Can renewable energy power the world?
Can renewable energy power the world?

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Can renewable energy power the world?

5.5 Stored energy and available power

Water held at a height represents gravitational potential energy. If m kilograms are raised through H metres, the stored potential energy in joules is given by the following simple equation in Figure 5.

Figure 5 Equation for stored potential energy, in joules

Thus about 10 joules of energy input are needed to lift one kilogram of anything vertically through one metre against the gravitational pull of the Earth, but the capacities of large reservoirs are usually given in cubic metres, rather than kilograms, so we can express the equation for stored energy as shown in Figure 6.

Figure 6 Stored potential energy in a hydro dam depends on height and water volume

This is therefore the energy that will be released when this volume of water falls through a vertical distance (H).

Next we will look at pumped storage and how this works to store electrical energy.


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