Hydroelectric Power

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  • Solar-Derived Energy Resources - Hydroelectric Power
    • The water cycle is driven by the energy from the Sun as water is warmed, evaporated and rises. As it cools and condenses the falling rain converts potential gravitational energy to kinetic energy. This continues as the water flows downhill towards the sea.
    • The amount of energy that can be harnessed depends on the volume of water and the velocity of its flow. The energy harnessed can be increased by using a large river and using a dam to collect water and increase the 'head' of the water.
    • The main types of HEP schemes are...
      • High head - low volume schemes, where a relatively small amount of water falls a long way down a hillside from a high reservoir
      • Low head - high volume schemes where a dam is built on a large river
      • Run of river schemes - where a small turbine is located in the river without a dam
    • Locational Factors
      • Reliable large volume water supply
      • Impermeable rock to prevent water soaking into the ground
      • Suitable valley shape so a relatively small dam can hold back a lot of water in the valley basin behind
      • No serious land use conflicts
      • Close to the consumers or an electricity grid to transport the energy
    • Pumped Storage HEP
      • When there is surplus electricity (eg at night) it can be used to pump water uphill, thus storing the energy as potential gravitational energy
        • The potential energy can be converted to kinetic energy by allowing the water to flow down to the lower reservoir generating electricity as it turns turbines.
          • This can be done when there is a sudden increase in demand for electricity. These power stations can respond to changes in demand much more rapidly than fossil fuel or nuclear stations
    • Environmental Impacts
      • Construction damage and habitat change
        • Extraction of  the sand, gravel, cement and rock used in dam construction
        • Transport and construction of access roads
        • Habitat loss during flooding of the reservoir
      • Impacts after construction is complete
        • The dam and reservoir divide the river into two sections that restricts the movement of animals,  including migrating fish
        • Dead organic matter from when the reservoir flooded or that is washed in later will decay. Under anaerobic conditions in the reservoir sediments, they may release methane instead of Carbon dioxide. Methane is a much more powerful greenhouse gas.
        • Reduced sedimentation downstream of the reservoir may increase bank erosion as there is less material arriving to replace what is lost


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