The document summarizes the pros and cons of various renewable energy sources including solar, wind, hydro, and biomass energy. It discusses that while solar and wind are free sources of energy, they have limitations based on weather and location. Hydroelectric power is inexpensive once dams are built but can damage ecosystems. Biomass energy utilizes waste but production and storage of raw materials is expensive. The document also provides examples of energy innovations and news articles on renewable energy projects.
24. Solar thermal: The most common solar concentrators is parabolic troughs —long, curved mirrors that concentrate sunlight on a liquid inside a tube that runs parallel to the mirror. The liquid, at about 300 degrees Celsius, runs to a central collector, where it produces steam that drives an electric turbine.
25. Photovoltaics In 1839, French scientist Edmund Becquerel discovered that certain materials would give off a spark of electricity when struck with sunlight. This photoelectric effect was used in primitive solar cells made of selenium in the late 1800s. In the 1950s, scientists at Bell Labs revisited the technology and, using silicon, produced solar cells that could convert four percent of the energy in sunlight directly to electricity. Within a few years, these photovoltaic (PV) cells were powering spaceships and satellites. The most important components of a PV cell are two layers of semiconductor material generally composed of silicon crystals.
27. Typical hydroelectric powerplant Hydroelectric energy is produced by the force of falling water. The capacity to produce this energy is dependent on both the available flow and the height from which it falls. Building up behind a high dam, water accumulates potential energy. This is transformed into mechanical energy when the water rushes down the sluice and strikes the rotary blades of turbine. The turbine's rotation spins electromagnets which generate current in stationary coils of wire. Finally, the current is put through a transformer where the voltage is increased for long distance transmission over power lines. (Source: Environment Canada )
34. 600 percent: The highest average efficiency of a ground source heat pump in the winter, compared to 250 percent for air-source pumps. 15: Percentage of the average household electricity bill that goes toward lighting alone. 9: Lowest wind speed (in miles per hour) from which it’s efficient to harness wind power. 750: Number of electricity providers that offer a green alternative. 280,475: Number of photovoltaic cells shipped domestically in 2007. 7: Percent of energy that came from renewable sources in 2007. 53: Percent of that renewable energy that was drawn from biomass fuels, the largest supplier, followed by hydroelectric (36%); solar, geothermal, and wind energy all contributed 5% or less.
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