Updated by David Roberts@drvoxdavid@vox.com Jul 2, 2017, 9:22am EDT

Solar power is still a fairly tiny portion of US electricity, but it is growing incredibly fast. This is exciting to people for all sorts of reasons — economic development, jobs, local/democratic/decentralized power, and just general tech-of-the-future gee-whizzery.

But it’s worth stepping back occasionally and reminding ourselves of the original and still greatest benefit of solar: namely, that it displaces fossil fuel electricity. And burning fossil fuels to create electricity kills people, so displacing fossil fuel power directly saves lives.

A study published in 2016 took a crack at quantifying the doesn’t-kill-people benefits of US solar.

Let’s back up a second.

In 2010, the Obama administration started talking about ways to make solar power competitive with traditional electricity generation. Out of those talks came the Department of Energy’s Sunshot Initiative, an ambitious plan to accelerate solar development and deployment. The program’s goals: to drive the cost of solar power down to 6 cents a kilowatt-hour by 2020, which would help expand solar to 14 percent of US electricity by 2030 and 27 percent by 2050.

To assess the program’s progress at its halfway point, and lay out a road map to 2020, the DOE commissioned a series of studies, gathered under the banner “On the Path to Sunshot.” There are eight of them, on all sorts of fascinating topics.

Of particular interest is the report that does something Sunshot never tried to do in its initial vision study: quantify the environmental and public health benefits of hitting those targets.

An assessment of the environmental and public health benefits of solar
The report is titled, appropriately enough, “The Environmental and Public Health Benefits of Achieving High Penetrations of Solar Energy in the United States.” It’s by a team drawn from Lawrence Berkeley National Laboratory (LBNL) and the National Renewable Energy Laboratory (NREL).

The researchers asked three simple questions. First, what are the cumulative environmental and public health benefits of the solar power that has been installed so far in the US, as of 2014? Second, what benefits would be secured if Sunshot’s targets for solar were hit? And third, where would those benefits be concentrated?

Now, some caveats. This modeling involved comparing solar to baseline scenarios in which no solar was built, in the first case, and in which no more solar is built after today, in the second. Neither of those is meant to be a realistic scenario.

And these modeling exercises are not meant to grant the administration, or the Sunshot Initiative, credit for all the solar that’s been built or credit for all the benefits. Obviously some solar would have been built, and will be built in the future, regardless of Obama’s policies. (And of course other low-carbon energies could achieve similar benefits.)

And finally, these are just benefits — no account of the costs of a large-scale shift to solar, which are real.

Okay, with all that said, on to the results!

1) Benefits of existing solar
Here are the annual benefits of the solar installed in the US to date:

benefits of solar
(DOE)
If you can’t see the chart, that’s:

Annual reduction of 17 million metric tons of CO2, which is, based on the central estimate of the social cost of carbon, “equivalent to an annual global benefit of $700 million.”
Annual reductions of “10,000, 10,300, and 1,200 metric tons of SO2, NOx, and PM2.5, respectively … which provide annual domestic air quality benefits of $890 million.”
Annual water “withdrawal and consumption savings of 294 billion gallons (0.8% of power sector total) and 7.6 billion gallons (0.5% or power sector total), respectively, with much of those savings located in drought-impacted California.”
It’s worth keeping in mind that the somewhat clinical phrase “domestic air quality benefits” is another way of describing fewer kids having asthma attacks, fewer adults missing workdays, and fewer people dying of respiratory and circulatory ailments.

It’s also worth keeping in mind that none of these social benefits are priced into the cost of solar; it is not compensated for its “positive externalities.” If it were, it would knock almost 5 cents a kilowatt-hour off the price, which would mean the Sunshot cost target was already achieved.

2) Benefits of solar at Sunshot target levels
Here are the benefits of hitting the Sunshot solar penetration targets (again, as compared with a scenario in which no new solar is built):

benefits of sunshot solar
(DOE)
For the chart-averse, that’s:

A cumulative savings of 10 percent of power sector emissions from 2015 to 2050, which represents a $259 billion global climate benefit.
Reductions in emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and fine particulate matter (PM2.5) sufficient to secure a cumulative $167 billion worth of avoided health and environmental damages.
Reduction of power sector water withdrawals by 46 trillion gallons (4 percent of total sector withdrawals) and water consumption by 5 trillion gallons (9 percent of total sector consumption). Importantly, water savings are concentrated in arid states.
The climate and pollution benefits together amount to $400 billion between 2015 and 2050, measured in present-value terms and using central estimates.

3) Where the benefits are concentrated
Finally, it’s interesting to note that the local benefits of solar vary significantly based on what kind of power it displaces. In places where it pushes aside coal (as opposed to natural gas or even wind), benefits are highest.

I already mentioned that the water-saving benefits of solar are overwhelmingly concentrated in arid California. Here’s where the local air quality benefits are concentrated:

solar air quality benefits
(DOE)
On the left are the monetized air quality benefits. On the right are the equivalent changes in solar prices if the benefits were included in costs. Looks like the heavily populated Northeastern corridor could use more solar!

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