Harnessing Forces. Power Take-Off for Ocean Energy Systems

Transcription

1 Harnessing Forces. Power Take-Off for Ocean Energy Systems The Drive & Control Company

2 2 Technology for Marine Energy Systems Ocean Energy: Renewable Reserves Just Offshore Anyone who has actually experienced the mighty power of ocean waves and currents will have an idea of the potential energy lying dormant in the seas. Many companies are currently working on a wide range of concepts for largescale power generation systems from this renewable energy source. We are still just at the start of this development and, as was the case a few decades ago with wind energy, Rexroth is supporting numerous projects at this early stage with power takeoff solutions. These are based on Rexroth hydraulic component- and system solutions, which are already proving to be exceptionally robust and reliable in a variety of marine applications. The experts are in agreement: Within a few decades innovative systems for the utilization of ocean energy will be able to generate at least as much electricity as 100 nuclear power stations. And there is another major advantage of ocean energy: Around two thirds of the world s population live in coastal regions. The proximity of wave energy converters to consumers simplifies infrastructure and reduces pipeline leakage. In contrast to solar energy, ocean energy is available anytime of day or night. Unlike wind energy there are always tides, currents and, to a certain degree, waves and these can be planned for in the long term. These power stations can thus be used within the network as base-load generators for supplying the power grids. The decisive criteria for the success of all ocean energy concepts are met by robust and reliable automation components, which are designed specifically to meet the harsh environmental conditions prevailing at sea level and below. Rexroth offers a unique treasure trove of experience for marine automation projects, as well as an extensive portfolio of specially developed components.

3 3 The Challenge for 4 Automation technology Tidal and Ocean Current Power Stations 6 Wave Energy Converters 8 Application Centers 10

4 4 Technology for Marine Energy Systems Automation Technology The Challenge for Automation Technology: Controlling factor 1,000 The sea is one of the most challenging environments of all when it comes to technical applications. The corrosive medium of salt water demands special materials and coatings. This high density of water generates extreme forces, which can fluctuate to the factor 1,000 or more through storms. With equipment installed firmly below the water surface maintenance work is extremely complex and costly if it is possible at all. In short: Ocean energy demands extremely robust, reliable and maintenance-free components and system solutions. Hydraulic components and system solutions from Rexroth developed specifically for use on offshore meet the stringent requirements of long-term application in ocean energy systems. Technologically speaking, hydraulics dispenses with the need for mechanical switching elements and is able to self-lubricate via the hydraulic medium itself. Hydraulic systems with variable displacement hydraulic motors are highly robust and are able to withstand extreme fluctuations in load, even where space is at a premium. Rexroth engineers have developed a new coating method based on the already extensively tried-and-tested

5 5 A6VM Hydraulic motor for generator drive Electrohydraulic pitch adjustment for tide energy power stations CERAMAX process. It guarantees additional protection against corrosion, which further improves long-term functional operation in salt water. Seals specially constructed for marine applications round off the seaworthiness of this system. Linear pump for wave energy power stations

6 6 Technology for Marine Energy Systems Tide and Ocean Current Power Stations Tide and Ocean Current Energy Converters: Going with the Flow Whether with tide or a natural ocean current: As with wind energy it is the flow that drives the rotors. Water, however, is 1,000 times denser than air and generates extremely high forces, even at low flow rates. This requires specifically thought-up concepts. Underwater rotors are able to pick up energy effectively with a diameter that is considerably smaller compared to wind turbines. Even at low speeds high forces act on the complete system. Generator gear technology, which is already known from wind energy, is one direction of development, and one in which Rexroth is firmly established as the world s leading supplier in the renewable energy sector. Another direction that the development is taking is demonstrated in the use of hydraulic converters. This straightforward and extremely robust concept converts rotational movement into a hydraulic flow, which drives a closed-loop controlled hydraulic, generatorcoupled motor and with a high degree of efficiency. On the pump side a slow-running hydraulic motor picks up the rotor speed, generating a volumetric flow. This energy feeds a fast-running motor with variable displacement axial piston, which drives the generator shaft directly into the grid frequency. This way the hydraulic converter can dispense with the need for costly closed-loop control electronics and frequency converters. One particular benefit is as follows: Thanks to the variable displacement options offered by the axial piston motor, the steplessly smooth adjustment of the transmission ratio not only absorbs peak de - mand, it also adapts to different current speeds, even without rotor adjustment. The hydraulic converter is thus able to achieve an optimum degree of efficiency across the complete tide cycle. Above all, this solution simplifies the overall design, as the variable displacement motors pick up directly the various directions of rotation at ebb and flow with the securely fixed systems. The dispersed construction method of hydraulics furthermore reduces the number of components under water: Only the robust rotor pump for the generation of the flow is positioned directly inside the installation. The system operator can install the hydraulic motorgenerator assembly above water: This reduces maintenance, at the same time also noticeably increasing availability.

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8 8 Technology for Marine Energy Systems Wave Power Stations Wave Energy Converters: From the Wave to Kilowatts

9 9 Fluid technology is particularly suited to the use of wave energy for power generation. It can convert linear motion into a closed-loop controlled rotational movement with a high degree of efficiency and a minimum of mechanics. And the particular challenge here: Maximum forces and wave travel speeds correlate within a wave cycle. High travel speeds of 1 2 m/s are typical of smaller waves, following rapidly in succession. Large waves, on the other hand, generate maximum forces of up to 500 kn 1 MN over a longer period. Whether speed or force: The input speed for the power take-off of any wave will fluctuate twice between zero and the maximum value for a typical duration of 10 seconds. Moreover, the power of the wave will increase by a factor of three in relation to the height of the wave. This gives us a power window, which attains the factor of 1,000 between minimum and maximum values. Hydraulics is able to cover such a broad spectrum and at a reasonable cost. The continuous up-and-down motion of waves is the most visible sign of the immense power there is in the sea. Wave energy converters have to be able to cover an extremely wide application window: Gentle waves in calm weather just as much as winter storms in Europe, hurricanes, typhoons or cyclones.

10 10 Technology for Marine Energy Systems Application Centers From Concept to Operation: Experience Counts The ideal automation partner for ocean energy systems will know the prerequisites for renewable energies and will have the experience in marine applications and components specifically designed for such. He will also be able to work with his own development personnel in the long term, as well as collaborating closely with system manufacturers. Who, other than Rexroth, can offer this combination? When the industrial development of wind energy systems began more than twenty years ago, Rexroth put itself forward as a technology partner right from the start, with solutions for both transmissions and drives and controls. Together with all major OEMs Rexroth increased the level of reliability and efficiency of these core components. From this the automation manufacturer developed a deep understanding of the particularly stringent requirements retaining to reliability in power generation systems. Marine applications have always been a part of Rexroth s core activities. Whether on board ships, typhoon-proof ferry bridges, barrages or offshore technology: Rexroth hydraulic components and systems are proving themselves on every ocean and under the toughest of conditions. Here, too, users are calculating in terms of decades when it comes to the design of their systems. In the Renewable Energies Applications Center Rexroth is combining all this experience and focusing on the development of automation solutions for ocean energy converters. The efficiency of the power take-off here equates to low power generation costs. Only if the investment costs are optimized as a whole, taking into account a long service life and total cost of ownership, including operational and maintenance costs, will ocean energy systems be able to reveal their true potential. This is the challenge currently faced by many a system manufacturer. Experience from wind energy and other major projects demonstrates again and again the necessity and relevance of close co-operation between system component supplier and system builder. As power take-off system supplier Rexroth supports system manufacturers right from the start with Wave-to-Wire computer simulations. Rexroth specialists are, in an interactive process, optimizing power take-off for the relevant system, as well as designing and supplying ready-to-install subassemblies. A competent partner with the strength of a global player behind him: Rexroth, your partner for the development and realization of ocean energy converters. Dredging Offshore

11 Sperrwerk (Photo source: Lower Saxony Water Management, Coastal Defense and Nature Conservation Agency) Ship lock The Drive & Control Company Rexroth is unique. No other brand on the world market can offer its customers the full range of drive and control technologies, both on a specialized and integrated basis. This is one of the reasons why we are best-in-class on a worldwide basis when it comes to furnishing technological driving, controlling and motion solutions; a standard to be constantly confirmed by mastering new challenges. In more than 80 countries around the world, with about 33,000 employees. This is possible thanks to an infrastructure purposefully designed with partnership and customer proximity in mind. Electric Drives and Controls Hydraulics Linear Motion and Assembly Technologies Pneumatics Service Ferry bridge As a company Bosch Rexroth looks back on more than 200 years of tradition. As a wholly owned subsidiary of Robert Bosch GmbH, we are part of a globally operating technology group. All this is both our drive and our commitment. And it is unique just like Bosch Rexroth. The Drive & Control Company.

12 Bosch Rexroth AG Hydraulics Zum Eisengießer Lohr, Germany Tel.: +49(0)9352/18-0 Fax: +49(0)9352/ info.bri@boschrexroth.de Printed in Germany RE 08028/11.08