Energy development is the field concerned with providing abundant and accessible energy to all humans. It is the progressive development of knowledge, skills and institutions for capturing ever more copious and diverse primary energy sources and converting them to ever more convenient secondary energy forms, such as electrical energy and cleaner fuels. In all steps both quantitative aspects, harnessing more energy, and qualitative aspects, more efficient use, are important. (See also Energy policy).

Dependence of humanity on external energy sources

All biological life depends on a supply of external energy. Most plants are capable of capturing and storing solar radiation, some bacteria employ natural sources of chemical energy. Many other organisms, all animals, and humans thrive on energy passed along in food chains.

Humans have found uses for energy in quantities far above our metabolic needs. Beyond stewardship of plants and animals that provide food and useful materials, humans utilize energy for advanced activities related to wellbeing (heating, cooking) or complex activities of human civilisations, such as transport, communication, warfare and social and leisure activities.

Humans employ knowledge, skills and institutions that enable them to survive, by use of energy, as individuals and societies, under diverse climatic conditions, in great numbers and often in comfort. Level of dependence of human societies on external energy sources differs, but so does the climate, comfort, freedom and output of each society.

Increased levels of human comfort and freedom require increased dependence on external energy sources. Energy development therefore embodies the idea of increasing human comfort and freedom by researching and implementing increasingly effective and responsible energy harvesting and utilisation schemes.

Limitations to energy development

Use of any given energy source in human societies encounters limits to quantitative expansion. At the beginning of the 21st century some issues have achieved global dimension. Principal fossil energy sources, such as oil and natural gas are approaching exhaustion that may occur within the span of a generation (see Hubbert peak hypothesis). Closely linked to energy development are concerns about the environmental effects of energy use, such as climate changes. Energy development issues are part of the much debated sustainable development problem.

Historic energy development schemes

Human societies have relied and currently rely on various energy development schemes. Schemes that are most powerful are considered in the energy development field to be more advanced in that they contribute better to human comfort and freedom. As humans and societies move from more primitive energy development schemes to more advanced ones, it is typically said from an energy development point of view that they are advancing because the energy limits on comfort and freedom are shrinking. Sources and technologies in this section are presented in order of increasing energy development.

Sources

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, all energy sources that have been developed for humanity are solar. And ultimately, solar energy itself is nuclear.

Animals (biomass solar)

Animals are energy sources as food to humans (see also animals as energy delivery technology below).

Plants (biomass solar)

Plants are energy sources as food to humans or as combustion materials.

Wind (hydrologic solar)

Wind is an exploitable kinetic energy carrying part of the hydrologic cycle driven by the sun.

Water mills (hydrologic solar)

Water mills have been an important source of energy both anciently and in modern times.

Fossil fuels (prehistoric solar)

Fossil fuels are ancient plant or animal matter that has decayed and been acted upon by geologic forces to produce hydrocarbons such as petroleum, natural gas or coal.

Nuclear reactions (atomic)

Controlled nuclear reactions provide energy as one chemical element (atom) changes into a different one.

Photovoltaic cells (solar electric)

Photovoltaic cells harness arriving solar light to excite electrons and produce usable electrical current.

Delivery technologies

While new sources of energy are only rarely made available by significant discoveries and technological advances, energy delivery schemes are only limited by creativity and economic feasibility. The anticipated use of fuel cells in cars, for example, is a delivery technology. This section presents some of the more common delivery technologies that have been important to historic energy development.

External combustion

Open fires and flames for heat and light are examples of external combustion, a primitive energy delivery technology. Many people still cook and boil water for drinking over fires. In some undeveloped countries, burning is used as a land clearing method, typically in order to grow crops. External combustion is generally powered by solar plant biomass or fossil fuels.

Animal domestication

Animal domestication is a primitive means of delivering energy for human use. Domesticated animals have been used to do work. Animals are of course powered directly or indirectly by solar plant biomass.

Shipping

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. Refined hydrocarbon fuels such as gasoline and LPG may also be delivered via aircraft.

Machinery

Sometimes energy is delivered or transported, usually across short distances, by mechanical means. Saw mills are examples of this kind of delivery; a system of belts or gears delivers hydroelectric energy to saws and other shop tools near a stream of water.

Pipeline networks

Pipeline networks are used to transport crude petroleum oil and its derivatives from wells to locations where they are refined, used, or further distributed by shipping.

Electric grids

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.

Many electrical grids face regular periods of limited supply, due to lack of supply, eg. under conditions of rapid economic growth. Grids have a predefined carrying capacity or load that cannot be exceeded. At peak times off use there may be rationing. These disturbances can be caused by interruptions at the production source or when part of the network is attacked or fails.

Grids may suffer from transient blackouts and brownouts. Often the cause is damage from a severe storm. During certain extreme space weather events solar wind can interfere with transmissions.

Industrialised countries such as Canada, the US, and Australia are among the highest per capita consumers of electricity in the world. A widespread electrical distribution network is undoubtably responsible for this ample supply. However these system are far from perfectly reliable for what many consider a vital necessity.

In the week of August 3rd 2003, the US set an all-time national record for electricity use of 90,000 gigawatts. CurrentEnergy (http://currentenergy.lbl.gov/) provides a realtime overview of the electricity supply and demand for California, Texas, and the Northeast of the US. African countries with few electrical grids have a correspondingly low annual per capita usage of electricity. One of the largest grids in the world supplies power to the state of Queensland, Australia. This network's service provision and its administration is an ongoing issues for that states politicans.

Storage technologies and infrastructure

Energy may be stored in many forms and it may be converted between these with some loss due to conversion efficiency. 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.

Chemical

Some natural forms of free energy are found in stable chemical compounds such as fossil fuels. Most coinsurances of chemical energy storage result from biological activity, since biological systems store energy in the form of chemical bonds. Man-made forms of chemical energy storage include hydrogen fuel, batteries and explosives such as cordite and dynamite.

Gravitational

The construction of dams is a method for storing energy in a gravitational field. Hydroelectric power is currently a small, but important part of the world's energy supply, contributing less than 5% of the world's total energy supply, but one-fifth of the world's electricity [1] (http://www.worldenergy.org/wec-geis/publications/reports/ser/overview.asp). Authorities are able to take very large projects such as the Snowy Mountains Scheme and the Three Gorges Dam to generate large qualities of electricity. The scale of these projects may severely impact local ecosystems.

Other examples are the counter-weights on elevators and the motion of a roller coaster.

Electrical

Electrical energy may be stored in capacitors. These are often used to produce high intensity releases of energy (such as a camera's flash)

Mechanical

Energy may also be stored in gases under pressure 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. Such systems save on expensive generating capacity since it only needs to meet average consumption rather than peak consumption.

On smaller scales, energy may be stored in mechanical systems such as springs or flywheels. Flywheel energy storage is currently being used for uninterruptible power supplies.

Future energy development

Main article: Future energy development

Extrapolations from current knowledge to future energy development 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. Modelling approaches offer ways to analyse diverse strategies, and hopefuly find a road to rapid and sustainable development of humanity. Short term energy crises are also a concern of energy development.

Existing technologies for new energy sources, such as new renewable energy technologies, nuclear fissionand fusion are promising, but need sustained research and development, including consideration of possible harmful side effects.