Understanding what makes coal nonrenewable, whether it is sustainable, and what alternatives exist is essential as we rethink energy production in a rapidly changing world.

Is coal renewable or nonrenewable?

Coal is classified as a nonrenewable energy source. This means it cannot be replenished on a human timescale which means once it is used it’s gone forever. Michigan State University classifies natural resources into 2 groups:

1. Renewable resources naturally replenish themselves on a human timescale. Examples include wind, sunlight, plants, and trees.
2. Nonrenewable resources do not naturally replenish themselves on a human timescale, meaning they either are gone forever once utilized or replenish incredibly slowly over millions of years. Examples of nonrenewable resources include coal, oil, and natural gas.

Coal forms naturally over millions of years through the compression of plant material buried under layers of soil and rock. Even though coal is formed through natural processes below the surface of the Earth, the timescale for its formation far exceeds the rate at which we consume it. For this reason, coal is classified as a nonrenewable energy source.

Is coal a sustainable energy source?

Although coal has been a staple of energy production for centuries, its supply is limited. Coal reserves are finite and, at current consumption rates, global supplies are estimated to last another 100 to 150 years. However, this timeline does not account for the environmental and economic costs associated with coal use.

Extracting and burning coal releases significant greenhouse gases and other pollutants, contributing to climate change and health issues. Transitioning to more sustainable energy sources is critical to avoid depleting these reserves and mitigating environmental damage.

Examples of other nonrenewable energy sources

Coal is not the only nonrenewable energy source. Other fossil fuels, such as oil and natural gas, also fall into this category. Like coal, oil and natural gas are formed from organic material over millions of years, making their replenishment rate far too slow to be considered renewable.

• Oil: Extracted through drilling, oil is refined into fuels like gasoline and diesel. Its widespread use has made it a cornerstone of global energy production, but its extraction and combustion contribute significantly to greenhouse gas emissions.
• Natural Gas: Often viewed as a cleaner alternative to coal and oil, natural gas is still nonrenewable. It is extracted through drilling and, in some cases, hydraulic fracturing. While it burns more cleanly than coal, it is still a finite resource.

These fossil fuels share the same inherent limitation as coal: they form far too slowly to be replenished at the rate we consume them.

Renewable alternatives to coal

As the world moves toward more sustainable energy solutions, several renewable energy sources have emerged as viable alternatives to coal:

• Solar Power: Harnessing energy from the sun using solar panels, solar power is a clean and abundant resource.
• Wind Energy: Is the largest source of renewable energy in the United States. Wind turbines convert kinetic energy from the wind into electricity, offering a renewable and emission-free source of power.
• Hydropower: Using the flow of water to generate electricity, hydropower is one of the oldest and most reliable renewable energy sources.
• Geothermal Energy: Tapping into heat from within the Earth, geothermal energy provides a consistent and sustainable power source.

These renewable alternatives in conjunction with natural gas are fueling the transition away from coal in Texas and around the United States. This transition is important not only to reduce our reliance on nonrenewable resources like coal but also to help combat climate change and promote a cleaner energy future.

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There are four main classifications or ranks of coal: anthracite, bituminous, subbituminous, and lignite.

Throughout Earth’s geological history, various processes such as tectonic movements can further bury coal seams deeper, subjecting them to even greater pressures and temperatures. This can enhance the quality of coal, transforming it into higher ranks.

The quality and characteristics of coal that eventually forms depend on the original plant material, the conditions under which it was buried, and the duration and intensity of the heat and pressure it was subjected to. This long process means that coal we use today began forming around 300 to 400 million years ago during the Carboniferous period, a time when the earth was covered with swampy forests.

Anthracite

Anthracite is the highest ranking of the four types of coal and contains 86% to 97% carbon. This type of coal is hard and brittle. This is the highest quality coal with the highest heating value among all types of coal. Anthracite takes the longest to form and is generally over 300 to 350 million years old. However, it makes up less than 1% of coal mining in the United States as it is very rarely found in the country. Anthracite is mainly used by the metals industry and is mined in northeastern Pennsylvania.

Bituminous

Bituminous coal is the second highest quality coal and the most common type of coal in the United States. It contains 45% to 86% carbon and began to form between 100 million and 300 million years old. Bituminous coal accounted for about 45% of total U.S. coal production in 2021. It is used to generate electricity and is important for making coking coal used in the iron and steel industry. The top five states for bituminous coal production are West Virginia, Pennsylvania, Illinois, Kentucky, and Indiana.

Subbituminous

Subbituminous coal contains 35% to 45% carbon and has a lower heating value than bituminous coal. It is at least 100 million years old. About 46% of total U.S. coal production in 2021 was subbituminous, with Wyoming and Montana being the major producers. Some sub-bituminous coal is also mined in Alaska, Colorado, and New Mexico.

While this type of coal is on the lower end of the quality ranking, it is easily and commonly found in thick beds near the surface of our planet. This makes the mining of subbituminous simpler and cheaper, which leads to lower prices.

Lignite

The lowest rank of coal, containing 25% to 35% carbon. It has the lowest energy content among coal types. Lignite deposits are relatively young and were not subjected to extreme heat or pressure. It is crumbly and has a high moisture content, which reduces its heating value. Lignite accounted for 8% of total U.S. coal production in 2021.

North Dakota and Texas are the primary producers, with smaller amounts coming from Louisiana, Mississippi, and Montana. Lignite is mostly used to generate electricity, but there is a facility in North Dakota that converts lignite to synthetic natural gas for use in natural gas pipelines in the eastern United States.

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Coal mining is the process of extracting coal from the earth. Coal miners use large machines to remove coal from underground or near the surface. Some coal deposits, known as coal beds or seams, are located close to the earth’s surface, making them easily accessible. There are also coal deposits that are deep underground.

Surface mining

Surface mining is a method commonly used when coal deposits are located relatively close to the surface, typically less than 200 feet underground. This type of mining involves the use of large machines that remove the topsoil and layers of rock, known as overburden, to expose the coal seams underneath. In some cases, mountaintop removal is employed, where the mountaintops are removed to access the coal seams beneath.

Surface mining is the preferred method for about two-thirds of coal production in the United States because it is generally more cost-effective compared to underground mining.

Underground mining

Underground mining, also known as deep mining, is used when the coal deposits are located more than 200 feet below the surface. Some underground mines can be incredibly deep, with tunnels extending for miles from vertical mine shafts. Miners descend into the deep mine shafts using elevators and then travel through long tunnels on small trains to reach the coal seams. Large machines are used by the miners to dig out the coal from these underground deposits.

How does the processing and transportation of coal work?

After coal is mined, it’s processed and then transported to consumers in a number of ways: 

Coal processing

Once the coal is extracted from the ground, it is often taken to a nearby preparation plant for cleaning and processing. This plant removes unwanted materials like rocks, dirt, ash, sulfur, and others to enhance the quality and heating value of the coal.

Coal transportation

Transporting coal can be costly compared to mining it. To reduce transportation expenses, some coal consumers, such as coal-fired power plants, are strategically located near coal mines. 

Conveyors, trams, and trucks are used for short distances within mines or to nearby consumers, but most coal (70%) is transported via rail. Barges and ships are sometimes used to transport coal across lakes, rivers, and oceans. 

Slurry pipelines, although not currently utilized in the United States, can transport a mixture of crushed coal and water.

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Coal is a sedimentary rock with a black or brownish-black color. It is found in underground deposits called coal beds or coal seams. Coal is primarily composed of carbon and hydrocarbons along with varying amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.

Due to it’s chemical makeup, coal is highly combustible. As a result, coal is used around the globe as an energy source to fuel electricity generation. The burning of coal produces significant pollutants and greenhouse gases that contribute to global warming.

How is coal formed?

Coal is formed from the remains of plants that lived millions of years ago. It starts with the plants absorbing energy from the sun through a process called photosynthesis. Over time, when these plants die, their remains get buried under layers of soil and other debris.

Over millions of years, the plants are transformed into coal through a series of biological, chemical, and physical changes. Factors influencing the formation of coal include:

• Quality and quantity of the original organic material
• Time
• Temperature
• Pressure
• Climactic conditions
• Geologic conditions

This formation process, known as coalification, occurs in several stages:

Stage 1: Accumulation of plant material

Coal formation begins in swampy areas where waterlogged conditions prevent the decay of dead plant material. Over time, layers of plant debris accumulate. These areas are often referred to as peat bogs or peat swamps.

359 to 299 million years ago during the Carboniferous period on Earth, climactic and geologic conditions were just right for the formation of peat bogs and marshes.

• The climate was warm and humid, which are great conditions for the growth of lush vegetation.
• Movement of tectonic plates led to the formation of low-lying basins with poor drainage.
• There were high levels of precipitation which is favorable for the formation of extensive swampy regions in low-lying areas.

Stage 2: Formation of peat

In those low-lying waterlogged regions, peat begins to form as plants die and sink beneath the surface. Decomposition is slower underwater compared to dry land due to the low oxygen content. Because plants were decomposing slower, this allowed for the development of thick layers of plants.

As new plant material adds to the layers, the weight and pressure increase on the lower layers. This pressure, along with microbial activity (in the initial stages), begins to compact the material, driving out some of the water and gases. The material at this stage is called peat, a brownish-black material that contains about 60% carbon.

Stage 3: Burial under sediments

As the plants layered on top of each other, geological changes, rising water levels, and precipitation continued to bury the peat under further layers of sediment. As the peat layers get buried deeper, they were subjected to increasing temperature and pressure. This stage significantly slows down the microbial activity and starts the chemical transformation of peat into coal.

Stage 4: Coalification

Buried peat undergoes further chemical changes and physical compaction due to the heat and pressure. This process increases the carbon content and decreases the oxygen, hydrogen, and nitrogen content. Moisture content also decreases during coalification. Over millions of years, this process transforms peat into coal.

Peat first turns into lignite coal, the first true type of coal. As the materials are buried deeper with ever increasing pressure and temperatures, lignite further transforms into subbituminous and bituminous coal. These types of coal are harder, more compact, and have a richer carbon content. Finally, if the conditions are right, bituminous coal can metamorphize into anthracite coal, the highest quality type of coal.

Types of coal

Coal is categorized into four main types, ranks, or classifications of coal. The rank of coal is determined by how long it has undergone the formation process.

Coal that has been under the earth for longer is generally a higher quality with a higher carbon content and heating value. The four main types of coal in order of quality from highest to lowest are anthracite, bituminous, subbituminous, and lignite.

As tectonic movements and other geologic processes push coal seams deeper underground, they are subjected to even greater pressures and higher temperatures. Higher pressure and hotter temperatures can enhance the quality of coal, which is why older, deeper coal is a higher quality when mined.

Depth beneath the surface, pressure, and temperature are not the only factors that contribute to the quality and characteristics of the resulting coal. Other factors include what the original plant or animal material was and the conditions of its original burial.

Coal we unearth today in underground or surface mines may have began forming over 300 million years ago during the Carboniferous period, a time when the earth was covered in swampy forests.

Anthracite

• Highest rank of coal containing 86% to 97% carbon
• Highest heating value among all coal types
• Less than 1% of coal mining in the United States
• Mainly used by the metals industry and is mined in northeastern Pennsylvania

Bituminous

• Contains 45% to 86% carbon
• Between 100 million and 300 million years old
• Bituminous coal accounted for about 45% of total U.S. coal production in 2021
• Used to generate electricity and is important for making coking coal used in the iron and steel industry
• Top five states for bituminous coal production are West Virginia, Pennsylvania, Illinois, Kentucky, and Indiana

Subbituminous

• Subbituminous coal contains 35% to 45% carbon
• Lower heating value than bituminous coal
• At least 100 million years old.
• 46% of total U.S. coal production in 2021 was subbituminous
• Wyoming and Montana are major producers, some sub-bituminous coal is also mined in Alaska, Colorado, and New Mexico

Lignite

• Lowest rank of coal, containing 25% to 35% carbon
• Lowest energy content among coal types
• Lignite deposits are relatively young and were not subjected to extreme heat or pressure
• Crumbly and has a high moisture content, which reduces its heating value
• Lignite accounted for 8% of total U.S. coal production in 2021
• North Dakota and Texas are the primary producers, with smaller amounts coming from Louisiana, Mississippi, and Montana
• Mostly used to generate electricity

Is coal renewable?

Coal is not considered a renewable resource because it takes hundreds of millions of years to form. That means we can consume more coal than the Earth can produce and hypothetically can eventually run out of coal to burn.

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Advantages of coal

1. Supply

Coal reserves across Earth are extensive and widely distributed. There is enough supply for many years into the future. According to the Energy Information Administration, there is enough coal to last at least another 422 years in the United States. Although, this is subject to change based on changes to ongoing rates of coal consumption. If we use less coal, the reserves will last longer and vice versa.

2. Energy density

In the world of electricity generation, energy density is a measure of the amount of energy stored in a fuel source per unit volume. For fuels, high energy density is a benefit because less fuel is required to generate the same amount of power compared to a fuel with lower energy density.

Coal has a much higher energy density than renewable energy sources such as wind and solar, which is wind and solar farms are often large operations that require a lot of land. Compared to other fossil fuels, coal has a lower energy density. Natural gas has the highest, followed by oil, then coal.

3. Coal’s infrastructure

Humans have relied on coal for electricity generation since 1882, with the opening of the Edison Electric Light Station. Since then, the infrastructure for mining, transporting, and utilizing coal for power has become widespread and well-established. In the United States alone, there are over 200 coal-fired plants in operation. However, that number continues to fall as we shift towards a greater emphasis on natural gas and renewable power generation.

4. Economics and job opportunities

As of 2023, there were over 36,000 people employed in the coal sector in the United States.

5. Relatively cheap

Compared to other fossil fuels like natural gas and petroleum, coal is much cheaper. According to the EIA, the weighted cost of coal between 2012 and 2022 sat around $2 per MMBtu (Million British Thermal Units). Natural gas ranged between $2 and $5 per MMBtu. Petroleum was the most expensive and volatile with costs between $7 and $16 per MMBtu.

6. Base load power generation

Coal-fired power plants are effective are generating base load power, or the minimum amount of power needed to supply an electrical grid at any given time. Coal and nuclear plants are often used for base load power because they are generally not designed to quickly turn off and on. On the other hand, natural gas power plants are often used for peaking, or to meet periods of high demand, because they can be turned off and on rather quickly.

Disadvantages of coal energy

1. Environmental impact and greenhouse gases

One of the most serious long-term global impacts of coal usage is its contribution to climate change and global warming. When coal is burned, it releases carbon dioxide, a greenhouse gas that traps heat in the atmosphere. This leads to adverse consequences such as droughts, rising sea levels, floods, extreme weather events, and loss of species. The severity of these impacts is directly related to the amount of carbon dioxide emitted, including from coal plants. In the U.S., coal power plants account for roughly one-quarter of energy-related carbon emissions.

2. Health risks from air pollution

When coal is burned, it releases various harmful pollutants into the air, such as mercury, lead, sulfur dioxide, nitrogen oxides, and particulates. These pollutants are linked to health issues like asthma, respiratory problems, heart diseases, cancer, neurological disorders, and premature death. Although the Environmental Protection Agency has set emission limits, many power plants lack the necessary pollution controls, and the future of these protections remains uncertain.

3. Coal mining is dangerous

According to the Bureau of Labor Statistics, coal miners are more likely to be killed, be severely injured, or develop fatal illness than other workers. Coal miners face many dangers in their line of work including but not limited to:

• Respiratory issues
• Fires and explosions
• Equipment injuries
• Heat strain
• Hearing damage and loss
• Falling rocks and cave-ins
• Drowning
• Falls

There are other jobs with higher injury rates such as logging and roofing.

4. Destruction of habitats and ecosystems

Per the EIA, coal surface mines were the source of over 60% of coal mined in the United States in 2022. Surface mines, as the name implies, take place on the surface of the Earth and wreck havoc on local areas. In some cases, coal mines rely on a process called mountaintop removal wherein explosives are used to blow up mountains to gain access to coal. These explosions destroy immediate areas and have significant negative impact on surrounding habitats and ecosystems.

5. Significant water usage

According to a study from 2014 on water consumption for coal electricity production, surface and underground mining may require between 6 and 130 gallons of water per metric ton of coal produced. The water use varies based on each individual coal operation. In 2022, the U.S. produced over 500 million tons of coal. That means each year coal mining is responsible for the use of hundreds of millions of gallons of water.

6. Generation of waste

Coal mining and power plants have significant effects on water sources. Coal ash, similar to the ash from a charcoal grill, is produced in large quantities by coal-fired power plants, with over 100 million tons generated annually. A considerable portion of this waste ends up in landfills, ponds, lakes, and other sites, posing a risk of water contamination over time. Coal mining also leads to acid rock drainage, destruction of mountain streams and valleys through mountaintop removal mining, and conflicts over water resources when coal plants rely heavily on local water supplies.

Sustainable alternatives to coal energy

One sustainable alternative to coal is natural gas. Natural gas is a cleaner burning fossil fuel compared to coal, emitting fewer pollutants and greenhouse gasses when burned. It produces lower levels of sulfur dioxide, nitrogen oxides, and particulate matter, which contribute to air pollution and respiratory issues. Natural gas combustion releases fewer carbon dioxide emissions, resulting in reduced contributions to climate change.

Natural gas can be used as a transition fuel in the shift towards renewable energy sources. It can complement intermittent renewable energy generation, such as wind and solar, by providing a reliable and flexible source of power for electricity generation. Natural gas power plants can quickly ramp up or down their output, helping to stabilize the electrical grid when renewable energy production fluctuates.

Renewable energy sources provide sustainable alternatives to coal. These sources harness energy from natural processes such as sunlight, wind, water, and heat from the Earth’s core. They produce clean electricity without emitting greenhouse gasses or contributing to air pollution.

Nuclear power generates electricity through controlled nuclear reactions. It produces significant amounts of energy without greenhouse gas emissions. However, the use of nuclear power raises concerns about the safe disposal of radioactive waste and the potential for accidents, making it a controversial option.

Biomass energy utilizes organic materials such as wood, agricultural waste, or dedicated energy crops to produce heat or electricity. Biomass can be burned directly or converted into biofuels like ethanol and biodiesel. When sustainably sourced, biomass energy can be carbon-neutral since the carbon emitted during combustion is absorbed by newly grown plants.

How burning coal produces energy

Coal accounted for 19.5% of the electricity generated in the United States in 2022, down from 42% in 2014. In 2021, coal supplied 9.5 quadrillion British thermal units (2,800 TWh) of primary energy to electric power plants, which made up 90% of coal’s contribution to the U.S. energy supply. Utilities buy more than 90% of the coal consumed in the United States. There were over 200 coal-powered units across the United States in 2022. Coal plants have been closing since the 2010s due to cheaper and cleaner natural gas and renewables.

The U.S. Energy Information Administration (EIA) projects that coal will account for 13% of electricity generation in 2050. This decline is due to a number of factors, including the continued rise of natural gas and renewable energy, the implementation of environmental regulations, and the closure of coal-fired power plants.

What is coal used for? 

Coal is the most common fuel used to generate electricity in the United States. Coal-fired power plants burn coal to heat water, which turns into steam and drives a turbine to generate electricity. It’s also used to heat iron ore in blast furnaces in order to make steel and to produce chemicals like ammonia. 

Some homes are heated by coal via coal-fired boilers that heat water and circulate heat through a system of pipes.

Coal as an energy source

Coal is the second-largest energy source in the U.S. for electricity generation (around 22%). A few coal-fire plants convert coal to a gas which can be used in gas turbines to generate power; others use steam turbines. 

How many coal power plants in the US?

Coal power stations, also known as coal-fired power plants or coal plants, are facilities that generate electricity by burning coal. They are large industrial complexes designed to efficiently convert the energy stored in coal into electrical energy.

As of 2023, there are 224 operational coal-fired power stations in the United States. These plants have a total capacity of 256 gigawatts (G.W.), which is about 19% of the country’s total electricity-generating capacity.

Environmental impact of coal power stations

Burning coal in power plants leads to the release of carbon dioxide (CO2) emissions, which contribute to climate change. 

Coal-fired power plants use technologies like “scrubbers” to remove pollutants from their emissions before they are released through smokestacks. However, the smoke still contains nitrogen oxides, sulfur dioxide, particulate matter (like soot), and heavy metals such as mercury, which can impact air quality and human health, even at considerable distances from the power plants.

Due to the U.S. Environmental Protection Agency’s Clean Power Plan and the low cost of natural gas, older coal plants are closing, and interest in new coal plants is declining.

Recent advancements in coal technology

Burning coal releases a lot of carbon dioxide (CO2) into the atmosphere, contributing to global warming. To address this issue, scientists are developing new technologies that aim to reduce or eliminate CO2 emissions. However, these technologies are expensive and energy-intensive, so it’s unsure whether they will be viable in the future.

Clean coal technology

Some existing methods to make coal cleaner include washing it to reduce emissions of ash and sulfur dioxide when burned, using electrostatic precipitators and fabric filters to remove fly ash from flue gasses, and employing flue gas desulfurization to reduce sulfur dioxide emissions. Low-NOx burners, re-burning techniques, and selective catalytic reduction can also help reduce nitrogen oxide emissions. Newer coal plants are more efficient, producing fewer emissions per unit of electricity generated. Advanced technologies like integrated gasification combined cycle (IGCC) and pressurized fluidized bed combustion (PFBC) can further increase efficiency.

There are also efforts to produce ultra-clean coal (UCC) with very low levels of ash and sulfur, which could be used as fuel in large marine engines. Gasification and sequestration technologies are being explored as well.

Carbon capture and storage

Carbon capture and storage (CCS) is a key aspect of ‘clean coal,’ involving capturing CO2 and storing it underground. Several methods exist for capturing CO2, but they are not yet optimized for large-scale coal power plants.

Early developments in carbon capture and storage (CCS) focused on capturing CO2 emissions from a single source and storing them in a specific location. However, as economies of scale became important, the focus shifted to creating hubs that collect, dehydrate, and transport CO2 from multiple sources. Currently, there are around 15 such hubs being established.

The Northern Lights Project in the North Sea, led by Equinor, Shell, and Total, is one of the most advanced hubs. It gathers CO2 emissions from various plants, initially around 0.8 million tonnes per year and later increasing to about 5 million tonnes per year. The CO2 is compressed, liquefied, and transported by dedicated ships to a storage site. The project aims to start operating in 2024.

Frequently asked questions

Conclusion

Going back to our earlier question: what is coal energy? It’s not a sustainable energy source for the future, even though it’s so widely used. While scientists and engineers are hard at work to ensure that coal is as clean as possible, the current solutions are still very expensive and not economically viable. Instead, we have to look at alternatives that are affordable but cleaner-burning. 

The future of coal energy

Currently, coal remains a significant contributor to global electricity generation, accounting for a little over one-third of the total. It also plays a vital role in industries like iron and steel. However, as we strive towards achieving the IEA’s Net Zero Emissions by 2050 Scenario, it is crucial to transition away from unabated coal generation by 2040.

To align with the Net Zero by 2050 Scenario, we must aim for an annual average reduction of approximately 8% in emissions from coal-fired power plants until 2030. This reduction is necessary to stay on track and meet our emissions targets. In order for coal to have a place as a cleaner energy source in the future, governments and the coal industry must collaborate to develop and deploy technologies that are less polluting and more efficient.

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