Future energy development faces great challenges due to an increasing 
world population, demands for higher standards of living, demands for less pollution and a much discussed end to fossil fuels. Failure would result in overpopulation and a Malthusian catastrophe.
General considerations
All the energy we consume is generated by using the four fundamental forces of nature: Gravity, electromagnetism, the weak nuclear force and the strong nuclear force to create work. Fission energy and fusion energy are generated by the strong nuclear force. Many renewables and fossil fuel energy comes from solar energy which comes from fusion energy. Radioactive decay energy is generated by the weak nuclear force. Tidal energy comes from the gravity energy of the Earth/Moon system.
Most human energy sources today use energy from sunlight, either directly like solar cells or in stored forms like fossil fuels. The exceptions are nuclear power, geothermal power and tidal power. 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 [1] (http://www.aims.ac.za/~mackay/oomm.html)[2] (http://www.world-builders.org/lessons/less/biomes/SunEnergy.html).
World energy production by source: Oil 40%, natural gas 22.5%, coal 23.3%, nuclear 6.5%, hydroelectric 7.0%, biomass and other 0.7% [3] (http://energy.cr.usgs.gov/energy/stats_ctry/Stat1.html). 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 [4] (http://www.spe.org/spe/jpt/jsp/jptmonthlysection/0,2440,1104_11038_1040074_1202151,00.html).
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 [5] (http://www.un.org/esa/population/unpop.htm). Still, economic growth probably requires a continued increase in energy consumption.
The Kardashev scale theory is a general method of classifying how technologically advanced a civilization is, based on the amount of usable energy a civilization has at its disposal.
Fossil fuels
Fossil fuels supply most of the energy consumed today. But fossil fuels have great problems with pollution, including contributing to global warming and mainly coal causing tens of thousands of deaths each year in the US alone. [6] (http://www.twnside.org.sg/title/plant.htm) They are also finite. See Hubbert peak for a discussion about the peaking of oil and other fossil fuels.
Energy production usually requires an energy investment. Drilling for oil or building a wind power plant requires energy. The fossil fuel reserves that are left are often increasingly more 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 reserve is no longer an energy source. This means that a large part of the fossil fuel reserves and especially the non-conventional ones cannot be used for energy production today. Such reserves may still be exploited in order to produce raw materials for plastics, fertilizers or even transportation fuel but now more energy is consumed than produced. New technology may ameliorate this problem if it can lower the energy investment required to extract and convert the reserves.
Oil
Conventional oil
Main article: Hubbert peak
The pessimists predict that conventional oil production will peak in 2007. 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).
Non-conventional oil
Main article: Non-conventional oil
Non-conventional types of production include: tar sands, oil shale and bitumen. These reserves are estimated to contain three times as much oil as the remaining conventional oil reserves but few are economically recoverable with current technology [7] (http://www.btinternet.com/~nlpwessex/Documents/DeutscheBankOil.htm). The mining and conversion to liquid fuel may cause these non-conventional oils to be significantly more polluting than conventional oil from drilling.
Oil can also be produced by thermal depolymerization (TDP) from organic wastes, and by the the conversion of coal or natural gas to liquid hydrocarbon through the Fischer-Tropsch process.
Natural gas
Conventional natural gas
The turning point for conventional natural gas will probably be somewhat later than for oil [8] (http://www.btinternet.com/~nlpwessex/Documents/DeutscheBankOil.htm). The pessimists predict a peak for conventional gas production between 2010 and 2020.
Non-conventional natural gas
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 [9] (http://www.naturalgas.org/overview/unconvent_ng_resource.asp)[10] (http://www.naturalgas.org/overview/resources.asp).
Vast quantities of methane hydrate are inferred from the actual finds. Methane hydrate is a clathrate,a crystaline form in which methane molecule is 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. Inferred quantities of methane hydrates exceed those of all other fossil fuels combined, including oil, conventional natural gas and coal [11] (http://www.iea.org/textbase/nppdf/free/2000/weo2001.pdf).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 [12] (http://www.mh21japan.gr.jp/english/mh21/02keii.html).
There are several companies developing the Fischer-Tropsch process to enable practical exploitation of so-called stranded gas reserves.
Coal
There are large but finite coal reserves which may increasingly be used as an energy source source during oil depletion. There are 200 years of proven reserves of coal at the current consumption. Reserves have increased by over 50% in the last 22 years and are expected to continue to increase [13] (http://wci.rmid.co.uk/uploads/RoleofCoal.pdf). Large amounts of coal waste that has been produced during coal mining and stored near the mines could become exploitable with new technology [14] (http://www.ultracleanfuels.com/main.htm).
Coal is traditionally viewed as one of the most polluting energy sources although this problem may be lessened with new ways of burning it and cleaning up the exhaust.
Nuclear power
Main article: Nuclear power
The United States would require at least an elevenfold increase in nuclear power production to replace current fossil fuel use for stationary power generation and transportation all by itself. Nuclear power may produce hydrogen at a low cost. This hydrogen may be used for enriching hydrogen poor hydrocarbon fuels or precursors (heavy oil, tar sands, coal, etc) that exist on North American soil.
At the present use rate, there are 50 years left of low cost known uranium reserves [15] (http://www.world-nuclear.org/info/inf75.htm). Given that the cost of fuel is a minor cost factor for fission power, more expensive, lower grade, sources of uranium could be used in the future. For example: extraction from seawater or granite. Another alternative would be to use thorium as fission fuel. Thorium is three times more abundant in the Earth crust than uranium [16] (http://www.world-nuclear.org/info/inf62.htm).
Current light water reactors burn the nuclear fuel poorly, leading to energy waste. Nuclear reprocessing [17] (http://www.world-nuclear.org/info/inf04.htm), 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 burn Uranium-235, fast breeder reactors produce Plutonium 239 from Uranium-238, and then fission that to produce electricity and thermal heat. 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 [18] (http://www-formal.stanford.edu/jmc/progress/cohen.html). Breeder technology has been used in several reactors [19] (http://www.world-nuclear.org/info/inf08.htm).
The possibility of reactor accidents, like the Three Mile Island and Chernobyl meltdowns, 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. Coal and hydropower has caused many more deaths per energy unit produced than nuclear [20] (http://www.world-nuclear.org/info/inf06.htm). 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 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. U.S nuclear waste from various locations is planned to be entombed inside Yucca Mountain, Nevada. Nuclear waste takes up little space compared to wastes from the chemical industry which remain toxic indefinitely [21] (http://www.world-nuclear.org/info/inf04.htm). In the future, fusion or ADS systems could eliminate waste [22] (http://www.world-nuclear.org/info/inf35.htm). In the meantime, spent fuel rods are stored in concrete casks close to the nuclear reactors [23] (http://www.wired.com/wired/archive/13.02/nuclear.html).
Advocates of nuclear power point out that it is a cost competitive way to produce energy versus fossil fuels, especially if you take into account fossil fuel externalities, the same way nuclear reactors have to pay for their pollution and plant decommissioning costs [24] (http://www.world-nuclear.org/info/inf02.htm). Using life cycle analysis, it takes 4-5 months of energy production from the nuclear plant to fully pay back the initial energy investment. Nuclear energy gives more energy per input energy than many other energy sources. If energy becomes scarce, this could be important [25] (http://www.world-nuclear.org/info/inf11.htm). It is possible to relatively rapidly increase the number of plants. New reactor designs have a construction time of 3-4 years.[26] (http://www.uic.com.au/nip16.htm). 43 plants were being built in 1983, 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 [27] (http://www.wired.com/wired/archive/12.09/china.html)[28] (http://www.world-nuclear.org/info/inf17.htm).
Fusion power could solve many of the problems of fission power (the technology mentioned above) but, despite research having started in the 1950s, no commercially useable reactor is expected within decades. One estimate is that there will be no commercial reactor before 2050 [29] (http://www.iter.org/index.htm). Many technical problems remain unsolved.
Renewable energy
Main article: Renewable energy
Another possible solution to an energy shortage or predicted future shortage would be to use some of the world’s remaining fossil fuel reserves as an investment in renewable energy infrastructure such as wind power, solar power, tidal power, geothermal power, hydropower and biomass like biodiesel. Before the industrial revolution, they were the only energy source used by humanity. Solid biomass like wood is still the main power source for many poor people in developing countries, where overuse may lead to deforestation and desertification
Hydropower is the only renewable today making a large contribution to world energy production. The long-term technical potential is believed to be 9 to 12 times current hydropower production, but increasingly, environmental concerns block new dams [30] (http://www.spe.org/spe/jpt/jsp/jptmonthlysection/0,2440,1104_11038_1040074_1202151,00.html).
Solar cells can convert around 15% of the incoming sunlight to electricity. Solar thermal collectors can capture 70-80% as usable heat. Researchers have estimated that algae farms could convert 10% into biodiesel energy. If built out as solar collectors, 1% 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 50-100 times that of an average hydro scheme. [31] (http://physicsweb.org/articles/world/14/6/2/1)
Wind power is one of the most cost competitive renewables today. Its long-term technical potential is believed to be up to 1.4 times total current world energy use [32] (http://www.spe.org/spe/jpt/jsp/jptmonthlysection/0,2440,1104_11038_1040074_1202151,00.html).
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 equivalant to 1/4 of total human energy consumption today [33] (http://www.spe.org/spe/jpt/jsp/jptmonthlysection/0,2440,1104_11038_1040074_1202151,00.html). Geothermal power has a very large potential if considering all the heat generated inside Earth. Other variations of utilizing energy from the sun also exist, see renewable energy.
Aside from hydropower and geothermal power, which are site-specific, renewable supplies generally have higher costs than fossil fuels if the externalized costs of pollution 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. The fact that small diesel generators are not hugely efficient and the fact that they consume fuel and make noise even when offload also makes renewables seem more desirable in this situation.
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. Furthur development of intermittent renewable power will require simultaneous development of energy storage systems like compressed air energy storage, hydroelectric pumped storage, or hydrogen storage to provide power when needed rather than when available. Intermittent energy sources may be limited to at most 20-30% of the electricity produced for the grid without such storage systems.
Most renewable sources are diffuse and require large land areas and great quantities of construction material for significant energy production. There is some doubt that they can be built out rapidly enough to replace fossil fuels [34] (http://physicsweb.org/articles/world/14/6/2/1).
There is some hope that furthur investment in R&D might bring down the cost of some renewable energy sources. 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. Larger scale production of renewable sources might also decrease unit costs.
Renewable sources currently make most sense in less developed areas of the world, where the population density cannot economically support the construction of an electrical grid or petroleum supply network. Without these investments, fossil fuel energy sources do not enjoy large economies of scale, and distributed, small-scale electrical generation from renewables is often cheaper.
Increased efficiency in current energy use
New technology may make better use of already available energy, examples being more efficient lightbulbs, 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. Mass transportation increases energy efficiency compared to widespread automobile use while air travel in its current form is regarded as inefficient. Thermal depolymerization 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. Note that none of these methods allows perpetual motion, some energy is always lost to heat.
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 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.
Energy storage and transportation fuel
There is a widely held misconception that hydrogen is an alternative energy source. As there are no uncombined hydrogen reserves on Earth (what there is resides in Earth’s outer exosphere), hydrogen is itself not a source of chemical energy. Hydrogen-based energy always involves conversion of an upstream energy source. Typically, this energy source is natural gas or electricity (generated by fossil fuels, nuclear or renewables). Biomass or coal gasification, photoelectrolysis, and genetically modified organisms have also been proposed as means to produce hydrogen.
Hydrogen may play a role as a means of storage of energy for intermittent power sources, like solar power, and as transportation fuel for vehicles (see Hydrogen economy). However, the idea is currently impractical: hydrogen is inefficient to produce, and expensive to store, transport, and convert back to electricity. New technology may change this in the future.
Alternatives to hydrogen as energy storage are discussed in renewable energy. Boron [35] (http://www.eagle.ca/~gcowan/boron_blast.html) or silicon [36] (http://www.dbresearch.com/PROD/DBR_INTERNET_EN-PROD/PROD0000000000079095.pdf) has also been proposed as better alternatives to hydrogen . Some energy will be lost when converting to and from storage and the storage systems will also add to the cost of the intermittent energy sources requiring them.
There are also other alternatives for transportation fuel. The Fischer-Tropsch process converts coal, natural gas, and low-value refinery products into diesel. This process was developed and used extensively in World War II by the Germans, who had limited access to crude oil supplies. It is today used in South Africa to produce most of country’s diesel from coal. [37] (http://www.eere.energy.gov/afdc/pdfs/epa_fischer.pdf) This technology could be used as an interim transportation fuel if conventional oil were to disappear. Coal itself has historically been used directly for transportation purposes in vehicles and boats using steam engines.
Liquid biofuel like methanol, ethanol and biodiesel can be used in internal combustion engines with minor modifications. Oil from thermal depolymerization is also usable in vehicles. Compared to hydrogen, these potential energy sources have the advantage of reusing existing engine technology and existing fuel distribution infrastructure.
Nuclear power has been used in large ships [38] (http://www.world-nuclear.org/info/inf34.htm). Electric vehicles and electric boats not using hydrogen are other alternatives. Some mass transportation systems, like trolleybus or metro, can use electricity directly from the grid and do not need a liquid fuel or battery.
Speculative
Abiogenic petroleum origin and cold fusion has been proposed as very controversial future sources of energy. Space exploration could yield energy sources from satellites (see solar power satellite), from the moon (see helium-3), from other planets (see abiogenic petroleum origin for a list of planets with hydrocarbons), and from a Dyson sphere. The accretion disc of a black hole can convert about 50% of the mass energy of an object into radiation, as opposed to nuclear fusion which can only convert a few percent of the mass to energy.
This article can be modified at the source http://en.wikipedia.org/wiki/Future_energy_development