Working with engineers from Pelamis wave power, Schaeffler’s bearing specialists have enabled a major breakthrough in the design of the next generation of renewable wave energy converters
Engineers at Pelamis Wave Power have been developing a renewable energy solution designed to offer both commercial viability and low environmental impact. With a company ethos of innovation, constant research and development and a readiness to question and challenge existing technological thinking, Pelamis has succeeded in overcoming the engineering challenge of operating continuously in the constantly active and variable marine environment.
Building on their experience producing the world’s first offshore wave energy converter, they have now developed a ‘P2’ design which is more efficient and cost-effective than its predecessors.
Crucial to the success of this new design are the bearings and seals. The main tube structures are connected by the main bearings units which use a combination of Schaeffler bearings, and there are four hydraulic rams at each main joint pivoting on precision bearing arrangements. As Mike Woods, Senior Engineer and Bearings Group Leader at Pelamis, points out: “Our biggest challenge has always been how we manage the loads and motions from such an active and constantly variable environment, whilst at the same time extracting as much power as possible.
"Working forces generated across each joint can be several hundred tonnes, which can present huge problems for the bearings as they have to take up the reactive forces coming back through the joints.”
Pelamis' first P1 wave energy converter was a simpler design which had separated hinged joints. Although this allowed useful working space between the axes, it had to carry high transferred loads and was unable to manage the combined motions necessary for the P2 configuration. Also, the bearings themselves were relatively high friction, making the system less energy efficient.
Says Woods: “Our engineering team had been trying to work out a way of overcoming this problem and eventually came up with the idea of bringing the axes, or joints, together. However, this meant a completely new bearing solution which was able to manage combined angles in a single package, so Pelamis engineers turned to Schaeffler for help and support.
Low-friction material eliminates stick-slip
Key to the success of this new joint concept was a new low-friction material designed and developed in-house by Schaeffler engineers. This modified PTFE fabric liner is a member of the Elgoglide family with low friction characteristics that has effectively eliminated the problem of ‘stick-slip’. This has allowed the operating envelope of the machine to be extended beyond the capabilities allowed by standard bearing materials.
“Now that we have been able to put all the bearings in one place, we have taken a major technological step forward," adds Woods. "As well as being a much more efficient bearing mechanism, the new design is a self-contained, modular bearing unit. It is a bit like being able to take an engine out of a car in one go; it allows us to improve our inspection procedures and reduce our exposure to technological risk."
Development of the P2 wave energy converter is a big step forward for Pelamis. Business Development Manager Max Carcas said: “We are very excited about the P2. The first unit, ordered by Eon, is now nearing completion and will be fully tested in the spring of next year, but we have already received major interest and potential further orders from leading utility companies — a first for a wave power project anywhere in the world.
"We are constantly striving to drive down costs whilst at the same time increasing energy capture, and by working with a supplier such as Schaeffler, we are confident that we will be able to achieve our goals.”
