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18.9: Review

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    After completing this chapter you should be able to...

    • Detail the percentage that renewable energy contributes to electricity generation and total energy consumption globally and in the United States.
    • Distinguish among the five main types of renewable energy, explain the mechanisms by which they are used, and discuss their advantages and disadvantages.
    • Distinguish between passive and active solar technologies and provide examples of each.
    • Explain how solar panels generate electricity.
    • Distinguish between geothermal power plants and geothermal (ground source) heat pumps.
    • Identify the main types of hydropower.
    • Explain how environmental damage associated with hydropower can be mitigated.
    • Explain why combustion of biofuels is carbon neutral.
    • Provide examples of biofuel use and evaluate their sustainability. 
    • Define energy conservation and provide examples of behaviors and technologies that conserve energy.

    Renewable energy sources can be replenished within a short timeframe. This includes wind, solargeothermalhydropower, and biofuels. Each is a direct or indirect form of solar energy with the exception of geothermal energy, which comes from deep underground, and tidal energy, a type of hydropower. Most forms of renewable energy generate electricity by turning a turbine, which powers a generator. For wind energy and hydropower, the motion of air or water, respectively, turns the turbine. For geothermal energy and biofuels, heat from the Earth or from burning organisms, respectively, produce steam, which turns a turbine. Solar panels generate electricity when light energy displaces electrons in semiconductors. 

    Generally, renewable energy sources generate little air pollution and are not major causes of climate change, but there are exceptions. A downside of renewables is that wind and solar can only be efficiently harnessed in certain locations and are intermittently available. Geothermal energy is more reliable, but geothermal power plants can typically only be built near geysers, volcanoes, or hot springs. Hydropower that involves dams and reservoirs destroys terrestrial habitats and disrupts aquatic species, but run-of-the-river hydroelectricity causes minimal damage. Biofuels are carbon neutral, capturing as much carbon dioxide as they release. Biofuels are most sustainable when they are made from materials that would otherwise be wasted. 

    Energy conservation involves reducing energy use or using it more efficiently. Examples of energy conservation include turning off lights and electronics when they are not in use, driving efficiently, and purchasing energy-efficient applicances.


    Melissa Ha (CC-BY-NC


    This page titled 18.9: Review is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha and Rachel Schleiger (ASCCC Open Educational Resources Initiative) .

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