Wind and solar energy are obviously essential in reducing carbon emissions, but they also have a remarkable side effect: saving lives. As they edge out fossil fuels, renewables are reducing not just carbon emissions, but also other air pollutants. And the result is an improvement in air quality, with a corresponding drop in premature deaths.

A paper in Nature Energy this week dives into the weeds by trying to estimate the economic benefits of wind and solar power across the whole of the US. Berkeley environmental engineer Dev Millstein and his colleagues estimate that between 3,000 and 12,700 premature deaths have been averted because of air quality benefits over the last decade or so, creating a total economic benefit between $30 billion and $113 billion. The benefits from wind work out to be more than 7¢ per kilowatt-hour, which is more than unsubsidized wind energy generally costs.

Death is in the air

Poor air quality is a tricky beast in public health, since it’s not obvious when someone dies as a result of air pollution. The World Health Organization estimates that air pollution leads to around 7 million premature deaths globally each year—people dying earlier than they otherwise would have from heightened incidence of cancer, heart disease, and respiratory disease.

In the US, air pollution is responsible for an estimated 200,000 premature deaths a year. Road transport (53,000 deaths) and electricity generation (52,000 deaths) are the two sectors contributing the lion's share of the problem. For perspective, the CDC reports that heart disease and cancer, the two biggest killers in the US, each claim around 600,000 lives each in a typical year. The third biggest killer, respiratory disease, is at 155,000.

Air pollution is contributing heavily to those totals, so renewable energy would undoubtedly reduce its contribution. And, since premature deaths cost money on a societal level, renewables would be providing some economic benefits as well.

There are a lot of moving parts involved in trying to figure out the economic benefits of renewables. Impact studies have been done before, but they’ve been limited to certain regions or short time periods. This study ambitiously tries to estimate the benefits from emissions that were avoided because of the increase in wind and solar energy from 2007 through 2015, and to do so for the whole of the US. Millstein and colleagues looked at carbon emissions, as well as sulphur dioxides, nitrogen oxides, and particulate matter, all of which contribute to poor air quality.

There are other factors that also need to be considered. A rise in renewables isn’t the only thing that has been changing in the energy sector: fuel costs and regulation have also played a role. How much of the benefit can be attributed to wind and solar power, and how much to other changes? The researchers used models that track the benefits attributable to renewable power as a proportion of the total reduction in emissions.

Regional differences also introduce complexity. For instance, “most wind power has been deployed in the centre of the country,” the researchers write, while "solar power is heavily concentrated in California.” Some areas of the country have more coal plants, and others have natural gas, which is lower in emissions than coal. To top it all off, emissions regulations aren’t consistent across the entire country.

This means that air pollution benefits were widely variable across different regions. For example, a huge uptick in wind power in a region previously dependent on coal would substantially change the air quality in that region, but a solar power plant far away from any fossil fuel production wouldn’t change the air quality all that much. Climate benefits, on the other hand, are not regionally specific—any climate benefits in the US are good news for the whole world.

Millstein and his colleagues used a range of different models to get an idea of the full scope of estimates that could be reached by using different sets of assumptions. That means that the true benefit probably falls somewhere in the estimated range.

Lives and money saved

The climate benefits of solar and wind power were hefty, but the majority of the benefit came from air quality improvements. The climate benefit estimates ranged from $5 billion to $106 billion, with an additional $30 billion to $113 billion in air quality and public health benefits. And that’s just the estimated economic benefits of the averted 3,000 to 12,000 premature deaths—it doesn't count things like sub-lethal medical issues and lost productivity, much less the personal benefits to individual lives.

The middle ranges of these estimates suggest that wind and solar are pulling their weight cost-wise, despite subsidies: “total central-value wind and solar air-quality and climate benefits are comparable to estimates of total federal and state financial support,” the authors write. The estimates also tie in with other models that have looked at benefits in specific regions, which is a good reliability check.

As emissions continue to fall, the relative improvement brought about by renewable energy will also start to decline. The best way to maximize investment might be to take into account those regional differences, the researchers write: “wind and solar deployments to those regions of the country that offer the greatest benefits (at the least cost) would offer additional gain.”

Nature Energy, 2017. DOI: doi:10.1038/nenergy.2017.134 (About DOIs).