1. Geothermal power stations use energy from the natural decay of radioactive substances in the       Earth.   2. Tidal power stations affect the environment because river estuaries have to be flooded.   3. Hydroelectric power station requires the building of a dam on an upland river valley.   4. Hydroelectric power station stores energy from surplus electricity.   5. a) Energy transformation in hydroelectric power stations:                    Gravitational potential energy    Kinetic energy    Kinetic    Electrical                           (stored in water)                  (falling water)     (turbine)    (Generator)        b) Energy transformations in solar cells:                                             Light energy            Electrical energy      c) Energy transformations in wind turbines:                                             Kinetic         Kinetic            Electrical                                             (Wind)          (turbine)           (Generator)