Coal Pollution Is Quietly Cutting Solar Power Output Worldwide

Solar power is growing fast. Coal is still getting in the way.

A new study led by researchers from the University of Oxford and University College London has found that air pollution from coal-fired power plants is reducing the output of solar panels around the world. The problem is not the panels. It is the air above them.

Tiny particles in the atmosphere, called aerosols, scatter and absorb sunlight before it reaches solar photovoltaic systems. That means solar farms produce less electricity than they could in cleaner air. The loss is large enough to matter for national energy plans, climate targets, and the real cost of coal.

The finding is simple and sharp:

Coal does not only pollute the air. It also weakens one of the main technologies meant to replace it.

The Hidden Drag on Solar Energy

The study, published in Nature Sustainability, mapped and assessed more than 140,000 solar PV installations worldwide. Researchers used satellite data, machine learning, atmospheric pollution data, and solar energy models to estimate how much electricity each site could generate, and how much was being lost because pollution blocked sunlight.

The numbers are serious.

Researchers found that aerosols reduced global solar electricity output by 5.8% in 2023. That equals 111 terawatt-hours of lost electricity. The study compares that loss to the annual generation of 18 medium-sized coal-fired power plants.

That is not a rounding error. That is power that solar panels were ready to produce but could not because pollution stood between the panels and the sun.

Another estimate from the research shows the wider effect of clouds and aerosols together. In 2023, more than a quarter of potential solar output was lost, with more than 20% due to clouds and another 6% from aerosols. That combined loss was a little more than 500 terawatt-hours, equal to the annual output of 84 coal plants with 1-gigawatt capacity each.

So there are two important facts:

• Clouds remain the larger natural barrier to solar power.
• Aerosols are a major human-made barrier, and coal is a key source.

The second point is the story.

Clouds are part of weather. Coal pollution is a choice.

Why Aerosols Matter

Aerosols are tiny particles suspended in the air. Some come from natural sources, such as dust blown from dry regions. Others come from human activity, especially fossil fuel burning.

Coal is a major source because it releases sulfur dioxide, which forms aerosols in the atmosphere. Coal burning also contributes carbon-rich particles and other pollutants that reduce solar clarity.

The study found that sulfur dioxide aerosols, mainly linked to coal burning, account for nearly half of the aerosols analyzed. Carbon-rich material, often tied to fossil fuels, accounts for another 18%.

That matters because solar panels depend on direct and diffuse sunlight. When pollution scatters or absorbs incoming solar radiation, less energy reaches the panels. Less light means less electricity.

It is that direct.

Dirty air lowers clean power.

There is another layer too. Aerosols can also affect cloud formation, which may cut solar output even further. The researchers said that part is harder to measure, so the study focused mainly on the direct effect of aerosols. But the real impact could be larger.

Coal and Solar Are Growing Side by Side

The problem is especially clear in places where coal plants and solar farms are expanding near each other.

China is the strongest example.

China is the world’s largest solar producer. In 2023, it generated 793.5 terawatt-hours of solar PV electricity, equal to 41.5% of the global total. But China also had the largest losses from aerosols. The study estimated that pollution reduced China’s solar output by 7.7%.

Researchers found that China’s solar losses closely matched the country’s coal-fired power capacity. In other words, places with heavy coal generation were often the same places where solar panels were losing more output.

The study estimated that around 29% of aerosol-related solar PV losses in China came directly from coal-fired power plants. Another report on the same findings placed the figure at about 30%, which points to the same conclusion.

Coal is not just competing with solar in the market. It is cutting into solar’s performance in the air.

That is the part many energy models miss.

The U.S. Sees Lower Losses

The losses are not spread evenly around the world.

In the United States, solar power is concentrated largely in the South and West. Coal plants are more common in the East and Northeast. Because the two systems are less often located together, aerosol-related solar losses are lower than in China.

The study estimated U.S. solar losses from aerosols at about 3%, less than half the loss rate seen in China.

That does not make the issue small. It means geography matters.

Where coal and solar operate side by side, coal pollution can reduce the output of nearby clean energy systems. Where they are farther apart, the effect may be lower.

The lesson is not only “build more solar.” It is also build cleaner air around solar.

Solar Growth Is Being Undercut

The study found that between 2017 and 2023, new solar installations added an average of 246.6 terawatt-hours of electricity each year. But aerosol-related losses from existing solar systems reached 74 terawatt-hours annually.

That means pollution losses were equal to nearly one-third of the average yearly gains from new solar capacity.

That is the hidden problem.

Countries spend money building new solar farms. Then polluted air takes away a chunk of the output.

It does not stop solar from growing. Solar production is still rising because countries are installing more capacity every year. But pollution means the world is getting less clean electricity than it could from the systems already built.

That is bad math.

China Shows Improvement

There is some good news.

China has been improving solar clarity. The study found that aerosol-related solar PV losses in China declined by an average of 0.96 terawatt-hours per year, or about 1.4% annually, between 2013 and 2023.

Researchers linked this improvement to stricter emissions standards and the use of ultra-low-emission technologies in coal-fired power plants. It was not mainly because China reduced coal capacity. It was because some coal plants became less polluting.

That proves policy can help.

Cleaner coal plants are not the final answer. But lower emissions can improve solar output while countries move away from coal.

Still, the bigger point remains: reducing coal use would bring stronger benefits.

The Real Cost of Coal Is Bigger Than the Power Bill

Coal is often defended because it is cheap. But this study shows part of why it looks cheap: many of its costs are hidden.

Coal damages health. It releases carbon pollution. It creates toxic coal ash. Now this research adds another cost: coal pollution reduces solar power generation.

That means coal can make clean energy look less productive than it really is.

Professor Myles Allen of the University of Oxford, who was not involved in the study, said scenarios that meet the Paris Agreement goals show a rapid move away from unabated coal, but that shift is not happening fast enough. He added that coal appears cheap because its real costs are hidden.

That is the core issue.

Coal’s price does not include the full damage it causes.

What Policymakers Need to Know

The study sends a clear warning to governments and energy planners. If they ignore pollution-related solar losses, they may overestimate how much power solar projects will generate.

That can lead to bad planning.

A grid operator may expect a solar farm to produce a certain amount of electricity. But if pollution reduces sunlight, real output comes in lower. That matters for supply, pricing, emissions planning, and climate targets.

The researchers argue that energy policy should treat air quality and renewable energy as connected issues, not separate ones.

Key takeaways:

• Aerosols reduced global solar output by 5.8% in 2023.
• That equals 111 terawatt-hours of lost electricity.
• Coal-fired power plants are a major source of the pollution causing those losses.
• China saw the largest effect, with solar output reduced by 7.7%.
• Around 29% of China’s aerosol-related solar losses were linked directly to coal plants.
• Cleaner air can make existing solar farms produce more power.
• Coal’s true cost includes lost renewable electricity, not just pollution and emissions.

The Bottom Line

Solar power is one of the cheapest and fastest-growing energy sources in the world. But it cannot perform at its best under polluted skies.

Coal pollution blocks sunlight. Solar panels lose output. The grid gets less clean power. Governments may overestimate progress.

That is the real story.

The energy transition is not only about building solar farms. It is also about cleaning the air they depend on.

Coal is not just old energy. It is actively reducing the performance of new energy.

Moving away from coal would cut emissions, improve health, and unlock more power from solar panels already in place. That is not theory. That is measurable.

Cleaner air means stronger solar.

And stronger solar means less need for coal.