Renewable Energy Explained: How Solar, Wind, Hydro, Geothermal and Biomass Work

The five main renewable energy sources

The U.S. Energy Information Administration (EIA) identifies five main renewable energy sources used for electricity and heat: biomass, geothermal, hydropower, solar and wind. Each converts a different natural resource — sunlight, moving air, flowing water, underground heat or organic matter — into usable energy.

Solar energy

EIA describes three solar technologies: photovoltaic (PV) cells that convert sunlight directly into electricity, solar thermal systems that heat water or air for buildings, and concentrated solar collectors that heat a fluid used to generate electricity.

Wind energy

Wind turbines convert moving air into electricity and are usually grouped into wind farms. According to EIA, most U.S. wind farms currently operate in the Central region of the country, with offshore wind expansion planned.

Hydropower

Hydropower generates electricity from flowing water. EIA distinguishes conventional hydropower, which uses dams or river flow to spin turbines, from pumped-storage hydropower, which moves water between two reservoirs at different elevations to store and release energy.

Geothermal energy

Geothermal energy is heat from inside the Earth. EIA's geothermal explainer lists three uses: bathing in hot springs, heating buildings, and generating electricity.

Biomass energy

Biomass energy comes from nonfossilized plant material. EIA groups it into three categories: biofuels such as ethanol and biodiesel for transportation, municipal solid waste and biogas burned to produce electricity, and wood — residues from forestry and wood pellets used for heating and cooking. EIA notes that wood is the second-largest source of renewable energy in the United States.

Global capacity vs. the U.S. electricity mix

The two metrics below are not directly comparable: global figures measure installed capacity (the maximum output a technology could produce), while the U.S. figures measure actual share of electricity generated in 2023. Global capacity data for the end of 2024 come from the International Renewable Energy Agency (IRENA), as reported by Balkan Green Energy News; U.S. generation shares come from EIA.

Globally, total renewable capacity reached 4.49 TW by the end of 2024, up 585 GW (+15.1%) from 2023 — the largest annual increase on record, according to the IRENA data cited by Balkan Green Energy News. Solar and wind together accounted for the large majority of that growth, while hydropower, bioenergy and geothermal expanded more slowly. In the United States, renewables overall supplied 21.4% of utility-scale electricity generation in 2023, behind fossil fuels (60.0%) and ahead of nuclear (18.6%), per EIA; wind was the single largest renewable contributor.

The same reporting noted that China accounted for 63.8% of all renewable capacity added worldwide in 2024, including 70.5% of new wind power and 61.5% of new solar photovoltaic capacity, and that the country now holds more than half of global solar capacity at 888 GW.

How to check which renewable source fits a location

Based on how each technology works according to EIA, these are the basic checks used to judge whether a renewable source is suited to a given site:

1. Check sunlight exposure: solar PV and solar thermal systems rely on converting sunlight directly into electricity or heat, so consistent sun exposure is the key requirement.
2. Assess local wind patterns: wind turbines need sufficient, consistent wind; in the U.S., most existing wind farms are concentrated in the Central region, with offshore sites being developed separately.
3. Look for flowing water: conventional hydropower needs a dam or river flow strong enough to spin a turbine, while pumped-storage hydropower needs two reservoirs at different elevations.
4. Identify geothermal heat: EIA lists hot springs, building heating and electricity generation as the main uses of geothermal heat, so local hot springs or underground heat resources indicate potential for these uses.
5. Secure a biomass feedstock: availability of wood residue, municipal solid waste, biogas sources, or crops for biofuels determines whether biomass energy production is practical, since each requires a steady supply of organic material.

Why the mix matters

No single renewable source dominates both measures. Solar leads in global installed capacity, hydropower is the largest renewable source by capacity after solar, and wind supplies the biggest share of actual U.S. renewable electricity generation. The differences reflect how capacity (what a plant could theoretically produce) differs from generation (what is actually produced).