Energy without end
Marine energy
Demonstration plant for a 20 kilowatt wave energy unit in Norway. Here Rexroth is responsible for engineering and delivering the hydraulic spring system (motor by Hägglunds, reservoir, piping, feed pumps).
Using the power of water in rivers has a very long history. Recovering energy from the seas is a newer development. The potential, however, is tremendous. Scientists and engineers estimate that the seas could deliver about onethird of today’s world electricity needs. Only test facilities have been built to date, used to run trials to determine the suitability of this technology — originating primarily in Germany — for everyday use. Among the numerous ideas available for using marine energy, two especially promising approaches to power generation are moving to the forefront: harvesting the energy in ocean currents and in wave action. Both tactics are based on a time-tested technology: hydraulic power transfer.
When using the ocean current, a rotor located underwater drives a hydraulic pump. This pump feeds the hydraulic fluid to an adjustable hydraulic motor that in turn drives the electrical generator. The charm of this solution: only the hydraulic pump is located underwater. It conveys energy to the generator itself, situated on land, by way of slender piping. This simplifies maintenance and improves reliability.
The second approach utilizes the rise and fall of the waves. There are especially daunting hurdles to be overcome here. Depending on the weather, the energy level can vary by a thousand-fold, from a calm sea to a hurricane. Mechanical gearing cannot handle such dynamics; hydraulics can. As the water rises and falls, hydraulic cylinders work like a bicycle pump to move hydraulic fluid. This creates pressure that, once again, drives an adjustable hydraulic motor. The adjustment mechanism compensates for the extreme variations in wave energy. Rexroth is using several prototypes and a complete test array to examine various solutions in regard to their suitability for daily use. Important in addition to costs are reliability, simplicity in maintenance, service life, availability and system efficiency.