Sources of Energy: A Comparison

Learn how turning toward cleaner energy sources means factoring in economic and energy needs alongside environmental ones.

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Two wind turbines are positioned amidst many solar panels

If you want to be eco-friendly, you should be driving an electric car. Right?

Unfortunately, it is not as simple as that. While electric cars do not pollute the air around them like a combustion engine does, they do need to be charged, leading to questions such as what energy source the electricity is coming from and whether that energy source is clean.

The overall evaluation of an energy source is based not only on how clean it is; it also has to be reliable, accessible, and affordable. Not all of these factors can be categorized neatly. For example, petroleum tends to be relatively affordable in the United States, but that is in part because the government subsidizes fossil fuel industries. Similarly, while wind energy tends to be relatively expensive, its cost has been steadily declining for years as its use increases.

To evaluate the options available, understanding fundamental facts about what types of energy are available and what trade-offs each presents is helpful.

There are three main categories of energy sources: fossil fuel, alternative, and renewable. Renewable is sometimes, but not always, included under alternative.

Fossil Fuels: Petroleum, Coal, and Natural Gas

Fossil fuels formed over millions of years ago as dead plants and animals were subjected to extreme heat and pressure in the earth’s crust. This natural process converted bones and other organic matter into carbon-rich substances that, when burned, generate energy. There are three main fossil fuels.

  • Petroleum is an umbrella term that includes products such as crude oil, which is refined into more familiar fuels such as gasoline, jet fuel, kerosene, and diesel. Petroleum and oil are often used interchangeably. It is extracted through drilling or hydraulic fracturing (also known as fracking).
  • Coal is a rock found close to the earth’s surface and is one of the world’s most abundant fossil fuels. It is extracted through surface mining (using machines to clear away the uppermost layers of rock and soil) and underground mining (using machines and miners to remove coal deep underground).
  • Natural gas, a mixture of gases trapped underneath the earth’s surface, is extracted in similar ways as oil. Advances in drilling and fracking have unlocked vast reserves of natural gas.

Fossil fuels are often called dirty energy sources because using them comes at a high—and often irreversible—cost to the environment. Carbon emissions, or the amount of carbon dioxide these fuels release into the atmosphere, add up over generations and cannot be taken back. Moreover, there is only a finite amount of these resources on earth. 

Renewable and Alternative Energy: Wind Power, Solar Power, Hydropower, Nuclear Energy, and Biofuels

Forms of energy not derived from fossil fuels include both renewable and alternative energy, terms that are sometimes used interchangeably but do not mean the same thing. Alternative energy broadly refers to any energy that is not extracted from a fossil fuel, but not necessarily only from a renewable source. For example, nuclear power generation most commonly uses uranium, an abundant but not technically renewable fuel. Renewable energy, on the other hand, includes sources such as sun and wind that occur naturally and continuously. 

There are five main renewable and alternative fuels.

  • Wind power is created when wind spins a turbine, or a windmill, which can be located on land or offshore. 
  • Solar power harnesses the sun’s energy in two ways: by converting the sun’s light directly into electricity when the sun is out (think solar panels), or solar thermal energy, which uses the sun’s heat to create electricity, a method that works even when the sun is down.
  • Hydropower is created when rapidly flowing water turns turbines inside a dam, generating electricity.
  • Nuclear energy is produced at power plants by the process of nuclear fission. The energy created during nuclear reactions is harnessed to produce electricity.
  • Biofuels, also referred to as biomass, are produced using organic materials (wood, agricultural crops and waste, food waste, and animal manure) that contain stored energy from the sun. Humans have used biomass since they discovered how to burn wood to make fire. Liquid biofuels, such as ethanol, also release chemical energy in the form of heat. 

Renewable and alternative energy sources are often categorized as clean energy because they produce significantly less carbon emissions compared to fossil fuels. But they are not without an environmental footprint.

Hydropower generation, for example, releases lower carbon emissions than fossil fuel plants do. However, damming water to build reservoirs for hydropower floods valleys, disrupting local ecosystems and livelihoods. In another case, biofuels are renewable but are cultivated on huge swaths of land and sometimes generate more carbon emissions than fossil fuels do.

Other considerations such as safety also matter. The likelihood of a meltdown at a nuclear facility is exceedingly small, but if one were to occur, the results would be catastrophic. In fact, concerns about the dangers associated with operating nuclear power plants have limited the expansion of nuclear energy.


Despite the diversity of energy sources available, most countries rely on the three major fossil fuels.

In 2018, more than 81 percent of the energy countries produced came from fossil fuels. Hydroelectricity and other renewable energy (14 percent) and nuclear energy (about 5 percent) accounted for the remainder. But not all countries consume energy at the same levels. For example, the United States, China, and European Union countries combined were responsible for half of the world’s total coal, natural gas, and oil consumption in 2018. Nor do all countries use the same mix of fuels. Norway primarily uses hydroelectric power, for example, but in Saudi Arabia oil reigns supreme. When choosing which types of energy to use, countries balance their economic needs with environmental concerns.

Electric Power Consumption by Country

Click on each country for information about its use of energy sources

Climate change has added new considerations and urgency to the decisions countries make about their energy sources.

Developing countries have different needs than developed countries—and they face a different set of energy challenges as consequences of climate change become more severe. Many developing countries are going through industrialization, the development of factories and mass production, which requires large amounts of energy. Some of these countries see fossil fuels as the best way to achieve those energy goals, though many are turning to alternative energy sources as well—seeing them as the future of energy consumption.

In 2015, 196 countries pledged to increase their use of clean energy as part of the Paris Agreement, an international treaty that allowed signatories to set their own goals for lower carbon emissions. As countries around the world push to adopt more clean energy sources, they will increasingly contend with the environmental and economic trade-offs that renewable sources present and the reality that opting for clean over dirty energy is not such a simple choice after all.