Beyond the oil, coal, and natural gas that still dominate global energy supply, a wide range of other sources can generate electricity, produce heat, or power vehicles. These alternatives span from solar and wind to nuclear fission, hydrogen, and biomass. Oil’s share of total energy demand recently fell below 30% for the first time in 50 years, and renewables now account for 32% of global electricity generation. Here’s a closer look at each major alternative and how it works.
Solar Energy
Solar power converts sunlight directly into electricity using photovoltaic panels or concentrates it to produce heat that drives a turbine. It’s one of the fastest-growing energy sources on the planet. Panels work even on cloudy days, though output drops significantly. Large-scale solar farms can cover hundreds of acres, while rooftop systems let individual homes offset much of their electricity use. The main limitation is intermittency: solar panels produce nothing at night and less during winter months, which is why battery storage and grid-level planning are essential companions to solar expansion.
Wind Energy
Wind turbines capture the kinetic energy of moving air and convert it into electricity through spinning blades connected to a generator. Onshore wind farms are now common across plains, ridgelines, and agricultural land, while offshore installations tap stronger, more consistent winds over the ocean. A single large offshore turbine can power thousands of homes. Like solar, wind is variable. Output depends on weather patterns, so grid operators pair wind generation with other sources or storage to keep supply steady.
Nuclear Energy
Nuclear power plants generate electricity by splitting atoms in a process called fission. Inside a reactor, fuel rods are immersed in water that serves as both a coolant and a way to sustain the chain reaction. The heat from fission turns water into steam, which spins a turbine to produce electricity. More than 400 commercial reactors operate worldwide, including 94 in the United States.
Nuclear’s major advantage is that it produces large amounts of reliable, round-the-clock electricity with virtually no carbon emissions during operation. Unlike solar and wind, a nuclear plant runs regardless of weather. The tradeoffs include the high upfront cost of building a plant, public concerns about safety, and the challenge of storing radioactive waste that remains hazardous for thousands of years. Nuclear contributed about 8% of the growth in global energy supply in 2024.
Hydroelectric Power
Hydropower uses the force of flowing or falling water to spin turbines. It’s one of the oldest and most established renewable energy sources. Large dams like those on major river systems can generate enormous amounts of electricity, while smaller “run-of-river” installations divert part of a stream without requiring a massive reservoir. Hydropower provides steady, controllable output that grid operators can ramp up or down quickly, making it a valuable partner for intermittent sources like wind and solar. Environmental concerns include disrupted fish migration, altered river ecosystems, and the displacement of communities by large reservoirs.
Geothermal Energy
Geothermal energy taps heat stored beneath the Earth’s surface. In regions with volcanic or tectonic activity, hot water and steam naturally rise close enough to the surface to drive turbines. Geothermal plants produce electricity around the clock with a tiny land footprint and minimal emissions. On a smaller scale, geothermal heat pumps use the stable underground temperature (typically around 50 to 60°F year-round) to heat and cool buildings efficiently, even in places without volcanic activity. The main limitation is geography: the best resources for electricity generation are concentrated in specific regions like Iceland, parts of the western United States, and East Africa’s Rift Valley.
Biomass and Biofuels
Biomass energy comes from organic materials: wood, crop residues, food waste, and even sewage. These can be burned directly for heat, converted into biogas through decomposition, or processed into liquid fuels. First-generation biofuels are made from sugar, starch, or vegetable oil, which is why ethanol from corn and biodiesel from soybeans are the most familiar examples.
More advanced approaches use thermochemical processes like gasification, which heats waste materials at high temperatures to produce a combustible gas. This technique works with municipal solid waste and various biomass blends, offering a way to both manage waste and recover energy. Biomass is sometimes called carbon-neutral because the plants absorbed carbon dioxide while growing, but that label depends on how the feedstock is sourced and whether forests or cropland are being sustainably managed.
Hydrogen as an Energy Carrier
Hydrogen isn’t an energy source you dig out of the ground. It’s an energy carrier, meaning you need energy to produce it, and then it stores that energy for later use. The cleanest method is electrolysis: using electricity to split water into hydrogen and oxygen. When the electricity comes from renewables or nuclear, the resulting “green hydrogen” produces zero greenhouse gas emissions.
Hydrogen can power fuel cells in vehicles, store excess renewable energy for later, or supply heat for industrial processes that are hard to electrify. The challenge right now is efficiency. Converting electricity to hydrogen and then back to usable energy involves losses at each step, making the overall process less efficient than using electricity directly. Research is focused on improving electrolyzer performance across a range of operating conditions and bringing costs down to make hydrogen competitive for transportation, shipping, and heavy industry.
Tidal and Wave Energy
The ocean holds enormous energy in its tides and waves. Tidal energy is highly predictable because it follows the gravitational pull of the moon, making it more reliable than wind or solar. Underwater turbines or barrage systems capture the flow of tidal currents, while wave energy devices harvest the up-and-down motion of surface waves. Both technologies are still in relatively early stages of commercial deployment. Harsh marine environments make equipment expensive to build and maintain, but coastal nations with strong tidal ranges are actively developing pilot projects.
How Your Body Uses Alternative Energy
The concept of “other energy sources” applies inside your body too. Your cells normally run on glucose, broken down from carbohydrates that provide about 4 calories per gram. Protein also supplies 4 calories per gram, while fat is the most energy-dense macronutrient at 9 calories per gram.
When carbohydrate intake drops sharply, such as during fasting, starvation, or a very low-carb diet, your body shifts its primary fuel source from glucose to fat. The liver breaks down fatty acids and converts them into molecules called ketone bodies, which are released into the bloodstream. Your heart, skeletal muscles, kidneys, and even your brain can use ketones to generate energy. This is especially important for the brain, which can’t burn fatty acids directly and normally depends almost entirely on glucose. During prolonged fasting, ketones become the brain’s principal backup fuel, crossing from the blood into brain tissue easily. This metabolic switch is a survival mechanism that keeps critical organs running when food is scarce.
The Shifting Global Energy Mix
The global energy landscape is changing faster than at any point in recent decades. In 2024, renewables accounted for the largest share of growth in global energy supply at 38%, followed by natural gas at 28%, coal at 15%, oil at 11%, and nuclear at 8%. Renewables and nuclear together contributed 40% of total electricity generation for the first time. Oil’s declining share of total energy demand, now below 30% after peaking at 46% half a century ago, reflects the accelerating diversification away from a single dominant fuel. No single alternative will replace fossil fuels on its own. The transition involves a mix of solar, wind, nuclear, hydro, geothermal, biomass, and hydrogen, each suited to different geographies, scales, and applications.