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 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.
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 biofuel, 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 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.