Water can be deployed in the energy system in various ways. Firstly, Electricity can be produced from gravity: potential and kinetic energy of falling or flowing water. This can refer to hydro-electric plants in mountains and rivers, tidal differences or
Table 6.1 Potential yields from wind at different speeds
Per m2 of rotor area
Yield Power Yield Power Yield Power
52 46 40 35 30
593 525 456 399 342
520 460 400 350 300
1434 1250 1100 950 830
awith a rotor diameter of 50 m.
wave energy. In coastal areas, old sea inlets can be used for tidal power generation if the height difference is big enough. Inundation plants are a possibility to simultaneously protect the land from to great pressures on the dikes of a low-laying country and generate power from the influx of seawater. This of course has stark effects on the hinterland. The specific type of polderland beneath the sea can enable continuous production of sustainable energy when water from outside the polder is continuously let into the polder and pumped out again through solar and wind power, which are discontinuous and often switched off when they interfere with common power plants (see Fig. 6.13). This principle of inlet plants should allow open water fluctuations.
A different means of extracting electrical power from water relates to the chemical differences between salty and fresh water. Where fresh water runs into the sea, chemo-electrical exchange through membranes can produce electricity: 'blue energy', of which there are two principles: osmosis and reversed electric dialysis.
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.