Americans use a lot of power: More than 300,000 miles (482,803 kilometers) of sprawling transmission lines wind through the United States.
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Most of that power comes from coal or other fossil fuels. This coal-fired plant in Pennsylvania is one of the 12 biggest carbon dioxide polluting power plants in the United States.
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Alternatives to fossil fuels are becoming more popular worldwide. Here, parabolic troughs make up a solar thermal array in Spain. The troughs concentrate the sun's rays in order to heat a fluid. The fluid is then used to produce steam.
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While solar thermal power is becoming a popular solar option, you're probably more familiar with photovoltaic (PV) solar panels. They convert sunlight directly into electricity.
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Photovoltaic (PV) panels are a top choice with homeowners because they're suitable for small-scale operations -- like a single-family home.
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While the sun is an obvious power source, there's also a lot of heat inside the Earth. Iceland has long used its glacial and volcanic geology to generate power; today, geothermal energy is gaining steam around the world.
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Geothermal power can even help make city streets safer for citizens. In Klamath Falls, Ore., the sidewalks don't freeze over because they're kept warm by geothermal energy.
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Geothermal power generation can come with risks, however. Enhanced geothermal power generation involves creating small fractures in rock deep below the surface of the Earth. Such cracks can cause earthquakes.
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Oceans make up most of the Earth, and their power can actually offer us an alternative energy source. Large waves like this one often generate powerful ocean currents.
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Many countries have turned to the power of the seas to generate electricity. Here, German Chancellor Angela Merkel reviews a model of an ocean wave power plant.
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While concerns for birds and human health win wind power some detractors, strategically placed farms are still a good option for clean power generation.
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One way to keep birds a little safer is to place wind generators in the ocean. Offshore windmill projects, like this one in the North Sea, seek to provide cleaner power to homes on shore.
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This photo might help you put the size of a wind turbine's blades into proper perspective. These blades will be placed atop 300-foot-tall (91-meter-tall) generators in Utah.
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Biofuels are made at least in part from renewable sources instead of from oil. A German gas station stocks a biodiesel mix. While the ethanol pipeline has made American ethanol transport easier, the environmental soundness of biofuels is still debated.
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While biofuels power cars, biomass generates electricity. This photo shows a pile of cut wood at a German bioenergy plant. Other biomass fuel sources include cow dung and plant remains.
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No, we weren't kidding with the cow dung. Some farmers extract methane from livestock waste.
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This prototype of a zeroHouse was designed in 2007 as an off-the-grid home. The energy gathered from the PV panels on top of the zeroHouse is stored in batteries so that the house keeps running well after sunset or after a few cloudy days.
Image Credit: Specht Harpman
In this diagram, you can see the layout of the modules of the zeroHouse. In addition to solar panels, the home also includes a rainwater cistern and an efficient design.
Image Credit: Specht Harpman
Even the windows in the zeroHouse are efficient: They're made from special material that resists heat flow to keep the climate control systems from wasting too much energy.
Image Credit: Specht Harpman
Another reason to consider living off the power grid: A strong electromagnetic pulse or a solar storm can wreck unprotected parts of the electrical grid and all sorts of electronics. A powerful solar storm could be disastrous.
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Many conservationists and lawmakers hope shifting to renewables will reduce emissions, as well as our dependence on oil. This offshore rig is operated by Aramco, the state-owned Saudi oil company.
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While renewable energy sources will help take a bite out of carbon dioxide emissions, it's also likely they'll need a more efficient, more reliable power grid -- namely, a smart grid -- to work at their fullest. For more information on energy, check out How Smart Grids Work.
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