Future energy development

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Future energy development faces great challenges due to an increasing world population, demands for higher standards of living, demands for less pollution and a possible end to fossil fuels. Without energy, the world's entire industrialized infrastructure would collapse; agriculture, transportation, waste collection, information technology, communications and much of the prerequisites that a developed nation takes for granted. A shortage of the energy needed to sustain this infrastructure could lead to a Malthusian catastrophe.

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[edit] General considerations

Almost all forms of terrestrial energy, such as fossil fuels, solar, wind, ocean thermal, and hydropower, can be traced back to energy received from the sun's fusion reactions. The only exceptions are tidal power, nuclear power, and geothermal energy. Tidal energy comes from the gravitational potential energy of the Earth/Moon system. Geothermal energy is believed to be generated primarily by radioactive decay inside the Earth.^[1]

Most human energy sources today use energy from sunlight, in the form of fossil fuels (coal, oil and gas). Once the stored forms are used up (assuming no contribution from the three previous energy sources and no energy from space exploration) then the long-term energy usage of humanity is limited to that from the sunlight falling on Earth. The total energy consumption of humanity today is equivalent to about 0.1-0.01% of that. But humanity cannot exploit most of this energy since it also provides the energy for almost all other lifeforms and drives the weather cycle [17][18].

U.S. energy consumption by sectors.

World energy production by source in 2004: Oil 40%, coal 23.3%, natural gas 22.5%, hydroelectric 7.0%, nuclear 6.5%, biomass and other 0.7%.^[2] In the U.S., transportation accounted for 28% of all energy use and 70% of petroleum use in 2001; 97% of transportation fuel was petroleum.^[3]

The United Nations projects that world population will stabilize in 2075 at nine billion due to the demographic transition. Birth rates are now falling in most developing nations and the population would decrease in several developed nations if there was no immigration.^[4] Since 1970, each 1% increase in the Gross world product has yielded a 0.64% increase in energy consumption.^[5]

In geology, resources refer to the amount of a specific substance that may be present in a deposit. This definition does not take into account the economic feasibility of exploitation or the fact that resources may not be recoverable using current or future technology. Reserves constitute those resources that are recoverable using current technology. They can be recovered economically under current market conditions. This definition takes into account current mining technology and the economics of recovery, including mining and transport costs, government royalties and current market prices. Reserves decrease when prices are too low for some of the substance to be recovered economically, and increase when higher prices make more of the substance economically recoverable. Neither of these terms consider the energy required for exploitation (except as reflected in economic costs) or whether there is a net energy gain or loss.

Energy production usually requires an energy investment. Drilling for oil or building a wind power plant requires energy. The fossil fuel resources (see above) that are left are often increasingly difficult to extract and convert. They may thus require increasingly higher energy investments. If the investment is greater than the energy produced, then the fossil resource is no longer an energy source. This means that a large part of the fossil fuel resources and especially the non-conventional ones cannot be used for energy production today. Such resources may still be exploited economically in order to produce raw materials for plastics, fertilizers or even transportation fuel but now more energy is consumed than produced. (They then become similar to ordinary mining reserves, economically recoverable but not net positive energy sources.) New technology may ameliorate this problem if it can lower the energy investment required to extract and convert the resources, although ultimately basic physics sets limits that cannot be exceeded.

The classification of energy sources into renewables and non-renewables is not without problems. Geothermal power and hydroelectric power are classified as renewable energy but geothermal sites eventually cool down and hydroelectric dams gradually become filled with silt which may be very expensive to remove. Although it can be argued that while a specific location may be depleted, the total amount of potential geothermal and hydroelectric power is not and a new power plant may sometimes be built on a different location. Nuclear power is not classified as a renewable but the amount of uranium in the seas may continue to be replenished by rivers through erosion of underground resources for as long as the remaining life of the Sun. Fossil fuels are finite but hydrocarbon fuel may be produced in several ways as described below.

Many of the current or potential future power production numbers given below do not subtract the energy consumed due to loss of energy from constructing the power facilities and distribution network, energy distribution itself, maintenance, inevitable replacement of old power production facilities and distribution network, backup capacity due to intermittent output, and energy required to reverse damage to the environment and other externalities. Net power production using life cycle analysis is more correct but more difficult and has many new uncertain factors.

[edit] History of predictions about future energy development

Ever since the beginning of the Industrial Revolution, the question of the future of energy supplies has occupied economists.

• 1865 - William Stanley Jevons published The Coal Question in which he claimed that reserves of coal would soon be exhausted and that there was no prospect of oil being an effective replacement.
• 1885 - U.S. Geological Survey: Little or no chance of oil in California.
• 1891 - U.S. Geological Survey: Little or no chance of oil in Kansas or Texas.
• 1914 - U.S. Bureau of Mines: Total future production of 5.7 billion barrels.
• 1939 - U.S. Department of the Interior: Reserves to last only 13 years.
• 1951 - U.S. Department of the Interior, Oil and Gas Division: Reserves to last 13 years.

(Data from Kahn et al. (1976) pp.94-5 infra)

• 1956 - Geophysicist M. King Hubbert predicts U.S. oil production will peak between 1965 and 1970 (peaked in 1971). Also predicts world oil production will peak "within half a century" based on 1956 data. This is Hubbert peak theory.
• 1989 - Predicted peak by Colin Campbell ("Oil Price Leap in the Early Nineties," Noroil, December 1989, pages 35-38.)
• 2004 - OPEC estimates it will nearly double oil output by 2025 (Opec Oil Outlook to 2025 Table 4, Page 12)

[edit] Fossil fuels

Main article: Fossil fuels

Fossil fuels supply most of the energy consumed today. They are relatively concentrated and pure energy sources and technically easy to exploit, and provide cheap energy if the costs of pollution and subsidies are ignored. Petroleum products provide almost all of the world's transportation fuel.

Pollution is a large problem. Fossil fuels contribute to global warming and acid rain. The use of fossil fuels, mainly coal, causes tens of thousands of deaths each year in the US alone from ailments like respiratory disease, cardiovascular disease, and cancer.^[6] Both derivatives from the hydrocarbon fuel itself like carbon dioxide and impurities like heavy metals, sulfur, and uranium contribute to the pollution. Natural gas is generally considered the least polluting of the fossil fuels with coal being the most polluting. Some of the non-conventional forms like oil shale may be significantly more polluting than the conventional ones. These problems may be lessened by new ways of burning the fuels and cleaning up the exhaust. The storage of the ashes and the pollutants recovered from the cleaning processes may also be a problem. Carbon dioxide is also implicated as a major factor in global warming. To ameliorate the greenhouse gas emissions from burning fossil fuels, various techniques have been proposed for carbon sequestration. Carbon sequestration is the permanent capture and storage of carbon dioxide and other pollutants resulting from the combustion of fossil fuels. Such proposed solutions would increase the cost of using fossil fuels. However, if the technologies were proven to be safe and acceptable to the public, they could allow the continued use of fossil fuels as the primary source of energy.

Governments usually provide various services which can be seen as subsidies artificially lowering the price of fossil fuels: A variety of oil- and transportation-related infrastructures and services such as providing roads and highway police for vehicles almost exclusively using fossil fuels; government agencies doing research on all aspects of fossil fuel technology; various tax breaks; and huge militaries and even wars to protect access to foreign fossil fuel reserves.^[7]

Fossil fuels are also finite. See Hubbert peak for a discussion about the projected production peak of oil and other fossil fuels. A minority view among Russian geologists, widely dismissed in Western nations, the abiogenic petroleum origin theory, assumes an infinite supply of petroleum and natural gas.

New technology can affect the date of the peaks for fossil fuels and how much energy each unit of fossil fuel produces: exploration may become less expensive and more accurate; the costs of drilling and mining may decrease; resources deeper in the ground may become recoverable; the percentage of fossil fuel recovered from a field may be significantly increased; improved monitoring systems may reduce production costs and extend the life of marginal wells; storage and transportation losses and costs may be reduced; and refining and power plants may become more efficient.^[8][9][10]

[edit] Oil

The organization ASPO predicts that conventional oil production will peak in 2007.

[edit] Conventional oil

Main article: Hubbert peak

Many independent petroleum geologists have projected conventional oil production to peak in 2005 to 2013 timeframe. There are many other predictions, one example is that the world conventional oil production will peak somewhere between 2020 and 2050, but that the output is likely to increase at a substantially slower rate after 2020 (Greene, 2003). Another recent study predicts the peak to somewhere between 2006 and 2037.^[11] Both the IEA and the EIA project that conventional oil production will continue to increase until at least 2025-2030.

[edit] Non-conventional oil

Main articles: Non-conventional oil, Oil shale, and Tar sands

Non-conventional types of production include: tar sands, oil shale and bitumen. These resources are estimated to contain three times as much oil as the remaining conventional oil resources, but few are economically recoverable with current technology^[12] although this may change.^[13] Recovery of oil from tar sands is now economically feasible, with billions of dollars being invested in new oil recovery plants. The Karrick process which has been used to extract oil from coal also looks increasingly attractive.

Another non-conventional oil for energy is pure plant oil.

[edit] Natural gas

Main article: Natural gas

[edit] Conventional natural gas

The global production peak for conventional natural gas will probably be somewhat later than for oil.^[14] Some predict a peak for conventional gas production between 2010 and 2020.

[edit] Non-conventional natural gas

Main article: Methane clathrate

There are large unconventional gas resources, like methane hydrate or geopressurized zones, that could increase the amount of gas by a factor of ten or more, if recoverable.^[15][16]

Large quantities of methane hydrate are inferred from the actual finds. Methane hydrate is a clathrate; a crystalline form in which methane molecules are trapped. The form is stable at low temperature and high pressure, conditions that exist at ocean depth of 500 meters or more, or under permafrost. Recent estimates of the size of the oceanic resource base constrained by direct sampling suggest the global inventory lies between 1×10¹⁵ and 5×10¹⁵ m³ (1 quadrillion to 5 quadrillion).^[17] This estimate, corresponding to 500-2500 gigatonnes carbon (Gt C), is smaller than the 5000 Gt C estimated for all other fossil fuel reserves but substantially larger than the ~230 Gt C estimated for other natural gas sources.^[18] Technology for extracting methane gas from the hydrate deposits in commercial quantities has not yet been developed. A research and development project in Japan is targeting commercial-scale technology by 2016.^[19]

There are several companies developing the Fischer-Tropsch process to enable practical exploitation of so-called stranded gas reserves.

[edit] Coal

Historical and projected world energy production by energy source, 1980-2025, Source: International Energy Outlook 2004, EIA. IEA makes a similar projection.

Main article: Coal

There are large but finite coal reserves which may increasingly be used as an energy source during oil depletion. There are today 200 years of economically exploitable reserves at the current rate of consumption. Reserves have increased by over 50 percent in the last 22 years and are expected to continue to increase.^[20] Coal resources are estimated to be ten times larger.^[21] Large amounts of coal waste that has been produced during coal mining and stored near the mines could become exploitable with new technology.^[22]

[edit] Nuclear power

Higher electricity use per capita correlates with a higher score on the Human Development Index(1997). Developing nations score much lower on these variables than developed nations. The continued rapid economic growth and increase in living standards in developing nations with large populations, like China and India, is dependent on a rapid and large expansion of energy production capacity.

Developing nations also use less total energy per capita. FSU/EE stands for Former Soviet Union and Eastern Europe. Source: EIA.

Developing nations use their energy less efficiently than developed nation, getting less GDP for the same amount of energy. One important cause is old technology. Notable is the very low energy efficiency in the former communist states. Source: EIA.

An increasing share of world energy consumption is predicted to be used by developing nations. Source: EIA.

Main article: Nuclear power

Depending on the type of fission fuel considered, estimates for existing supply at known usage rates varies from thousands of years for Uranium-238 to several decades for the currently popular Uranium-235. At the present use rate, there are 50 years left of known uranium-235 reserves at the current extraction price per kilogram.^[23] Given that the cost of fuel is a minor cost factor for fission power, more expensive, more difficult to extract sources of uranium could be used in the future. For example, doubling the price of uranium, which would have only little effect on the overall cost of nuclear power, would increase reserves to at least 200 years. To put this in perspective; a doubling in the cost of natural uranium would increase the total cost of nuclear power by 5%. On the other hand, if the price of natural gas was doubled, the cost of gas-fired power would increase by about 60%. Another alternative would be to use thorium as fission fuel. Thorium is three times more abundant in the Earth crust than uranium,^[24] and much more of the thorium can be used (or, more precisely, converted into Uranium-233 and then used).

Current light water reactors burn the nuclear fuel poorly, leading to energy waste. Nuclear reprocessing^[25] or burning the fuel better using different reactor designs would reduce the amount of waste material generated and allow better use the available resources. As opposed to current light water reactors which use uranium-235 (0.7 percent of all natural uranium), fast breeder reactors convert the more abundant uranium-238 (99.3 percent of all natural uranium) into plutonium for fuel. It has been estimated that there is anywhere from 10,000 to five billion years worth of Uranium-238 for use in these power plants^[26] . Breeder technology has been used in several reactors.^[27] However, the breeder reactor at Dounreay in Scotland, Monju in Japan and the Superphénix at Creys-Malville in France, in particular, have all had difficulties and were not economically competitive and have been decommissioned. The People's Republic of China intends to build breeders.^[28]

The possibility of nuclear meltdowns and other reactor accidents, such as the Three Mile Island accident and the Chernobyl disaster, have caused much public fear. Research is being done to lessen the known problems of current reactor technology by developing automated and passively-safe reactors. Historically, however, coal and hydropower power generation have both been the cause of more deaths per energy unit produced than nuclear power generation.^[29] Various kinds of energy infrastructure might be attacked by terrorists, including nuclear power plants, hydropower plants, and liquified natural gas tankers. Nuclear proliferation is the spread from nation to nation of nuclear technology, including nuclear power plants but especially nuclear weapons. New technology like SSTAR ("small, sealed, transportable, autonomous reactor") may lessen this risk.

The long-term radioactive waste storage problems of nuclear power have not been fully solved. Several countries have considered using underground repositories. Nuclear waste takes up little space compared to wastes from the chemical industry which remain toxic indefinitely.^[30] Spent fuel rods are now stored in concrete casks close to the nuclear reactors.^[31] The amounts of waste can be reduced in several ways. Both nuclear reprocessing and fast breeder reactors can reduce the amounts of waste. Subcritical reactors or fusion reactors could greatly reduce the time the waste has to be stored.^[32] Subcritical reactors may also be able to do the same to already existing waste.

Advocates of nuclear power argue that nuclear power is a cost competitive way to produce energy versus fossil fuels when taking into account externalities associated with both forms of energy production.^[33] Also, nuclear power has a high energy return on energy investment (EROI). Using life cycle analysis, it takes 4-5 months of energy production from the nuclear plant to fully pay back the initial energy investment^[34] . Advocates also claim that it is possible to relatively rapidly increase the number of plants. Typical new reactor designs have a construction time of three to four years.^[35] In 1983, 43 plants were being built, before an unexpected fall in fossil fuel prices stopped most new construction. Developing countries like India and China are rapidly increasing their nuclear energy use.^[36][37]

Fusion power could solve many of the problems of fission power (the technology mentioned above) but, despite research having started in the 1950s, no commercial fusion reactor is expected before 2050^[38] . Many technical problems remain unsolved. Proposed fusion reactors commonly use deuterium, an isotope of hydrogen, as fuel and in most current designs also lithium. Assuming a fusion energy output equal to the current global output and that this does not increase in the future, then the known current lithium reserves would last 3000 years, lithium from sea water would last 60 million years, and a more complicated fusion process using only deuterium from sea water would have fuel for 150 billion years.^[39]

[edit] Renewable energy

Main article: Renewable energy

Before the Industrial Revolution renewable energy was largely the only energy source used by humanity. Solid biofuels, such as wood, are still the main power source for many poor people in developing countries.

[edit] Hydroelectricity

Main article: Hydroelectricity

Hydroelectricity is the only renewable energy used today that makes a large contribution to world energy production. The long-term technical potential is believed to be 9 to 12 times current hydropower production, but environmental concerns increasingly block new dam construction.^[40] There is a growing interest in mini-hydro projects^[41], which avoid many of the problems of the larger dams.

[edit] Solar power

Main article: Solar power

Commercial solar cells can presently convert about 20 percent of the energy of incident sunlight to electrical energy. If built out as solar collectors, 1 percent of the land today used for crops and pasture could supply the world's total energy consumption. A similar area is used today for hydropower, as the electricity yield per unit area of a solar collector is 50 to 100 times that of an average hydro scheme.^[42] Solar cells can also be placed on top of existing urban infrastructure and does then not require re-purposing of cropland or parkland. The German government currently has a huge photovoltaic energy initiative, which is being watched with interest by other countries. Researchers have estimated that algae farms could convert 10 percent of the energy of incident light into biodiesel energy. Solar thermal collectors can capture 70 to 80 percent of insolation as usable heat. Passive solar and Solar chimneys can heat and cool residences and other buildings. A solar updraft tower is another concept.

[edit] Wind power

Main article: Windpower

Wind power is one of the most cost-competitive renewables today. Its long-term technical potential is believed five times current global energy consumption, or 40 times current electricity demand. This would require about 13 percent of all land area, or that land area with Class 3 or greater potential at a height of 80 meters. It assumes a placement of six large wind turbines per square kilometer on land. Offshore resources experience mean wind speeds about 90 percent greater than that of land, so offshore resources could contribute substantially more energy.^[43][44] This number could also increase with higher altitude ground based or airborne turbines.^[45]

[edit] Geothermal power

Main article: Geothermal power

Geothermal power and tidal power are the only renewables not dependent on the sun but are today limited to special locations. All available tidal energy is equivalent to one-fourth of total human energy consumption today. Geothermal power has a very large potential if considering all the heat existing inside Earth, although the heat flow from the interior to the surface is only 1/20,000 as great as the energy received from the Sun or about 2-3 times that from tidal power.^[46] At the moment Iceland and New Zealand are two of the greatest users of geothermal energy, although many others also have potential. Countries are also researching hot-dry-rock geothermal technologies which have some possibilities.

[edit] Ocean thermal energy conversion and Wave power

Main article: Ocean thermal energy conversion

Ocean thermal energy conversion and tidal power are other renewables with large potential. Several other variations of utilizing energy from the sun also exist, see renewable energy. Currently there are plans under way to produce mass scale wave energy plants as those with hydroelectricity.

[edit] Bioenergy

Main article: Biofuels

Biomass (burning biological materials to generate heat), biofuels (processing biological materials to generate fuels such as biodiesel and ethanol), and biogas (using anaerobic digestion to generate methane from biodegradable material & biodegradable waste) are other renewables. Systems such as advanced anaerobic digesters offer the ability to produce medium sized power generation (2MW-10MW) facilities and offer flexibility. They can recover value from biodegradable waste whilst producing power from a renewable energy source.^[47]

[edit] Considerations about renewable energy

Some renewable sources are diffuse and require land and construction material for energy production. The large and sometimes remote areas may also increase energy loss and cost from distribution. On the other hand, some forms allow small-scale production and may be placed very close to or directly at consumer households, businesses, and industries which reduces or eliminates distribution problems.

The large areas affected also means that some renewable energy sources may have some negative environmental impact, although populated suburbs have already been impacted by human development. Hydroelectric dams, like the Aswan Dam, have adverse consequences both upstream and downstream. Some flooded areas also contain decaying organic material that release gases contributing to global warming if not captured. The mining and refining of large amounts of construction material will also affect the environment in the short term.

Aside from hydropower and geothermal power, which are site-specific, renewable supplies often have higher costs than fossil fuels if the impacts of pollution, climate change, and resource depletion are ignored, as is common. Renewables like wind and solar are cost effective in remote areas that are off grid because the cost of a grid connection is high, as is the cost of transporting diesel fuel. Many forms of renewables are cost effective in remote, underdeveloped, and/or low population density areas that are off the grid or on unreliable grids. Transmission of electricity through large grids remote from conventional energy sources is also expensive, and embedding small renewable projects in such locations can cut energy losses significantly. The inefficiency, noise, and refueling requirements of small diesel generators are also factors in favor of renewables in this situation.

Renewable sources are economically viable in less developed areas of the world, where the population density cannot support the financial investment of an electrical grid or petroleum supply network. In such situations, fossil fuel energy sources do not realize economies of scale, and distributed, small-scale electrical generation from renewables is usually more economical and operationally reliable.

Solar thermal is already cost effective for water heating. Grid connected solar cells can be cost effective in a spot-priced market because they generate electricity during peak usage periods when electricity is most costly and because they produce electricity at the point of use thereby avoiding transmission costs.

It is widely expected that renewable energy sources will continue to drop in costs as additional investments are made in R&D and as increased mass production improves the economies of scale. Nuclear power has been subsidized by 0.5-1 trillion dollars since the 1950s. No comparable investment has yet been made in renewable energy. Even so, the technology is improving rapidly. For example, solar cells are a hundred times less expensive today than the 1970s and development continues.^[48][49] Solar breeder technologies, where the energy used to make solar cells is itself solar energy, is also being investigated.^[50]

[edit] Increased efficiency in current energy use

New technology may make better use of already available energy through improved efficiency, such as more efficient fluorescent lamps, engines, and insulation. Using heat exchangers, it is possible to recover some of the energy in waste warm water and air, for example to preheat incoming fresh water. Hydrocarbon fuel production from pyrolysis could also be in this category, allowing recovery of some of the energy in hydrocarbon waste. Meat production is energy inefficient compared to the production of protein sources like soybean or Quorn. Already existing power plants often can and usually are made more efficient with minor modifications due to new technology. New power plants may become more efficient with technology like cogeneration. New designs for buildings may incorporate techniques like passive solar. Light-emitting diodes are gradually replacing the remaining uses of light bulbs. Note that none of these methods allows perpetual motion, as some energy is always lost to heat.

Mass transportation increases energy efficiency compared to widespread conventional automobile use while air travel is regarded as inefficient. Conventional combustion engine automobiles have continually improved their efficiency and may continue to do so in the future, for example by reducing weight with new materials. Hybrid vehicles can save energy by allowing the engine to run more efficiently, regaining energy from braking, turning off the motor when idling in traffic, etc. More efficient ceramic or diesel engines can improve mileage. Electric vehicles such as Maglev, trolleybuses, and PHEVs are more efficient during use (but maybe not if doing a life cycle analysis) than similar current combustion based vehicles, reducing their energy consumption during use by 1/2 to 1/4. Microcars or motorcycles may replace automobiles carrying only one or two people. Transportation efficiency may also be improved by in other ways, see automated highway system.

Electricity distribution may change in the future. New small scale energy sources may be placed closer to the consumers so that less energy is lost during electricity distribution. New technology like superconductivity or improved power factor correction may also decrease the energy lost. Distributed generation permits electricity "consumers", who are generating electricity for their own needs, to send their surplus electrical power back into the power grid.

Various market-based mechanisms have been proposed as means of increasing efficiency, such as deregulation of electricity markets, Negawatt power, and trading of emission rights.

[edit] Energy storage and transportation fuel

There is a widely held misconception that hydrogen is an alternative energy source. There are no uncombined hydrogen reserves on Earth that could provide energy like fossil fuels or uranium. Uncombined hydrogen is instead produced with the help of other energy sources. It may play an important role in a future hydrogen economy as a general energy storage system, used both to smooth power output by intermittent power sources, like solar power, and as transportation fuel for vehicles and aircraft.

Many renewable energy systems produce intermittent power. Other generators on the grid can be throttled to match varying production from renewable sources, but most of this throttling capacity is already committed to handling variations in load. Further development of intermittent renewable power will require some combination of grid energy storage, demand response, and spot pricing. Intermittent energy sources may be limited to at most 20-30% of the electricity produced for the grid without such measures. If electricity distribution loss and costs are managed, then intermittent power production from many different sources would increase the overall reliability of the grid. Renewables that are not intermittent include hydroelectric power, geothermal power, tidal power, Energy tower, ocean thermal energy conversion, high altitude airborne wind turbines, biofuel, and solar power satellites. Solar photovoltaics, although technically intermittent, produces electricity during peak periods, and hence does reduce the need for peaking power plants. Demand response programs, which send market pricing signals to consumers, can be a very effective way of managing variations in electricity production; for example, hydrogen production can increase when excess electricity is being produced, and conversely, hot water heaters can be automatically set to a lower temperature when production is lower.

There are also other alternatives for transportation fuel. Various chemical processes can convert the carbon and hydrogen in coal, natural gas, plant and animal biomass, and organic wastes into short hydrocarbons suitable as transportation fuels. Examples of such fuels are Fischer-Tropsch diesel, methanol, dimethyl ether, or syngas. Such diesel was used extensively in World War II by the Germans, who had limited access to crude oil supplies. Today South Africa produces most of country's diesel from coal.^[51] A long term oil price above 35 USD may make such liquid fuels economical on a large scale (See coal). Some of the energy in the original source will be lost in the conversion process. Compressed natural gas can itself be used as a transportation fuel. Also coal itself can be used as transportation fuel, historically coal has been used directly for transportation purposes in vehicles and boats using steam engines.

Carbon dioxide in the atmosphere can be converted to hydrocarbon fuel with the help of energy from another source. The energy can come from sunlight using natural photosynthesis which can produce various biofuels such as biodiesel, straight vegetable oil, alcohol fuels, or biomass which can be broken down into the fuels mentioned above. The energy could also come from sunlight using future artificial photosynthesis technology.^[52][53] Another alternative for the energy is electricity or heat from renewables or nuclear power.^[54][55] Compared to hydrogen, many hydrocarbons fuels have the advantage of reusing existing engine technology and existing fuel distribution infrastructure.

Electric vehicles and electric boats using batteries or non-hydrogen fuel cells are other alternatives. Electricity may be the only power source or combined with other fuels in hybrid vehicles. Nuclear power has been used in large ships.^[56] High technology sails could provide some of the power for ships.^[57] Several companies are proposing vehicles using compressed air for power.^[58][59] Airships require less onboard fuel than a traditional aircraft and combining airship technology with glider technology may eliminate onboard fuel completely.^[60] Personal rapid transit and some mass transportation systems, like trolleybus, metro or magnetic levitation trains, can use electricity directly from the grid and do not need a liquid fuel or battery.

Boron,^[61] silicon,^[62] and zinc^[63] have also been proposed as energy storage solutions.

[edit] Speculative

In the long-term future space exploration could yield a number of energy sources, though they are unlikely to be relevant in tackling humanity's current difficulties with energy sources.

The nearest-term possibility is solar power satellites, where solar cells are placed on orbiting platforms in 24-hour sunlight; the energy is then beamed to earth as microwaves received by arrays of receiving antennas. A fundamental development in space launch technology (such as a space elevator) would be required to make them economically viable. In order to overcome the launch costs of solar power satellites, O'Neill et al proposed using lunar material for a low profile, rapid (90 day doubling time) expansion system for creating such a massive industrial development using partially self-replicating systems under telepresence control of remote human workers^[64]

Fissionable materials could theoretically be obtained from asteroid mining; however, the technical barriers to asteroid mining are probably considerably higher than those of breeder reactors, which remove any practical supply constraints on fission power. Another interesting long-term possibility is the mining of helium-3 from the Moon for use in aneutronic fusion reactors, which have several advantages over the fusion reactor designs currently being experimented with. Helium-3 is unavailable in quantity on Earth. However, even "conventional" fusion power reactors are decades away from commercialization. Another suggestion is electrodynamic tethers.

In the very distant future, a spacefaring humanity has a number of options for very large-scale power generation; as well as fusion and very large-scale solar power (of which the ultimate such is the Dyson sphere) there has been speculation as to how an extremely advanced society might exploit the mass-energy conversion capabilities of black holes (like the accretion disc). Such technologies are obviously far, far, beyond our present capabilities, and are at this stage essentially thought experiments for engineers and science fiction writers.

[edit] See also

• 2000 Watt society
• Action on climate change
• Carbon sequestration
• Comparison of automobile fuel technologies
• Comparison of power plants
• Distributed generation
• Earth's energy budget
• Energy conservation
• Energy crisis
• Energy: world resources and consumption
• Environmental concerns with electricity generation
• Fusion power
• Hydrogen economy
• Inertial fusion energy
• Kardashev scale
• Liquid nitrogen economy
• Lithium economy
• Low-carbon economy
• Mitigation of global warming
• Nuclear power phase-out
• Oil phase-out in Sweden
• Peak Oil
• Power harvesting
• Renewable energy
• Synthetic Liquid Fuels Program
• The Hype about Hydrogen
• Thermal depolymerization
• Tribrid vehicle
• Vegetable oil economy
• Wind farm
• Wind power
• World energy resources and consumption
• Zinc economy

[edit] External links

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[edit] Organizations

• IEA Energy Information Centre
  • World Energy Outlook series, free before 2003, different focus each year
  • Free publications from IEA
• WEC Survey of Energy Resources
  • Online publications from WEC
  • Links to a broad range of international governmental and non-governmental organisations
• U.S. Energy Information Agency
  • International energy outlook 2004
  • Related Energy Links
• U.S. The Alternative Fuels Data Center
• U.S. Office of Fossil Energy
• Rocky Mountain Institute articles on energy
• Electricity Storage Association on articles on energy storage
• Information Network on the Technology of Utilisation and Sustainability of Energy Resources
• CleanEnergyTalk - An online community dedicated to education about renewable energy and it's future in society.
• ASPO Association for the Study of Peak Oil & Gas
• Energy and Climate publications from the Tellus Institute
• OPEC, Organisation of Oil Exporting Countries
  • Open Oil Outlook to 2025

[edit] Articles

• Order of Magnitude Morality
• Do we need nuclear power?
• Progress and its sustainability
• Nine Critical Questions to Ask About Alternative Energy
• World energy beyond 2050
• Critical Hour: Three Mile Island, The Nuclear Legacy, And National Security Online book by Albert J. Fritsch, Arthur H. Purcell, and Mary Byrd Davis (2005)
• Alternate Energy: The Investing Perspective

[edit] References

• Greene, D.L. & J.L. Hopson. (2003). Running Out of and Into Oil: Analyzing Global Depletion and Transition Through 2050 ORNL/TM-2003/259, Oak Ridge National Laboratory, Oak Ridge, Tennessee, Octobe
• Kahn, H. et al. (1976) The Next 200 Years: A Scenario for America and the World ISBN 0-349-12071-4
• Rodenbeck, Christopher T. and Chang, Kai, "A Limitation on the Small-Scale Demonstration of Retrodirective Microwave Power Transmission from the Solar Power Satellite", IEEE Antennas and Propagation Magazine, August 2005, pp. 67–72.
• The above sites Solar Power Satellites Office of Technology Assessment, US Congress, OTA-E-144, Aug. 1981.

[edit] Inline references

• http://www.madsci.org/posts/archives/mar2002/1017275290.Es.r.html

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