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'''Future energy development''', providing for the world's future energy needs, currently faces great challenges. These include an increasing ], demands for higher ], a need for less ], a need to avert ], and a possible end to ]s (see ]). Without energy, the world's entire industrialized infrastructure would collapse; ], ]ation, ], ], 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 ].

{{environmental technology}}

{{Portal|Energy}}

== General considerations ==
{{main | Energy development }}

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 ] reactions. The only exceptions are ], ], and ]. 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.<ref>{{cite web
| url=http://www.newscientist.com/article.ns?id=mg18725103.700&feedId=online-news_rss091
| title=First measurements of Earth's core radioactivity
| work=]}}</ref>

Most 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 percent of that. Covering a vast area like the ] with ] generation would provide the total current world energy usage.<ref> </ref><ref> </ref>

]

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%.<ref>{{cite web
| url=http://energy.cr.usgs.gov/energy/stats_ctry/Stat1.html
| title=United States Energy and World Energy Production and Consumption Statistics
| work=USGS
| accessdate=2006-03-24}}</ref> 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.<ref name="skov"/>

The ] projects that ] will stabilize in 2075 at nine billion due to the ]. Birth rates are now falling in most developing nations and the population would decrease in several developed nations if there was no ].<ref>{{cite web
| url= http://www.un.org/esa/population/unpop.htm
| title= ] Population Division Home Page
| accessdate= 2008-01-19 }} </ref> Since 1970, each 1 percent increase in the ] has yielded a 0.64 percent increase in energy consumption.<ref>{{cite web
| url= http://www.iea.org/Textbase/nppdf/free/2000/weo2002.pdf
| title= ''World Energy Outlook 2002''
|author= |last= |first= |authorlink= |coauthors=
|date= | year= 2002 |month= |format= ] |work=
| publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref>

In ], ''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 ] 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 ]s, ]s 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 ] but geothermal sites eventually cool down and ] gradually become filled with ], 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 ]. 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 ]. Net power production using ] analysis is more correct but more difficult and has many new uncertain factors.

== History of predictions about future energy development ==

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

* 1865 — ] 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 — ]: Little or no chance of oil in ].
* 1891 — U.S. Geological Survey: Little or no chance of oil in ] or ].
* 1914 — ]: 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 ] 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 ].
* 1989 — Predicted peak by ] ("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)

The ] is a long list of failed and sometimes fraudulent inventions of machines which produce useful energy "from nowhere" — that is, without requiring additional energy input.

== Fossil fuels ==
{{Main|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. ] products provide almost all of the world's transportation fuel.

] is a large problem. Fossil fuels contribute to ] and ]. The use of fossil fuels, mainly coal, causes tens of thousands of deaths each year in the US alone from ailments like respiratory disease, ], and ].<ref>{{cite web
| url= http://www.ecomall.com/greenshopping/cleanair.htm
| title= Study Says Coal Plant Pollution Kills 30,000 a Year
|author= |last= |first= |authorlink= |coauthors=
|date= |year= |month= |format= |work= |publisher=
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }}</ref> Both derivatives from the hydrocarbon fuel itself like ] and impurities like ], ], and ] 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 ] and the pollutants recovered from the cleaning processes may also be a problem. Carbon dioxide is also implicated as a major factor in ]. To ameliorate the greenhouse gas emissions from burning fossil fuels, various techniques have been proposed for ]. Carbon sequestration is the permanent ] 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 military infrastructure and even wars to protect access to foreign fossil fuel reserves.<ref>{{cite web
| url= http://www.ucsusa.org/clean_energy/fossil_fuels/the-hidden-cost-of-fossil-fuels.html
| title= The Hidden Cost of Fossil Fuels
|author= |last= |first= |authorlink= |coauthors=
| date= 08/10/05 |work= | publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref>

Fossil fuels are also finite. See ] 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 ] 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 ] and ] 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.<ref>{{cite web
| url= http://www.fe.doe.gov/
| title= Office of Fossil Energy Home Page
| publisher= ]
| accessdate= 2008-01-19 }} </ref><ref>{{cite web
| url= http://www.gasandoil.com/goc/features/fex40407.htm
| title= Laser beams soon may be drilling oil and gas wells
|author= |last= |first= |authorlink= |coauthors=
| date= 14-01-2004 |work= | publisher= Alexander's Gas & Oil Connections
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref><ref>{{cite web
| url= http://www.energybulletin.net/3555.html
| title= Peak production in the news again
|author= Oliver L. Campbell
| date= 6 Dec 2004 |work= |publisher=
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref>

=== Oil ===

<!-- ] predicts that conventional oil production will peak in 2007.]] -->

==== Conventional oil ====

: ''Main article: ]''

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.<ref>{{cite web
| url= http://www.esf.edu/efb/hall/pdfs/Hallocetal04.pdf
| title= Forecasting the limits to the availability and diversity of global conventional oil supply
| author= John L. Hallock Jr.
| coauthors= Pradeep J. Tharakan, Charles A.S. Hall, Michael Jefferson, Wei Wu
| date= 31 July 2003 | format= ] |work= |publisher= ''Energy''
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> Some analysts believe world-wide oil production has already peaked.<ref>
{{cite web
| url=http://www.princeton.edu/hubbert/current-events.html
| title=Current Events - Join us as we watch the crisis unfolding
| date=2007-01-19
| publisher=]
| author=Kenneth S. Deffeyes
| language=English
}}</ref><ref>{{cite web
| url=http://raisethehammer.org/article/643/
| title=Yes, We're in Peak Oil Today
| publisher=Raise the Hammer
| date=2007-10-22
| author=Ryan McGreal
| language=English
}}</ref><ref>
{{cite web
| url=http://www.energywatchgroup.org/fileadmin/global/pdf/EWG_Oilreport_10-2007.pdf
| title=Crude Oil: The Supply Outlook
| publisher=Energy Watch Group | format= ]
| date=2007-10
| author=Dr. Werner Zittel, Jorg Schindler
| language=English
}}</ref><ref>
{{cite web
| url=http://www.davidstrahan.com/blog/?p=67
| title=Oil production has peaked – al-Huseini
| date=2007-10-29
| language=English
}}</ref>

Both the ] and the ] project that conventional oil production will continue to increase until at least 2025-2030. However their predictions are criticized for expecting economic pressure to cause more oil production (which has not been the case over the past 18 months, despite ] during the same time period), and their reliance on a 2000 ] survey which predicts a radical departure in oil discoveries from the steady decline observed over the past 40 years.<ref>
{{cite web
| url=http://www.energywatchgroup.org/fileadmin/global/pdf/EWG_Oilreport_10-2007.pdf
| title=Crude Oil: The Supply Outlook
| publisher=Energy Watch Group | format= ]
| date=2007-10
| author=Dr. Werner Zittel, Jorg Schindler
| language=English
}}</ref>

==== Non-conventional oil ====
{{Main|Non-conventional oil|Oil shale|Tar sands}}

Non-conventional types of production include: ]s, ] and ]. 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<ref name="db-2004">{{cite web
| url= http://www.btinternet.com/~nlpwessex/Documents/DeutscheBankOil.htm
| title= "Energy Prospects After The Petroleum Age"
|author= |last= |first= |authorlink= |coauthors=
|date= 2 December 2004 |work= |publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }}</ref> although this may change.<ref>{{cite web
| url= http://www.worldoil.com/Magazine/MAGAZINE_DETAIL.asp?ART_ID=2378&MONTH_YEAR=Aug-2004
| title= "Energy issues fade among US election-year topics."
| author= John McCaughey | date= August 2004 |work= |publisher= ''World Oil'' magazine
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }}</ref> Recovery of oil from tar sands is now economically feasible, with billions of dollars being invested in new oil recovery plants. The ] which has been used to extract oil from coal also looks increasingly attractive.

Another non-conventional oil for energy is ].

=== Natural gas ===
{{Main|Natural gas}}

==== Conventional natural gas ====

The global production peak for conventional natural gas will probably be somewhat later than for oil.<ref name="db-2004"/> Some predict a peak for conventional gas production between 2010 and 2020.

==== Non-conventional natural gas ====
{{Main|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.<ref>{{cite web
| url= http://www.naturalgas.org/overview/unconvent_ng_resource.asp
| title= Unconventional Natural Gas Resources
|author= |last= |first= |authorlink= |coauthors=
|date= | year= 2004 |month= |format= |work= | publisher= NaturalGas.org
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref><ref>{{cite web
| url= http://www.naturalgas.org/overview/resources.asp
| title= How Much Natural Gas is there?
|author= |last= |first= |authorlink= |coauthors=
|date= | year= 2004 |month= |format= |work= | publisher= NaturalGas.org
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref>

Large quantities of methane hydrate are inferred from the actual finds. Methane hydrate is a ]; a ]line form in which ] 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 ]. Recent estimates of the size of the oceanic resource base constrained by direct sampling suggest the global inventory lies between 1{{e|15}} and 5{{e|15}} m³ (1 quadrillion to 5 quadrillion). This estimate, corresponding to 500–2,500 gigatonnes carbon (Gt&nbsp;C), is smaller than the 5000 Gt&nbsp;C estimated for all other fossil fuel reserves but substantially larger than the ~230 Gt&nbsp;C estimated for other natural gas sources.<ref>{{cite web
| url= http://www.iea.org/textbase/nppdf/free/2000/weo2001.pdf
| title= ''World Energy Outlook 2001''
|author= |last= |first= |authorlink= |coauthors=
|date= | year= 2001 |month= |format= ] |work=
| publisher= ]
| accessdate= 2008-01-19 }}</ref> Technology for extracting methane gas from the hydrate deposits in commercial quantities has not yet been developed. A research and development project in ] is targeting commercial-scale technology by 2016.<ref>{{cite web
| url= http://www.mh21japan.gr.jp/english/mh21/02keii.html
| title= Japan's Methane Hydrate Exploitation Program / Background and Organization
|author= |last= |first= |authorlink= |coauthors=
|date= |year= |month= |format= |work= |publisher=
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref>

There are several companies developing the ] to enable practical exploitation of so-called ]s.

=== Coal ===

]. ] makes a similar projection.]]
{{Main|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.<!-- Bad link.
<ref>{{cite web
| url= http://wci.rmid.co.uk/uploads/RoleofCoal.pdf
| title=
|author= |last= |first= |authorlink= |coauthors=
|date= |year= |month= |format= |work= |publisher=
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref>--> Coal resources are estimated to be ten times larger.<ref>{{cite web
| url= http://www.worldenergy.org <!-- Bad link. http://www.worldenergy.org/wec-geis/publications/reports/ser/coal/coal.asp -->
| title= Wold Energy Council
|author= |last= |first= |authorlink= |coauthors=
|date= |year= |month= |format= |work= |publisher=
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> Large amounts of coal waste that has been produced during coal mining and stored near the mines could become exploitable with new technology.<ref>{{cite web
| url= http://www.ultracleanfuels.com/main.htm
| title= Ultra Clean Fuels Technology Home Page
|author= |last= |first= |authorlink= |coauthors=
|date= |year= |month= |format= |work= |publisher= Ultra Clean Fuels
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref>

== Nuclear power ==

<!-- Note to editors. All of this section has been moved to the ] article. Please make edits there and not here. -->
](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.]]
] and ]. Source: EIA.]]
]. Source: EIA.]]
]
{{Main|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 (as of 2007) about 70 years left of known ] reserves economically recoverable at an uranium price of US$ 130/kg.<ref name="uranium">
{{cite web
| url = http://www.world-nuclear.org/info/inf75.htm
| title = Supply of Uranium
| accessdate = 2007-10-20
}}</ref>
The nuclear industry argue 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, such as lower-grade ores, and if prices increased enough, from sources such as granite and seawater.<ref name="uranium" /> Increasing the price of uranium would have little effect on the overall cost of nuclear power; a doubling in the cost of natural uranium would increase the total cost of nuclear power by 5 percent. On the other hand, if the price of natural gas was doubled, the cost of gas-fired power would increase by about 60 percent.<ref>
{{cite web
| url = http://www.world-nuclear.org/info/inf02.html
| title = The Economics of Nuclear Power
| accessdate = 2007-10-20
}}</ref> Another alternative would be to use ] as fission fuel. Thorium is three times more abundant in Earth's crust than uranium,<ref>
{{cite web
| url = http://www.world-nuclear.org/info/inf62.htm
| title = Thorium
| accessdate = 2007-10-20
}}</ref> and much more of the thorium can be used (or, more precisely, converted into Uranium-233 and then used).

Current ]s burn the nuclear fuel poorly, leading to energy waste. ]<ref name="wm">
{{cite web
| url = http://www.world-nuclear.org/info/inf04.html
| title = Waste Management in the Nuclear Fuel Cycle
| accessdate = 2007-10-20
}}</ref> or burning the fuel better using different reactor designs would reduce the amount of waste material generated and allow better use of the available resources. As opposed to current light water reactors which use ] (0.7 percent of all natural uranium), ] convert the more abundant ] (99.3 percent of all natural uranium) into ] 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.<ref>
{{cite web
| url = http://www-formal.stanford.edu/jmc/progress/cohen.html
| title = How long will nuclear energy last?
| accessdate = 2007-10-20
}}</ref> Breeder technology has been used in several reactors. However, the breeder reactor at ] in Scotland, ] in Japan and the ] at Creys-Malville in France, in particular, have all had difficulties and were not economically competitive and have been ]. The ] intends to build breeders.<ref>
{{cite web
| url = http://www.nti.org/db/china/fbrprog.htm
| title = China's Fast Breeder Reactor (FBR) Program
| accessdate = 2007-10-20
}}</ref>

The possibility of ]s and other reactor accidents, such as the ] and the ], have caused much public fear. Research is being done to lessen the known problems of current reactor technology by developing automated and ] reactors. Historically, however, coal and hydropower power generation have both been the cause of more deaths per energy unit produced than nuclear power generation.<ref>
{{cite web
| url = http://ee.ucd.ie/erc/events/nuclear/Crawley.pdf
| title = Risks versus benefits in energy production
| accessdate = 2007-10-20
}}</ref><ref>{{cite web |url= http://www.theage.com.au/news/national/nuclear-power-cheaper-safer-than-coal-and-gas/2006/06/04/1149359609052.html
| title = Nuclear power 'cheaper, safer' than coal and gas
| accessdate = 2007-10-20
}}</ref> Various kinds of energy infrastructure might be attacked by ], including nuclear power plants, hydropower plants, and ] ]s. ] is the spread from nation to nation of nuclear technology, including nuclear power plants but especially ]s. New technology like ] ("small, sealed, transportable, autonomous reactor") may lessen this risk.

The long-term ] 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.<ref name="wm" /> Spent fuel rods are now stored in concrete casks close to the nuclear reactors.<ref>
{{cite web
| url = http://www.wired.com/wired/archive/13.02/nuclear.html
| title = Nuclear Now!
| accessdate = 2007-10-20
}}</ref> The amounts of waste can be reduced in several ways. Both ] and ]s can reduce the amounts of waste. ]s or fusion reactors could greatly reduce the time the waste has to be stored.<ref>
{{cite web
| url = http://www.world-nuclear.org/info/inf35.html
| title = Accelerator-driven Nuclear Energy
| accessdate = 2007-10-20
}}</ref> Subcritical reactors may also be able to do the same to already existing waste.

The ] of nuclear power is not simple to evaluate, because of high capital costs for building and very low fuel costs. Comparison with other power generation methods is strongly dependent on assumptions about construction timescales and capital financing for nuclear plants. See ].

Depending on the source different energy return on energy investment (]) are claimed. Advocates (using life cycle analysis) argue that it takes 4–5 months of energy production from the nuclear plant to fully pay back the initial energy investment.<ref>
{{cite web
| url = http://www.world-nuclear.org/info/inf11.html
| title = Energy Analysis of Power Systems
| accessdate = 2007-10-20
}}</ref> Opponents claim that it depends on the grades of the ores the fuel came from, so a fully pay back can vary from 10 to 18 years.<ref>
{{cite web
| url = http://www10.antenna.nl/wise/537/gl/clean.html
| title = World Information Service on Energy
| accessdate = 2007-10-20
}}</ref>

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.<ref>
{{cite web
| url = http://www.uic.com.au/nip16.htm
| title = Advanced Nuclear Power Reactors
| accessdate = 2007-10-20
}}</ref> 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.<ref>
{{cite web
| url = http://www.wired.com/wired/archive/12.09/china.html
| title = Let a Thousand Reactors Bloom
| accessdate = 2007-10-20
}}</ref><ref>
{{cite web
| url = http://www.world-nuclear.org/info/inf17.html
| title = Plans For New Reactors Worldwide
| accessdate = 2007-10-20
}}</ref> However, a ] report on nuclear energy argues that a rapid expansion of nuclear power may create shortages in building materials such as reactor-quality concrete and steel, skilled workers and engineers, and safety controls by skilled inspectors. This would drive up current prices.<ref>
{{cite web
| url = http://www.cfr.org/content/publications/attachments/NuclearEnergyCSR28.pdf
| title = Nuclear Energy — Balancing benefits and risks
| accessdate = 2007-10-20
}}</ref>

] could solve many of the problems of ] (the technology mentioned above) but, despite research having started in the 1950s, no commercial fusion reactor is expected before 2050.<ref>
{{cite web
| url = http://www.iter.org/index.htm
| title = What is ITER
| accessdate = 2007-10-20
}}</ref> Many technical problems remain unsolved. Proposed fusion reactors commonly use ], an ] of ], as fuel and in most current designs also ]. 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.<ref>
{{cite web
| url = http://www.fusie-energie.nl/artikelen/ongena.pdf
| title = Energy for future centuries | format= ]
| accessdate = 2007-10-20
}}</ref>

== Renewable energy ==

=== Hydroelectricity ===
{{Main|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.<ref name="skov">{{cite web
| url= http://www.spe.org/spe/jpt/jsp/jptmonthlysection/0,2440,1104_11038_1040074_1202151,00.html
| title= World Energy Beyond 2050
| last=Skov
| first=Arlie M.
| date=]
| publisher= Society of Petroleum Engineers
| archiveurl=http://web.archive.org/web/20070309115708/http://www.spe.org/spe/jpt/jsp/jptmonthlysection/0,2440,1104_11038_1040074_1202151,00.html
| archivedate=2007-03-09
| accessdate=2008-01-19 }} </ref> There is a growing interest in ] projects,<ref>{{cite web
| url= http://www.british-hydro.co.uk/
| title= 1.0 Mini-hydro: a step-by-step guide
|author= |last= |first= |authorlink= |coauthors=
|date= | year= 2004 |month= |format= |work= | publisher= British Hydro Association
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> which avoid many of the problems of the larger dams.

=== Solar power ===

], ], ], was clad in ] panels at a cost of £5.5 million. It started feeding electricity to the ] in November 2005.]]
{{Main|Solar power}}

Commercial ]s can presently convert about 15 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.<ref name="physicsweb">{{cite web
| url= http://physicsweb.org/articles/world/14/6/2/1
| title= Do we need nuclear power?
|author= |last= |first= |authorlink= |coauthors=
| date= Jun 5, 2001 |work= | publisher= Physicsworld.com
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> Solar cells can also be placed on top of existing urban infrastructure (see ]) or in little-used land like deserts and does then not require re-purposing of cropland or parkland. The ] currently has a huge ] 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 ] energy.{{Fact|date=October 2007}} ] collectors can capture 70 to 80 percent of ] as usable heat. ] and ]s can heat and cool residences and other buildings. A ] is another concept. When solar gets cheap enough to compete with other energy resources, it holds huge potential to convey electricity to regions with under-developed grid systems.

=== Wind power ===
{{Main|Wind power}}
Wind power is one of the most cost-competitive renewables today. Its long-term technical potential is believed to be 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.<ref>{{cite web
| url= http://www.stanford.edu/group/efmh/winds/global_winds.html
| title= Evaluation of global wind power
| author= Cristina L. Archer | coauthors= Mark Z. Jacobson
| date= 3 February 2005 |work= | publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref><ref>{{cite web
| url= http://www.ens-newswire.com/ens/may2005/2005-05-17-09.asp#anchor6
| title= Global Wind Map Shows Best Wind Farm Locations
|author= |last= |first= |authorlink= |coauthors=
| date= May 17, 2005 |work= | publisher= Environment News Service
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> This number could also increase with higher altitude ground based or airborne turbines.<ref>{{cite web
| url= http://www.wired.com/news/planet/0,2782,67121,00.html?tw=wn_tophead_2
| title= "Windmills in the Sky"
| author= David Cohn
| date= 04.06.05 | publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref>

=== Geothermal power ===
{{Main|Geothermal power}}
Geothermal power and ] 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.<ref name="skov"/> At the moment ] and ] are two of the greatest users of geothermal energy, although many others also have potential. Countries are also researching ] geothermal technologies which have some possibilities.

=== Ocean thermal energy conversion ===
{{main|Ocean thermal energy conversion}}
Ocean thermal energy conversion is another renewable with large potential. Several other variations of utilizing energy from the sun also exist, see ]. Circulating cool water from deep in the ocean up to the surface, and warm water from the surface to the depths produces temperature differentials that useful power can be extracted from.

=== Bioenergy ===
{{Main|Biofuel}}

] (burning biological materials to generate heat), ] (processing biological materials to generate fuels such as ] and ]), and ] (using ] to generate ] from ] material & ]) are other renewables. Systems such as advanced ]s offer the ability to produce medium-sized power generation (2–10&nbsp;MW) facilities and offer flexibility. They can cost-effectively recover value from ] (like citrus peels) whilst producing power from a renewable energy source.<ref> (PDF), Finstein, M. S., Zadik, Y., Marshall, A. T. & Brody, D. (2004) The ArrowBio Process for Mixed Municipal Solid Waste – Responses to “Requests for Information”, Proceedings for Biodegradable and Residual Waste Management, Proceedings. (Eds. E. K. Papadimitriou & E. I. Stentiford), Technology and Service Providers Forum, p. 407–413.</ref> The efficiency of some types of biofuel production can be enhanced with ]. Most carbon-based biofuels emit ] ] during their production and consumption. They often consume land, water, and agricultural resources that might otherwise be used for food production.

=== Wave power ===
{{main|Wave power}}
Wave power is the extraction of energy from waves in large bodies of water such as oceans and large lakes. Wave power is a form of renewable energy that is on the rise. It should not be confused with Tidal power, which involves construction of a dam or "power tower" (which is basically a large tube which waves push air through to create power with turbines), which are both structures connected to the land. Wave power is harnessed by other means, including floating objects or machines on the floor of the body of water (see ]).

=== Tidal power ===

: ''Main article: ]''

Tidal energy involves building a ] across the opening to a tidal basin, called an ]. The dam, called a ], is composed of ]s, located within ]s in the dam that rotate when a tide comes in, generating electricity.

=== 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 ], 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 ] 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 ], 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, ] are a hundred times less expensive today than the 1970s and development continues.<ref name="physicsweb"/><ref>{{cite web
| url= http://news.nationalgeographic.com/news/2005/01/0114_050114_solarplastic.html
| title= "Spray-On Solar-Power Cells Are True Breakthrough"
| author= Stefan Lovgren
| date= January 14, 2005 |work= | publisher= '']''
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> Solar breeder technologies, where the energy used to make solar cells is itself solar energy, is also being investigated.<ref>{{cite web
| url= http://www.nrel.gov/pv/thin_film/docs/environmental_aspects_of_pv_power_systems_iea_workshop.pdf
| title= Environmental Aspects of PV Power Systems
| author= E. A. Alsema | coauthors= E. Nieuwlaar | date= 12/1997 | format= ] |work=
| publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= }} </ref>

== Increased efficiency in current energy use ==

New technology may make better use of already available energy through improved efficiency, such as more efficient ]s, ]s, and ]. Using ]s, 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 ] could also be in this category, allowing recovery of some of the energy in hydrocarbon waste. ] production is energy inefficient compared to the production of protein sources like ] or ]. Already existing ] 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 ]. New designs for buildings may incorporate techniques like ]. ]s are gradually replacing the remaining uses of ]s. Note that none of these methods allows ], as some energy is always lost to heat.

] increases energy efficiency compared to widespread conventional automobile use while ] 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. ] 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 ] or ] engines can improve mileage. ] such as ], ]es, and ]s 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. ]s or motorcycles may replace automobiles carrying only one or two people. Transportation efficiency may also be improved by in other ways, see ].

] 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 ] or improved ] may also decrease the energy lost. ] 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, ], and trading of emission rights. Smart appliances that require only intermittent use (like laundry machines and dishwashers) could be programmed to start only when demand is low at night or during sunny or windy periods of peak production in the case of solar and wind power.

== Energy storage and transportation fuel ==

There is a widely held misconception that ] 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 ] as a general ] 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 ], ], and ]. 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, ], ocean thermal energy conversion, high altitude airborne wind turbines, ], and ]s. Solar photovoltaics, although technically intermittent, produces electricity during peak periods, and hence does reduce the need for ]. 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 ]. Various chemical processes can convert the carbon and hydrogen in coal, natural gas, plant and animal ], and organic wastes into short hydrocarbons suitable as transportation fuels. Examples of such fuels are ] diesel, ], ], or ]. 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.<ref>{{cite web
| url= http://www.eere.energy.gov/afdc/pdfs/epa_fischer.pdf
| title= Clean Alternative Fuels: Fischer-Tropsch
|author= |last= |first= |authorlink= |coauthors=
|date= |year= |month= |format= |work=
| publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> A long term oil price above 35 USD may make such liquid fuels economical on a large scale (See ]). Some of the energy in the original source will be lost in the conversion process. ] 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 ].

] 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 ] which can produce various ] such as ], ]s, or biomass which can be broken down into the fuels mentioned above. The energy could also come from sunlight using future ] technology.<ref>{{cite web
| url= http://www.bnl.gov/bnlweb/pubaf/pr/2003/bnlpr090903.htm
| title= Designing a Better Catalyst for “Artificial Photosynthesis”
|author= |last= |first= |authorlink= |coauthors=
|date= September 9, 2003 |work= |publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref><ref>
{{cite web
| url= http://www.lbl.gov/Science-Articles/Archive/sabl/2005/May/01-solar-to-fuel.html
| title= Solar to Fuel: Catalyzing the Science
|author= |last= |first= |authorlink= |coauthors=
|date= May 13, 2005 |work= |publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> Another alternative for the energy is electricity or heat from renewables or nuclear power.<ref>{{cite web
| url= http://www.newscientist.com/article.ns?id=dn2620
| title= "Carbon dioxide turned into hydrocarbon fuel"
|author= Eugenie Samuel
|date= 02 August 2002 |work= |publisher= '']''
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref><ref>
{{cite web
| url= http://www.americanenergyindependence.com/recycleco2.html
| title= CO2 Recycling: Capturing Carbon Dioxide Directly from the Air
|author= |last= |first= |authorlink= |coauthors=
|date= |year= |month= |format= |work= |publisher= AmericanEnergyIndependence.com
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> Compared to hydrogen, many hydrocarbons fuels have the advantage of reusing existing engine technology and existing fuel distribution infrastructure.

] and ]s using ] or non-hydrogen ]s are other alternatives. Electricity may be the only power source or combined with other fuels in ]s. Nuclear power has been used in large ships.<ref>{{cite web
| url= http://db.world-nuclear.org/info/inf34.html
| title= Nuclear-Powered Ships
|author= |last= |first= |authorlink= |coauthors=
|date= March 2007 |work= |publisher= World Nuclear Association
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> High technology ] could provide some of the power for ships.<ref>{{cite web
| url= http://technology.newscientist.com/article/mg18524881.600.html
| title= "The new age of sail"
|author= Mick Hamer
|date= 26 February 2005 |work= |publisher= '']''
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> Several companies are proposing vehicles using ] for power.<!-- Bad link. <ref>{{cite web
| url= http://www.freep.com/money/autonews/aircar18_20040318.htm
| title=
|author= |last= |first= |authorlink= |coauthors=
|date= |year= |month= |format= |work= |publisher=
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= }} </ref> --><ref>
{{cite web
| url= http://science.slashdot.org/article.pl?sid=05/04/03/2335206&from=rss
| title= Car Powered by Compressed Air
|author= |last= |first= |authorlink= |coauthors=
|date= Apr 04, 2005 |format= |work= |publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> ]s require less onboard fuel than a traditional aircraft and combining airship technology with ] technology may eliminate onboard fuel completely.<ref>{{cite web
| url= http://www.worldchanging.com/archives/002239.html
| title= Airships Plus Gliders
| author= Jeremy Faludi | date= February 28, 2005 |work= | publisher= Worldchanging
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> ] and some ] systems, like ], ] or ]s, can use electricity directly from the grid and do not need a liquid fuel or battery.

],<ref>{{cite web
| url= http://www.eagle.ca/~gcowan/boron_blast.html
| title= Boron: A Better Energy Carrier than Hydrogen?
|author= Graham R.L. Cowan
|date= | year= 2004 |month= |format= |work= |publisher=
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> ],<ref>{{cite web
| url= http://www.dbresearch.com/PROD/DBR_INTERNET_EN-PROD/PROD0000000000079095.pdf
| title= Silicon as an intermediary between renewable energy and hydrogen
| author= Norbert Auner | date= May 5, 2004 | format= ] |work=
| publisher= ]
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> and ]<ref>{{cite web
| url= http://ergosphere.blogspot.com/2005/06/zinc-miracle-metal.html
| title= Zinc: Miracle metal?
|author= |last= |first= |authorlink= |coauthors=
|date= June 29, 2005 |work= |publisher= The Ergosphere
|pages= |language= |doi= |archiveurl= |archivedate= |quote=
| accessdate= 2008-01-19 }} </ref> have also been proposed as energy storage solutions.

== Space exploration ==

In the long-term future ] 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 ]s, where ]s are placed on orbiting platforms in 24-hour sunlight; the energy is then beamed to earth as ]s received by arrays of receiving antennas. A fundamental development in space launch technology (such as a ]) 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 ] control of remote human workers<ref> ]; Driggers, G.; and ]: "New Routes to Manufacturing in Space". ''Astronautics and Aeronautics'', vol. 18, October 1980, pp. 46–51.</ref>

Fissionable materials could theoretically be obtained from ]; 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 ] from the ] for use in ] 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 ]s.

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 ]) there has been speculation as to how an extremely advanced society might exploit the mass-energy conversion capabilities of ]s (like the ]). Such technologies are obviously far beyond our present capabilities, and are at this stage essentially ]s for engineers and science fiction writers.

== See also ==
{{EnergyPortal}}

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== References ==
{{reflist|2}}

== Further reading ==

* Greene, D.L. & J.L. Hopson. (2003). 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.

== External links ==
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=== Organizations ===

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=== Articles ===

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* Online book by Albert J. Fritsch, Arthur H. Purcell, and Mary Byrd Davis (2005)
* , ''The Quaker Economist'', vol. 7, #155, 2007.

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