1 Background to hydroelectricity

Water power, or hydropower, became a major ‘modern’ energy source over a hundred years ago, supplying the input for some of the earliest electric power stations. Hydroelectricity has now become a well­ established technology, delivering in 2014 a little over 16% of the world’s annual electricity; or nearly 4000 terawatt hours (TWh). (IEA, 2016).

This type of power, like most renewable energy sources, is indirect solar power, and has been contributing to local energy supplies for many centuries, for example in the water wheels shown in the figures below.

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Figure 1 Waterwheel type – overshot – water falls onto blades with closed sides

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Figure 2 Waterwheel type – undershot – driven by water pressure against lower blades

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Figure 3 Waterwheel type – breastshot – water strikes paddles at about the level of the wheel axle

What hydropower resources are available? You’ll look at that next.