Guest Blog: The Energy Inefficiency of Fossil Fuels

by Nancy LaPlaca

Power plants waste 65% of their energy. Cars waste even more.

The fossil-fueled cars we drive today are extremely inefficient. What does that mean? It means that 70-80% of the energy in the gasoline that you put into your car doesn’t do any work, it doesn’t move a car an inch. Instead, that huge amount of energy is released into the atmosphere as heat and pollution.

As the fossil fuel age starts to show signs of wear and tear we will all learn more about the “primary” energy sources we depend on so much but rarely think about. Primary energy sources are fuels like coal and fossil gas and petroleum.

Primary Versus Secondary Sources of Energy

The primary source is then converted into work, whether it’s gasoline powering your car or coal generating electricity in a power plant. When energy is converted from one form to another, a certain amount of energy is lost. That “lost energy” is heat and pollution.

Our current fleet of gasoline-powered cars that waste so much fuel are called Internal Combustion Engine (ICE) vehicles. That “waste” is the air pollution that makes us sick, the heat that feeds climate chaos, and the black carbon and hazardous air pollutants that give our kids asthma, send us to the hospital, and bring on heart attacks. We must reduce these pollutants as quickly as possible, eliminating 50% by 2030 in order to stabilize our climate.

As communities of color know all too well, they are on the frontlines of this choking and dangerous air pollution, with young children especially vulnerable to the hazards of these toxic pollutants.

Sankey Diagram

Figure 1 below, a Sankey diagram, illustrates these inefficiencies. A Sankey diagram is a type of flow chart where the width of the arrow is proportional to the flow rate. In other words, the wider the arrow, the larger the flow rate.

For example, the dark green arrow at the bottom of the chart represents the flow of petroleum in the U.S. Following the dark green arrow from left to right, you will see that petroleum used in transportation is highly inefficient, with most of the energy wasted (light gray). But the inefficiency of fossil-fueled machines isn’t just automobiles, it includes power plants.

Power Plants Average 35% Efficiency

Power plants are slightly better than gasoline-powered vehicles at an average 35-40% efficiency. Coal plants are usually the least efficient, that is, they use the most energy to generate electricity, while fossil gas combined cycle power plants are generally more efficient, averaging ~45% efficiency. In addition to being inefficient, coal plants emit huge amounts of toxic mercury, create acid rain and emit many hazardous air pollutants.

Duke Energy Converted 50 Year Old Coal Plants to Run on Fossil Gas

In North Carolina, the issue of the inefficiency of power plants is particularly important because Duke Energy has converted so many old coal plants to run on fossil gas. According to engineering experts, when a coal plant is converted to run on fossil gas, it loses 3-5% efficiency and thus is even less efficient than a coal plant.

Another problem is that Duke Energy converted these very old coal plants to fossil gas using the plant’s initial permit. Despite the fact these conversions cost hundreds of millions of dollars, the North Carolina Utilities Commission (NCUC) did not require Duke Energy to file a new application for a power plant permit or require any review.

These 50-year-old former coal plants that have been converted to run on largely fracked fossil gas are expected to run another 30 years. And with the cost of fossil gas doubling in the past 6 months, all these converted gas plants could become very expensive.

We can and must do better. We cannot ignore the damages and inefficiencies of power plants and gasoline-powered vehicles. The technologies to replace these fossils are available, cost-effective, and give us good jobs we can be proud of. Let’s do it!

Nancy LaPlaca is an energy expert with almost 40 years of experience in public policy. Throughout the Fall of 2021 Nancy is leading our webinar series ‘Pulling Back the Curtain: Who’s Charting Our Energy Future‘ to help aspiring clean energy advocates reshape North Carolina’s energy landscape. You can learn more about this series and register for upcoming webinars at

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