Over the last decade, unprecedented spikes in oil prices have made it clear that our current dependence on polluting, non-renewable fossil fuels is no longer a viable solution to meeting our energy needs. But in the search for energy alternatives, it is sometimes difficult to get a balanced perspective on how practical, clean, or sustainable our energy alternatives really are. Many sources of information are propagated by the industries they support; other sources are promoted by those determined to nay-say every alternative energy option by blowing the drawbacks out or proportion and ignoring the advantages of these options relative to our current fossil fuel dependence. Amid all the noise and competing agendas, it can be difficult to discern the true, scientific facts in their proper context.



Knowing all the facts about our energy options is essential to deciding how we'll power our future. All the energy options in this guide offer significant advantages over our current fossil fuel dependence, but not all are created equal. A myriad of factors must be considered in order to ensure a healthy, sustainable future.

NATURAL GAS:

What it is: Natural gas is a fossil fuel formed when organic matter is exposed to extreme heat and pressure over the course of thousands of years. It is sometimes referred to as shale gas because reserves of natural gas are commonly found in shale formations. Once considered either useless or inaccessible, the popularity of natural gas skyrocketed in the United States in 2008 when the discovery of domestic natural gas reserves and new extraction methods occurred concurrently with unprecedented spikes in gasoline prices

Uses: Natural gas can be used to generate electricity and heat homes. Several cities have converted some or all of their bus fleet to run on natural gas, though high prices and the scarcity of fueling stations have made natural gas passenger vehicles slow to catch on.

Advantages: Frequently referred to as a “clean” gas, natural gas produces greenhouse gas emissions such as carbon dioxide at a much lower level than petroleum. According to the Environmental Protection Agency (EPA), when burned as a fuel, natural gas produces about half the amount of carbon dioxide as coal or oil and less than one third the amount of nitrous oxides. Due to its abundant domestic supply, natural gas is, at present, considerably less expensive than oil.

Disadvantages: The most common and most controversial method of obtaining natural gas is hydraulic fracturing, commonly known as fracking, wherein hard-to-reach gas reserves are accessed by injecting high-pressure streams of fluid into the surrounding rock. Many of the concerns surrounding fracking are identical to those surrounding oil drilling, such as pollution of air and water supplies, destruction of surrounding habitats, and the generation of harmful byproducts. Fracking is particularly alarming, however, in that it has increasingly been associated with earthquakes. In a particularly well-publicized report the Oklahoma Geological Survey examined the connections between fracking activity and a series of roughly 50 earthquakes that occurred near a fracking site in Garvin County in early 2011.

Sustainability: In his 2012 State of the Union address President Obama, citing a projection that was released in 2011 by the Potential Gas Committee, famously declared that the United States has “a supply of natural gas that can last America nearly 100 years.” Since the president's speech, the 100 year claim has been widely questioned. In his comprehensive analysis of the Potential Gas Committee's report, Slate's Chris Nelder explains that that number includes reserves that have not yet been confirmed as viable natural gas sources. The combined proven and probable sources of natural gas would produce a 23-year supply; proven sources contain a supply of a mere 11 years.

Even if one were to take the claim of 100 years worth of energy at face value, 100 years is not really much time, just long enough for today's consumers to pawn the energy problem off on the next generation. And while natural gas prices are comparatively low today, that price is likely to rise as its use becomes more widespread and reserves become depleted. Natural gas is at best a stop-gap measure useful for easing US dependence on foreign oil sources while we seek more sustainable fuel alternatives.

BIOFUELS

What it is: Biofuels are fuels composed of organic materials. The most commonly used biofuels are ethanol, an alcohol-based fuel made from corn, sugar cane, and other plant matter known as feedstocks, and biodiesel, which is composed of plant or animal oils and can even be derived from used cooking grease.

Uses: Biofuels are used to power motor vehicles. They are typically used in the form of a blend of biofuel and fossil fuel. Regular gasoline engines, including small engines such as lawn mowers, can function on a 10% ethanol blend while gasoline engines with a flex fuel option can run on a blend of up to 85% ethanol. According to the U.S. Energy Information Administration, most gasoline sold in the United States contains some amount of ethanol. Biodiesel can be used in a blend or in its pure form, though most vehicle manufacturers approve of blends ranging from 5% - 20% biodiesel. Biodiesel is expected to be increasingly used in jet fuel in the coming decades.

Advantages: One major advantage to biofuels is that they can be incorporated into existing vehicle infrastructure with relative ease. There are some noteworthy environmental advantages to biofuels as well: according to a 2012 study conducted by Swiss Federal Laboratories for Materials and Science Technology (Empa), with only a couple exceptions, fuels derived from plants produce fewer greenhouse gas emissions than their fossil fuel-based counter parts, including natural gas.

Disadvantages: Because the term biofuel refers to a group of fuels rather than one specific type of fuel, it’s difficult to assess the environmental impacts of the group as a whole. The lower greenhouse gas emissions produced from the burning of biofuels are offset somewhat by the fact that the use of biofuels often results in lower fuel economy. According to fueleconomy.gov, the use of both ethanol and biodiesel blends results in decreased mileage.

The bigger biofuel environmental concern, however, relates land use. Many experts believe that any reduction in greenhouse gas emissions resulting from the use of biofuels is negated by the deforestation and tremendous energy consumption needed to grow the crops from which biofuels are derived. Another frequently cited concern is that the cultivation of biofuel crops will threaten world food security by depleting land resources and displacing food crops. The use of algae as a biofuel crop has been proposed as a way to mitigate these problems. A 2010 study published by Environmental Science and Technology, however, found greenhouse gas emissions and energy consumption resulting from algae cultivation to be significantly higher than that of traditional fuel crops.

Sustainability: Despite their drawbacks, biofuels are derived from renewable sources and have great potential to substantially reduce our dependence on fossil fuels, but the technology has a long way to go. More efficient methods of harnessing energy from biomass crops and more sustainable agricultural practices are needed before biofuels can offer significant economic or environmental advantages over petroleum.

BIOGAS

What it is: Biogas is gas emitted when organic matter decomposes in the absence of oxygen in a process known as anaerobic digestion. Common sources of biogas are landfills, waste treatment plants, and manure from agricultural sites. Biogas is composed primarily of methane gas and carbon dioxide. Higher concentrations of methane result in biogas that burns cleaner.

Uses: Biogas can be used to generate heat and electricity and can be distributed through existing natural gas distribution networks. Refined biogas can also be used as fuel in natural gas vehicles.

Advantages: Because sources of biogas are abundant and free it has the potential to serve as a low-cost energy alternative. Projects are underway in several developing nations, including Nepal, Vietnam, Chile, Uganda, and Bangladesh that have the potential to make biogas recovered from latrines and agricultural production a major source of affordable, renewable energy.

Widespread use of biogas as a fuel and energy source has tremendous potential to reduce greenhouse gas emissions, diminish the amount of space needed to store waste, and prevent the deforestation, habitat destruction, and harmful byproducts associated with the mining of fossil fuels. Biogas reduces greenhouse emissions both by displacing fossil fuels and by harnessing the energy of naturally occurring gases that would otherwise contribute to climate change. The main byproduct of biogas refinement is a nutrient-rich sludge that can be used as a natural fertilizer.

The popularity of biogas in developing regions is due in large part to its inexpensiveness. That said, there's no reason developed nations and individual households can't utilize this resource as well. Unlike just about any other means of generating renewable energy (solar panels, geothermal ground pumps, wind turbines, etc), anaerobic digesters can be built using low-tech, inexpensive materials. A video by The Urban Farming Guys demonstrates how to make a homemade biodigester to generate biogas for use in the home.

Disadvantages: As with most fuels, some energy consumption is required to power the biogas refinement process. A comprehensive comparison and analysis of biogas versus natural gas emissions found that natural gas produced fewer carbon emissions than biogas during some stages of the refinement process whereas biogas outperformed natural gas when it came to emissions generated during electricity production. A study comparing the environmental impact of coal usage with biogas usage found that biogas production generated roughly the same amount of carbon emissions or less than its coal counterpart but that unlike coal, these emissions were largely offset by the emissions that were diverted from the atmosphere in order to produce biogas. Substantial emissions from biogas occur primarily during large-scale production and are generally not a concern for individual households.

Sustainability: Biogas is recycling at its best. It is derived from (very) renewable resources and produces a byproduct that benefits the surrounding environment. In all, biogas has enormous potential to replace fossil fuels as an inexpensive, efficient, sustainable, environmentally friendly energy source.

SOLAR POWER

What it is: Solar power is energy harnessed directly from the sun. The most common method of generating solar power is through the use of solar panels composed of photovoltaic (PV) cells which use photons from sunlight to generate energy. Another, less common method of harnessing solar energy through concentrating solar systems, which focus sunlight into concentrated beams to boil liquid and create steam.

Uses: Solar power is used to generate electricity, and for heating and cooling purposes. Solar panels can be installed on both commercial and residential buildings and the energy they generate is integrated into the existing power grid.

Advantages: The advantages of solar power are fairly straightforward; while solar panels can be expensive to purchase and install, they draw energy from a source that's abundant and free without creating any pollution in the process. When a household's solar panels generate more energy than the household consumes, the residence can actually receive credits or even payments from the local utility company as compensation for energy supplied to the power grid.

Disadvantages: Rapid advances in solar technology have done a great deal to mitigate many of the obstacles and drawbacks associated with solar power. For example, high costs and energy consumption used to construct solar panels were once widely cited disadvantages, but recent innovations have resulted in solar panels that work more efficiently and require less energy -- and therefore less money -- to produce.

Despite these advances, environmental difficulties remain. Of particular concern is hazardous waste, namely contaminated water and sludge, generated in the process of manufacturing solar panels. In the absence of on-site waste treatment systems, many solar panel manufactures have to transport this waste to a designated disposal site, thereby contributing to fossil fuel consumption and increasing their carbon footprint. Moreover, solar panels have an estimated lifespan of 20 to 25 years, and it remains to be seen how dead panels will be disposed of.

Solar power can be unreliable, and buildings with solar panels usually still depend on other sources to satisfy their energy needs. The efficiency of solar panels is affected by factors such as pollution and weather and, of course, they only work during daylight hours. Various methods of storing solar energy exist, but their development has been slow, and as a result, these methods are, for the present, not cost-effective. Finally, solar panels work best on a south-facing, relatively flat roofs. Across the country, community solar gardens offer new options for residents whose homes are not well-situated for solar panels, but elsewhere the design and positioning of a house determine whether solar panels are a viable energy option.

Sustainability: Radiation from the sun generates far more direct energy than human beings on this earth will ever need. The sustainability of solar power will ultimately depend on finding solutions for storing solar power and on addressing solar technology's current environmental drawbacks.

HYDROELECTRICITY

What it is: Hydroelectricity is electricity generated by the movement of high volumes of water, usually from a major river, passing through a turbine, which in turn activates an electric generator. Hydroelectric power plants depend on dams to control the flow of water through the turbines.

Uses: Hydropower is used to generate electricity which is distributed via the existing power grid. The United States has been generating hydroelectricity since 1879 when the first hydroelectric plant was built in Niagara Falls. According to the EPA, hydroelectricity currently accounts for nine percent of the United States' electricity supply and a full 20 percent of global electricity, according to National Geographic.

Advantages: The process of generating hydroelectricity does not result in any solid waste, water pollutants, or air pollutants. Once a hydroelectric facility is established, it is able to generate electricity at no cost (not including labor and maintenance), making it the cheapest method of generating electricity according to National Geographic.

Disadvantages: Dams are a crucial element in the process of efficiently harnessing hydropower, but their presence can adversely affect nearby wildlife. Fish populations are particularly vulnerable, as dams can disrupt their migration patterns and alter the temperature and oxygen content of the surrounding water, making it inhospitable to the native aquatic species. Flooding caused by damming often displaces local residents and can destroy wildlife habitats as well.

Like solar power, hydropower is an intermittent energy source, and the ability of hydroelectric plants to generate electricity can be severely limited during periods of drought. Moreover, hydroelectricity is not available everywhere. In order to reap the benefits of hydropower, hydroelectric plants must be located at high elevations where water flows rapidly downstream.

Sustainability: Because hydroelectric plants depend on the movement of water rather than the water itself, the water that passes through hydroelectric turbines is returned unaltered to its source almost immediately. Hydroelectricity plants won't deplete the sources they depend on, but other factors can. Naturally occurring phenomena such as changes in weather patterns, as well as human activities such as agricultural production and deforestation, can threaten a region's hydroelectric capacity by causing once roaring rivers to slow to a trickle or run dry.

WIND POWER

What it is: Wind power uses the same basic principles as hydropower, only it's air movement, rather than water movement, that propels the turbines which convert kinetic energy into electricity. Wind turbines range in height from 30 feet to 20 building stories and are recognizable by their tall, thin structures and rotating propeller-like blades.

Uses: Wind power is used to generate electricity. Wind turbines can be used in much the same way as solar panels, providing electricity to individual residences or grouped together into wind farms to power whole communities. As with solar power, excess electricity generated by wind power can be absorbed into the existing power grid.

Advantages: As with hydropower and solar power, the process of generating electricity from wind results in no carbon emissions, no water pollution, and no solid waste. Wind turbines also take up minimal space and can be located on land that's used concurrently for other purposes such as farmland or livestock grazing.

Disadvantages: The impact of wind turbines on nearby wildlife -- namely flying species such as birds and bats -- is sometimes blown out of proportion. While it's true that these animals are sometimes killed by turbine blades, far more are killed annually by cars, power lines, and skyscrapers. Those who live near wind turbines sometimes complain about the machines' noise and unsightliness.

Like solar power, wind power is a variable energy source; turbines are dependent on the presence of wind to generate electricity. And as with most alternative energy technologies, upfront costs are often an obstacle for homeowners. Technology with the potential to mitigate these problems is constantly evolving, but for the time being both commercial and residential turbines are heavily funded by government incentives, making the cost-effectiveness of wind power a source of debate.

Sustainability: For as long as the sun continues burning, the conditions that create wind will exist on this earth. Our capacity to generate electricity from wind, however, will depend on efficient use of wind turbines. Though it was once assumed that wind power could be increased indefinitely by simply erecting more turbines, recent studies have found that the placement of wind turbines in relation to one another can affect the turbines' energy generating capacity. The presence of the turbines themselves effectively slows air flow, potentially reducing the effectiveness of nearby turbines. When wind farms grow large enough, they can actually alter local air flow patterns.

Because the effective use of wind power is dependent on factors such as weather patterns and turbine positioning and location, (according to Wind Energy Development, some of the best wind sites are located at remote locations far from consumers), it is unlikely that wind power will ever serve as a primary electricity source, but as a supplemental source it can do a great deal to reduce our dependence on non-renewable resources.

GEOTHERMAL ENERGY

What it is: Geothermal energy is heat generated by a layer of magma beneath the earth's crust. Steam is produced in a process known as geothermal convection wherein water seeps into the earth's crust, becomes heated by geothermal activity, and rises back to the surface. Varying degrees of geothermal energy are available just about anywhere, but the regions with the most geothermal energy potential are those located on or around fault lines where seismic activity results in earthquakes, hot springs, geysers, and active volcanoes.

Uses: Geothermal energy can be used to generate electricity, heat water, and power indoor heating and cooling systems. Geothermal power plants, such as the Geysers of California, can meet the electricity needs of thousands of nearby residents. In regions with abundant natural hot springs, the heat from geothermal energy can be accessed directly simply by piping water from these springs into homes and businesses. On a smaller scale, geothermal energy can be accessed through the use of ground source heat pumps which can be used to heat and cool individual residences.

Advantages: Unlike wind and solar energy, access to geothermal energy does not fluctuate as a result of weather patterns or daylight hours. While large scale geothermal energy production can sometimes temporarily exhaust geothermal resources (see “Sustainability”), the amount of energy supplied by the earth's heat generally remains stable and constant.

Disadvantages: The extraction of geothermal heat from underground sources can result in the release of naturally occurring greenhouse gases, such as sulfur dioxide and carbon dioxide, that are found below ground. For example, a typical geothermal power plant releases roughly one eighth the amount of carbon emissions as the typical coal plant. Geothermal power plants sometimes utilize hydraulic fracturing (fracking) methods similar to those used to extract natural gas and which are believed to trigger earthquakes.

The cost of both small and large scale geothermal production can be a major obstacle. According to Energy Informative, the cost of planning and constructing a 1 megawatt (MW) geothermal power plant can run anywhere from $2 - 7 million. To put that in perspective, the Geysers geothermal plant in California has an operating capacity of 725 MW. On a residential scale, ground source pumps can cost between $3,000 and $10,000 to purchase and install. While these pumps can save hundreds of dollars per year in household heating and cooling costs and often pay for themselves within a decade, high upfront costs, relative scarcity of qualified installers, and potential complications with installation can deter many consumers.

Sustainability: According to the Union of Concerned Scientists, “The amount of heat within 10,000 meters (about 33,000 feet) of Earth's surface contains 50,000 times more energy than all the oil and natural gas resources in the world.”

While geothermal heat is a constantly occurring phenomenon, large-scale geothermal energy production can deplete the reserves from which this energy is harvested by removing water faster than it's replaced. To avoid this, many geothermal energy plants re-inject water underground after using it. Because some methods of converting hot water supplies into energy lose a large percentage of this water to evaporation, additional water is sometimes transported from elsewhere to be re-injected at the site.

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Energy generation and distribution are complex processes, and ultimately there is probably no one-size-fits-all solution to meeting the country's -- or the world's -- energy needs. For now, knowledge is power, and the choices we make today will lay the groundwork for a sustainable, environmentally-friendly future.

Sources

Natural Gas:

New York Times. Natural gas.

Oklahoma Geological Survey. 2011. Examination of possibly induced seismicity from hydraulic fracturing in the Eola Field, Garvin County, Oklahoma.

Potential Gas Committee. 2010. Potential supply of natural gas in the United States.

Slate. 2011. What the Frack?

U.S. Environmental Protection Agency. 2013. Natural gas.

2013. Natural gas extraction - Hydraulic fracturing

Biofuel:

Environmental Science and Technology. 2010. Environmental life cycle comparison of algae to other bioenergy feedstocks.

National Geographic. Uses of Biofuel.

Science Daily. 2012. New data on the biofuel ecobalance: most biofuels not 'green.'

Treehugger. 2012. All biofuels are 'nonsense' says Nobel-winning photosynthesis expert Hartmut Michel.

U.S. Department of Energy. 2013. Biodiesel.

2013. Ethanol.

U.S. Energy Information Administration. 2013. FAQs: How much ethanol is in gasoline and how does it affect fuel economy?

U.S. Environmental Protection Agency. 2002. A comprehensive analysis of biodiesel impacts on exhaust emissions.

Worldwatch Institute. 2013. Study: biofuels more efficient as electricity source.

Biogas:

InTech. 2010. Chapter Six: Environmental technology assessment of natural gas compared to biogas. Natural Gas.

IOP Science. 2008. Cow power: the energy and emissions benefits of converting manure to biogas.

Treehugger. 2006. Biogas generation progress in developing nations.

U.S. Department of Energy. 2013. Renewable natural gas (biogas).

Solar Power

Associated Press. 2013. Solar industry grapples with hazardous wastes.

The Energy Collective. 2013. Can energy storage make wind and solar energy as reliable as coal?

Energy Informative. 2012. Solar power pros and cons.

The Guardian. 2010. Are solar panels the next e-waste?

Treehugger. 2008. How does solar energy work?

2011. Clever optical furnace could cut in half the energy required to make solar cells.

Hydroelectricity

National Geographic. Hydropower.

SciDev Net. 2013. Deforestation dries up dams threatening hydropower.

U.S. Environmental Protection Agency. 2013. Hydroelectricity.

Wind Power

National Geographic. Wind power.

2013. Wind power and the thrum of lawsuits.

Treehugger. 2013. Global wind power capacity may be overestimated.

Wind Power Development Programmatic EIS. Wind energy basics.

Geothermal Energy

Energy Informative. 2012. Geothermal energy pros and cons.

Union of Concerned Scientists. 2009. How geothermal energy works.

http://www2.epa.gov/hydraulicfracturing