Energy development
Energy development is the ongoing effort to provide sustainable energy resources through knowledge, skills, and constructions. When harnessing energy from primary energy sources and converting them into more convenient secondary energy forms, such as electrical energy and cleaner fuel, both emissions (reducing pollution) and quality (more efficient use) are important.

# Dependence on external energy sources
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, in general, 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, traffic congestion, pollution, production, and greenhouse gas emissions of each society.
Increased levels of human comfort generally induce increased dependence on external energy sources, although the application of energy efficiency and conservation approaches allows a certain degree of mitigation of the dependence.  Wise energy use therefore embodies the idea of balancing human comfort with reasonable energy consumption levels by researching and implementing effective and sustainable energy harvesting and utilization measures.

# Limitations to energy development
A key limit to the development of any particular energy source is availability of the underlying resource.  Most of the world's main energy sources are based on the consumption of non-renewable resources (petroleum, coal, natural gas, and uranium).  While still a small segment of the energy supply, renewable sources such as wind power and solar power are growing rapidly in market share.
Closely linked to energy development are concerns about the possible environmental effects of energy use, such as climate changes.  Energy development issues are part of the much debated sustainable development problem.

# Primary energy sources
Primary energy sources are substances or processes with concentrations of energy at a high enough potential to be feasibly encouraged to convert to lower energy forms under human control for human benefit.  Except for nuclear fuels, tidal energy and geothermal energy, all terrestrial energy sources are from current solar insolation or from fossil remains of plant and animal life that relied directly and indirectly upon sunlight, respectively. And ultimately, solar energy itself is the result of the Sun's nuclear fusion.  Geothermal power from hot, hardened rock above the magma of the earth's core is the result of the accumulation of radioactive materials during the formation of Earth which was the byproduct of a previous supernova event.

## Fossil fuels
Fossil fuels, in terms of energy, involve the burning of 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.

### Pros
- The technology and infrastructure already exist for the use of fossil fuels (although oil and natural gas are approaching peak production, and will require a transition to other fuels and/or other measures.
- Commonly-used fossil fuels in liquid form such as light crude oil, gasoline, and LPG are easy to distribute.
- Petroleum energy density in terms of volume (cubic space) and mass (weight) is superior to some alternative energy sources (or energy storage devices, like a battery (electricity)). Energy density is important in land-and-air transportation fuel tanks.

### Cons
- Petroleum-powered vehicles are very inefficient. Only about 15% of the energy from the fuel they consume is converted into useful motion.   The rest of the fuel-source energy is inefficiently expended as waste heat. The heat and gaseous pollution emissions harm our environment.
- The inefficient atmospheric combustion (burning) of fossil fuels in vehicles, buildings, and power plants contributes to urban heat islands.
- The combustion of fossil fuels leads to the release of pollution into the atmosphere. According to the Union of Concerned Scientists, a typical coal plant produces in one year:
3,700,000 tons of  carbon dioxide (CO2), the primary cause of global warming.
10,000 tons of sulfur dioxide (SO2), the leading cause of acid rain.
500 tons of small airborne particles, which result in chronic bronchitis, aggravated asthma, and premature death, in addition to haze-obstructed visibility.
10,200 tons of nitrogen oxides (NOx), (from high-temperature atmospheric combustion), leading to formation of ozone (smog) which inflames the lungs, burning lung tissue making people more susceptible to respiratory illness.
720 tons of carbon monoxide (CO), resulting in headaches and additional stress on people with heart disease.
220 tons of hydrocarbons, toxic volatile organic compounds (VOC), which form ozone.
170 pounds of mercury, where just 1/70th of a teaspoon deposited on a 25 acre lake can make the fish unsafe to eat.
225 pounds of arsenic, which will cause cancer in one out of 100 people who drink water containing 50 parts per billion.
114 pounds of lead, 4 pounds of cadmium, other toxic heavy metals, and trace amounts of uranium.
- 3,700,000 tons of  carbon dioxide (CO2), the primary cause of global warming.
- 10,000 tons of sulfur dioxide (SO2), the leading cause of acid rain.
- 500 tons of small airborne particles, which result in chronic bronchitis, aggravated asthma, and premature death, in addition to haze-obstructed visibility.
- 10,200 tons of nitrogen oxides (NOx), (from high-temperature atmospheric combustion), leading to formation of ozone (smog) which inflames the lungs, burning lung tissue making people more susceptible to respiratory illness.
- 720 tons of carbon monoxide (CO), resulting in headaches and additional stress on people with heart disease.
- 220 tons of hydrocarbons, toxic volatile organic compounds (VOC), which form ozone.
- 170 pounds of mercury, where just 1/70th of a teaspoon deposited on a 25 acre lake can make the fish unsafe to eat.
- 225 pounds of arsenic, which will cause cancer in one out of 100 people who drink water containing 50 parts per billion.
- 114 pounds of lead, 4 pounds of cadmium, other toxic heavy metals, and trace amounts of uranium.
- Dependence on fossil fuels from volatile regions or countries creates energy security risks for dependent countries. Oil dependence in particular has led to war, major funding of radical terrorists, monopolization, and socio-political instability.
- Fossil fuels are non-renewable, un-sustainable resources, which will eventually decline in production and become exhausted, with dire consequences to societies that remain highly dependent on them. (Fossil fuels are actually slowly forming continuously, but we are using them up at a rate approximately 100,000 times faster than they are formed.)
- Extracting fossil fuels is becoming more difficult as we consume the most accessible fuel deposits. Extraction of fossil fuels is becoming more expensive and more dangerous as mines get deeper and oil rigs must drill deeper, and go further out to sea.
- Extraction of fossil fuels results in extensive environmental degradation, such as the strip mining and mountaintop removal of coal.
Since these power plants are thermal engines, and are typically quite large, waste heat disposal becomes an issue at high ambient temperature. Thus, at a time of peak demand, a power plant may need to be shut down or operate at a reduced power level, as sometimes do nuclear power plants, for the same reasons.

## Biomass, biofuels, and vegetable oil
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.
Vegetable oil is generated from sunlight 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.

### Pros
- Biomass production can be used to burn organic waste products resulting from agriculture. This type of recycling encourages the philosophy that nothing on this Earth should be wasted. The result is less demand on the Earth's resources, and a higher carrying capacity for Earth because non-renewable fossil fuels are not consumed.
- Biomass is abundant on Earth and is generally renewable. In theory, we will never run out of organic waste products as fuel, because we are continuously producing them. In addition, biomass is found throughout the world, a fact that should alleviate energy pressures in third world nations.
- When methods of biomass production other than direct combustion of plant mass are used, such as fermentation and pyrolysis, there is little effect on the environment. Alcohols and other fuels produced by these alternative methods are clean burning and are feasible replacements to fossil fuels.
- Since CO2 is first taken out of the atmosphere to make the vegetable oil and then put back after it is burned in the engine, there is no net increase in CO2. Vegetable oil therefore does not contribute to the problem of greenhouse gas.
- Vegetable oil has a higher flash point and therefore is safer than most fossil fuels.
- Transitioning to vegetable oil could be relatively easy as biodiesel works where diesel works, and straight vegetable oil takes relatively minor modifications.
- The World already produces more than 100 billion gallons a year for food industry, so we have experience making it.
- Algaculture has the potential to produce far more vegetable oil per acre than current plants.
- Infrastructure for biodiesel around the World is significant and growing.

### Cons
- Direct combustion of any carbon-based fuel leads to air pollution similar to that from fossil fuels.
- Some researchers claim that when biomass crops are the product of intensive farming, ethanol fuel production results in a net loss of energy after one accounts for the fuel costs of petroleum and natural-gas fertilizer production, farm equipment, and the distillation process.
- There is a long list of reasons why even non-food based cellulosic ethanol cannot solve our energy crisis or global warming problems.
- Direct competition with land use for food production and water use.
- Current production methods would require enormous amounts of land to replace all gasoline and diesel.  With current technology, it is not feasible for biofuels to replace the demand for petroleum.
- Even with the most-optimistic energy return on investment claims, in order to use 100% solar energy to grow corn and produce ethanol (fueling machinery with ethanol, distilling with heat from burning crop residues, using NO fossil fuels at all), the consumption of ethanol to replace only the current U.S. petroleum use would require three quarters of all the cultivated land on the face of the Earth.

## Hydroelectric energy
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.

### Pros
- Hydroelectric power stations can promptly increase to full capacity, unlike other types of power stations. This is because water can be accumulated above the dam and released to coincide with peak demand.
- Electricity can be generated constantly, so long as sufficient water is available.
- Hydroelectric power produces no primary waste or pollution.
- Hydropower is a renewable resource.
- Hydroelectricity assists in securing a country's access to energy supplies.
- Much hydroelectric capacity is still undeveloped, such as in Africa.

### Cons
- The construction of a dam can have a serious environmental impact on the surrounding areas. The amount and the quality of water downstream can be affected, which affects plant life both aquatic, and land-based. Because a river valley is being flooded, the local habitat of many species are destroyed, while people living nearby may have to relocate their homes.
- Hydroelectricity can only be used in areas where there is a sufficient supply of water.
- Flooding submerges large forests (if they have not been harvested). The resulting anaerobic decomposition of the carboniferous materials releases methane, a greenhouse gas.
- Dams can contain huge amounts of water. As with every energy storage system, failure of containment can lead to catastrophic results, e.g. flooding.
- Hydroelectric plants rarely can be erected near load centers, requiring long transmission lines.
- Global warming is causing reduced rainfall in some regions, reducing the available water in dammed reservoirs (such as Lake Powell in the Southwestern United States).

## Tidal Power Generation
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.

## Nuclear energy
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 heat released, heats water to create steam, which spins a turbine generator, producing electricity.
Depending on the type of fission fuel considered, estimates for existing supply at known usage rates varies from several decades for the currently popular Uranium-235 to thousands of years for uranium-238. At the present use rate, there are (as of 2007) about 70 years left of known uranium-235 reserves economically recoverable at a uranium price of US$ 130/kg. 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.  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.
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; for example a rough estimate predicts that the extraction of uranium from granite will consume at least 70 times more energy than what it will produce in a reactor. As many as eleven countries have depleted their uranium resources, and only Canada has mines left which produce better than 1% concentration ore. Seawater seems to be equally dubious as a source.  As a consequence an eventual doubling in the price of uranium will give a marginal increase in the volumes that are being produced.
Another alternative would be to use thorium as fission fuel. Thorium is three times more abundant in Earth's crust than uranium, and much more of the thorium can be used (or, more precisely, bred into Uranium-233, reprocessed and then used as fuel).  India has around 32 percent of the worlds reserves of thorium and intends on using it for itself because the country has run out of uranium.
Current light water reactors burn the nuclear fuel poorly, leading to energy waste. Nuclear reprocessing 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 uranium-235 (0.7 percent of all natural uranium), fast breeder reactors convert the more abundant uranium-238 (99.3 percent of all natural uranium) into plutonium for fuel. It has been estimated that there is anywhere from 10,000 to five billion years worth of Uranium-238 for use in these power plants. Fast breeder technology has been used in several reactors. However, the fast breeder reactors at Dounreay in Scotland, Monju in Japan and the Superphenix at Creys-Malville in France, in particular, have all had difficulties and were not economically competitive and most have been decommissioned. The People's Republic of China intends to build breeders.  India has run out of uranium and is building thermal breeders that can convert Th-232 into U-233 and burn it.
Some nuclear engineers think that pebble bed reactors, in which each nuclear fuel pellet is coated with a ceramic coating, are inherently safe and are the best solution for nuclear power.  They can also be configured to produce hydrogen for hydrogen vehicles.  China has plans to build pebble bed reactors configured to produce hydrogen.
The possibility of nuclear meltdowns and other reactor accidents, such as the Three Mile Island accident and the Chernobyl disaster, have caused much public fear. Research is being done to lessen the known problems of current reactor technology by developing automated and passively-safe reactors. Historically, however, coal and hydropower power generation have both been the cause of more deaths per energy unit produced than nuclear power generation. Various kinds of energy infrastructure might be attacked by terrorists, including nuclear power plants, hydropower plants, and liquified natural gas tankers. Nuclear proliferation is the spread from nation to nation of nuclear technology, including nuclear power plants but especially nuclear weapons. New technology like SSTAR ("small, sealed, transportable, autonomous reactor") may lessen this risk.
The long-term radioactive waste storage problems of nuclear power have not been fully solved. Several countries have considered using underground repositories. Nuclear waste takes up little space compared to wastes from the chemical industry which remain toxic indefinitely. 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 fast 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 way of dealing with waste today is by geological storage.
The economics 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 Economics of new nuclear power plants.
Depending on the source different energy return on energy investment (EROI) are claimed. Advocates (using life cycle analysis) argue that it takes 45 months of energy production from the nuclear plant to fully pay back the initial energy investment. Opponents claim that it depends on the grades of the ores the fuel came from, so a full payback can vary from 10 to 18 years, and that the advocates' claim was based on the assumption of high grade ores (the yields are getting worst, as the ores are leaner, for less than 0.02% ores, the yield is less then 50%).
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. 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. However, a Council on Foreign Relations 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.

### Pros
- The energy content of a kilogram of uranium or thorium, if spent nuclear fuel is reprocessed and fully utilized, is equivalent to about 3.5 million kilograms of coal.
- The cost of making nuclear power, with current legislation, is about the same as making coal power, which is considered very inexpensive (see Economics of new nuclear power plants).  If a carbon tax is applied, nuclear does not have to pay anything because nuclear does not emit toxic gases such as CO2, NO, CO, SO2, arsenic, etc. that are emitted by coal power plants.
- Nuclear power plants are guarded with the nuclear reactor inside a reinforced containment building, and thus are relatively impervious to terrorist attack or adverse weather conditions (see Nuclear safety in the U.S.).
- Because of the fear of a nuclear disaster, nuclear safety has become a major issue.
- Nuclear power does not produce any primary air pollution or release carbon dioxide and sulfur dioxide into the atmosphere. Therefore, it contributes only a small amount to global warming or acid rain.
- Coal mining is the second most dangerous occupation in the United States. Nuclear energy is much safer per capita than coal derived energy.
- For the same amount of electricity, the life cycle emissions of nuclear is about 4% of coal power.  Depending on the report, hydro, wind, and geothermal are sometimes ranked lower, while wind and hydro are sometimes ranked higher (by life cycle emissions).
- According to a Stanford study, fast breeder reactors have the potential to power humans on earth for billions of years, making it sustainable.

### Cons
- The improper operation of a badly designed nuclear reactor with no containment vessel near human settlements can be catastrophic in the event of an uncontrolled  power increase in the reactor, as shown by the Chernobyl disaster in the Ukraine (former USSR), where large areas of land were affected by radioactive contamination.
- The human, environmental, and economic costs from a successful terrorist attack on a nuclear power reactor that results in the release of substantial quantities of radioactive material to the environment could be great.
- Waste produced from nuclear fission of uranium is both poisonous and highly radioactive, requiring maintenance and monitoring at the storage sites. However, if nuclear fuel is reprocessed, the separated radioactive fission product waste will decay to such a level of radioactivity in 300-500 years.
- There can be connections between nuclear power and nuclear weapon proliferation, since many reactor designs require large-scale uranium enrichment facilities.
- The limited liability for the owner of a nuclear power plant in case of a nuclear accident differs per nation while nuclear installations are sometimes built close to national borders.
- Since nuclear power plants are typically quite large power plants, and are, fundamentally, thermal engines, waste heat disposal becomes an issue at high ambient temperature. Thus, at a time of peak demand, a power reactor may need to be shut down or operate at a reduced power level, as do large coal-fired plants, for the same reasons.

## Fusion power
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.

## Wind power
This type of energy 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.

### Pros
- Wind power produces no water or air pollution that can contaminate the environment, because there are no chemical processes involved in wind power generation. Hence, there are no waste by-products, such as carbon dioxide.
- Power from the wind does not contribute to global warming because it does not generate greenhouse gases.
- Wind generation is a renewable source of energy, which means that we will never run out of it.
- Wind towers can be beneficial for people living permanently, or temporarily, in remote areas. It may be difficult to transport electricity through wires from a power plant to a far-away location and thus, wind towers can be set up at the remote setting.
- Farming and grazing can still take place on land occupied by wind turbines.
- Those utilizing wind power in a grid-tie configuration will have backup power in the event of a power outage.
- Due to the ability of wind turbines to coexist within agricultural fields, siting costs are frequently low.

### Cons
- Wind is unpredictable; therefore, wind power is not predictably available. When the wind speed decreases less electricity is generated. This makes wind power unsuitable for base load generation.
- Wind farms may be challenged in communities that consider them an eyesore or view obstructor.
- Wind farms, depending on the location and type of turbine, may negatively affect bird migration patterns and may pose a danger to the birds themselves. Newer, larger wind turbines have slower moving blades which are visible to birds.

## 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. In the Phoenix, Arizona area, for example, the average annual solar radiation is 5.7 kWh/m2/day, or 2080.5 kWh/m2/year. Electricity demand in the continental U.S. is 3.7*1012 kWh per year. Thus, at 100% efficiency, an area of 1.8x10^9 sq. m (around 700 square miles) would need to be covered with solar panels to replace all current electricity production in the US with solar power, and at 20% efficiency, an area of approximately 3500 square miles (3% of Arizona's land area). The average solar radiation in the United States is 4.8 kwh/m2/day, but reaches 89 kWh/m2/day in parts of Southwest.
The cost, assuming $500/meter2, would be about $5-10 trillion dollars.OR
China is aggressively more-than-doubling 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.

### Pros
- Solar power imparts no fuel costs.
- Solar power is a renewable resource. As long as the Sun exists, its energy will reach Earth.
- Solar power generation releases no water or air pollution, because there is no combustion of fuels.
- In sunny countries, solar power can be used in remote locations, like a wind turbine. This way, isolated places can receive electricity, when there is no way to connect to the power lines from a plant.
- Solar energy can be used very efficiently for heating (solar ovens, solar water and home heaters) and daylighting.
- Coincidentally, solar energy is abundant in regions that have the largest number of people living off grid  in developing regions of Africa, Indian subcontinent and Latin America. Hence cheap solar, when available, opens the opportunity to enhance global electricity access considerably, and possibly in a relatively short time period.
- Photovoltaic systems are subsidized, up to $5 USD per watt in some American states.
- Passive solar building design and zero energy buildings are demonstrating significant energy bill reduction, and some are cost-effectively off the grid.
- Photovoltaic equipment cost has been steadily falling, the production capacity is rapidly rising, and the U.S. Administration expects its Solar America Initiative to help make amortized PV electricity price competitive for the new generation of zero energy buildings.
- Distributed point-of-use photovoltaic systems eliminate expensive long-distance electric power transmission losses.
- Photovoltaics are much more efficient in their conversion of solar energy to usable energy than biofuel from plant materials.

### Cons
- Solar electricity is currently more expensive than grid electricity.
- Solar heat and electricity are not available at night and may be unavailable due to weather conditions; therefore, a storage or complementary power system is required for off-the-grid applications.
- Limited energy density: Average daily insolation in the contiguous U.S. is 37 kWh/m2. (see picture)
- Solar cells produce DC which must be converted to AC (using a grid tie inverter) when used in currently existing distribution grids. This incurs an energy loss of 412%.
- A photovoltaic power station is expensive to build, and the energy payback time  the time necessary for producing the same amount of energy as needed for building the power device  for photovoltaic cells is about 15 years, depending primarily on location.
- Solar panels collect dust and require cleaning. Dust on the panels significantly reduces the transfer of energy from solar radiation to electric current.

## Geothermal energy
Geothermal energy harnesses the heat energy present underneath the Earth. 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.

### Pros
- Geothermal energy is base load power.
- Economically feasible in high grade areas now.
- Low deployment costs.
- Geothermal power plants have a high capacity factor; they run continuously day and night with an uptime typically exceeding 95%.
- Once a geothermal power station is implemented, the energy produced from the station is practically free. A small amount of energy is required in order to run a pump, although this pump can be powered by excess energy generated at the plant.
- Geothermal power stations are relatively small, and have a lesser impact on the environment than tidal or hydroelectric plants. Because geothermal technology does not rely on large bodies of water, but rather, small, but powerful jets of water, like geysers, large generating stations can be avoided without losing functionality.
- Geothermal is now feasible in areas where the earth's crust is thicker.  Using enhanced geothermal technology, it's possible to drill deeper and inject water to generate geothermal power.
- Geothermal energy does not produce air or water pollution if performed correctly.

### Cons
- Geothermal power extracts small amounts of minerals such as sulfur that are removed prior to feeding the turbine and re-injecting the water back into the injection well.

# Increased efficiency in energy use
Efficiency is increasing by about 2% a year, and absorbs most of the requirements for energy development. New technology makes better use of already available energy through improved efficiency, such as more efficient fluorescent lamps, engines, and insulation. Using heat exchangers, it is possible to recover some of the energy in waste warm water and air, for example to preheat incoming fresh water. Hydrocarbon fuel production from pyrolysis could also be in this category, allowing recovery of some of the energy in hydrocarbon waste. Meat production is energy inefficient compared to the production of protein sources like soybean or Quorn. Already existing power plants often can and usually are made more efficient with minor modifications due to new technology. New power plants may become more efficient with technology like cogeneration. New designs for buildings may incorporate techniques like passive solar. Light-emitting diodes are gradually replacing the remaining uses of light bulbs. Note that none of these methods allows perpetual motion, as some energy is always lost to heat.
Mass transportation increases energy efficiency compared to widespread conventional automobile use while air travel is regarded as inefficient. Conventional combustion engine automobiles have continually improved their efficiency and may continue to do so in the future, for example by reducing weight with new materials. Hybrid vehicles can save energy by allowing the engine to run more efficiently, regaining energy from braking, turning off the motor when idling in traffic, etc. More efficient ceramic or diesel engines can improve mileage. Electric vehicles such as Maglev, trolleybuses, and PHEVs are more efficient during use (but maybe not if doing a life cycle analysis) than similar current combustion based vehicles, reducing their energy consumption during use by 1/2 to 1/4. Microcars or motorcycles may replace automobiles carrying only one or two people. Transportation efficiency may also be improved by in other ways, see automated highway system.
Electricity distribution may change in the future. New small scale energy sources may be placed closer to the consumers so that less energy is lost during electricity distribution. New technology like superconductivity or improved power factor correction may also decrease the energy lost. Distributed generation permits electricity "consumers", who are generating

# Energy transportation
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.
- Fuels
- Electric grids

# Energy storage
Methods of energy storage have been developed, which transform electrical energy into forms of potential energy. A method of energy storage may be chosen based on stability, ease of transport, ease of energy release, or ease of converting free energy from the natural form to the stable form.

## Compressed air vehicles
The Indian company, Tata, is planning to release a compressed air powered car in 2008.

## Battery-powered vehicles
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, nuclear, or hydroelectric.

### Pros
- Produces zero emissions to help counteract the effects of global warming, as long as the electricity comes from a source which produces no greenhouse gases.
- Batteries are a mature technology, no new expensive research and development is needed to implement technology.
- Current lead acid battery technology offers 50+ miles range on one charge.
- The Tesla Roadster has a 200 mile (321.8688 km) range on one charge.
- Batteries make it possible for stationary alternative energy generation such as solar, wind, hydroelectric, or nuclear
- Electric motors are 90% efficient compared to about 20% efficiency of an internal combustion engine.
- Battery electric vehicles have fewer moving parts than internal combustion engines, thus improving the reliability of the vehicle.
- Battery electric vehicles are quiet compared to internal combustion engines.
- Multiple electric vehicles sold out including the General Motors EV1 and the Tesla Roadster proving the demand for battery electric vehicles.
- Operation of a battery electric vehicle is approximately 2 to 4 cents per mile.  About a sixth the price of operating a gasoline vehicle.
- The use of battery electric vehicles may reduce the dependency on fossil fuels, depending on the source of the electricity.

### Cons
- Current battery technology is expensive.
- Battery electric vehicles have a relative short range compared to internal combustion engine vehicles.
- Batteries are highly toxic.  Spent vehicle batteries present an environmental hazard.
- Grid infrastructure and output would need to be improved significantly to accommodate a mass-adoption of grid-charged electric vehicles.

## Hydrogen economy
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.

### Pros
- Hydrogen is colorless, odorless and entirely non-polluting, yielding pure water vapor (with minimal NOx) as exhaust when combusted in air. This eliminates the direct production of exhaust gases that lead to smog, and carbon dioxide emissions that enhance the effect of global warming.
- Hydrogen is the lightest chemical element and has the best energy-to-weight ratio of any fuel (not counting tank mass).
- Hydrogen can be produced anywhere; it can be produced domestically from the decomposition of water.  Hydrogen can be produced from domestic sources and the price can be established within the country.
- Electrolysis combined with fuel-cell regeneration is more than 50% efficient.

### Cons
- Other than some volcanic emanations, hydrogen does not exist in its pure form in the environment, because it reacts so strongly with oxygen and other elements.
- It is impossible to obtain hydrogen gas without expending energy in the process. There are three ways to manufacture hydrogen;
By breaking down hydrocarbons  mainly methane. If oil or gases are used to provide this energy, fossil fuels are consumed, forming pollution and nullifying the value of using a fuel cell. It would be more efficient to use fossil fuel directly.
By electrolysis from water  The process of splitting water into oxygen and hydrogen using electrolysis consumes large amounts of energy. It has been calculated that it takes 1.4 joules of electricity to produce 1 joule of hydrogen (Pimentel, 2002).
By reacting water with a metal such as sodium, potassium, or boron.  Chemical by-products would be sodium oxide, potassium oxide, and boron oxide.  Processes exist which could recycle these elements back into their metal form for re-use with additional energy input, further eroding the energy return on energy invested.
- By breaking down hydrocarbons  mainly methane. If oil or gases are used to provide this energy, fossil fuels are consumed, forming pollution and nullifying the value of using a fuel cell. It would be more efficient to use fossil fuel directly.
- By electrolysis from water  The process of splitting water into oxygen and hydrogen using electrolysis consumes large amounts of energy. It has been calculated that it takes 1.4 joules of electricity to produce 1 joule of hydrogen (Pimentel, 2002).
- By reacting water with a metal such as sodium, potassium, or boron.  Chemical by-products would be sodium oxide, potassium oxide, and boron oxide.  Processes exist which could recycle these elements back into their metal form for re-use with additional energy input, further eroding the energy return on energy invested.
- There is currently modest fixed infastructure for distribution of hydrogen that is centrally produced, amounting to several hundred kilometers of pipeline. An alternative would be transmission of electricity over the existing electrical network to small-scale electrolyzers to support the widespread use of hydrogen as a fuel.
- Hydrogen is difficult to handle, store, and transport. It requires heavy, cumbersome tanks when stored as a gas, and complex insulating bottles if stored as a cryogenic liquid. If it is needed at a moderate temperature and pressure, a metal hydride absorber may be needed. The transportation of hydrogen is also a problem because hydrogen leaks effortlessly from containers.
- Some current fuel cell designs, such as proton exchange membrane fuel cells, use platinum as a catalyst. Widescale deployment of such fuel cells could place a strain on available platinum resources. Reducing the platinum loading, per fuel cell stack, is the focus of R&D.
- Electricity transmission and battery electric vehicles are far more efficient for storage, transmission and use of energy for transportation, neglecting the energy conversion at the electric power plant. As with distributed production of hydrogen via electrolysis, battery electric vehicles could utilize the existing electricity grid until widespread use dictated an expansion of the grid.

## Energy storage types
- Chemical
- Gravitational
- Electrical capacitance
- Mechanical
- Pressure:
- Flywheels and springs

# Future energy development
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.
Existing technologies for new energy sources, such as renewable energy technologies, particularly wind power and solar power, are promising. Nuclear fission is also promoted, and each need sustained research and development, including consideration of possible harmful side effects.  Jacques Cousteau spoke of using the salinization of water at river estuaries as an energy source, which would not have any consequences for a million years, and then stopped to point out that since we are going to be on the planet for a billion years we had to be looking that far into the future. Nuclear fusion and artificial photosynthesis are other energy technologies being researched and developed.
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.
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. The peaking of world hydrocarbon production (Peak oil) may test Malthus critics.

## History of predictions about future energy development
Ever since the beginning of the Industrial Revolution, the question of the future of energy supplies has occupied economists.
- 1865  William Stanley Jevons published The Coal Question in which he claimed that reserves of coal would soon be exhausted and that there was no prospect of oil being an effective replacement.
- 1885  U.S. Geological Survey: Little or no chance of oil in California.
- 1891  U.S. Geological Survey: Little or no chance of oil in Kansas or Texas.
- 1914  U.S. Bureau of Mines: Total future production of 5.7  (Expression error: Missing operand for *. ).
- 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.945 infra)
- 1956  Geophysicist M. King Hubbert predicts U.S. oil production will peak between 1965 and 1970 (peaked in 1971). Also predicts world oil production will peak "within half a century" based on 1956 data. This is Hubbert peak theory.
- 1989  Predicted peak by Colin Campbell ("Oil Price Leap in the Early Nineties," Noroil, December 1989, pages 35-38.)
- 2004  OPEC estimates it will nearly double oil output by 2025 (Opec Oil Outlook to 2025 Table 4, Page 12)
The history of perpetual motion machines 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.