Low-carbon power in the context of "Electric locomotive"

Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other renewable sources combined and also more than nuclear power. Hydropower can provide large amounts of low-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems. A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand. Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less greenhouse gas than fossil fuel-powered energy plants. However, when constructed in lowland rainforest areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted.

Construction of a hydroelectric complex can have significant environmental impact, principally in loss of arable land and population displacement. They also disrupt the natural ecology of the river involved, affecting habitats and ecosystems, and siltation and erosion patterns. While dams can ameliorate the risks of flooding, dam failure can be catastrophic.

Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by nuclear fission of uranium and plutonium in nuclear power plants. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators in some space probes such as Voyager 2. Reactors producing controlled fusion power have been operated since 1958 but have yet to generate net power and are not expected to be commercially available in the near future.

The first nuclear power plant was built in the 1950s. The global installed nuclear capacity grew to 100 GW in the late 1970s, and then expanded during the 1980s, reaching 300 GW by 1990. The 1979 Three Mile Island accident in the United States and the 1986 Chernobyl disaster in the Soviet Union resulted in increased regulation and public opposition to nuclear power plants. Nuclear power plants supplied 2,602 terawatt hours (TWh) of electricity in 2023, equivalent to about 9% of global electricity generation, and were the second largest low-carbon power source after hydroelectricity. As of November 2025, there are 416 civilian fission reactors in the world, with overall capacity of 376 GW, 63 under construction and 87 planned, with a combined capacity of 66 GW and 84 GW, respectively. The United States has the largest fleet of nuclear reactors, generating almost 800 TWh per year with an average capacity factor of 92%. The average global capacity factor is 89%. Most new reactors under construction are generation III reactors in Asia.

Energy is sustainable if it "meets the needs of the present without compromising the ability of future generations to meet their own needs." Definitions of sustainable energy usually look at its effects on the environment, the economy, and society. These impacts range from greenhouse gas emissions and air pollution to energy poverty and toxic waste. Renewable energy sources such as wind, hydro, solar, and geothermal energy can cause environmental damage but are generally far more sustainable than fossil fuel sources.

The role of non-renewable energy sources in sustainable energy is controversial. Nuclear power does not produce carbon pollution or air pollution, but has drawbacks that include radioactive waste, the risk of nuclear proliferation, and the risk of accidents. Switching from coal to natural gas has environmental benefits, including a lower climate impact, but may lead to a delay in switching to more sustainable options. Carbon capture and storage can be built into power plants to remove their carbon dioxide (CO₂) emissions, but this technology is expensive and has rarely been implemented.

An energy transition (or energy system transformation) is a major structural change to energy supply and consumption in an energy system. Currently, a transition to sustainable energy is underway to limit climate change. Most of the sustainable energy is renewable energy. Therefore, another term for energy transition is renewable energy transition. The current transition aims to reduce greenhouse gas emissions from energy quickly and sustainably, mostly by phasing-down fossil fuels and changing as many processes as possible to operate on low carbon electricity. A previous energy transition perhaps took place during the Industrial Revolution from 1760 onwards, from wood and other biomass to coal, followed by oil and later natural gas.

Over three-quarters of the world's energy needs are met by burning fossil fuels, but this usage emits greenhouse gases. Energy production and consumption are responsible for most human-caused greenhouse gas emissions. To meet the goals of the 2015 Paris Agreement on climate change, emissions must be reduced as soon as possible and reach net-zero by mid-century. Since the late 2010s, the renewable energy transition has also been driven by the rapidly falling cost of both solar and wind power. After 2024, clean energy is cheaper than ever. Global solar module prices fell 35 percent to less than 9 cents/kWh. EV batteries saw their best price decline in seven years. Another benefit of the energy transition is its potential to reduce the health and environmental impacts of the energy industry.