The Pentland Firth is the strait that lies between the far north of mainland Scotland and the Orkney Islands. It's a wild area with some of the fastest tides in the world, where the power of the sea is being harnessed by tidal turbines sitting on the sea bed. But this type of green energy is still very expensive to generate - so what is the future of tidal and wave power? We explore some of the ground breaking projects being developed in the region and speak to companies who are trying to reduce costs to make the energy more viable. Produced and presented by Theo Leggett (Image: A MeyGen turbine being installed on the sea bed. Credit: MeyGen)