definition of Wikipedia
Energy development is the effort to provide sufficient primary energy sources and secondary energy forms for supply, cost, impact on air pollution and water pollution, mitigation of climate change with renewable energy.
Technologically advanced societies have become increasingly dependent on external energy sources for transportation, the production of many manufactured goods, and the delivery of energy services. This energy allows people who can afford the cost to live under otherwise unfavorable climatic conditions through the use of heating, ventilation, and/or air conditioning. Level of use of external energy sources differs across societies, as do the climate, convenience, levels of traffic congestion, pollution and availability of domestic energy sources.
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally replenished). Renewable energy is an alternative to fossil fuels and was commonly called alternative energy in the 1970s and 1980s. In 2009, about 16% of global final energy consumption came from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from hydroelectricity. New renewables (small hydro, modern biomass, wind, solar, geothermal, and biofuels) accounted for another 2.8% and is growing very rapidly. The share of renewables in electricity generation was around 19.4%, with 16.1% of global electricity coming from hydroelectricity and 3.3% from new renewables.
Wind power is growing at the rate of 21% annually, with a worldwide installed capacity of 238 gigawatts (GW) in 2011, and is widely used in Europe, Asia, and the United States. At the end of 2011, cumulative global photovoltaic (PV) installations surpassed 69 GW, an increase of almost 70%, and PV power stations are commonplace in Germany, Italy, and Spain. Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 megawatt (MW) SEGS power plant in the Mojave Desert. The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW. Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18% of the country's automotive fuel. Ethanol fuel is also widely available in the USA.
Climate change concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization. New government spending, regulation and policies helped the industry weather the global financial crisis better than many other sectors. Scientists have advanced a plan to power 100% of the world's energy with wind, hydroelectric, and solar power by the year 2030, recommending renewable energy subsidies and a price on carbon reflecting its cost for flood and related expenses.
While many renewable energy projects are large-scale, renewable technologies are also suited to rural and remote areas, where energy is often crucial in human development. Globally, an estimated 3 million households get power from small solar PV systems. Micro-hydro systems configured into village-scale or county-scale mini-grids serve many areas. More than 30 million rural households get lighting and cooking from biogas made in household-scale digesters. Biomass cookstoves are used by 160 million households.
Wind, water, and solar power using current technology can supply all of the world's energy by 2030, and has the advantage that consumption is reduced by 30%. Excess production would be used to produce hydrogen for use in ships and airplanes. It also has the advantage that it lasts for as long as we are on the planet, vs. less than a century for most of the non-renewable resources. Conventional production of oil peaked in 2006, and the more we use the faster it will be depleted. An investment in non-renewable resources of $8 trillion is required to maintain current levels of production for 25 years, a cost that is avoided by transitioning instead to renewables. A 2010 study estimated that Australia could transition to 100% renewables for $370 billion over a ten year period - about $8/household/week. Driving an electric car is like buying gasoline for $0.60/gallon, although in 2012 an electric car is over $8,000 more than one powered by gasoline. If they were mass produced, this differential would be reversed. The most expensive part, the battery, is projected to be reduced from $12,000 to $1,500 by 2020. Charging an electric car from roof mounted solar panels is almost free, other than the cost of installation, which could be included in the purchase price of the home. Electric cars have almost no maintenance costs. The EV1, an advanced prototypical electric car, was brought in once every 5,000 miles just to rotate the tires and re-fill the windshield washer fluid.
Wind power harnesses the power of the wind to propel the blades of wind turbines. These turbines cause the rotation of magnets, which creates electricity. Wind towers are usually built together on wind farms. Wind power is growing at the rate of 21% annually, with a worldwide installed capacity of 238 gigawatts (GW) in 2009, and is widely used in Europe, Asia, and the United States.
At the end of 2011, worldwide nameplate capacity of wind-powered generators was 238 gigawatts (GW). Energy production was 430 TWh, which is about 2.5% of worldwide electricity usage. Several countries have achieved relatively high levels of wind power penetration, such as 21% of stationary electricity production in Denmark, 18% in Portugal, 16% in Spain, 14% in Ireland, and 9% in Germany in 2010. By 2011, at times over 50% of electricity in Germany and Spain came from wind and solar power. As of 2011, 83 countries around the world are using wind power on a commercial basis.
Many of the largest operational onshore wind farms are located in the USA. As of 2012, the Alta Wind Energy Center is the largest onshore wind farm in the world, with a capacity of 1020 MW of power, followed by the Roscoe Wind Farm (781.5 MW). The Walney Wind Farm in the Irish Sea is the largest offshore wind farm in the world at 367 MW, followed by Thanet Wind Farm (300 MW) in the English Channel.
In hydro energy, the gravitational descent of a river is compressed from a long run to a single location with a dam or a flume. This creates a location where concentrated pressure and flow can be used to turn turbines or water wheels, which drive a mechanical mill or an electric generator.
In some cases with hydroelectric dams, there are unexpected results. One study shows that a hydroelectric dam in the Amazon has 3.6 times larger greenhouse effect per kW•h than electricity production from oil, due to large scale emission of methane from decaying organic material, though this is most significant as river valleys are initially flooded, and are of much less consequence for more boreal dams. This effect applies in particular to dams created by simply flooding a large area, without first clearing it of vegetation. There are however investigations into underwater turbines that do not require a dam. And pumped-storage hydroelectricity can use water reservoirs at different altitudes to store wind and solar power.
Solar power involves using solar cells to convert sunlight into electricity, using sunlight hitting solar thermal panels to convert sunlight to heat water or air, using sunlight hitting a parabolic mirror to heat water (producing steam), or using sunlight entering windows for passive solar heating of a building. It would be advantageous to place solar panels in the regions of highest solar radiation.
At the end of 2011, cumulative global photovoltaic (PV) installations surpassed 69 GW and PV power stations are common in Germany, Italy, and Spain. Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 megawatt (MW) SEGS power plant in the Mojave Desert.
China is increasing worldwide silicon wafer capacity for photovoltaics to 2,000 metric tons by July 2008, and over 6,000 metric tons by the end of 2010. Significant international investment capital is flowing into China to support this opportunity. China is building large subsidized off-the-grid solar-powered cities in Huangbaiyu and Dongtan Eco City. Much of the design was done by Americans such as William McDonough.
Many solar photovoltaic power stations have been built, mainly in Europe. As of April 2012, the largest photovoltaic (PV) power plants in the world are the Charanka Solar Park (India, 214 MW), and the Golmud Solar Park (China, 200 MW).
Biomass production involves using garbage or other renewable resources such as corn or other vegetation to generate electricity. When garbage decomposes, the methane produced is captured in pipes and later burned to produce electricity. Vegetation and wood can be burned directly to generate energy, like fossil fuels, or processed to form alcohols. Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18% of the country's automotive fuel. Ethanol fuel is also widely available in the USA.
Vegetable oil is generated from sunlight, H2O, and CO2 by plants. It is safer to use and store than gasoline or diesel as it has a higher flash point. Straight vegetable oil works in diesel engines if it is heated first. Vegetable oil can also be transesterified to make biodiesel, which burns like normal diesel.
Geothermal energy harnesses the heat energy present underneath the Earth, and is capable of supplying all of our energy. Two wells are drilled. One well injects water into the ground to provide water. The hot rocks heat the water to produce steam. The steam that shoots back up the other hole(s) is purified and is used to drive turbines, which power electric generators. When the water temperature is below the boiling point of water a binary system is used. A low boiling point liquid is used to drive a turbine and generator in a closed system similar to a refrigeration unit running in reverse. There are also natural sources of geothermal energy: some can come from volcanoes, geysers, hot springs, and steam vents. The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW. Geothermal power has the advantage that it is not variable, like most of the other renewable sources. There are four factors to consider in providing 100% of a country's energy from renewable sources - transmission when local resources are greater or less than needed, storage for the same reason, excess capacity to provide sufficient demand, and use of biomass or geothermal to fill in for when wind and solar are insufficient. While the solutions are not fundamentally different from those used with conventional non-renewable sources, the technology is. For example, transmission lines and storage have been used almost since the beginning of electricity use, but as late as 2008 wind power and solar power provided less than 0.25% of total energy (1/400th). A study in Germany by the University of Kassel showed that a combination of wind, solar, storage, and biomass could supply all of Germany's electricity.
Tidal power can be extracted from Moon-gravity-powered tides by locating a water turbine in a tidal current, or by building impoundment pond dams that admit-or-release water through a turbine. The turbine can turn an electrical generator, or a gas compressor, that can then store energy until needed. Coastal tides are a source of clean, free, renewable, and sustainable energy.
Fossil fuels sources burn coal or hydrocarbon fuels, which are the remains of the decomposition of plants and animals. There are three main types of fossil fuels: coal, petroleum, and natural gas. Another fossil fuel, liquefied petroleum gas (LPG), is principally derived from the production of natural gas. Heat from burning fossil fuel is used either directly for space heating and process heating, or converted to mechanical energy for vehicles, industrial processes, or electrical power generation.
Nuclear power stations use nuclear fission to generate energy by the reaction of uranium-235 inside a nuclear reactor. The reactor uses uranium rods, the atoms of which are split in the process of fission, releasing a large amount of energy. The process continues as a chain reaction with other nuclei. The energy heats water to create steam, which spins a turbine generator, producing electricity.
Stated estimates for fission fuel supply at known usage rates vary vastly, from several decades to billions of years; among other differences between the former and the latter estimates, some assume usage only of the currently popular uranium-235, and others assume the factor of a hundred fuel efficiency increase which would come from utilizing uranium-238 through breeder reactors. The Earth's crust contains around 40 trillion tons of uranium and 120 trillion tons of thorium, but, depending on assumptions, reserve figures can be millions of times less for the portion assumed affordable to extract in the future, for the amount of quality ores of far above average crustal concentration.
At the present rate of use, there are (as of 2007) about 70 years left of presently inventoried uranium-235 reserves identified as economically recoverable at the current natural uranium price of US$ 130/kg. (For any typical element, though, the amount of proved reserves inventoried at a time may be considered "a poor indicator of the total future supply of a mineral resource"; among examples with other elements, tin, copper, iron, lead, and zinc all had both production from 1950 to 2000 and reserves in 2000 much exceed world reserves in 1950, which would be impossible except for how "proved reserves are like an inventory of cars to an auto dealer" at a time rather than the total affordable to extract in the future).
The nuclear industry argues that the cost of fuel is a minor cost factor for fission power; if needed, 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. 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 with typical present reactors by 5 percent (without considering usage of breeder reactors for handling greater uranium price rise). On the other hand, if the price of natural gas was doubled, the cost of gas-fired power would increase by about 60 percent.
Opponents on the other hand argue that the correlation between price and production is not linear, but as the ores' concentration becomes smaller, the difficulty (energy and resource consumption are increasing, while the yields are decreasing) of extraction rises very fast, and that the assertion that a higher price will yield more uranium is overly optimistic. As many as eleven countries have depleted their uranium resources, and only Canada has mines left that produce better than 1% concentration ore. Some state uranium from seawater is dubious as a source.
Nuclear meltdowns and other reactor accidents, such as the Fukushima I nuclear accident (2011), Three Mile Island accident (1979) and the Chernobyl disaster (1986), have caused much public concern. Research is being done to lessen the known problems of current reactor technology by developing automated and passively safe reactors. Historically, however, coal and hydropower power generation have both been the cause of more deaths per energy unit produced than nuclear power generation.
Nuclear proliferation is the spread of nuclear technology which may happen from nation to nation or through other black market channels, including nuclear power plants and related technology including nuclear weapons.
The long-term radioactive waste storage problems of nuclear power have not been 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. Spent fuel rods are now stored in concrete casks close to the nuclear reactors. The amounts of waste could be reduced in several ways. Both nuclear reprocessing and breeder reactors could reduce the amounts of waste. Subcritical reactors or fusion reactors could greatly reduce the time the waste has to be stored. Subcritical reactors may also be able to do the same to already existing waste. The only long-term way of dealing with waste today is by geological storage.
At present, nuclear energy is in decline, according to a 2007 World Nuclear Industry Status Report presented by the Greens/EFA group in the European Parliament. The report outlines that the proportion of nuclear energy in power production has decreased in 21 out of 31 countries, with five fewer functioning nuclear reactors than five years ago. There are currently 32 nuclear power plants under construction or in the pipeline, 20 fewer than at the end of the 1990s.
Thorium can be used as fuel in a nuclear reactor. One of the early pioneers of the technology was U.S. physicist Alvin Weinberg at Oak Ridge National Laboratory in Tennessee, who helped develop a working nuclear plant using liquid fuel in the 1960s. A thorium fuel cycle offers several potential advantages over a uranium fuel cycle including much greater abundance on Earth, superior physical and nuclear properties of the fuel, enhanced proliferation resistance, and reduced nuclear waste production. Nobel laureate Carlo Rubbia at CERN (European Organization for Nuclear Research), has worked on developing the use of thorium as an alternative to uranium in reactors. Rubbia states that a tonne of thorium can produce as much energy as 200 tonnes of uranium, or 3,500,000 tonnes of coal. In event of a thorium fuel cycle, even common granite rock with 13 ppm (0.0013%) thorium concentration (just twice the crustal average, along with 4 ppm uranium) contains potential nuclear energy equivalent to 50 times the entire rock's mass in coal, although there is no tendency to resort to such very low-grade deposits as long as much higher-grade deposits remain available and cheaper to extract.
Fusion power could solve many of the problems of fission power (the technology mentioned above) but, despite research having started in the 1950s, no commercial fusion reactor is expected before 2050. Many technical problems remain unsolved. Proposed fusion reactors commonly use deuterium, an isotope of hydrogen, as fuel and in most current designs also lithium. Assuming a fusion energy output equal to the current global output and that this does not increase in the future, then the known current lithium reserves would last 3000 years, lithium from sea water would last 60 million years, and a more complicated fusion process using only deuterium from sea water would have fuel for 150 billion years.
The following chart does not include the external costs of using fossil fuels.
|█ Conventional oil||█ Unconventional oil||█ Biofuels||█ Coal||█ Nuclear||█ Wind|
|Colored vertical lines indicate various historical oil prices. From left to right:|
|— 1990s average||— January 2009||— 1979 peak||— 2008 peak|
Price of oil per barrel (bbl) at which energy sources are competitive.
Large energy subsidies are present in many countries (Barker et al., 2001:567-568). Currently governments subsidize fossil fuels by $557 billion per year. Economic theory indicates that the optimal policy would be to remove coal mining and burning subsidies and replace them with optimal taxes. Global studies indicate that even without introducing taxes, subsidy and trade barrier removal at a sectoral level would improve efficiency and reduce environmental damage. Removal of these subsidies would substantially reduce GHG emissions and stimulate economic growth.
Efficient energy use, sometimes simply called energy efficiency, is the goal of efforts to reduce the amount of energy required to provide products and services. For example, insulating a home allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature. Installing fluorescent lights or natural skylights reduces the amount of energy required to attain the same level of illumination compared to using traditional incandescent light bulbs. Compact fluorescent lights use two-thirds less energy and may last 6 to 10 times longer than incandescent lights. Improvements in energy efficiency are most often achieved by adopting a more efficient technology or production process.
There are various motivations to improve energy efficiency. Reducing energy use reduces energy costs and may result in a financial cost saving to consumers if the energy savings offset any additional costs of implementing an energy efficient technology. Reducing energy use is also seen as a key solution to the problem of reducing emissions. According to the International Energy Agency, improved energy efficiency in buildings, industrial processes and transportation could reduce the world's energy needs in 2050 by one third, and help control global emissions of greenhouse gases.
Energy efficiency and renewable energy are said to be the twin pillars of sustainable energy policy. In many countries energy efficiency is also seen to have a national security benefit because it can be used to reduce the level of energy imports from foreign countries and may slow down the rate at which domestic energy resources are depleted.
While new sources of energy are only rarely discovered or made possible by new technology, distribution technology continually evolves. The use of fuel cells in cars, for example, is an anticipated delivery technology. This section presents some of the more common delivery technologies that have been important to historic energy development. They all rely in some way on the energy sources listed in the previous section.
Water is commonly stored by dams and transported through canals and aqueducts to where it is needed, converting annual rainy seasons to year round water availability.
Shipping is a flexible delivery technology that is used in the whole range of energy development regimes from primitive to highly advanced. Currently, coal, petroleum and their derivatives are delivered by shipping via boat, rail, or road. Petroleum and natural gas may also be delivered via pipeline and coal via a Slurry pipeline. Refined hydrocarbon fuels such as gasoline and LPG may also be delivered via aircraft. Natural gas pipelines must maintain a certain minimum pressure to function correctly. Ethanol's corrosive properties make it harder to build ethanol pipelines. The higher costs of ethanol transportation and storage are often prohibitive.
Electricity grids are the networks used to transmit and distribute power from production source to end user, when the two may be hundreds of kilometres away. Sources include electrical generation plants such as a nuclear reactor, coal burning power plant, etc. A combination of sub-stations, transformers, towers, cables, and piping are used to maintain a constant flow of electricity. Grids may suffer from transient blackouts and brownouts, often due to weather damage. During certain extreme space weather events solar wind can interfere with transmissions. Grids also have a predefined carrying capacity or load that cannot safely be exceeded. When power requirements exceed what's available, failures are inevitable. To prevent problems, power is then rationed.
Industrialised countries such as Canada, the US, and Australia are among the highest per capita consumers of electricity in the world, which is possible thanks to a widespread electrical distribution network. The US grid is one of the most advanced, although infrastructure maintenance is becoming a problem. CurrentEnergy provides a realtime overview of the electricity supply and demand for California, Texas, and the Northeast of the US. African countries with small scale electrical grids have a correspondingly low annual per capita usage of electricity. One of the most powerful power grids in the world supplies power to the state of Queensland, Australia.
Methods of energy storage have been developed, which transform electrical energy into forms of potential energy. A method of energy storage may be chosen on the basis of stability, ease of transport, ease of energy release, or ease of converting free energy from the natural form to the stable form.
The most common form of utility electricity storage is pumped-storage hydroelectricity, where excess energy pumps water into a higher elevation reservoir. When electrical energy is required, the process is reversed: falling water turns a turbine, generates electricity, and returns to the lower reservoir. The motor used to pump the water up operates in reverse as a generator and the pump operates in reverse as a turbine. Hydroelectric power is currently an important part of the world's energy supply, generating one-fifth of the world's electricity. Most hydro-storage facilities were developed so that baseload power plants could run continuously, and use hydro-storage to store the night time excess for use during day time peaks. When most of our electricity comes from wind power and solar power, the reverse will be needed - hydro-storage will be used to store excess generation during periods of wind and sunshine for use in times without wind or sun.
Some natural forms of energy are found in stable chemical compounds such as fossil fuels. Most systems of chemical energy storage result from biological activity, which store energy in chemical bonds. Man-made forms of chemical energy storage include hydrogen fuel, synthetic hydrocarbon fuel, batteries and explosives such as cordite and dynamite.
There are several technologies to store heat. Thermal energy from the sun, for example, can be stored in a reservoir or in the ground for daily or seasonal use. Thermal energy for cooling can be stored in ice. Many thermal power plants are set up near coal or oil fields. The thermal power plant is used since fuel is burnt to produce heat energy, which is converted into electrical energy .
Energy may also be stored in pressurized gases or alternatively in a vacuum. Compressed air, for example, may be used to operate vehicles and power tools. Large-scale compressed air energy storage facilities are used to smooth out demands on electricity generation by providing energy during peak hours and storing energy during off-peak hours. All storage systems save on generating capacity since primary energy sources only need to meet average consumption rather than peak consumption. A critical factor in design of compressed-air storage systems is the heat evolved during compression; a large amount of heat is given off when gases are compressed, and subsequent expansion requires the gas to resorb this heat. In spite of the large cyclic efficiency loss in simple schemes, compressed air storage has still been applied in electrical grid applications, where low-cost off-peak baseload energy can be stored for later release during peaks.
Electrical energy may be stored in capacitors. Capacitors are often used to produce high intensity releases of energy (such as a camera's flash).
Hydrogen can be manufactured at roughly 77 percent thermal efficiency by the method of steam reforming of natural gas. When manufactured by this method it is a derivative fuel like gasoline; when produced by electrolysis of water, it is a form of chemical energy storage as are storage batteries, though hydrogen is the more versatile storage mode since there are two options for its conversion to useful work: (1) a fuel cell can convert the chemicals hydrogen and oxygen into water, and in the process, produce electricity, or (2) hydrogen can be burned (less efficiently than in a fuel cell) in an internal combustion engine.
Batteries are used to store energy in a chemical form. As an alternative energy, batteries can be used to store energy in battery electric vehicles. Battery electric vehicles can be charged from the grid when the vehicle is not in use. Because the energy is derived from electricity, battery electric vehicles make it possible to use other forms of alternative energy such as wind, solar, geothermal, or hydroelectric.
Compressed air vehicles would be propelled entirely or partly by energy stored in compressed air. However, cyclic efficiency is low since it is difficult to store the heat of compression and return it to the air during expansion. Certain specialized vehicles, for example, mine locomotives, have been built and used for many years.
The environmental movement emphasizes sustainability of energy use and development. Renewable energy is sustainable in its production; the available supply will not be diminished for the foreseeable future - millions or billions of years. "Sustainability" also refers to the ability of the environment to cope with waste products, especially air pollution. Sources which have no direct waste products (such as wind, solar, and hydropower) are seen as ideal in this regard.
Fossil fuels such as petroleum, coal, and natural gas are not renewable. For example, the timing of worldwide peak oil production is being actively debated but it has already happened in some countries. Fossil fuels also make up the bulk of the world's current primary energy sources. With global demand for energy growing, the need to adopt alternative energy sources is also growing. Fossil fuels are also a major source of greenhouse gas emissions, leading to concerns about global warming if consumption is not reduced.
Energy conservation is an alternative or complementary process to energy development. It reduces the demand for energy by using it more efficiently.
Some observers contend that the much talked about idea of "energy independence" is an unrealistic and opaque concept. They offer "energy resilience" as a more sensible goal and more aligned with economic, security and energy realities. The notion of resilience in energy was detailed in the 1982 book Brittle Power: Energy Strategy for National Security. The authors argued that simply switching to domestic energy would be no more secure inherently because the true weakness is the interdependent and vulnerable energy infrastructure of the United States. Key aspects such as gas lines and the electrical power grid are centralized and easily susceptible to major disruption. They conclude that a "resilient energy supply" is necessary for both national security and the environment. They recommend a focus on energy efficiency and renewable energy that is more decentralized.
More recently former Intel Corporation Chairman and CEO Andrew Grove has touted energy resilience, arguing that complete independence is infeasible given the global market for energy. He describes energy resilience as the ability to adjust to interruptions in the supply of energy. To this end he suggests the U.S. make greater use of electricity. Electricity can be produced from a variety of sources. A diverse energy supply will be less impacted by the disruption in supply of any one source. He reasons that another feature of electrification is that electricity is "sticky" – meaning the electricity produced in the U.S. is more likely to stay there because it cannot be transported overseas. According to Grove, a key aspect of advancing electrification and energy resilience will be converting the U.S. automotive fleet from gasoline-powered to electric-powered. This, in turn, will require the modernization and expansion of the electrical power grid. As organizations such as the Reform Institute have pointed out, advancements associated with the developing smart grid would facilitate the ability of the grid to absorb vehicles en masse connecting to it to charge their batteries.
Extrapolations from current knowledge to the future offer a choice of energy futures. Some predictions parallel the Malthusian catastrophe hypothesis. Numerous are complex models based scenarios as pioneered by Limits to Growth. Modeling approaches offer ways to analyze diverse strategies, and hopefully find a road to rapid and sustainable development of humanity. Short term energy crises are also a concern of energy development. Some extrapolations lack plausibility, particularly when they predict a continual increase in oil consumption.
Energy production usually requires an energy investment. Drilling for oil or building a wind power plant requires energy. The fossil fuel resources (see above) that are left are often increasingly difficult to extract and convert. They may thus require increasingly higher energy investments. If the investment is greater than the energy produced, then the fossil resource is no longer an energy source. This means that a large part of the fossil fuel resources and especially the non-conventional ones cannot be used for energy production today. Such resources may still be exploited economically in order to produce raw materials for plastics, fertilizers or even transportation fuel but now more energy is consumed than produced. (They then become similar to ordinary mining reserves, economically recoverable but not net positive energy sources.) New technology may ameliorate this problem if it can lower the energy investment required to extract and convert the resources, although ultimately basic physics sets limits that cannot be exceeded.
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. The peaking of world hydrocarbon production (peak oil) may lead to significant changes, and require sustainable methods of production.
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