With the exception of tidal energy, our focus thus far has been on land-based energy sources. Meanwhile, the ocean absorbs a prodigious fraction of the Sun’s incident energy, creating thermal gradients, currents, and waves whipped up by winds. Let’s put some scales on the energetics of these sources and see if we may turn to them for help. We’ve got our three boxes ready: abundant, potent, and niche (puny). Time to do some sorting! Thermal Gradients Wherever there is a thermal gradient, our eyes light up because we can create a heat flow across the gradient and capture some fraction of the energy flow to do useful work. This is called a heat engine , the efficiency of which is capped by the theoretical maximum ( T h − T c )/ T h , where “h” and “c” subscripts refer to absolute temperatures of the hot and cold reservoirs, respectively. In the ocean, we are rather limited in how much gradient is available. The surface does not tend to exceed 30°C (303 K), while the depths cannot get
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In a hydroelectric power station water is stored behind a dam in a reservoir. This water has gravitational potential energy. the water runs down pipes (potential to kinetic energy) to turn the turbine the turbine is connected to a generator to produce electricity (kinetic to electrical energy) At pumped storage hydroelectric stations water is pumped back into the reservoir when there are periods of low power demand. This is often when there is excess energy being produced by other power stations. This stores energy and during higher demand periods the water can be allowed to flow back down to produce electricity just like a normal power station. Such a system saves energy and also can be turned on quickly at times of peak demand.