? 發問於 科學及數學化學 · 1 十年前

About water power?

Questions

Q1.......what are some of the environmental prob-lems associated with large-scale hydro dams?

Q2.......Explain how or why electricity derived from moving water can be considered renewable energy.

Q3.......what type of location would be best suited for a micro-hydro electrical system?

Q4.......what are the advantages of waterpower over fossil for making electriciy?

1 個解答

評分
  • 1 十年前
    最愛解答

    1. Large hydroelectric projects can be disruptive to surrounding aquatic ecosystems. For instance, studies have shown that dams along the Atlantic and Pacific coasts of North America have reduced salmon populations by preventing access to spawning grounds upstream, even though most dams in salmon habitat have fish ladders installed. Salmon smolt are also harmed on their migration to sea when they must pass through turbines. This has led to some areas barging smolt downstream during parts of the year. Turbine and power-plant designs that are easier on aquatic life are an active area of research.

    Generation of hydroelectric power impacts on the downstream river environment. Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. Since turbines are often opened intermittently, rapid or even daily fluctuations in river flow are observed. For example, in the Grand Canyon, the daily cyclic flow variation caused by Glen Canyon Dam was found to be contributing to erosion of sand bars. Dissolved oxygen content of the water may change from pre-construction conditions. Water exiting from turbines is typically much colder than the pre-dam water, which can change aquatic faunal populations, including endangered species.

    Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In many cases, no amount of compensation can replace ancestral and cultural attachments to places that have spiritual value to the displaced population. Additionally, historically and culturally important sites can be flooded and lost. Such problems have arisen at the Three Gorges Dam project in China, the Clyde Dam in New Zealand and the Ilısu Dam in Southeastern Turkey.

    2. Renewable energy is energy which can be replenished at the same rate it is used. Renewable energy sources contribute approximately 25% of human energy use worldwide. The prime source of renewable energy is solar radiation, i.e. sunlight. The Earth-Atmosphere system supports approximately 5.4 x 1024 joules per year in the solar radiation cycle (Sorensen, 2004).

    Mankind's traditional uses of wind, water, and solar power are widespread in developed and developing countries; but the mass production of electricity using renewable energy sources has become popular only recently, reflecting the major threats of climate change due to pollution, concerns about the exhaustion of fossil fuels, and the environmental, social and political risks of fossil fuels and nuclear power. Many countries and organizations promote renewable energies through taxes and subsidies. Varying definitions of the term renewable energy have been adopted to define eligibility under these policies.

    3. the best site would be at the mouth of the river (where the river and the sea meet), engineers also need to consider other people, environmental problems, the water need to be strong and steady, the weather and other important factors.

    4. The major advantage of hydro systems is elimination of the cost of fuel. Hydroelectric plants are immune to price increases for fossil fuels such as oil, natural gas or coal, and do not require imported fuel. Hydroelectric plants tend to have longer lives than fuel-fired generation, with some plants now in service having been built 50 to 100 years ago. Operating labor cost is usually low since plants are automated and have few personnel on site during normal operation.

    Pumped storage plants currently provide the only commercially important means for energy storage on a scale useful for a utility. Low-value generation in off-peak times occurs because fossil-fuel and nuclear plants cannot be entirely shut down on a daily basis. This energy is used to store water that can be released during high load daily peaks. Operation of pumped-storage plants improves the daily load factor of the generation system.

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