• Question: How can the energy in waves and tidals generate electricity

    Asked by musaa to David on 15 Jun 2011.
    • Photo: David Ingram

      David Ingram answered on 15 Jun 2011:

      Waves: we use the waves to make a float move (either up-and-down in heave or side-to-side in surge) and use the motion of the float to drive a generator. The generator can be a traditional rotary one, in which case we need to use hydraulics to convert from the linear motion of the float to the rotary motion of the generator, or we can use a linear generator. Both Oyster (from Aquamarine Power) and Pelamis (from Pelamis Wave Power) work in this way. The floats are BIG – Oyster is the size of a house and Pelamis the length of an intercity train!

      An alternative is to use the waves to move air up-and-down in a column. We then use an air turbine to convert the air movement to rotation and run a generator. The LIMPET (from WaveGen) wave power plant on Islay has been doing this for more than 10 years.

      Tides: You use something like an underwater wind turbine to change the motion of the water into rotation and drive a generator. SeaGen (from Marine Current Turbines) generates 1.2MW into the grid in Strangford. Other machines on test at the European Marine Energy Centres (EMEC) in Orkney come from Tidal Generation Limited (a Rolls-Royce company), OpenHydro, Atlantis power and Hammerfest Strom.

      There is video of the Tocado turbine (in Holland) on the EquiMar project’s you tube channel equimarvid as well as pictures of SeaGen

      An alternative in waves

Comments

  • Photo: Will

    Will commented on :

    David, do these technologies provide a more consistent input of power to the grid than wind energy? I’ve heard lately that wind power is turning out to be an expensive red herring for sustainability because we can’t replace conventional power plant with it due to it’s unpredictability of generation.

  • Photo: David

    David commented on :

    Tidal is predictable 1000’s of years into the future – it’s intermittent as there are times of day when the tide doesn’t flow so we need some sort of base-load generation or energy storage to smooth out generation. Each turbine needs to store about 3 hours of energy every 12 hours.

    Wave is more predictable than wind as wind conditions thousands of miles away generate waves over a large area so on the west coast of the UK you can predict 48 hours into the future but there are still days when the sea is calm.

    To say wind is a red herring is a little harsh but it certainly cant get us out of the energy gap we are falling into on its own