Main energy resources available on Earth
Principles of energy • National and global energy resources
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Key concepts
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Fossil fuels: coal, oil and natural gas
Fossil fuels store chemical energy formed from ancient biomass under heat and pressure over millions of years. Burning fossil fuels converts chemical energy into thermal energy and mechanical or electrical energy in power stations or engines. Fossil fuels release carbon dioxide and other pollutants when burned; sulfur compounds from coal produce acid rain unless removed from exhaust gases. Fossil fuels are non-renewable because reserves are finite and form far more slowly than they are used.
Nuclear fuel
Nuclear fuel uses energy released by nuclear fission in heavy isotopes such as uranium. Nuclear reactors convert nuclear energy into thermal energy to produce steam and drive turbines for electricity generation. Nuclear power produces large amounts of continuous electricity with low direct carbon emissions, but generates radioactive waste and requires strict safety measures. Nuclear fuel is non-renewable at present given current technologies and available fissile materials.
Bio-fuel and biomass
Bio-fuels and biomass store chemical energy in recently living organisms or organic waste. Burning or converting biomass releases chemical energy for heating, electricity generation or transport fuels. Bio-fuels qualify as renewable when sourcing and regrowth rates match or exceed use, but scale and land-use requirements can limit sustainability and compete with food production. Biomass combustion also produces emissions, so processing and fuel choice affect environmental impact.
Wind energy
Wind turbines convert kinetic energy of moving air into electrical energy via rotating blades and generators. Wind power produces no direct waste products and scales from single turbines to large farms. Wind energy is intermittent: low wind yields little power and very strong gusts can force shutdown to avoid damage. Site selection, consistency of wind and connection to the grid determine practical output and reliability.
Hydro-electricity
Hydroelectric generation converts gravitational potential energy of stored or flowing water into electrical energy using turbines. Large-scale hydroelectric schemes supply steady electricity and permit rapid response to demand changes. Hydroelectric projects require suitable topography and river flow; dams and reservoirs can cause habitat loss and social impacts where flooding of land occurs. Run-of-river schemes reduce storage but depend strongly on flow rates and seasonal variation.
Geothermal energy
Geothermal energy uses the Earth’s internal heat as hot water or steam to produce heat or drive turbines. Regions with volcanic activity or shallow hot rock yield the highest power densities and direct heating opportunities. Geothermal supply is effectively renewable at local scales but requires suitable geology and investment in drilling; overuse can reduce local temperatures or reservoir pressure. Iceland and similar regions exploit geothermal extensively for electricity and heating.
Tidal energy
Tidal energy converts the predictable rise and fall of sea levels into electricity using barrages, tidal turbines or lagoons. Tidal power is highly predictable because tides follow astronomical cycles. Tidal schemes require suitable coastal geography and can cause ecological and navigation impacts; high capital costs and limited suitable sites restrict widespread deployment.
Solar energy (the Sun)
Solar energy arrives as electromagnetic radiation from the Sun. Photovoltaic cells convert sunlight directly into electricity; solar thermal systems concentrate heat for electricity or heating. Solar supply is renewable and widely available, but output fluctuates with weather and day–night cycles. Geographic latitude and local climate determine average yield, and storage or backup generation is necessary for continuous supply.
Water waves
Wave energy extracts kinetic and potential energy from surface water motion using devices such as oscillating water columns or floating converters. Wave power offers a large energy density in exposed coastal regions and produces low direct emissions. Wave energy is variable with weather and sea state, requires marine engineering and faces challenges from device survivability and maintenance in harsh ocean conditions.
Key notes
Important points to keep in mind