This article was created as part of the Student Science Communication Project, by a student from Allegheny College. All SSCP articles have been reviewed by internal EoE editors, and by independent experts on each topic.
Renewable energy is energy that is created from renewable resources, which can be used sustainably and are naturally regenerated. The main renewable energy sources of today are hydroelectric, biomass, biofuel, geothermal, solar, and wind. One of the greatest benefits to renewable energy is much lower carbon dioxide emissions as opposed to carbon-intensive fossil fuels such as coal, oil, and natural gas. Each renewable energy source has its benefits and costs, and there is no single renewable energy source that can provide a complete substitute for fuels that are currently used like coal and oil. One proposed strategy for renewable energy to power the United States is the 25 x ’25 movement—twenty-five percent of energy in America will come from renewable sources by 2025. This plan would use multiple renewable energy sources to offset the use of fossil fuels. The European Union has also set a renewable energy goal, abbreviated 20/20/20. This stands for twenty percent of energy to come from renewable energy sources by 2020.
Direct Solar energy is provided by incident solar radiation. It can be used for thermal applications using solar collectors, passive building design, generation of electricity using solar photovoltaic panels, and solar thermal energy. This energy is ideal in areas of intense sun, such as deserts. Solar energy is dependent only on the availability of solar energy and is therefore reliable for large expanses of the globe. Solar energy only needs to be complemented when the sun is hidden by clouds, during darkness or when stored energy is depleted. Solar photovoltaic energy can be stored by charging batteries or other systems, while solar thermal energy can be stored in masonry or circulating water and can therefore be used for some time after the sun becomes temporarily unavailable. Solar power has economic limitations that have halted widespread use, its main challenge being that fossil fuels are still comparatively inexpensive, given the underregulation of carbon emissions and subsidies. However, private homeowners and businesses have independently installed solar panels for other social or personal reasons.
Hydroelectric power is energy created and captured when allowing water to move downhill. Water at higher elevations has more potential energy due to gravity and falling water is used to turn a turbine and generator which creates electrical energy. Often this process is facilitated by damming a river to ensure a constant supply of water that can be moved through the turbines. In general, hydroelectric energy output is consistent, although dry seasons can cause a decrease and rain and snow melt may greatly increase energy output. Five countries rely on hydroelectricity for more than half of their electric power: Brazil, Canada, Norway, Switzerland, and Venezuela. Paraguay derives 100% of its energy from hydroelectricity. Although hydroelectricity is beneficial to reduce carbon dioxide emissions, it causes other environmental impacts including habitat loss via flooding and displacement of people by dam construction, as well as reduction of anadromous fish habitat. Hydroelelectricy does not require any fossil fuels to run the plant once it has been built. This makes the economics of hydroelectricity very favorable because it is not affected by rising oil prices. The most controversial hydroelectric plant is the Three Gorges Dam. While it has a capacity of 22,500 MW, it also displaces millions of people in the process and cost a host of environmental issues, from sedimentation to biodiversity loss.
Geothermal energy is available in three forms: building heating and cooling using ground source or geothermal heat pumps, Enhanced Geothermal Systems, and electricity generation at high temperature geothermal locations. The simpler geothermal heat pump involves drilling wells into the Earth until achieving a constant temperature of about 55 degrees. To heat the buildings, a heat pump circulates air from the building down into the Earth to the constant 55 degree temperature and then brings the now-warmer air back into the building. The same heat pump cools the building in summer transferring the heat from the building into the Earth’s 55 degree heat sink. The other system is far more complex, and potentially could be utilized across the entire world. This process is called Enhanced Geothermal Systems (EGS) and involves drilling into the ground. Cold water is then pumped into heated rock and the pressure built up forces heat out of the rock into the water creating steam that is used to turn a turbine to make electricity. The water is cooled after spinning the turbine and pumped into the ground again, so there is no wasted water. Another use of geothermal energy is capturing heat from hot springs and using that to heat buildings and provide hot tap water. Iceland is the biggest user of this form of geothermal energy. Nearly every building is heated from hot springs in Iceland and about 50% of its energy needs are met through geothermal energy. Some positive aspects of this energy source is that it does not rely on weather events to provide power, and that it can be done at any time, unlike solar and wind.
Biomass energy is obtained by burning organic material in the form of ethanol (biofuel), pellets, and gasification. Ethanol or biofuel can be made of different plant products, most commonly corn and sugar cane, but also grasses such as switchgrass. Ethanol is different from all of the other renewable energy sources because it is liquid. This makes ethanol particularly relevant to the energy sector because it could replace oil as fuel for cars and other machinery that rely on oil. Ethanol is made from plant sugars, which is why corn and sugar cane are most commonly used in the research and development of ethanol. There are some drawbacks to corn-based ethanol such as the environmental impacts due to high water use, gas consumption for the farm vehicles, and possible increases in related food prices. In a sustainable manner of farming involving low-till agriculture, crop waste are returned to the soil, providing nutrients to the soil. Using crop residue to make ethanol removes nutrients from the soil, but industrial agriculture simply relies on fertilizers to replace natural nutrients, creating a whole new set of environmental hazards. Another environmental issue with corn is water usage. Corn requires a substantial amount of water, and the energy to pump water to the field can require more energy than the ethanol provides. There are also concerns about using corn as a fuel source because it competes with corn used for food.
In order to produce biomass energy, plant residue can be co-fired with coal to produce electricity. Biofuels have the potential to achieve carbon neutrality as a fuel source. The carbon dioxide that is emitted is taken out of the atmosphere by plant growth but some is then returned as it is burned. In the United States and other developed countries, biomass pellets are the most commercial form of burning biomass.
Wind energy uses wind turbines to convert mechanical energy through the movement of wind into electrical energy by spinning a turbine and generator. Turbines are placed to maximize the efficiency of turning the blades. Wind energy depends on wind produced through changing weather patterns. When placed in high wind locations, wind farms can capture great quantities of energy and is being implemented in many places to offset fossil energy used, as with solar and hydroelectric energy. The top countries who derive the most wind power to meet their energy needs are the Denmark (19.1%), Portugal (11.3%), and Spain (11.1%). The countries with the highest wind power capacity are United States, Germany, and China. One challenge facing wind power is vigorous community resistance to placing turbines nearby. The Not In My Backyard (NIMBY) principle limits areas that are ideal for wind power because of the perceived visual pollution. One solution to this is offshore wind power that does not significantly obscure views while still providing power.
Renewable Energy Policy
Between 1989 and 2004, the European Union and the United States have each spent an average of about 200 million dollars (US) per year on research and development of renewable energy sources. Each member country of the European Union has its own energy strategies. For example wind energy is dominant in Denmark, while Germany has a more diverse renewable energy portfolio involving wind, solar, and biomass. The European Union has a basic renewable energy policy, but it usually defers to each member country to set its own standards. The European Union advocates for research and development, while setting renewable energy goals for its members.
The United States uses much less renewable energy in its energy portfolio than it could. As leadership has changed in 2008 in Congress and in the White House, more attention is paid to renewable energy sources. A bill that has passed the House of Representatives and is currently in the Senate is the American Clean Energy and Security Act of 2009. The bill would create emissions caps that applies to seven greenhouse gases: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride. The goals of the bill for all industries that produce mass amounts of greenhouse gases (over 25,000 tons) are 3% under 2005 levels by 2012, 17% under 2005 levels by 2020, 42% under 2005 levels by 2030, and 83% under 2005 levels by 2050.
When the federal government seemed ineffective, some states implemented their own energy standards. Most notable is California, which has adopted the Renewable Portfolio Standard committing to derive electricity from renewable energy sources, mainly solar power. In addition California and four other states, have committed to a policy mechanism called feed-in tariffs which are designed to promote the use of renewable energy sources. Feed-in tariffs compel electric grid utilities to buy renewable electricity to provide power to its customers.
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