There are many good reasons to burn less coal: It’s polluting, expensive, damaging to human health, and emits more carbon pollution than any other form of electricity.

But an oft-overlooked factor is that burning fuel to generate electricity is astonishingly inefficient. Major energy losses are an unavoidable consequence of converting heat into motion, which is how conventional power plants generate electricity. They typically burn coal or gas to heat water, which makes steam that spins the blades of a turbine that interacts with magnets to generate electricity. More than two-thirds of the energy in coal is vented off as waste heat in the multistep process of making electricity.

By contrast, wind turbines, hydroelectric turbines, and solar panels skip the step of burning fossil fuels to heat water. Instead, a turbine powered by wind or water simply turns as the current of air or water flows by it. And solar panels convert the sun’s energy into electricity using semiconductors. No steam is required for either process.

The major differences in efficiency are best appreciated visually. The animation below sums it up.

An animated gif shows that because the process for generating electricity from the sun is less wasteful than generating it from coal, a small amount of solar energy can displace a surprising amount of coal burning.

Key takeaways

  • Today’s fleet of coal-burning power plants in the U.S. has an average operating efficiency of 32%, meaning 68% of the energy in coal is lost in the process of converting it to electricity.
  • Methane gas — often called “natural” gas — is a bit better, with 44% efficiency, on average.
  • In this analysis, renewables are defined as the sum of electricity generated by hydropower, wind, and solar.
  • With renewables, no fuel is burned, so there is no energy lost in the conversion of fuel to electricity. Renewables don’t capture 100% of the solar energy, wind, or water that moves past them, but there’s little pollution or resource use. Once a turbine or a solar panel captures energy, that entire quantity of energy is available for use.
  • Selecting one example from the graph above, coal and renewables generated approximately the same amount of electricity in February 2022 — around 250,000 billion British thermal units, or BTUs.
  • But the amount of coal needed to make 250,000 billion BTUs of electricity was 780,000 billion BTUs.
  • In other words, 250,000 billion BTUs of renewables replaced 780,000 billion BTUs of coal. That is to say, every unit of renewable electricity that’s used to replace coal saves three times that amount of energy. That’s an impressive return on investment.
  • Electricity brings a societal benefit — it’s essential for powering modern life. But for every kilowatt-hour of benefit derived from coal, the impacts are levied on three times that amount. That price tag — heat-trapping carbon pollution, particulate pollution, and coal ash — come from all of the coal that heads into the power plant, even though the majority of the energy contained in the coal never reaches our outlets.
  • No form of energy is without environmental and social consequences, but they certainly are not all equal. Energy that’s cleaner and more efficient is a clear improvement in many ways.

Notes and sources

The efficiency of power plants is measured by their heat rate, which is the BTUs of energy required to generate one kWh of electricity. The Energy Information Administration lists the heat rate for different types of power plants, for each year since 2011.

Data for the amount of electricity generated by coal and renewables is from the Energy Information Administration.

Find more details and infographics on the efficiency of electric power generation in this article: Energy loss is the single-biggest component of today’s electricity system.

Karin Kirk is a geologist and freelance writer with a background in climate education. She's a scientist by training, but the human elements of climate change occupy most of her current work. Karin is...