Electricity comes from a mix of fuels and natural forces, with fossil fuels still generating about 60% of the world’s power. Coal and natural gas are the dominant sources, followed by renewable energy (wind, solar, and hydropower) at around 30% and nuclear energy at roughly 9%. The balance is shifting quickly, but understanding what actually powers the grid starts with knowing how each source turns raw energy into the current flowing through your walls.
How Most Electricity Gets Made
Nearly every power plant on Earth works on the same basic principle: something spins a turbine connected to a generator, and the generator converts that spinning motion into electrical current. The difference between power sources mostly comes down to what does the spinning. In coal and natural gas plants, burning fuel creates steam or hot gas that pushes turbine blades. In wind farms, moving air does the job. In hydroelectric dams, falling water takes over. Solar panels are the major exception, generating electricity without any moving parts at all.
Coal: The Oldest Grid Fuel
Coal-fired power plants burn crushed coal in a furnace to heat water into high-pressure steam. That steam blasts through a series of blades mounted on a rotor shaft, spinning a generator to produce electricity. After passing through the turbine, the steam is cooled back into water and cycled through again. It’s a straightforward process, and coal powered the earliest electric grids in the late 1800s.
Coal remains a significant global fuel, though its share is declining. It produces more carbon dioxide per unit of electricity than any other major source: about 2.3 pounds of CO2 for every kilowatt-hour generated. That’s more than double the emissions from natural gas. Coal plants also release sulfur dioxide, nitrogen oxides, and particulate matter, which is why many countries are actively retiring them.
Natural Gas: The Largest Single Source
Natural gas has overtaken coal as the top electricity fuel in many countries, including the United States, where it generated about 43% of all power in 2023. Globally, gas and coal together account for the bulk of that 61% fossil fuel share.
Gas plants come in two main designs. Simple-cycle plants work like jet engines: they burn natural gas to create hot, expanding gases that spin a turbine directly. Combined-cycle plants take this a step further by capturing the waste heat from that first turbine, using it to boil water and drive a second steam turbine. This two-stage approach dramatically improves efficiency. A well-designed combined-cycle plant can convert about 70% of the fuel’s energy into electricity, compared to roughly 33% for a typical coal plant.
Natural gas produces about 0.96 pounds of CO2 per kilowatt-hour, less than half of coal’s emissions. That lower carbon footprint, combined with gas plants’ ability to ramp up and down quickly to match demand, has made natural gas a bridge fuel as grids add more renewables.
Nuclear Energy
Nuclear power plants generate about 19% of U.S. electricity and roughly 9% globally. They use uranium fuel, where atoms of uranium are split in a controlled chain reaction called fission. Each time an atom splits, it releases a large amount of heat. That heat is used to boil water into steam, which spins a turbine and generator, just like in a coal or gas plant. The difference is the heat source: nuclear reactions rather than combustion.
Most reactors work in one of two ways. In pressurized designs, water heated by the reactor core flows through a sealed loop into a heat exchanger, where it heats a separate water supply to create steam. In boiling-water designs, the water inside the reactor itself turns to steam and feeds directly to the turbine. Either way, no fuel is burned and no CO2 is released during generation. A single uranium fuel pellet, about the size of a pencil eraser, contains as much energy as a ton of coal.
Solar Power
Solar panels work completely differently from every other major electricity source. Instead of spinning a turbine, they convert sunlight directly into electric current using semiconductor materials, typically silicon.
Here’s how it works: sunlight is made up of photons, tiny packets of energy. When photons hit a solar cell, some are absorbed by the semiconductor material, knocking electrons loose from their atoms. The cell is manufactured so its front surface attracts these free electrons, creating a buildup of negative charge on one side and positive charge on the other. This imbalance creates voltage, the same kind of electrical pressure you’d find between the terminals of a battery. Connect the cell to a circuit and those electrons flow as usable electricity.
Solar energy is the fastest-growing electricity source worldwide and a major reason renewables are projected to reach 37% of global generation by 2026.
Wind Power
Wind turbines convert the kinetic energy of moving air into electricity using the same aerodynamic principles that keep airplanes aloft. As wind flows across a turbine blade, air pressure drops on one side and increases on the other, creating lift. That lift force is stronger than drag, so the blade spins.
The spinning rotor connects to a generator, either directly or through a gearbox that speeds up the rotation. In direct-drive turbines, a large ring of permanent magnets rotates with the blades, passing through stationary copper coils to induce an electric current. Gearbox-equipped turbines use a smaller, faster-spinning generator to achieve the same result. The electricity produced is alternating current (AC), which transformers then step up to higher voltages for transmission across the grid.
Hydroelectric Power
Hydropower is the oldest renewable electricity source and still one of the most efficient. A hydroelectric dam stores water at a height, giving it gravitational potential energy. When gates open, the weight of the water above creates enormous pressure at the bottom of the dam, forcing water through turbines at high speed. Those turbines spin generators to produce electricity.
Hydroelectric plants typically convert about 90% of the water’s available energy into electricity. That’s far higher than any fossil fuel plant. Some of the remaining 10% loss comes from the generator itself, but part of it is unavoidable: you can’t extract all of a water stream’s kinetic energy, or it would stop moving and block the flow behind it.
Hydropower’s main limitation is geography. You need a river with enough flow and a suitable site for a dam, which means most of the best locations in developed countries are already in use.
The Current Global Mix
In the United States, the 2023 breakdown was roughly 60% fossil fuels, 19% nuclear, and 21% renewables. Globally, the picture is similar but with a slightly higher renewable share (30%) because of large hydropower systems in countries like China, Brazil, and Canada.
That mix is changing fast. The International Energy Agency projects that low-emission sources, renewables plus nuclear, will account for nearly half of all global electricity by 2026. Fossil fuels’ share is expected to drop from 61% to 54% in the same period. The growth is driven largely by solar and wind installations, which have become cheaper to build than new fossil fuel plants in most parts of the world. Still, coal and natural gas will continue generating the majority of the world’s electricity for years, partly because existing plants have decades of operational life remaining and partly because solar and wind need backup sources for times when the sun isn’t shining or the wind isn’t blowing.