Alternative energy is any energy source that is an alternative to fossil fuel. These alternatives are intended to address concerns about such fossil fuels, such as its high carbon dioxide emissions, an important factor in global warming. Marine energy, hydroelectric, wind, geothermal and solar power are all alternative sources of energy.
The nature of what constitutes an alternative energy source has changed considerably over time, as have controversies regarding energy use. Because of the variety of energy choices and differing goals of their advocates, defining some energy types as "alternative" is considered very controversial.
|Oxford Dictionary||Energy fueled into ways that do not use up natural resources or harm the environment.|
|Princeton WordNet||Energy derived from sources that do not use up natural resources or harm the environment.|
|Responding to Climate Change 2007||Energy derived from nontraditional sources (e.g., compressed natural gas, solar, hydroelectric, wind).|
|Natural Resources Defense Council||Energy that is not popularly used and is usually environmentally sound, such as solar or wind energy (as opposed to fossil fuels).|
|Materials Management||Fuel sources that are other than those derived from fossil fuels. Typically used interchangeably for renewable energy. Examples include: wind, solar, biomass, wave and tidal energy.|
|Torridge District Council||Energy generated from alternatives to fossil fuels. Need not be renewable.|
Historians of economies have examined the key transitions to alternative energies and regard the transitions as pivotal in bringing about significant economic change. Prior to the shift to an alternative energy, supplies of the dominant energy type became erratic, accompanied by rapid increases in energy prices.
Coal as an alternative to wood
In the late medieval period, coal was the new alternative fuel to save the society from overuse of the dominant fuel, wood. The deforestation had resulted in shortage of wood, at that time soft coal appeared as a savior. Historian Norman F. Cantor describes how:
- "Europeans had lived in the midst of vast forests throughout the earlier medieval centuries. After 1250 they became so skilled at deforestation that by 1500 AD they were running short of wood for heating and cooking... By 1500 Europe was on the edge of a fuel and nutritional disaster, [from] which it was saved in the sixteenth century only by the burning of soft coal and the cultivation of potatoes and maize."
Petroleum as an alternative to whale oil
Whale oil was the dominant form of lubrication and fuel for lamps in the early 19th century, but the depletion of the whale stocks by mid century caused whale oil prices to skyrocket setting the stage for the adoption of petroleum which was first commercialized in Pennsylvania in 1859.
Ethanol as an alternative to fossil fuels
Main article: Ethanol fuel
In 1917, Alexander Graham Bell advocated ethanol from corn, wheat and other foods as an alternative to coal and oil, stating that the world was in measurable distance of depleting these fuels. For Bell, the problem requiring an alternative was lack of renewability of orthodox energy sources. Since the 1970s, Brazil has had an ethanol fuel program which has allowed the country to become the world's second largest producer of ethanol (after the United States) and the world's largest exporter. Brazil’s ethanol fuel program uses modern equipment and cheap sugar cane as feedstock, and the residual cane-waste (bagasse) is used to process heat and power. There are no longer light vehicles in Brazil running on pure gasoline. By the end of 2008 there were 35,000 filling stations throughout Brazil with at least one ethanol pump.
Cellulosic ethanol can be produced from a diverse array of feedstocks, and involves the use of the whole crop. This new approach should increase yields and reduce the carbon footprint because the amount of energy-intensive fertilizers and fungicides will remain the same, for a higher output of usable material. As of 2008, there are nine commercial cellulosic ethanol plants which are either operating, or under construction, in the United States.
Second-generation biofuels technologies are able to manufacture biofuels from inedible biomass and could hence prevent conversion of food into fuel." As of July 2010, there is one commercial second-generation (2G) ethanol plant Inbicon Biomass Refinery, which is operating in Denmark.
Coal gasification as an alternative to petroleum
In the 1970s, President Jimmy Carter's administration advocated coal gasification as an alternative to expensive imported oil. The program, including the Synthetic Fuels Corporation was scrapped when petroleum prices plummeted in the 1980s. The carbon footprint and environmental impact of coal gasification are both very high.
Existing types of alternative energy
- Hydro electricity captures energy from falling water.
- Nuclear energy uses nuclear fission to release energy stored in the atomic bonds of heavy elements.
- Wind energy is the generation of electricity from wind, commonly by using propeller-like turbines.
- Solar energy is the use of sunlight. Light can be changed into thermal (heat) energy or directly into electricity via photovoltaic devices.
- Geothermal energy is the use of the earth's internal heat to boil water for heating buildings or generating electricity.
- Biofuel and ethanol are plant-derived gasoline substitutes for powering vehicles.
- Hydrogen can be used as a carrier of energy, produced by various technologies such as cracking of hydrocarbons or water electrolysis.
Ice storage air conditioning and thermal storage heaters are methods of shifting consumption to use low cost off-peak electricity. When compared to resistance heating, heat pumps conserve electrical power (or in rare cases mechanical or thermal power) by collecting heat from a cool source such as a body of water, the ground or the air.
Thermal storage technologies allow heat or cold to be stored for periods of time ranging from diurnal to interseasonal, and can involve storage of sensible energy (i.e. by changing the temperature of a medium) or latent energy (e.g. through phase changes of a medium (i.e. changes from solid to liquid or vice versa), such as between water and slush or ice). Energy sources can be natural (via solar-thermal collectors, or dry cooling towers used to collect winter's cold), waste energy (such as from HVAC equipment, industrial processes or power plants), or surplus energy (such as seasonally from hydropower projects or intermittently from wind farms). The Drake Landing Solar Community (Alberta, Canada) is illustrative. Borehole thermal energy storage allows the community to get 97% of its year-round heat from solar collectors on the garage roofs. The storages can be insulated tanks, borehole clusters in substrates ranging from gravel to bedrock, deep aquifers, or shallow pits that are lined and insulated. Some applications require inclusion of a heat pump.
Renewable energy vs non-renewable energy
Main article: Renewable energy
Renewable energy is generated from natural resources—such as sunlight,wind, rain, tides and geothermal heat—which are renewable (naturally replenished). When comparing the processes for producing energy, there remain several fundamental differences between renewable energy and fossil fuels. The process of producing oil, coal, or natural gas fuel is a difficult and demanding process that requires a great deal of complex equipment, physical and chemical processes. On the other hand, alternative energy can be widely produced with basic equipment and natural processes. Wood, the most renewable and available alternative fuel, emits the same amount of carbon when burned as would be emitted if it degraded naturally. Nuclear power is an alternative to fossil fuels that is non-renewable, like fossil fuels, nuclear ones are a finite resource.
Ecologically friendly alternatives
A renewable energy source such as biomass is sometimes regarded as a good alternative to providing heat and electricity with fossil fuels. Biofuels are not inherently ecologically friendly for this purpose, while burning biomass is carbon-neutral, air pollution is still produced. For example, the Netherlands, once leader in use of palm oil as a biofuel, has suspended all subsidies for palm oil due to the scientific evidence that their use "may sometimes create more environmental harm than fossil fuels". The Netherlands government and environmental groups are trying to trace the origins of imported palm oil, to certify which operations produce the oil in a responsible manner. Regarding biofuels from foodstuffs, the realization that converting the entire grain harvest of the US would only produce 16% of its auto fuel needs, and the decimation of Brazil's CO2 absorbing tropical rain forests to make way for biofuel production has made it clear that placing energy markets in competition with food markets results in higher food prices and insignificant or negative impact on energy issues such as global warming or dependence on foreign energy. Recently, alternatives to such undesirable sustainable fuels are being sought, such as commercially viable sources of cellulosic ethanol.
Relatively new concepts for alternative energy
Carbon-neutral and negative fuels
Main articles: Carbon-neutral fuel and Methanol economy
Carbon-neutral fuels are synthetic fuels (including methane, gasoline, diesel fuel, jet fuel or ammonia) produced by hydrogenating waste carbon dioxide recycled from power plant flue-gas emissions, recovered from automotive exhaust gas, or derived from carbonic acid in seawater. Commercial fuel synthesis companies suggest they can produce synthetic fuels for less than petroleum fuels when oil costs more than $55 per barrel. Renewable methanol (RM) is a fuel produced from hydrogen and carbon dioxide by catalytic hydrogenation where the hydrogen has been obtained from water electrolysis. It can be blended into transportation fuel or processed as a chemical feedstock.
The George Olah carbon dioxide recycling plant operated by Carbon Recycling International in Grindavík, Iceland has been producing 2 million liters of methanol transportation fuel per year from flue exhaust of the Svartsengi Power Station since 2011. It has the capacity to produce 5 million liters per year. A 250 kilowatt methane synthesis plant was constructed by the Center for Solar Energy and Hydrogen Research (ZSW) at Baden-Württemberg and the Fraunhofer Society in Germany and began operating in 2010. It is being upgraded to 10 megawatts, scheduled for completion in autumn, 2012.Audi has constructed a carbon-neutral liquefied natural gas (LNG) plant in Werlte, Germany. The plant is intended to produce transportation fuel to offset LNG used in their A3 Sportback g-tron automobiles, and can keep 2,800 metric tons of CO2 out of the environment per year at its initial capacity. Other commercial developments are taking place in Columbia, South Carolina,Camarillo, California, and Darlington, England.
Such fuels are considered carbon-neutral because they do not result in a net increase in atmospheric greenhouse gases. To the extent that synthetic fuels displace fossil fuels, or if they are produced from waste carbon or seawater carbonic acid, and their combustion is subject to carbon capture at the flue or exhaust pipe, they result in negative carbon dioxide emission and net carbon dioxide removal from the atmosphere, and thus constitute a form of greenhouse gas remediation.
Such renewable fuels alleviate the costs and dependency issues of imported fossil fuels without requiring either electrification of the vehicle fleet or conversion to hydrogen or other fuels, enabling continued compatible and affordable vehicles. Carbon-neutral fuels offer relatively low cost energy storage, alleviating the problems of wind and solar intermittency, and they enable distribution of wind, water, and solar power through existing natural gas pipelines.
Nighttime wind power is considered the most economical form of electrical power with which to synthesize fuel, because the load curve for electricity peaks sharply during the day, but wind tends to blow slightly more at night than during the day, so, the price of nighttime wind power is often much less expensive than any alternative. Germany has built a 250 kilowatt synthetic methane plant which they are scaling up to 10 megawatts.
Algae fuel is a biofuel which is derived from algae. During photosynthesis, algae and other photosynthetic organisms capture carbon dioxide and sunlight and convert it into oxygen and biomass. This is usually done by placing the algae between two panes of glass. The algae creates three forms of energy fuel: heat (from its growth cycle), biofuel (the natural "oil" derived from the algae), and biomass (from the algae itself, as it is harvested upon maturity).
The heat can be used to power building systems (such as heat process water) or to produce energy. Biofuel is oil extracted from the algae upon maturity, and used to create energy similar to the use of biodiesel. The biomass is the matter left over after extracting the oil and water, and can be harvested to produce combustible methane for energy production, similar to the warmth felt in a compost pile or the methane collected from biodegradable materials in a landfill. Additionally, the benefits of algae biofuel are that it can be produced industrially, as well as vertically (i.e. as a building facade), thereby obviating the use of arable land and food crops (such as soy, palm, and canola).
Biomass briquettes are being developed in the developing world as an alternative to charcoal. The technique involves the conversion of almost any plant matter into compressed briquettes that typically have about 70% the calorific value of charcoal. There are relatively few examples of large scale briquette production. One exception is in North Kivu, in eastern Democratic Republic of Congo, where forest clearance for charcoal production is considered to be the biggest threat to Mountain Gorilla habitat. The staff of Virunga National Park have successfully trained and equipped over 3500 people to produce biomass briquettes, thereby replacing charcoal produced illegally inside the national park, and creating significant employment for people living in extreme poverty in conflict affected areas. 
Biogas digestion deals with harnessing the methane gas that is released when waste breaks down. This gas can be retrieved from garbage or sewage systems. Biogas digesters are used to process methane gas by having bacteria break down biomass in an anaerobic environment.  The methane gas that is collected and refined can be used as an energy source for various products.
Biological hydrogen production
Hydrogen gas is a completely clean burning fuel; its only by-product is water. It also contains relatively high amount of energy compared with other fuels due to its chemical structure.
2H2 + O2 → 2H2O + High Energy
High Energy + 2H2O → 2H2 + O2
This requires a high-energy input, making commercial hydrogen very inefficient. Use of a biological vector as a means to split water, and therefore produce hydrogen gas, would allow for the only energy input to be solar radiation. Biological vectors can include bacteria or more commonly algae. This process is known as biological hydrogen production. It requires the use of single celled organisms to create hydrogen gas through fermentation. Without the presence of oxygen, also known as an anaerobic environment, regular cellular respiration cannot take place and a process known as fermentation takes over. A major by-product of this process is hydrogen gas. If this could be implemented on a large scale, then sunlight, nutrients and water could create hydrogen gas to be used as a dense source of energy. Large-scale production has proven difficult. Not until 1999, was it even possible to induce these anaerobic conditions by sulfur deprivation. Since the fermentation process is an evolutionary back up, turned on during stress, the cells would die after a few days. In 2000, a two-stage process was developed to take the cells in and out of anaerobic conditions and therefore keep them alive. For the last ten years, finding a way to do this on a large-scale has been the main goal of research. Careful work is being done to ensure an efficient process before large-scale production, however once a mechanism is developed, this type of production could solve our energy needs.
Main article: Hydroelectricity
Hydroelectricity provided 75% of the worlds renewable electricity in 2013. Much of the electricity used today is a result of the heyday of conventional hydroelectric development between 1960 and 1980, which has virtually ceased in Europe and North America due to environmental concerns. Globally there is a trend towards more hydroelectricity. From 2004 to 2014 the installed capacity rose from 715 to 1,055 GW. A popular alternative to the large dams of the past is run-of-the-river where there is no water stored behind a dam and generation usually varies with seasonal rainfall. Using run-of-the-river in wet seasons and solar in dry seasons can balance seasonal variations for both. Another move away from large dams is small hydro, these tend to be situated high up on tributaries, rather than on main rivers in valley bottoms.
Offshore wind farms are similar to land-based wind farms, but are located on the ocean. Offshore wind farms can be placed in water up to 40 metres (130 ft) deep, whereas floating wind turbines can float in water up to 700 metres (2,300 ft) deep. The advantage of having a floating wind farm is to be able to harness the winds from the open ocean. Without any obstructions such as hills, trees and buildings, winds from the open ocean can reach up to speeds twice as fast as coastal areas.
Significant generation of offshore wind energy already contributes to electricity needs in Europe and Asia and now the first offshore wind farms are under development in U.S. waters. While the offshore wind industry has grown dramatically over the last several decades, especially in Europe, there is still uncertainty associated with how the construction and operation of these wind farms affect marine animals and the marine environment.
Traditional offshore wind turbines are attached to the seabed in shallower waters within the nearshore marine environment. As offshore wind technologies become more advanced, floating structures have begun to be used in deeper waters where more wind resources exist.
Marine and hydrokinetic energy
Marine and Hydrokinetic (MHK) or marine energy development includes projects using the following devices:
- Wave power is the transport of energy by wind waves, and the capture of that energy to do useful work – for example, electricity generation or pumping water into reservoirs. A machine able to exploit significant waves in open coastal areas is generally known as a wave energy converter.
- Tidal power turbines are placed in coastal and estuarine areas and daily flows are quite predictable.
- In-stream turbines in fast-moving rivers
- Ocean current turbines in areas of strong marine currents
- Ocean thermal energy converters in deep tropical waters.
In the year 2015 ten new reactors came online and 67 more were under construction including the first eight new Generation III+ AP1000 reactors in the US and China and the first four new Generation III EPR reactors in Finland, France and China. Reactors are also under construction in Belarus, Brazil, India, Iran, Japan, Pakistan, Russia, Slovakia, South Korea, Turkey, Ukraine and United Arab Emirates.
Thorium nuclear power
Main article: Thorium fuel cycle
Further information on power production see: Thorium-based nuclear power
Thorium is a fissionable material for possible future use in a thorium-based reactor. Proponents of thorium reactors claims several potential advantages over a uranium fuel cycle, such as thorium's greater abundance, better resistance to nuclear weapons proliferation, and reduced plutonium and actinide production. Thorium reactors can be modified to produce Uranium-233, which can then be processed into highly enriched uranium, which has been tested in low yield weapons, and is unproven on a commercial scale.
Investing in alternative energy
As an emerging economic sector, there are limited stock market investment opportunities in alternative energy available to the general public. The public can buy shares of alternative energy companies from various stock markets, with wildly volatile returns. The recent IPO of SolarCity demonstrates the nascent nature of this sector- within a few weeks, it already had achieved the second highest market cap within the alternative energy sector.
Investors can also choose to invest in ETFs (exchange-traded funds) that track an alternative energy index, such as the WilderHill New Energy Index. Additionally, there are a number of mutual funds, such as Calvert's Global Alternative Energy Mutual Fund that are a bit more proactive in choosing the selected investments.
Recently, Mosaic Inc. launched an online platform allowing residents of California and New York to invest directly in solar. Investing in solar projects had previously been limited to accredited investors, or a small number of willing banks.
Over the last three years publicly traded alternative energy companies have been very volatile, with some 2007 returns in excess of 100%, some 2008 returns down 90% or more, and peak-to-trough returns in 2009 again over 100%. In general there are three sub-segments of “alternative” energy investment: solar energy, wind energy and hybrid electric vehicles. Alternative energy sources which are renewable and have lower carbon emissions than fossil fuels are hydropower, wind energy, solar energy, geothermal energy, and bio fuels. Each of these four segments involve very different technologies and investment concerns.
For example, photovoltaic solar energy is based on semiconductor processing and accordingly, benefits from steep cost reductions similar to those realized in the microprocessor industry (i.e., driven by larger scale, higher module efficiency, and improving processing technologies). PV solar energy is perhaps the only energy technology whose electricity generation cost could be reduced by half or more over the next five years. Better and more efficient manufacturing process and new technology such as advanced thin film solar cell is a good example of that helps to reduce industry cost.
The economics of solar PV electricity are highly dependent on silicon pricing and even companies whose technologies are based on other materials (e.g., First Solar) are impacted by the balance of supply and demand in the silicon market. In addition, because some companies sell completed solar cells on the open market (e.g., Q-Cells), this creates a low barrier to entry for companies that want to manufacture solar modules, which in turn can create an irrational pricing environment.
In contrast, because wind power has been harnessed for over 100 years, its underlying technology is relatively stable. Its economics are largely determined by siting (e.g., how hard the wind blows and the grid investment requirements) and the prices of steel (the largest component of a wind turbine) and select composites (used for the blades). Because current wind turbines are often in excess of 100 meters high, logistics and a global manufacturing platform are major sources of competitive advantage. These issues and others were explored in a research report by Sanford Bernstein.
Alternative energy in transportation
Due to steadily rising gas prices in 2008 with the US national average price per gallon of regular unleaded gas rising above $4.00 at one point, there has been a steady movement towards developing higher fuel efficiency and more alternative fuel vehicles for consumers. In response, many smaller companies have rapidly increased research and development into radically different ways of powering consumer vehicles. Hybrid and battery electric vehicles are commercially available and are gaining wider industry and consumer acceptance worldwide.
For example, Nissan USA introduced the world's first mass-production electric vehicle, the Nissan Leaf. A plug-in hybrid car, the Chevrolet Volt also has been produced, using an electric motor to drive the wheels, and a small four-cylinder engine to generate additional electricity.
Making alternative energy mainstream
Before alternative energy becomes mainstream there are a few crucial obstacles that it must overcome. First there must be increased understanding of how alternative energies are beneficial; secondly the availability components for these systems must increase; and lastly the pay-back period must be decreased.
For example, electric vehicles (EV) and plug-in hybrid electric vehicles (PHEV) are on the rise. These vehicles depend on investment in home and public charging infrastructure, as well as implementing much more alternative energy for future transportation.
There are numerous organizations within the academic, federal, and commercial sectors conducting large scale advanced research in the field of alternative energy. This research spans several areas of focus across the alternative energy spectrum. Most of the research is targeted at improving efficiency and increasing overall energy yields.
In the US, multiple federally supported research organizations have focused on alternative energy in recent years. Two of the most prominent of these labs are Sandia National Laboratories and the National Renewable Energy Laboratory (NREL), both of which are funded by the United States Department of Energy and supported by various corporate partners. Sandia has a total budget of $2.4 billion while NREL has a budget of $375 million.
With the increasing consumption levels of energy, it is projected that the levels would increase by 21% in 2030. The cost of the renewables was relatively cheaper at $2.5m/MW as compared to the non-renewables & 2.7m/MW. Evidently, the use of renewable energy is a cost effective method of obtaining energy. Additionally, their use also dispenses with the trade-off that has existed between environmental conservation and economic growth.
Mechanical energy associated with human activities such as blood circulation, respiration, walking, typing and running, is ubiquitous but usually wasted. It has attracted tremendous attention from researchers around the globe to find methods to scavenge such mechanical energies. The best solution currently is to use piezoelectric materials, which can generate flow of electrons when deformed. Various devices using piezoelectric materials have been built to scavenge mechanical energy. Considering that the piezoelectric constant of the material plays a critical role in the overall performance of a piezoelectric device, one critical research direction to improve device efficiency is to find new material of large piezoelectric response. Lead Magnesium Niobate-Lead Titanate (PMN-PT) is a next-generation piezoelectric material with super high piezoelectric constant when ideal composition and orientation are obtained. In 2012, PMN-PT Nanowires with a very high piezoelectric constant were fabricated by a hydro-thermal approach and then assembled into an energy-harvesting device. The record-high piezoelectric constant was further improved by the fabrication of a single-crystal PMN-PT nanobelt, which was then used as the essential building block for a piezoelectric nanogenerator.
Main article: Solar energy
Solar energy can be used for heating, cooling or electrical power generation using the sun.
Solar heat has long been employed in passively and actively heated buildings, as well as district heating systems. Examples of the latter are the Drake Landing Solar Community is Alberta, Canada and numerous district systems in Denmark and Germany. In Europe, there are two programs for the application of solar heat: the Solar District Heating (SDH) and the International Energy Agency's Solar Heating and Cooling (SHC) program.
The obstacles preventing the large scale implementation of solar powered energy generation is the inefficiency of current solar technology, and the cost. Currently, photovoltaic (PV) panels only have the ability to convert around 16% of the sunlight that hits them into electricity.
Both Sandia National Laboratories and the National Renewable Energy Laboratory (NREL), have heavily funded solar research programs. The NREL solar program has a budget of around $75 million and develops research projects in the areas of photovoltaic (PV) technology, solar thermal energy, and solar radiation. The budget for Sandia’s solar division is unknown, however it accounts for a significant percentage of the laboratory’s $2.4 billion budget.
Several academic programs have focused on solar research in recent years. The Solar Energy Research Center (SERC) at University of North Carolina (UNC) has the sole purpose of developing cost effective solar technology. In 2008, researchers at Massachusetts Institute of Technology (MIT) developed a method to store solar energy by using it to produce hydrogen fuel from water. Such research is targeted at addressing the obstacle that solar development faces of storing energy for use during nighttime hours when the sun is not shining. The Zhangebei National Wind and Solar Energy Storage and Transmission Demonstration Project northwest of Beijing, uses batteries to store 71 MWh, integrating wind and solar energy on the grid with frequency and voltage regulation.
In February 2012, North Carolina-based Semprius Inc., a solar development company backed by German corporation Siemens, announced that they had developed the world’s most efficient solar panel. The company claims that the prototype converts 33.9% of the sunlight that hits it to electricity, more than double the previous high-end conversion rate.
Main article: Wind power
Wind energy research dates back several decades to the 1970s when NASA developed an analytical model to predict wind turbine power generation during high winds. Today, both Sandia National Laboratories and National Renewable Energy Laboratory have programs dedicated to wind research. Sandia’s laboratory focuses on the advancement of materials, aerodynamics, and sensors. The NREL wind projects are centered on improving wind plant power production, reducing their capital costs, and making wind energy more cost effective overall.
The Field Laboratory for Optimized Wind Energy (FLOWE) at Caltech was established to research alternative approaches to wind energy farming technology practices that have the potential to reduce the cost, size, and environmental impact of wind energy production.
Renewable energies such as wind, solar, biomass and geothermal combined, supplied 1.3% of global final energy consumption in 2013.
Main articles: Biomass and Biogas
Biomass can be regarded as "biological material" derived from living, or recently living organisms. It most often refers to plants or plant-derived materials which are specifically called lignocellulosic biomass. As an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into: thermal, chemical, and biochemical methods. Wood remains the largest biomass energy source today; examples include forest residues (such as dead trees, branches and tree stumps), yard clippings, wood chips and even municipal solid waste. In the second sense, biomass includes plant or animal matter that can be converted into fibers or other industrial chemicals, including biofuels. Industrial biomass can be grown from numerous types of plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane, bamboo, and a variety of tree species, ranging from eucalyptus to oil palm (palm oil).
Biomass, biogas and biofuels are burned to produce heat/power and in doing so harm the environment. Pollutants such as sulphurous oxides (SOx), nitrous oxides (NOx), and particulate matter (PM) are produced from this combustion. The World Health Organisation estimates that 7 million premature deaths are caused each year by air pollution, and biomass combustion is a major contributor of it. The use of biomas is carbon neutral over time, but is otherwise similar to burning fossil fuels.
Main article: Ethanol biofuels
As the primary source of biofuels in North America, many organizations are conducting research in the area of ethanol production. On the Federal level, the USDA conducts a large amount of research regarding ethanol production in the United States. Much of this research is targeted toward the effect of ethanol production on domestic food markets.
The National Renewable Energy Laboratory has conducted various ethanol research projects, mainly in the area of cellulosic ethanol.Cellulosic ethanol has many benefits over traditional corn based-ethanol. It does not take away or directly conflict with the food supply because it is produced from wood, grasses, or non-edible parts of plants. Moreover, some studies have shown cellulosic ethanol to be more cost effective and economically sustainable than corn-based ethanol.Sandia National Laboratories conducts in-house cellulosic ethanol research and is also a member of the Joint BioEnergy Institute (JBEI), a research institute founded by the United States Department of Energy with the goal of developing cellulosic biofuels.
Main article: Biofuel
From 1978 to 1996, the National Renewable Energy Laboratory experimented with using algae as a biofuels source in the "Aquatic Species Program.” A self-published article by Michael Briggs, at the University of New Hampshire Biofuels Group, offers estimates for the realistic replacement of all motor vehicle fuel with biofuels by utilizing algae that have a natural oil content greater than 50%, which Briggs suggests can be grown on algae ponds at wastewater treatment plants. This oil-rich algae can then be extracted from the system and processed into biofuels, with the dried remainder further reprocessed to create ethanol.
The production of algae to harvest oil for biofuels has not yet been undertaken on a commercial scale, but feasibility studies have been conducted to arrive at the above yield estimate. In addition to its projected high yield, algaculture— unlike food crop-based biofuels — does not entail a decrease in food production, since it requires neither farmland nor fresh water. Many companies are pursuing algae bio-reactors for various purposes, including scaling up biofuels production to commercial levels.
Several groups in various sectors are conducting research on Jatropha curcas, a poisonous shrub-like tree that produces seeds considered by many to be a viable source of biofuels feedstock oil. Much of this research focuses on improving the overall per acre oil yield of Jatropha through advancements in genetics, soil science, and horticultural practices. SG Biofuels, a San Diego-based Jatropha developer, has used molecular breeding and biotechnology to produce elite hybrid seeds of Jatropha that show significant yield improvements over first generation varieties. The Center for Sustainable Energy Farming (CfSEF) is a Los Angeles-based non-profit research organization dedicated to Jatropha research in the areas of plant science, agronomy, and horticulture. Successful exploration of these disciplines is projected to increase Jatropha farm production yields by 200-300% in the next ten years.
Main article: Geothermal electricity
Geothermal energy is produced by tapping into the heat within the earths crust. It is considered sustainable because that thermal energy is constantly replenished. However, the science of geothermal energy generation is still young and developing economic viability. Several entities, such as the National Renewable Energy Laboratory and Sandia National Laboratories are conducting research toward the goal of establishing a proven science around geothermal energy. The International Centre for Geothermal Research (IGC), a German geosciences research organization, is largely focused on geothermal energy development research.
Main article: Hydrogen fuel
Over $1 billion has been spent on the research and development of hydrogen fuel in the United States. Both the National Renewable Energy Laboratory and Sandia National Laboratories have departments dedicated to hydrogen research. Much of this work centers on hydrogen storage and fuel cell technologies
Further information: Renewable energy debate, Disadvantages of hydroelectricity, Tidal power § Tidal power issues, and Issues relating to biofuels
The generation of alternative energy on the scale needed to replace fossil energy, in an effort to reverse global climate change, is likely to have significant negative environmental impacts. For example, biomass energy generation would have to increase 7-fold to supply current primary energy demand, and up to 40-fold by 2100 given economic and energy growth projections. Humans already appropriate 30 to 40% of all photosynthetically fixed carbon worldwide, indicating that expansion of additional biomass harvesting is likely to stress ecosystems, in some cases precipitating collapse and extinction of animal species that have been deprived of vital food sources. The total amount of energy capture by vegetation in the United States each year is around 58 quads (61.5 EJ), about half of which is already harvested as agricultural crops and forest products. The remaining biomass is needed to maintain ecosystem functions and diversity. Since annual energy use in the United States is ca. 100 quads, biomass energy could supply only a very small fraction. To supply the current worldwide energy demand solely with biomass would require more than 10% of the Earth’s land surface, which is comparable to the area use for all of world agriculture (i.e., ca. 1500 million hectares), indicating that further expansion of biomass energy generation will be difficult without precipitating an ethical conflict, given current world hunger statistics, over growing plants for biofuel versus food.
Given environmental concerns (e.g., fish migration, destruction of sensitive aquatic ecosystems, etc.) about building new dams to capture hydroelectric energy, further expansion of conventional hydropower in the United States is unlikely. Windpower, if deployed on the large scale necessary to substitute fossil energy, is likely to face public resistance. If 100% of U.S. energy demand were to be supplied by windmills, about 80 million hectares (i.e., more than 40% of all available farmland in the United States) would have to be covered with large windmills (50m hub height and 250 to 500 m apart). It is therefore not surprising that the major environmental impact of wind power is related to land use and less to wildlife (birds, bats, etc.) mortality. Unless only a relatively small fraction of electricity is generated by windmills in remote locations, it is unlikely that the public will tolerate large windfarms given concerns about blade noise and aesthetics.
Biofuels are different from fossil fuels in regard to net greenhouse gases but are similar to fossil fuels in that biofuels contribute to air pollution. Burning produces airborne carbon particulates, carbon monoxide and nitrous oxides.
Renewable alternative forms of energy have faced opposition from multiple groups, including conservatives and liberals. Around twelve states have passed proposals written to inhibit the alternative energy movement. Kansas lawmakers struck down a bill to phase out renewable energy mandates but face the possibility of the bill reappearing.
The opposition cites the potentially high cost of branching out to these alternatives in order to support the continuation and reliance on fossil fuels. Ohio's mandate to phase in alternative energy faces opposition who believe higher electricity prices will result, while supporters fear the loss of economic development and jobs that alternative energy could bring.
With nuclear meltdowns in Chernobyl and Fukushima, nuclear power presents a constant danger and is more unlikely to be a popular alternative source. The costs of maintaining nuclear facilities, the potential risk of meltdowns, and the cost of cleaning up meltdowns are cited as reasons behind the movement away from the use of nuclear energy. In some countries nuclear power plants cannot compete with fossil fuels currently due to the latter's lower price and availability. Nuclear power plants also face competition from the increasing renewable energy subsidies.
Alternative fuels, known as non-conventional and advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels like; fossil fuels (petroleum (oil), coal, and natural gas), as well as nuclear materials such as uranium and thorium, as well as artificial radioisotope fuels that are made in nuclear reactors.
Some well-known alternative fuels include biodiesel, bioalcohol (methanol, ethanol, butanol), refuse-derived fuel, chemically stored electricity (batteries and fuel cells), hydrogen, non-fossil methane, non-fossil natural gas, vegetable oil, propane and other biomass sources.
The main purpose of fuel is to store energy, which should be in a stable form and can be easily transported to the place of use.
Almost all fuels are chemical fuels. The user employs this fuel to generate heat or perform mechanical work, such as powering an engine. It may also be used to generate electricity, which is then used for heating, lighting, or other purpose.
Main article: Biofuel
Biofuels are also considered a renewable source. Although renewable energy is used mostly to generate electricity, it is often assumed that some form of renewable energy or a percentage is used to create alternative fuels. Research is ongoing into finding more suitable biofuel crops and improving the oil yields of these crops. Using the current yields, vast amounts of land and fresh water would be needed to produce enough oil to completely replace fossil fuel usage.
Main article: Biomass
Biomass in the energy production industry is living and recently dead biological material which can be used as fuel or for industrial production. It has become popular among coal power stations, which switch from coal to biomass in order to convert to renewable energy generation without wasting existing generating plant and infrastructure. Biomass most often refers to plants or plant-based materials that are not used for food or feed, and are specifically called lignocellulosic biomass. As an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel.
Main article: Algae fuel
Algae-based biofuels have been promoted in the media as a potential panacea to crude oil-based transportation problems. Algae could yield more than 2000 gallons of fuel per acre per year of production. Algae based fuels are being successfully tested by the U.S. Navy Algae-based plastics show potential to reduce waste and the cost per pound of algae plastic is expected to be cheaper than traditional plastic prices.
Biodiesel is made from animal fats or vegetable oils, renewable resources that come from plants such as jatropha, soybean, sunflowers, corn, olive, peanut, palm, coconut, safflower, canola, sesame, cottonseed, etc. Once these fats or oils are filtered from their hydrocarbons and then combined with alcohol like methanol, biodiesel is brought to life[clarification needed] from this chemical reaction. These raw materials can either be mixed with pure diesel to make various proportions, or used alone. Despite one’s mixture preference, biodiesel will release smaller number of pollutants (carbon monoxide particulates and hydrocarbons) than conventional diesel, because biodiesel burns both cleanly and more efficiently. Even with regular diesel’s reduced quantity of sulfur from the ULSD (ultra-low sulfur diesel) invention, biodiesel exceeds those levels because it is sulfur-free.
Main articles: Alcohol fuel, Butanol fuel, Ethanol fuel, and Methanol fuel
Methanol and ethanol fuel are primary sources of energy; they are convenient fuels for storing and transporting energy. These alcohols can be used in internal combustion engines as alternative fuels. Butanol has another advantage: it is the only alcohol-based motor fuel that can be transported readily by existing petroleum-product pipeline networks, instead of only by tanker trucks and railroad cars.
Ammonia (NH3) can be used as fuel. Benefits of ammonia include no need for oil, zero emissions, low cost, and distributed production reducing transport and related pollution.
Carbon-neutral and negative fuels
Carbon neutral fuel is synthetic fuel—such as methane, gasoline, diesel fuel or jet fuel—produced from renewable or nuclear energy used to hydrogenate waste carbon dioxide recycled from power plant flueexhaust gas or derived from carbonic acid in seawater. Such fuels are potentially carbon neutral because they do not result in a net increase in atmospheric greenhouse gases. To the extent that carbon neutral fuels displace fossil fuels, or if they are produced from waste carbon or seawater carbonic acid, and their combustion is subject to carbon capture at the flue or exhaust pipe, they result in negative carbon dioxide emission and net carbon dioxide removal from the atmosphere, and thus constitute a form of greenhouse gas remediation. Such carbon neutral and negative fuels can be produced by the electrolysis of water to make hydrogen used in the Sabatier reaction to produce methane which may then be stored to be burned later in power plants as synthetic natural gas, transported by pipeline, truck, or tanker ship, or be used in gas to liquids processes such as the Fischer–Tropsch process to make traditional transportation or heating fuels.
Carbon-neutral fuels have been proposed for distributed storage for renewable energy, minimizing problems of wind and solar intermittency, and enabling transmission of wind, water, and solar power through existing natural gas pipelines. Such renewable fuels could alleviate the costs and dependency issues of imported fossil fuels without requiring either electrification of the vehicle fleet or conversion to hydrogen or other fuels, enabling continued compatible and affordable vehicles. Germany has built a 250-kilowatt synthetic methane plant which they are scaling up to 10 megawatts.Audi has constructed a carbon neutral liquefied natural gas (LNG) plant in Werlte, Germany. The plant is intended to produce transportation fuel to offset LNG used in their A3 Sportback g-tron automobiles, and can keep 2,800 metric tons of CO2 out of the environment per year at its initial capacity. Other commercial developments are taking place in Columbia, South Carolina,Camarillo, California, and Darlington, England.
The least expensive source of carbon for recycling into fuel is flue-gas emissions from fossil-fuel combustion, where it can be extracted for about US $7.50 per ton. Automobile exhaust gas capture has also been proposed to be economical but would require extensive design changes or retrofitting. Since carbonic acid in seawater is in chemical equilibrium with atmospheric carbon dioxide, extraction of carbon from seawater has been studied. Researchers have estimated that carbon extraction from seawater would cost about $50 per ton.Carbon capture from ambient air is more costly, at between $600 and $1000 per ton and is considered impractical for fuel synthesis or carbon sequestration.
Nighttime wind power is considered[by whom?] the most economical form of electrical power with which to synthesize fuel, because the load curve for electricity peaks sharply during the warmest hours of the day, but wind tends to blow slightly more at night than during the day. Therefore, the price of nighttime wind power is often much less expensive than any alternative. Off-peak wind power prices in high wind penetration areas of the U.S. averaged 1.64 cents per kilowatt-hour in 2009, but only 0.71 cents/kWh during the least expensive six hours of the day. Typically, wholesale electricity costs 2 to 5 cents/kWh during the day. Commercial fuel synthesis companies suggest they can produce fuel for less than petroleum fuels when oil costs more than $55 per barrel. The U.S. Navy estimates that shipboard production of jet fuel from nuclear power would cost about $6 per gallon. While that was about twice the petroleum fuel cost in 2010, it is expected to be much less than the market price in less than five years if recent trends continue. Moreover, since the delivery of fuel to a carrier battle group costs about $8 per gallon, shipboard production is already much less expensive. However, U.S. civilian nuclear power is considerably more expensive than wind power. The Navy's estimate that 100 megawatts can produce 41,000 gallons of fuel per day indicates that terrestrial production from wind power would cost less than $1 per gallon.
Hydrogen & formic acid
Main article: Hydrogen fuel
Hydrogen is an emissionless fuel. The byproduct of hydrogen burning is water, although some mono-nitrogen oxides NOx are produced when hydrogen is burned with air.
Main article: Formic acid
Another fuel is formic acid. The fuel is used by converting it first to hydrogen, and using that in a fuel cell. Formic acid is much more easy to store than hydrogen.
Hydrogen/compressed natural gas mixture
Main article: HCNG
HCNG (or H2CNG) is a mixture of compressed natural gas and 4-9 percent hydrogen by energy.
Liquid nitrogen is another type of emissionless and efficient fuel.
The air engine is an emission-free piston engine using compressed air as fuel. Unlike hydrogen, compressed air is about one-tenth as expensive as fossil fuel, making it an economically attractive alternative fuel.
Main article: Autogas
Propane is a cleaner burning, high performance fuel derived from multiple sources. It is known by many names including propane, LPG (liquified propane gas), LPA (liquid propane autogas), Autogas and others. Propane is a hydrocarbon fuel and is a member of the natural gas family.
Propane as an automotive fuel shares many of the physical attributes of gasoline while reducing tailpipe emissions and well to wheel emissions overall. Propane is the number one alternative fuel in the world and offers an abundance of supply, liquid storage at low pressure, an excellent safety record and large cost savings when compared to traditional fuels.
Propane delivers an octane rating between 104 and 112 depending on the composition of the butane/propane ratios of the mixture. Propane autogas in a liquid injection format captures the phase change from liquid to gas state within the cylinder of the combustion engine producing an "intercooler" effect, reducing the cylinder temperature and increasing air density. The resultant effect allows more advance on the ignition cycle and a more efficient engine combustion.
Propane lacks additives, detergents or other chemical enhancements further reducing the exhaust output from the tailpipe. The cleaner combustion also has fewer particulate emissions, lower NOx due to the complete combustion of the gas within the cylinder, higher exhaust temperatures increasing the efficiency of the catalyst and deposits less acid and carbon inside the engine which extends the useful life of the lubricating oil.
Propane autogas is generated at the well alongside other natural gas and oil products. It is also a by-product of the refining processes which further increase the supply of Propane to the market.
Propane is stored and transported in a liquid state at roughly 5 bar (73 psi) of pressure. Fueling vehicles is similar to gasoline in speed of delivery with modern fueling equipment. Propane filling stations only require a pump to transfer vehicle fuel and does not require expensive and slow compression systems when compared to compressed natural gas which is usually kept at over 3,000 psi (210 bar).
In a vehicle format, propane autogas can be retrofitted to almost any engine and provide fuel cost savings and lowered emissions while being more efficient as an overall system due to the large, pre-existing propane fueling infrastructure that does not require compressors and the resultant waste of other alternative fuels in well to wheel lifecycles.
Natural gas vehicles
Compressed natural gas (CNG) and liquified natural gas (LNG) are two cleaner combusting alternatives to conventional liquid automobile fuels.
Compressed natural gas fuel types
Compressed natural gas (CNG) vehicles can use both renewable CNG and non-renewable CNG.
Conventional CNG is produced from the many underground natural gas reserves are in widespread production worldwide today. New technologies such as horizontal drilling and hydraulic fracturing to economically access unconventional gas resources, appear to have increased the supply of natural gas in a fundamental way.
Renewable natural gas or biogas is a methane‐based gas with similar properties to natural gas that can be used as transportation fuel. Present sources of biogas are mainly landfills, sewage, and animal/agri‐waste. Based on the process type, biogas can be divided into the following: biogas produced by anaerobic digestion, landfill gas collected from landfills, treated to remove trace contaminants, and synthetic natural gas (SNG).
Around the world, this gas powers more than 5 million vehicles, and just over 150,000 of these are in the U.S. American usage is growing at a dramatic rate.
Because natural gas emits little pollutant when combusted, cleaner air quality has been measured in urban localities switching to natural gas vehicles Tailpipe CO2 can be reduced by 15–25% compared to gasoline, diesel. The greatest reductions occur in medium and heavy duty, light duty and refuse truck segments.
CO2 reductions of up to 88% are possible by using biogas.
Similarities to hydrogen Natural gas, like hydrogen, is another fuel that burns cleanly; cleaner than both gasoline and diesel engines. Also, none of the smog-forming contaminates are emitted. Hydrogen and natural gas are both lighter than air and can be mixed together.
Nuclear power and radiothermal generators
Main articles: Nuclear power and radiothermal generator
Nuclear power is any nuclear technology designed to extract usable energy from atomic nuclei via controlled nuclear reactions. The only controlled method now practical uses nuclear fission in a fissile fuel (with a small fraction of the power coming from subsequent radioactive decay). Use of the nuclear reaction nuclear fusion for controlled power generation is not yet practical, but is an active area of research.
Nuclear power is usually used by using a nuclear reactor to heat a working fluid such as water, which is then used to create steam pressure, which is converted into mechanical work for the purpose of generating electricity or propulsion in water. Today, more than 15% of the world's electricity comes from nuclear power, and over 150 nuclear-powered naval vessels have been built.
In theory, electricity from nuclear reactors could also be used for propulsion in space, but this has yet to be demonstrated in a space flight. Some smaller reactors, such as the TOPAZ nuclear reactor, are built to minimize moving parts, and use methods that convert nuclear energy to electricity more directly, making them useful for space missions, but this electricity has historically been used for other purposes. Power from nuclear fission has been used in a number of spacecraft, all of them unmanned. The Soviets up to 1988 orbited 33 nuclear reactors in RORSAT military radar satellites, where electric power generated was used to power a radar unit that located ships on the Earth's oceans. The U.S. also orbited one experimental nuclear reactor in 1965, in the SNAP-10A mission. No nuclear reactor has been sent into space since 1988.
Thorium fuelled nuclear reactors
Thorium-based nuclear power reactors have also become an area of active research in recent years. It is being backed by many scientists and researchers, and Professor James Hansen, the former Director at NASA Goddard Institute for Space Studies has reportedly said, “After studying climate change for over four decades, it’s clear to me that the world is heading for a climate catastrophe unless we develop adequate energy sources to replace fossil fuels. Safer, cleaner and cheaper nuclear power can replace coal and is desperately needed as an essential part of the solution”.Thorium is 3-4 times more abundant within nature than uranium, and its ore, monazite, is commonly found in sands along bodies of water. Thorium has also gained interest because it could be easier to obtain than uranium. While uranium mines are enclosed underground and thus very dangerous for the miners, thorium is taken from open pits. Monazite is present in countries such as Australia, the United States and India, in quantities large enough to power the earth for thousands of years. As an alternative to uranium fuelled nuclear reactors, thorium has been proven to add to proliferation, produces radioactive waste for deep geological repositories like technetium-99 (half-life over 200,000 years), and has a longer fuel cycle.
For a list of experimental and presently-operating thorium-fueled reactors, see thorium fuel cycle#List of thorium fueled reactors.
In addition, radioisotopes have been used as alternative fuels, on both land and in space. Their use on land is declining due to the danger of theft of isotope and environmental damage if the unit is opened. The decay of radioisotopes generates both heat and electricity in many space probes, particularly probes to outer planets where sunlight is weak, and low temperatures is a problem. Radiothermal generators (RTGs) which use such radioisotopes as fuels do not sustain a nuclear chain reaction, but rather generate electricity from the decay of a radioisotope which has (in turn) been produced on Earth as a concentrated power source (fuel) using energy from an Earth-based nuclear reactor.
- ^"Is Algae Based Biofuel a Great Green Investment Opportunity". Green World Investor. 2010-04-06. Archived from the original on 17 June 2010. Retrieved 2010-07-11.
- ^"Navy demonstrates alternative fuel in riverine vessel". Marine Log. 2010-10-22. Retrieved 2010-07-11.
- ^"Can algae-based plastics reduce our plastic footprint?". Smart Planet. 2009-10-07. Retrieved 2010-04-05.
- ^Wheeler, Jill (2008). Alternative Cars. ABDO. p. 21. ISBN 978-1-59928-803-1.
- ^Don Hofstrand (May 2009). "Ammonia as a transportation fuel". AgMRC Renewable Energy Newsletter.
- ^"NH3 Fuel Association".
- ^Zeman, Frank S.; Keith, David W. (2008). "Carbon neutral hydrocarbons"(PDF). Philosophical Transactions of the Royal Society A. 366: 3901–18. Bibcode:2008RSPTA.366.3901Z. doi:10.1098/rsta.2008.0143. Archived from the original(PDF) on May 25, 2013. Retrieved September 7, 2012. (Review.)
- ^Wang, Wei; Wang, Shengping; Ma, Xinbin; Gong, Jinlong (2011). "Recent advances in catalytic hydrogenation of carbon dioxide"(PDF). Chemical Society Reviews. 40 (7): 3703–27. doi:10.1039/C1CS15008A. Retrieved September 7, 2012. [permanent dead link] (Review.)
- ^ abMacDowell, Niall; et al. (2010). "An overview of CO2 capture technologies". Energy and Environmental Science. 3 (11): 1645–69. doi:10.1039/C004106H. Retrieved September 7, 2012. (Review.)
- ^ abEisaman, Matthew D.; et al. (2012). "CO2 extraction from seawater using bipolar membrane electrodialysis"(PDF). Energy and Environmental Science. 5 (6): 7346–52. doi:10.1039/C2EE03393C. Archived from the original(PDF) on January 21, 2013. Retrieved September 7, 2012.
- ^Graves, Christopher; Ebbesen, Sune D.; Mogensen, Mogens; Lackner, Klaus S. (2011). "Sustainable hydrocarbon fuels by recycling CO2 and H2O with renewable or nuclear energy". Renewable and Sustainable Energy Reviews. 15 (1): 1–23. doi:10.1016/j.rser.2010.07.014. Retrieved September 7, 2012. (Review.)
- ^ abcSocolow, Robert; et al. (June 1, 2011). Direct Air Capture of CO2 with Chemicals: A Technology Assessment for the APS Panel on Public Affairs(PDF) (peer reviewed literature review). American Physical Society. Retrieved September 7, 2012.
- ^ abGoeppert, Alain; Czaun, Miklos; Prakash, G.K. Surya; Olah, George A. (2012). "Air as the renewable carbon source of the future: an overview of CO2 capture from the atmosphere". Energy and Environmental Science. 5 (7): 7833–53. doi:10.1039/C2EE21586A. Retrieved September 7, 2012. (Review.)
- ^House, K.Z.; Baclig, A.C.; Ranjan, M.; van Nierop, E.A.; Wilcox, J.; Herzog, H.J. (2011). "Economic and energetic analysis of capturing CO2 from ambient air"(PDF). Proceedings of the National Academy of Sciences of the United States of America. 108 (51): 20428–33. Bibcode:2011PNAS..10820428H. doi:10.1073/pnas.1012253108. Retrieved September 7, 2012. (Review.)
- ^Lackner, Klaus S.; et al. (2012). "The urgency of the development of CO2 capture from ambient air". Proceedings of the National Academy of Sciences of the United States of America. 109 (33): 13156–62. Bibcode:2012PNAS..10913156L. doi:10.1073/pnas.1108765109. PMC 3421162. PMID 22843674. Retrieved September 7, 2012.
- ^ abcPearson, R.J.; Eisaman, M.D.; et al. (2012). "Energy Storage via Carbon-Neutral Fuels Made From CO2, Water, and Renewable Energy"(PDF). Proceedings of the IEEE. 100 (2): 440–60. doi:10.1109/JPROC.2011.2168369. Archived from the original(PDF) on May 12, 2013. Retrieved September 7, 2012. (Review.)
- ^ abPennline, Henry W.; et al. (2010). "Separation of CO2 from flue gas using electrochemical cells". Fuel. 89 (6): 1307–14. doi:10.1016/j.fuel.2009.11.036. Retrieved September 7, 2012.
- ^Graves, Christopher; Ebbesen, Sune D.; Mogensen, Mogens (2011). "Co-electrolysis of CO2 and H2O in solid oxide cells: Performance and durability". Solid State Ionics. 192 (1): 398–403. doi:10.1016/j.ssi.2010.06.014. Retrieved September 7, 2012.
- ^Fraunhofer-Gesellschaft (May 5, 2010). "Storing green electricity as natural gas". fraunhofer.de. Retrieved September 9, 2012.
- ^Center for Solar Energy and Hydrogen Research Baden-Württemberg (2011). "Verbundprojekt 'Power-to-Gas'" (in German). zsw-bw.de. Archived from the original on February 16, 2013. Retrieved September 9, 2012.
- ^Center for Solar Energy and Hydrogen Research (July 24, 2012). "Bundesumweltminister Altmaier und Ministerpräsident Kretschmann zeigen sich beeindruckt von Power-to-Gas-Anlage des ZSW" (in German). zsw-bw.de. Archived from the original on September 27, 2013. Retrieved September 9, 2012.
- ^Okulski, Travis (June 26, 2012). "Audi's Carbon Neutral E-Gas Is Real And They're Actually Making It". Jalopnik (Gawker Media). Retrieved 29 July 2013.
- ^Rousseau, Steve (June 25, 2013). "Audi's New E-Gas Plant Will Make Carbon-Neutral Fuel". Popular Mechanics. Retrieved 29 July 2013.
- ^Doty Windfuels
- ^CoolPlanet Energy Systems
- ^Air Fuel Synthesis, Ltd.
- ^Musadi, M.R.; Martin, P.; Garforth, A.; Mann, R. (2011). "Carbon neutral gasoline re-synthesised from on-board sequestrated CO2"(PDF). Chemical Engineering Transactions. 24: 1525–30. doi:10.3303/CET1124255. Retrieved September 7, 2012.
- ^DiMascio, Felice; Willauer, Heather D.; Hardy, Dennis R.; Lewis, M. Kathleen; Williams, Frederick W. (July 23, 2010). Extraction of Carbon Dioxide from Seawater by an Electrochemical Acidification Cell. Part 1 - Initial Feasibility Studies (memorandum report). Washington, DC: Chemistry Division, Navy Technology Center for Safety and Survivability, U.S. Naval Research Laboratory. Retrieved September 7, 2012.
- ^Willauer, Heather D.; DiMascio, Felice; Hardy, Dennis R.; Lewis, M. Kathleen; Williams, Frederick W. (April 11, 2011). Extraction of Carbon Dioxide from Seawater by an Electrochemical Acidification Cell. Part 2 - Laboratory Scaling Studies (memorandum report). Washington, DC: Chemistry Division, Navy Technology Center for Safety and Survivability, U.S. Naval Research Laboratory. Retrieved September 7, 2012.
- ^Bloomberg Energy PricesBloomberg.com (compare to off-peak wind power price graph.) Retrieved September 7, 2012.
- ^Holte, Laura L.; Doty, Glenn N.; McCree, David L.; Doty, Judy M.; Doty, F. David (2010). Sustainable Transportation Fuels From Off-peak Wind Energy, CO2 and Water(PDF). 4th International Conference on Energy Sustainability, May 17–22, 2010. Phoenix, Arizona: American Society of Mechanical Engineers. Retrieved September 7, 2012.
- ^Willauer, Heather D.; Hardy, Dennis R.; Williams, Frederick W. (September 29, 2010). Feasibility and Current Estimated Capital Costs of Producing Jet Fuel at Sea (memorandum report). Washington, DC: Chemistry Division, Navy Technology Center for Safety and Survivability, U.S. Naval Research Laboratory. Retrieved September 7, 2012.
- ^Sovacool, B.K. (2011). Contesting the Future of Nuclear Power: A Critical Global Assessment of Atomic Energy, World Scientific, p. 126.
- ^Rath, B.B., U.S. Naval Research Laboratory (2012). Energy After Oil(PDF). Materials Challenges in Alternative and Renewable Energy Conference, February 27, 2012. Clearwater, Florida: American Ceramic Society. p. 28. Retrieved September 7, 2012.