A cartoon with a man pouring coffee into a complicated homemade coffee maker that he says he modeled after thermodynamic power plants.

Traditional electricity generation has a thermodynamics problem: Burning fuel to generate electricity creates waste heat that siphons off most of the energy. By the time electricity reaches your outlet, about two-thirds of the original energy has been lost in the process.

This is true only for “thermal generation” of electricity, which includes coal, natural gas, and nuclear power. Renewables like wind, solar, and hydroelectricity don’t need to convert heat into motion, so it doesn’t lose energy.

The problem of large energy losses also plagues internal combustion engines. In a gasoline-powered car, about 80% of the energy in the gas tank never reaches the wheels. (For details, see the previous post comparing the efficiency of electric vehicles and internal combustion engines.)

Fossil-fueled power plants are more efficient than a car’s engine, but they still face the same hurdle. In both cases, converting energy from one form to another leaves only a fraction of the original energy remaining to accomplish the intended task.

Traditional thermal power plants lose most of the energy that enters them

Over the years, the most common way to generate electricity has been through thermal generation, the process of which begins by generating heat. That heat is then used to boil water and create steam, which turns a turbine that produces electricity. The fuel source can be coal, natural gas, or nuclear fission, but the process is the same – and less efficient. Most of the energy that goes into a thermal power plant is discharged as waste heat. An additional small loss comes from the energy used to operate the power plant itself.

In a contemporary thermal power plant, 56% to 67% of the energy entering it is lost in conversion. But the effects of mining, processing, greenhouse gas emissions, particulates, and other forms of pollution are imposed on the entire amount of fuel consumed at the upstream end of the process, not just the minority that finally reaches your outlets. . The same is true for the price tag, of course, which is more noticeable as the cost of natural gas rises.

How are the sources filled?

The efficiency of power plants is measured by their heat, which is the BTUs of energy required to generate one kWh of electricity. This simple math compares the total amount of energy entering the power plant with the amount of electricity leaving the plant and going out to the grid.

The Energy Information Administration lists heat rates for different types of power plants, and the average operating efficiencies of thermal power plants in the US in 2020 are:

  • Natural gas: 44% efficient, meaning that 56% of the energy in the gas is lost, with 44% of the energy being converted into electricity.
  • Coal: 32% efficiency
  • Nuclear: 33% efficient

Efficiency of renewables

What about the efficiency of renewables? A wind turbine is about 35 to 47% efficient. But wait, isn’t that the same low efficiency as coal and gas power plants? Well, yes…and no.

Comparing renewable energy to fossil fuels is not an apples-to-apples comparison, because renewables do not use fuel.

A coal plant with 32% efficiency still burns 100% of its coal. The impact of burning coal is based on how much coal is burned, not how much electricity is generated at the end of the process. But a wind turbine that converts 32% of the wind that passes through it into electricity does not waste anything.

Although wind turbines only capture part of the wind that passes through them, that is not as problematic as the inefficiencies of fossil fuel plants, because the wind itself is free, non-polluting, and constantly supplied by the atmosphere. The same cannot be said for coal or gas.

However, the more efficient a given wind turbine is, the less it will need. So effectiveness is important, albeit in a different way.

Solar panels range from around 18% to 25% efficiency, with efficiency steadily increasing in recent years. As with wind, the inefficiency of a solar panel does not mean that the Sun must emit more energy to power the panel. But more efficient solar panels generate more electricity from each panel, saving materials and land space.

Hydropower is the champion of efficiency, reaching almost 90% efficiency in converting moving water into electricity. Part of the impressive efficiency of hydroelectricity is that dams funnel water directly through turbines, while wind turbines simply sit in the middle of moving air and convert some of it into electricity.

The replacement of thermal electricity generation can reduce the total energy consumption

Electricity generation accounts for 24% percent of US greenhouse gas emissions. An unrecognized benefit of replacing fossil-fueled thermal electric generation with wind, solar, or hydropower is that all the fuel that becomes waste heat does not need to be replaced. More efficient methods of generating electricity have made the whole problem obsolete.

Consider a coal plant that consumes 1,000 megawatts of coal per hour and produces 320 megawatts of electricity per hour. Only a small number need to be replaced with a different energy source. But that replacement would save 1,000 megawatts worth of pollution and fuel costs. Additionally, switching to naturally efficient forms of energy means that less energy, overall, is needed.

Energy loss is more than energy use

The figure below shows how energy flows in the current US power grid. This information is more often described from the bottom end of the power plants, but by including all the fuel that goes into the power plants, it is easier to understand the amount of energy used in the whole process – and the A large amount of energy can be saved as coal and natural gas are replaced by renewables.

Using the above figures from 2021, and taking into account the whole host of energy sources, more energy is lost in conversion than is produced as electricity. The biggest part of today’s electricity system is energy loss.

Energy transmission and storage cause less energy loss

Regardless of the source of electricity, it must be transferred from the power plant to the end users. Transmission and distribution cause small power outages, about 5% of the US average, according to the EIA. The longer the distance traveled, the greater the loss of electricity from the transmission lines, and this loss of energy is the same no matter what type of energy enters the grid.

Energy storage is an increasingly common part of electricity supply, and storage is an important element in decarbonizing the electricity grid. How much energy do batteries lose? The round-trip efficiency of large, lithium-ion batteries used by utilities was around 82% in 2019, meaning that 18% of the original energy was lost in the process of storing and releasing it. Batteries have become more efficient over time, and the Department of Energy’s grid storage research uses battery efficiency of 86% in its estimates.

Better way

Since fossil fuels have been the norm for most of the world’s energy for more than a century, the thermodynamic challenges of burning the fuel have long been accepted as an inevitable side effect.

The Energy Information Administration euphemistically describes these energy losses as “a thermodynamically essential part” to produce thermal electricity.

But as the world looks at changing energy supplies, large-scale energy losses are neither necessary nor a part of modern electricity. A cleaner, more sustainable grid can lower overall energy consumption, generate less pollution overall, and emit less pollution to the climate. One can consider these developments to be the critical “must-have parts” of tomorrow’s energy system.


The author is grateful to the analysts of the Energy Information Administration for their help in navigating the nuances of energy conversion losses. For more details on how the energy content of renewables and fossil fuels compares, see Alternative Methods for Energy Capture in Non-Combustible Renewables or a description of two methods of comparing renewable electric generation with other sources.

Tom Toro is a cartoonist and writer who has published over 200 cartoons in The New Yorker since 2010.

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