’s not clear which is the optimum at the moment.”
It makes for a complex situation. “Whereas tidal energy has decided on a three bladed horizontal axis turbine, we haven’t seen that kind of convergence of technology when it comes to wave energy.” In fact, he added “while large engineering companies have moved in to support tidal power, by contrast large OEMs have not been convinced wave technology is sufficiently mature”.
He explained: “From a technology point of view the key factor is survivability. As we’ve seen recently the weather can produce enormous waves: generating devices must be able to handle all types of sea conditions.”
“Secondly you have reliability: ideally you want to keep the design as simple as possible,” he said. Admittedly, this applies to the big moving parts as on top of this is a whole layer of complexity: “You need control systems along with a certain amount of redundancy and you may want to tune the responses through the moorings. You need a condition monitoring system because you want to see and understand if and how certain elements are deteriorating.” He added that even supposedly marinised ‘off the shelf’ components have failed on wave devices when exposed to the elements, so amongst its many support mechanisms, Catapult has analysed component failure modes.
Mr Cheeseman also echoed the point brought up by Chris Ridgwell, that of a fundamental issue with the development pathway itself: “The problem is that it takes a lot of time and money to thoroughly go through the design and development process and device developers are often small companies funded by private investors and venture capitalists. Where pressure to provide a return on investment is characterised by the need to get a device into the water and connected to the grid it often compells developers to try to leap ahead without really proving the core principles of their design.
In third and fourth place come price and scalability, two interrelated factors.
“Above all we need to generate power cost effectively: unless its prices are comparable with other types of low carbon systems such as offshore wind which has a target of £100 per MWh by around 2020, it simply won’t find buyers.”
Here the very first design steps can impact final costs: for example the choice of materials has an increasing influence when everything is scaled up. Of course, how easy it is to deploy and link up devices into an array is also important.
He explained first movers have had to contend with more than focusing on their design, it’s also about enabling technology like mooring and connection systems, plus “the electronics also need to account for the hugely variable voltage and frequency in the initial conversion process and make sure that outgoing electricity fits within the parameters of the grid”.
For those developers who want an independent, expert appraisal, Catapult runs a Technology Assessment Process (TAP), that looks at evidence such as the origins of the concept, the engineering behind it, the testing process “and collectively provides a client with a report indicating where that particular device is along the pathway toward design maturity, technology readiness” said Mr Cheeseman. “Where appropriate, based on the findings from the TAP, the report will provide a potential development roadmap to pre-commercial technical maturity.”
Having said this, there are no guarantees: unfortunately both Pelamis and Aquamarine failed to remain afloat despite many years of development, testing and design improvement.
By Stevie Knight