Waves and tidal-currents are very promising sources of energy for the production of electricity. In certain areas such as the UK, the amount of incident natural power from these sources is truly enormous. Huge efforts, particularly in Scotland, are going into the development of marine generators that are able to land electrical energy from the oceans. Artemis technology has its roots in the fascinating problem of efficiently converting marine energy into electricity and we have close connections with most of the leading companies.
Artist’s impression by ETSU from late 1970s: Stephen Salter’s ‘Duck’ showing proposed power-take-off system.
Wave energy converters have to deal with the highly irregular forces and slow moving inputs induced by wave action. Tidal-current rotors have to use very low rotation speeds and correspondingly high torques in order to avoid cavitation as the tips of their blades pass near the waters surface. The Digital Displacement® ring-cam pumps that Artemis has developed for wind-turbine power conversion are ideal for these kinds of conditions. The multiple lobes of the ring-cam effectively ‘gear up’ very low pump shaft speeds to a higher cylinder actuation frequency.
At the output end of the system, wave and tidal-current systems have to spin the shafts of electrical generators. It’s most convenient if this can be done at high constant speed so that conventional wound-rotor synchronous generators can be used. Artemis developed its first Digital Displacement® ‘generator drive motor’, in a joint project with Pelamis Wave Power and with support from Carbon Trust. This technology has been progressively developed and refined for the Artemis wind-turbine transmission.
Digital Displacement® technology bridges the two requirements of a variable-speed at the ‘wet’ end and constant speed at the ‘wire’ end by allowing a variable displacement pump to supply fluid to a variable-displacement motor – with moderately sized hydraulic accumulators providing a buffer between input and output.