ocr: Alternative energy sources Even the most etficient windmills, such as our modern wind turbines, use a small proportion of the wind's energy. As the wind will never run out, it is called a renewable energy source. This is very different to energy sources such as coal, oil, and gas. These are known as fossil fuels and have taken many millions of years to form and could be used up very quickly. Using renewable energy sources, such as wind, allows us to conserve our supplies of fossil fuels.
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