By Sonia Aggarwal, Mike O’Boyle, and Amol Phadke

150 million Americans regularly breathe unhealthy, polluted air. But recently announced targets to achieve 100 percent clean power by the House Select Committee on the Climate Crisis and Joe Biden’s presidential campaign would eliminate all air pollution from power plants.

The public health benefits of realizing 100 percent zero carbon electricity by 2035 would be enormous. New analysis from Energy Innovation’s Energy Policy Simulator shows that reaching 100 percent by 2035 would avoid around 16,000 premature deaths in that year, as well as 425,000 asthma attacks, 19,000 heart attacks, and more, as shown in the table below. Moreover, avoiding all these negative health impacts creates massive economic productivity gains – getting to 100 percent in 2035 would avoid losing about 1.7 million workdays to poor health.

Beyond improving health, getting to 100 percent zero carbon electricity would also be a boon for the climate, eliminating more than a quarter of America’s greenhouse gas (GHG) emissions in 2035. Zero carbon electricity can also enable further emissions reductions from transport, buildings, and industry via electric vehicles, efficient electric appliances, and electric industrial processes. Moreover, successfully decarbonizing our electricity sector would provide spillover benefits beyond our borders—in the form of technology available at lower costs to help reduce GHG emissions in other countries, as well as a clear signal to the world that U.S. is serious about addressing climate change.

All these social benefits – health and climate – really add up. The avoided climate damages between 2020 and 2035 total about $500 billion, using the social cost of carbon developed under the Obama administration. Economists would value the avoided health impacts over the same period around $690 billion, so the combined health and climate benefits of achieving 100 percent zero carbon electricity reach about $1.2 trillion by 2035 (assuming a 3 percent discount rate).

If these public health and climate benefits were not reason enough to decarbonize the electricity system, getting onto this path drives investment, supporting at least 500,000 healthy and safe new jobs just when our economy could really use them in the current situation of massive unemployment.

Given these overwhelming benefits, the critical outstanding question is whether all this will be affordable for American electricity consumers, and the answer is thankfully “yes!”

The 2035 Report, a recent study by researchers from the University of California-Berkeley, confirms the U.S. could get 90 percent of its electricity from zero carbon sources by 2035. Detailed grid modeling underlying the study shows electricity demand being met reliably in every hour between now and 2035 under a variety of weather scenarios. What’s more, ever-cheaper wind, solar, and batteries enable us to reach 90 clean electricity while reducing wholesale electricity costs 10 percent from today’s levels.

Compared with other studies of its kind, the 2035 Report focused on how affordable it would be to get most of the way there on decarbonizing the electricity sector, much faster than conventional wisdom has typically suggested. And most of the public health and economic benefits come from reaching 90 percent, so it’s a no-regrets path to start down now.

But of course, when we talk about 90 percent clean by 2035, the next questions become: What about that last 10 percent, especially considering recently announced policy goals calling for 100 percent? How would we build on 90 percent to get to 100 percent clean? What would the system look like, and how quickly could we realistically achieve 100 percent? Could we even do it by 2035 without breaking the bank, or the electric grid for that matter?

Many academics, researchers, and consultants have explored questions about how to decarbonize the last 10 percent of the electricity system. Unlike the first 90 percent, which can be achieved with well-known and commercially proven technologies, the last 10 percent raises serious questions about how to best match clean electricity supply with demand, especially during multi-week periods of low wind and sun, or when seasonal demand (for heat or air conditioning, for example) does not match regional clean energy availability. And if the imperative is reducing overall pollution and climate impacts, there are cheaper and easier sources for the same reductions—from our vehicles or buildings, for example.

But to explore whether 100 percent zero carbon electricity is possible by 2035, let’s start with a couple stats about the first 90 percent. First, the 2035 Report shows that developers would need to install solar and wind at double the historical-best rate throughout the 2020s, and triple the historical-best rate in the 2030s. This increased pace will be challenging, but certainly reasonable. So reasonable, in fact, that there is likely some room to go even faster if the policy environment is right.

Second, the 2035 Report findings indicate it is possible to decrease wholesale electricity rates by approximately 10 percent from today’s levels even as the system reaches 90 percent zero carbon. This creates a reasonable budget to get rid of the last ~200 million metric tons of carbon dioxide (CO₂) emissions while keeping wholesale costs similar to today’s levels.

An illustrative analysis by the University of California-Berkeley and Energy Innovation team indicates America may be able to reach a zero-carbon electricity system without meaningfully raising wholesale electricity rates from today’s levels with a combination of technologies not yet commercialized but currently on the horizon:

• Using hydrogen produced by green electricity in gas turbines retrofitted to burn pure hydrogen
• Using hydrogen produced by green electricity in in fuel cells
• Burning synthetic methane or biogas in existing gas plants
• Capturing and sequestering CO₂ from existing gas plants
• Direct air capture of CO₂ from ambient air

Green hydrogen is already capturing the attention of large utilities that are serious about decarbonization such as Los Angeles Department of Water and Power (LADWP) and NextEra Energy. LADWP’s latest planned 840 megawatt (MW) natural gas plant will run on 30 percent hydrogen on day one of its operation beginning in 2025, with plans to run it on 100 percent hydrogen by 2045. NextEra has proposed a $65 million pilot in Florida that will use a 20 MW electrolyzer to produce 100 percent green hydrogen from solar power, and blend it into another existing gas plant.

Meanwhile, Europe’s latest hydrogen strategy is calling for 6 gigawatts (GW) of electrolyzers by 2024, scaling to 40 GW by 2030. Given that the continent has less than 1 GW of electrolyzers today, this will require a massive scale-up in a relatively short timeframe. This is worth watching, and if successful, has a real chance of helping to bring down costs of electrolysis in the U.S.

Using conservative cost estimates for hydrogen retrofits and green hydrogen costs from electrolyzers (a relatively mature—but still relatively expensive—technology), we find that retrofitting all the remaining gas plants in the 2035 Report to burn 100 percent green hydrogen would cost somewhere between 11.7-14.8 cents per kilowatt-hour (cents/kWh). Combined with the costs of the first 90 percent zero carbon electricity, this pathway would result in overall wholesale electricity rates around 5.3-5.6 cents/kWh in 2035, which is quite similar to today’s average rate of 5.2 cents/kWh.

Another pathway for green hydrogen in the electric power sector would be as storage via fuel cells. Producing the last 10 percent of zero carbon electricity beyond the 90 percent zero carbon system modeled in the 2035 Report would result in electricity rates in the range of 8.5-14.3 cents/kWh, resulting in overall wholesale electricity rates ranging from 5-5.6 cents/kWh in 2035, which is right in the range of today’s average rate.

Green synthetic methane relies on chemical processes to convert green hydrogen into methane to be burned in existing gas power plants. This zero-carbon fuel source has the advantage of being directly usable in existing power plants, however it requires additional energy to convert electrolyzed hydrogen into methane, increasing input fuel costs relative to hydrogen. Blending synthetic methane with biomethane, captured from landfills or dairy farms, could reduce these input costs, though biomethane sources are relatively limited. At the same time, transporting green synthetic methane (a potent greenhouse gas in itself) using existing natural gas pipeline infrastructure could still result in significant leakage, offsetting the emissions benefits.

Using conservative cost estimates for green methane, we find burning 100 percent green methane in the remaining gas fleet from the 2035 Report would cost about 12.6-14.7 cents/kWh, resulting in overall wholesale electricity rates around 5.4-5.6 cents/kWh in 2035, which is as again similar to today’s average rate.

Carbon capture and sequestration has been piloted in the U.S. The Petra Nova power plant project in Texas retrofitted an existing coal-fired power plant to capture 90 percent of its emissions. The captured CO₂ is compressed, dried, and transported to the West Ranch Oil Field in Jackson County, Texas, then pumped underground to boost oil production in a process called “enhanced oil recovery.” However, it is important to note Petra Nova was recently mothballed because low oil prices no longer justify purchasing the captured CO₂ for enhanced oil recovery. The whole carbon capture, transport, and sequestration process is still relatively expensive, and only economically justified as a pilot when used for oil recovery at relatively high oil prices.

Using conservative cost estimates for retrofitting existing gas plants with carbon capture technology, and accounting for transportation and sequestration costs, we find capturing 90 percent of carbon emissions from the remaining gas fleet in the 2035 Report would cost about 11.4 cents/kWh, resulting in overall wholesale power costs around 5.3 cents/kWh in 2035, which is about the same as today’s average wholesale rate. Note this would leave about 20 million tonnes of electric power sector GHG emissions, which would need to be offset in other ways – perhaps via direct air capture, as described next.

Direct air capture (DAC) of CO₂ is a nascent technology with potential to scale and see cost reductions over time. A recent techno-economic assessment of DAC found that demonstration projects could capture CO₂ at costs around $350/ton today. The same study (and projections by company Carbon Engineering) found costs could drop below $200/ton with significant commercialization. Using waste heat could further reduce costs.

DAC is a particularly flexible option to offset the final electric sector emissions because it does not require co-location with any generator, and could also provide grid benefits by operating as a flexible source of electricity demand, running when “excess” zero carbon electricity is being generated. As such, DAC could complement any other pathway to 100 percent, and provides a de facto cost ceiling for reaching net zero emissions for the electricity system.

Using best available cost estimates for capturing the approximately 200 million tonnes of CO₂ emitted by the remaining gas fleet in the 2035 Report, and accounting for transportation and sequestration costs, we find using DAC for offsets would imply an equivalent “cost of generation” for the last 10 percent of between 11-19 cents/kWh.

Where exactly this option lands in this range depends on whether DAC is deployed at any meaningful scale in the 2020s, and whether that deployment results in cost reductions over time. These estimates would put total average wholesale power costs for 100 percent net zero electricity using DAC for the last 10 percent somewhere between 5.2-6 cents/kWh in 2035, which is as much as 15 percent higher than today’s average wholesale rate.

In sum…

It’s true that eliminating the last 10 percent of electricity system emissions is more expensive than the first 90 percent, and the priority should remain on accelerating clean energy build-out now to get on either pathway. But summiting the 100 percent mountain is likely not as hard as pessimists would have us believe, especially since it is possible to deliver the first 90 percent zero carbon system, keeping the grid in balance in every hour, while reducing power costs 10 percent from today’s levels.

At least four promising technology pathways exist today to reach 100 percent clean electricity by 2035 without meaningfully raising wholesale costs from today’s levels, and a fifth might raise them 15 percent. Combining these pathways, along with further expected cost declines from solar, wind, and storage, as well as more potential contribution from demand-side flexibility, we are optimistic these cost estimates could be bested by America’s world-class innovators. Add in significant federal research and development funding, and further cost reductions and innovation are likely.

But a clear and specific policy target is essential to set us on the way. With no time to lose, now is the time for ambitious leadership. A zero-carbon electricity system is achievable and affordable, so what are we waiting for?

Amol Phadke is a senior scientist and affiliate at the Goldman School of Public Policy, University of California-Berkeley