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World power usage in terawatts (TW), 1965-2005. ^[1]

Global power usage in successively increasing detail^[2][3]

Energy Intensity of different economies The graph shows the amount of energy it takes to produce a US $ of GNP for selected countries. GNP is based on 2004 purchasing power parity and 2000 dollars adjusted for inflation.^[4]

Energy consumption per capita versus the GNP per capita The graph plots the per capita energy versus the per capita income for all countries with more than 20 million inhabitants, the data more than 90% of the world's population. The image shows the broad relation between wealth and energy consumption.^[5]

GDP and Energy consumption in Japan from 1958 - 2000 The data shows the strong correlation between GDP and energy use, however it also shows that this link can be broken. After the oil shocks of 1973 and 1979 the energy use stagnated while Japan's GDP continued to grow, after 1985, under the influence of the then much cheaper oil, energy use resumed its historical relation to GDP.^[6]

Worldwide overview of nuclear power. Nations in very faint green are constructing their first reactor, those red have decommissioned their last.^{[citation needed]}

Worldwide energy supply in TW^[4]

Remaining Oil Breakdown of the remaining 57 ZJ oil on the planet in ZJ(=10²¹J). The annual oil consumption was 0.18 ZJ in 2005. There is significant uncertainty surrounding these numbers. The 11 ZJ of future additions to the recoverable reserves could be optimistic.^[7][8]

World renewable energy in 2005 (except 2004 data for items marked* or **).^[3]

Available renewable energy. The volume of the cubes represent the amount of available wind and solar energy. The small red cube shows the proportional global energy consumption. Values are in TW =10¹² Watt. The amount of available renewable energy dwarfs the global consumption.^[9]

Solar energy as it is dispersed on the planet and radiated back to space. Values are in PW =10¹⁵ Watt.^[10]

The remaining world energy resources are large, compared to world energy consumption. To make it easier to compare the numbers, this article uses SI units and prefixes and measures energy rate (or power) in watts (W) and amounts of energy in joules (J).

In 2004, the average total worldwide power consumption of the human race was 15 TW (= 1.5 x 10¹³ W) with 86.5% from burning fossil fuels.^[1] This is equivalent to 0.5 ZJ (= 5 x 10²⁰ J) per year, although there is at least 10% uncertainty in the world's energy consumption. Not all of the world's economies track their energy consumption with the same rigor, and the exact energy content of a barrel of oil or a ton of coal will vary with quality.

Most of the world energy resources are from the sun's rays hitting earth - some of that energy has been preserved as fossil energy, some is directly or indirectly usable e.g. via wind, hydro or wave power. The term solar constant is the amount of incoming solar electromagnetic radiation per unit area, measured on the outer surface of Earth's atmosphere, in a plane perpendicular to the rays. The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly 1366 watts per square meter, though it fluctuates by about 6.9% during a year - from 1412 W/m2 in early January to 1321 W/m2 in early July, due to the earth's varying distance from the sun, and by a few parts per thousand from day to day. For the whole Earth, with a cross section of 127,400,000 km², the power is 1.740×10¹⁷ W, plus or minus 3.5%.

The remaining worldwide energy resources are large, with the remaining fossil fuels totaling an estimated 0.4 YJ (1 YJ = 10²⁴J) and the available nuclear fuel such as uranium exceeding 2.5 YJ. Fossil fuels range from 0.6-3 YJ if estimates of reserves of methane clathrates are accurate and become technically extractable. Mostly thanks to the Sun, the world also has a renewable usable energy flux that exceeds 120 PW (8,000 times 2004 total usage), or 3.8 YJ/yr, dwarfing all non-renewable resources. Even that amount is also only a minute amount of the sun's total energy output, due to the small solid angle the earth's outline makes with the sun.

Since the advent of the industrial revolution, the worldwide energy consumption has been growing steadily. In 1890 the consumption of fossil fuels roughly equaled the amount of biomass fuel burned by households and industry. In 1900, global energy consumption equaled 0.7 TW(=10¹² Watt.)^[11]

Main article: fossil fuel

The twentieth century saw a rapid twentyfold increase in the use of fossil fuels. Between 1980 and 2004, the worldwide annual growth rate was 2%. ^[1] According to the US Energy Information Administration's 2006 estimate, the estimated 15TW total energy consumption of 2004 was divided as follows, with fossil fuels supplying 86% of the world's energy:

Coal fueled the industrial revolution in the 18^th and 19^th century. With the advent of the automobile, airplanes and the spreading use of electricity, oil became the dominant fuel during the twentieth century. The growth of oil as the largest fossil fuel was further enabled by steadily dropping prices from 1920 until 1973. After the oil shocks of 1973 and 1979, during which the price of oil increased from 5 to 45 US dollars per barrel, there was a shift away from oil.^[12] Coal and nuclear became the fuels of choice for electricity generation and conservation measures increased energy efficiency. In the US the average car more than doubled the number of miles per gallon. Japan, who bore the brunt of the oil shocks, made spectacular improvements and now has the highest energy efficiency in the world.^[5] Over the last forty years, the use of fossil fuels has continued to grow and their share of the energy supply has increased. In the last three years, coal, which is one of the dirtiest sources of energy,^[13] has become the fastest growing fossil fuel.^[14]. Photovoltaics are rapidly becoming available to replace fossil fuels as the dominant energy source. Note the earlier comparison of availability: The total resources of all fossil fuels amount to about 0.4 YJ total, while the availability of solar power is 3.8 YJ per year.

Main articles: Nuclear energy policy and Nuclear power by country

In 2005 nuclear energy accounted 6.3% of world's total primary energy supply.^[15] The nuclear power production in 2006 accounted 2,658 TWh, which was 16% of world's total electricity production.^[16][17] In November 2007, there were 439 operational nuclear reactors worldwide, with total capacity of 372,002 MWe. A further 33 reactors were under construction, 94 reactors were planned and 222 reactors were proposed.^[16] Among the nations not currently using nuclear power, 25 countries are building them, or are proposing to do so.^[18] A few nations have announced plans to phase out nuclear power altogether, but to date only Italy has done so (though Italy continues to import electricity from nations with active nuclear power plants).^[19] In addition, while Austria^[20], the Philippines^[21] and North Korea^[22] have built nuclear power stations, these nations abandoned them before they could be fueled and operated.

Main article: Renewable energy

In 2004, renewable energy supplied around 7% of the world's energy consumption.^[23] The renewables sector has been growing significantly since the last years of the 20th century, and in 2005 the total new investment was estimated to have been 38 billion US dollars. Germany and China lead with investments of about 7 billion US dollars each, followed by the United States, Spain, Japan, and India. This resulted in an additional 35 GW of capacity during the year.^[3]

Main article: hydropower

Worldwide hydroelectricity consumption reached 816 GW in 2005, consisting of 750 GW of large plants, and 66 GW of small hydro installations. Large hydro capacity totaling 10.9 GW was added by China, Brazil and India during the year, but there was a much faster growth (8%) in small hydro, with 5 GW added, mostly in China where some 58% of the world's small hydro plants are now located.^[3]

In the Western world, although Canada is the largest producer of hydroelectricity in the world, the construction of large hydro plants has stagnated due to environmental concerns.^[24]

Main articles: biomass and biofuel

Until the end of the nineteenth century biomass was the predominant fuel, today it has only a small share of the overall energy supply. Electricity produced from biomass sources was estimated at 44 GW for 2005. Biomass electricity generation increased by over 100% in Germany, Hungary, the Netherlands, Poland and Spain. A further 220 GW was used for heating (in 2004), bringing the total energy consumed from biomass to around 264 GW. The use of biomass fires for cooking is excluded.^[3]

World production of bioethanol increased by 8% in 2005 to reach 33 billion litres (8.72 billion US gallons), with most of the increase in the United States, bringing it level to the levels of consumption in Brazil.^[3] Biodiesel increased by 85% to 3.9 billion litres (1.03 billion US gallons), making it the fastest growing renewable energy source in 2005. Over 50% is produced in Germany.^[3]

Main article: Wind power

According to the Global Wind Energy Council, the installed capacity of wind power increased by 25.6% in from the end of 2005 to end of 2006 to total 74 GW with over half the increase in the United States, Germany, India and Spain.^[25] Doubling of capacity took about three and half years. The total installed capacity is approximately three times that of the actual average power produced as the nominal capacity represents peak output; actual capacity is generally from 25-40% of the nominal capacity.^{[citation needed]}

Main article: Solar energy

Solar energy used during 2005 was approximately 93.4 GW, however the available resources are 3.8 YJ/yr (120,000 TW). Only a small fraction of available resources are sufficient to entirely replace fossil fuels and nuclear power as an energy source, however it is likely that at least biodiesel will always be used in certain types of transport. Assuming that our current rate of usage remains constant, we will run out of conventional oil in 35 years, coal in 200 yrs. In practice neither will actually run out, as natural constraints will force production to decline as the remaining reserves dwindle.^[26][27]

In 2005 grid-connected photovoltaic electricity was the fastest growing renewable energy after biodiesel. During the year consumption increased by 55% on 2004 to bring the installed capacity to 3.1 GW. Over half of the increase was in Germany, now the world's largest consumer of photovoltaic electricity (followed by Japan). It was estimated that there was a further 2.3 GW of off-grid electricity produced, bringing the total to 5.4 GW.^[3]

Portugal has opened the world's most powerful photovoltaic solar power plant. The 11 megawatt solar power plant, comprising 52,000 photovoltaic modules is based in southern Portugal which is one of the sunniest places in Europe. It produces sufficient energy to power 8000 homes (see Renewable energy in Portugal).^[28]

The consumption of solar hot water and solar space heating was estimated at 88 GWt (gigawatts of thermal power) in 2004. The heating of water for unglazed swimming pools is excluded.^[3]

Main article: Geothermal power

Geothermal energy is used commercially in over 70 countries.^[29] By the end of 2005 worldwide use for electricity had reached 9.3 GW, with an additional 28 GW used directly for heating.^[3] If heat recovered by ground source heat pumps is included, the non-electric use of geothermal energy is estimated at more than 100 GW.^[29]

See also: Energy by country

Energy consumption broadly tracks with gross national product, although there is a significant difference between the consumption levels of the United States with 11.4 kW per person and Japan and Germany with 6 kW per person. Canada has the highest energy consumption per person, whereas the lowest energy consumption takes place in developing and under-developed economies. In developing countries such as India the per person energy use is closer to 0.5 kW.^{[citation needed]}

The most significant growth of energy consumption is currently taking place in China, which has been growing at 5.5% per year over the last 25 years. Its population of 1.3 billion people is currently consuming energy at a rate of 2 kW per person.^{[citation needed]}

One metric of efficiency is energy intensity. This is a measure of the amount of energy it takes a country to produce a dollar of gross domestic product. Japan and the UK are among the most efficient in the world, while developing countries lack the resources to buy energy.^{[citation needed]}

Industrial users (agriculture, mining, manufacturing, and construction) consume about 37% of the total 15 TW. Personal and commercial transportation consumes 20%; residential heating, lighting, and appliances use 11%; and commercial uses (lighting, heating and cooling of commercial buildings, and provision of water and sewer services) amount to 5% of the total. ^[30]

The other 27% of the world's energy is lost in energy transmission and generation. In 2005, global electricity consumption equaled 2 TW. The energy used to generate 2 TW of electricity is approximately 5 TW, as the efficiency of a typical existing power plant is around 38%.^[31] The new generation of gas-fired plants reaches a substantially higher efficiency of 55%. Coal is the most popular fuel for the world's electricity plants.^[32]

Main article: Fossil fuel

Remaining reserves of conventional fossil fuels are estimated as:^[8]

Significant uncertainty exists for these numbers. The estimation of the remaining fossil fuels on the planet depends on a detailed understanding of the Earth crust. This understanding is still less than perfect. While modern drilling technology makes it possible to drill wells in up to 3 km of water to verify the exact composition of the geology, one half of the ocean is deeper than 3 km, leaving about a third of the planet beyond the reach of detailed analysis.^{[citation needed]} At the same time, long before fossil fuels run out, the effect of continuing to use them at current rates would cause havoc to the climate through global warming.^[33]

Main article: World coal reserves

Coal is the most abundant fossil fuel. According to the International Energy Agency the proven reserves of coal are around 909 billion tonnes, which could sustain at the current production rate for 155 years.^[34] This was the fuel that launched the industrial revolution and has continued to grow in use; China, which already has many of the worlds most polluted cities,^[35] was in 2007 building about two coal fired power plants every week.^[36][37] Coal is the fastest growing fossil fuel and its large reserves would make it a popular candidate to meet the energy demand of the global community, short of global warming concerns and other pollutants.^[38] With the Fischer-Tropsch process it is possible to make liquid fuels such as diesel and jet fuel from coal. The Stop Coal campaign calls for a moratorium on the construction of any new coal plants and on the phase out of all existing plants, citing concern for global warming.^[39] In the United States, 49% of electricity generation comes from burning coal.^[40]

See also: Oil reserves and Peak oil

It is estimated that there may be 57 ZJ of oil reserves on Earth (although estimates vary from low of 8 ZJ,^[1] consisting of currently proven and recoverable reserves, to a maximum of 110 ZJ^{[citation needed]}) consisting of available, but not necessarily recoverable reserves, and including optimistic estimates for unconventional sources such as tar sands and oil shale. Current consensus among the 18 recognized estimates of supply profiles is that the peak of extraction will occur in 2020 at the rate of 93-million barrels per day (mbd). Current oil consumption is at the rate of 0.18 ZJ per year (31.1 billion barrels) or 85-mbd.

There is growing consensus that peak oil production may be reached in the near future, resulting in severe oil price increases.^{[citation needed]} A 2005 French Economics, Industry and Finance Ministry report suggested a worst-case scenario that could occur as early as 2013.^[41] There are also theories that peak of the global oil production may occur in as little as 2-3 years. The ASPO predicts peak year to be in 2010. Some other theories present the view that it has already taken place in 2005.^{[citation needed]}

There is a broad consensus among scientists that we are not close to running out of fossil fuels.^[9][42] Despite this abundance, political considerations over the security of supplies, environmental concerns related to global warming and sustainability will move the world's energy consumption away from fossil fuels. The concept of peak oil shows that we have used about half of the available petroleum resources, and predicts a decrease of production.

A government led move away from fossil fuels would most likely create economic pressure through carbon emissions trading and green taxation. Some countries are taking action as a result of the Kyoto Protocol, and further steps in this direction are proposed. For example, the European Commission has proposed that the energy policy of the European Union should set a binding target of increasing the level of renewable energy in the EU's overall mix from less than 7% today to 20% by 2020.^[43]

See also: Nuclear power and Nuclear energy policy

See also: Nuclear fuel

The International Atomic Energy Agency estimates the remaining uranium resources to be equal to 2500 ZJ.^[44] This assumes the use of Breeder reactors which are able to create more fissile material than they consume. IPCC estimated uranium deposits for once-through fuel cycles reactors to be only 17 ZJ but then they go on to say that exploration for uranium is still at its infancy.^[45]

Resources and technology do not constrain the capacity of nuclear power to contribute to meeting the energy demand. However, political and environmental concerns about nuclear safety and radioactive waste started to limit the growth of this energy supply at the end of last century, particularly due to a number of nuclear accidents. Concerns about nuclear proliferation mean that the development of nuclear power by countries such as Iran is being actively discouraged by the international community.

Fusion power is what powers the stars. It generates large quantities of heat by fusing the nuclei of hydrogen isotopes. The heat can theoretically be harnessed to generate electricity. The temperatures and pressures needed to sustain fusion make it a very difficult process to control and doing so is an unsolved technical challenge. The tantalizing potential of fusion is its theoretical ability to supply vast quantities of energy, with relatively little pollution.^[46] Both the United States and the European Union are supporting a moderate level of fusion-based research, along with other countries.

Main article: Renewable resource

Renewable resources are available each year, unlike non-renewable resources which are eventually depleted. A simple comparison is a coal mine and a forest. While the forest could be depleted, if it is managed properly it represents a continuous supply of energy, vs the coal mine which once it has been exhausted is gone. Most of earth's available energy resources are renewable resources. Renewable resources account for more than 93 percent of total U.S. energy reserves. Annual renewable resources were multiplied times thirty years for comparison with non-renewable resources. In other words, if all non-renewable resources were uniformly exhausted in 30 years, they would only account for 7 percent of available resources each year, if all available renewable resources were developed.^[47]

Main article: Solar energy

Renewable energy sources are even larger than the traditional fossil fuels and in theory can easily supply the world's energy needs. 89 PW^[9] of solar power fall on the planet's surface. While it is not possible to capture all, or even most, of this energy, capturing less than 0.02% would be enough to meet the current energy needs. Barriers to further solar generation include the high price of silicon used to make solar cells, reliance on weather patterns to generate electricity, a lack of space for solar cells in areas of high demand such as cities and they don't produce electricity during the night. The latter is a particular problem in the high northern and southern latitude countries as energy demand is highest during the winter while availability of solar energy is lowest. Globally, solar is the fastest growing source of energy with an annual average growth of 35%, as seen during the past few years. Japan, Europe, China, U.S. and India are the major growing investors in solar energy. Advances in technology and economies of scale along with demand for solutions to global warming have led photovoltaics to become the most likely candidate to replace nuclear and fossil fuels.^[48]

Main article: Wind power

The available wind energy estimates range from 300 TW to 370 TW.^[9] Using the lower estimate, just 5% of the available wind energy would supply the current worldwide energy needs. Most of this wind energy is available over the open ocean. The oceans cover 71% of the planet and wind tends to blow stronger over open water because there are fewer obstructions.

Main articles: Wave power and Tidal power

At the end of 2005, 0.3 GW of electricity was produced by tidal power.^[3] Thanks to the gravitational pull of the moon (68%) and the sun (32%) there is 3 TW of tidal energy available of which approximately 1 percent is practical to exploit. The best site for capturing tidal energy is the much studied Bay of Fundy on the eastern border of the US and Canada. North America's only tidal power station is a 20 MW demonstration unit at the mouth of the Annapolis river in Nova Scotia.^[49]

Waves are derived from wind and wind is derived from solar energy, at each conversion there is approximately two orders drop in available energy. The energy in waves that wash against our shores add up to 3 TW.^[50]

Main article: Geothermal power

Estimates of exploitable worldwide geothermal energy resources vary considerably. According to a 1999 study, it was thought that this might amount to between 65 and 138 GW of electrical generation capacity 'using enhanced technology'.^[51]

A 2006 report by MIT that took into account the use of Enhanced Geothermal Systems (EGS) concluded that it would be affordable to generate 100 GWe (gigawatts of electricity) or more by 2050, just in the United States, for a maximum investment of 1 billion US dollars in research and development over 15 years.^[29]

The MIT report calculated the world's total EGS resources to be over 13 YJ, of which over 200 ZJ would be extractable, with the potential to increase this to over 2 YJ with technology improvements - sufficient to provide all the world's energy needs for several millennia.^[29]

Main articles: biomass and biofuel

Production of biomass and biofuels are growing industries as interest in sustainable fuel sources is growing. Utilizing waste products avoids a food vs. fuel trade-off, and burning methane gas reduces global warming, because even though it releases carbon dioxide, carbon dioxide is 23 times less of a greenhouse gas than is methane.

Main article: hydropower

Hydroelectric power now supplies about 715,000 MWe or 19% of world electricity (16% in 2003). Large dams are still being designed. Nevertheless, hydroelectric power is probably not a major option for the future of energy production in the developed nations because most major sites within these nations are either already being exploited or are unavailable for other reasons, such as environmental considerations.

Japan and Germany have started to make some investments in solar energy. They are now the largest consumers of photovoltaic cells in the world despite their unfavorable geographic locations. Denmark and Germany have installed 3 GW and 17 GW of wind power respectively. In 2005, wind generated 18.5% of all the electricity in Denmark.^[52] Brazil invests in ethanol production from sugar cane which is now a significant part of the transportation fuel in that country. Starting in 1965, France made large investments in nuclear power and to this date three quarters of its electricity comes from nuclear reactors.^[53] Switzerland is planning to cut its energy consumption by more than half to become a 2000 Watt society by 2050 and the United Kingdom is working towards a zero energy building standard for all new housing by 2016. In 2005, the Swedish government announced the oil phase-out in Sweden with the intention to become the first country to break its dependence on fossil fuel by 2020.

In the twenty first century, some of these different energy paths might become more mainstream and start replacing the ubiquitous fossil fuels. It should be noted that between 1950 and 1984, as the Green Revolution transformed agriculture around the globe, world grain production increased by 250%. The energy for the Green Revolution was provided by fossil fuels in the form of fertilizers (natural gas), pesticides (oil), and hydrocarbon fueled irrigation.^[54] The peaking of world hydrocarbon production (Peak oil) may test Malthus critics.^[55]

Energy Portal

Sustainable development Portal

• Category:Energy by country
• Carbon emissions by country
• Earth's energy budget
• Electricity consumption by country
• Electricity generation
• Energy development
• Energy use and conservation in the United Kingdom
• Energy use in the United States
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• Peak oil
• Kardashev scale

• International Energy Agency. (2006) World Energy Outlook 2006. ISBN 92-64-10989-7
• Smil, Vaclav. (2003) Energy at the crossroads MIT Press. ISBN 0-262-19492-9
• Tester, Jefferson W. et al. (2005) Sustainable Energy: Choosing Among Options. The MIT Press. ISBN 0-262-20153-4
• Yergin, Daniel (1993). The Prize. Simon & Schuster: New York. ISBN 0-671-79932-0

• World Energy Outlook
• Official Energy Statistics from the US government
• Annual Energy Review 2006, DOE/EIA-0384(2006), by the U.S. Department of Energy's Energy Information Administration (PDF)
• Statistical Review of World Energy 2007, annual review by BP