Since most dams use gravity, a hydroelectric
dam's energy output depends largely on the
height difference between the reservoir
water source and the outflow. Water flow
along the rivers is another important
factor, as is the age and efficiency of a
Many of the world's older dams will need to
be upgraded or "repowered" in the coming
decades to improve efficiency, which will be
expensive but could ultimately add another
30 GW to the global energy mix.
Hydro projects range in size and output from
the "micro" hydro projects of less than 100
kilowatts (kW) to China's Three Gorges Dam,
the largest in the world, which will have a
capacity of over 22 GW once all of its
generators go into operation.
Wave power is on
of the lesser known renewable energy sources currently being
considered. Using wave energy as a renewable power source is
exciting because of the massive possible production. Unlike wind
and the sun, waves are always moving through the sea, making
wave energy a tempting source of electricity.