California’s Charge

The state has made an ambitious plan: 100 percent carbon-free electricity by 2045. Four experts weigh in on how—and whether it’s possible—to get there.

September 2023

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California’s Charge

Wind-Solar Farm, Palm Springs, Calif. Photo: Murat Taner/Getty Images

California has 39 million people. With industry from agriculture to tech to film, it boasts the fifth-largest GDP in the world. Powering up all that life and industry is a whole lot of natural gas—for the grid alone, enough to generate 105,356 gigawatt-hours, comprising 38 percent of the state’s electricity in 2021. (Coal contributed 3 percent.)

But natural gas—the production and use of which emits carbon dioxide and methane—is on the chopping block. With climate change bearing down, extreme weather events on the rise, and the health costs of air pollution growing, the state wants to lessen its greenhouse gas emissions, in part by dramatically increasing its use of renewable and carbon-free energy. Through decades of effort, California has already shrunk its emissions to pre-1990 levels. Now, a massive experiment is in the offing: getting to zero. In December, regulators approved a roadmap for implementing what the governor’s office calls “the most ambitious climate action of any jurisdiction in the world,” a plan that intends to make the state’s economy fully carbon-neutral by 2045. The effort will involve everything from reforming the power grid and adapting to electric vehicles to ramping up carbon-capture technologies and reducing emissions in building construction and operation. 

One fundamental piece of the puzzle will be transitioning to 100 percent carbon-free electricity, which legislators set as a goal in 2018, with interim benchmarks added in 2022. In 2021, 59 percent of California’s electricity generation came from renewable or carbon-free resources, roughly a quarter of which came online in the three years prior. The state forecasts a need for 148 additional gigawatts of renewables over the next 20 years to meet its goal—a growth of 400 percent over current capacity. “The only way to achieve our goals is to build more clean energy, faster,” the governor’s office says in the plan.

But getting to zero can’t be done simply by scaling up production. Senior editor Jill Patton, ’03, MA ’04, talks with four experts from the academic, private, and public sectors about some of the main challenges in reaching the 2045 electricity goal, and how—working together—we might solve them in the years ahead.


Arun Majumdar

Arun Majumdar is dean of the Stanford Doerr School of Sustainability. He is a professor of mechanical engineering and of energy science and engineering. He also serves as chair of the advisory board to the U.S. Secretary of Energy.

Amy Guy Wagner with her dog.

Amy Guy Wagner, ’03, MS ’04, MS ’08, provides consulting services to utilities and clean energy companies on energy transition topics. She spent seven years as a senior expert at McKinsey & Co. before joining Evolved Energy Research this fall.

Jason Glickman

Jason Glickman, ’02, MS ’02, is executive vice president for engineering, planning, and strategy at PG&E, which provides power to 16 million people in Northern and Central California. He previously spent 14 years at Bain & Co., leading its utilities and renewables practice in the Americas and globally.

Yi Cui

Yi Cui is a professor of materials science and engineering and of energy science and engineering. He is director of the Precourt Institute for Energy in the Stanford Doerr School of Sustainability and one of the world’s leading battery researchers. He also directs Stanford’s new Sustainability Accelerator.

Portraits by Timothy Archibald


Stanford: Let’s start with a foundational question. Why is the move to 100 percent carbon-free electricity important?

Amy Guy Wagner: I think that you can answer that from a personal basis. I live in Northern California in the fire-risk zone. Climate risks and impacts have become much more real in my day-to-day life. And that’s true for many Californians. We’ve seen a lot more extreme weather. We’ve seen a lot more heat events, as well as fires and droughts, and even big storms. I think we all feel the impact much more directly, and the imperative is quite clear now.

Arun Majumdar: If you really want an economy that has net-zero emissions, getting the electricity system carbon-free is a necessity. Otherwise, you’re not going to get there. You have to get clean fuel as well—but carbon-free electricity is essential.

For the first time in human history, carbon-free electricity from renewables is one of the cheapest ways to produce electricity in many parts of the world, at scale. There’s an opportunity to move fast on this, whereas in many other cases—for example, trying to decarbonize the food or steel industries—it’s much, much harder.

It’s not going to be easy. There’s no sugarcoating this one. But I think it’s doable.

And why California?

Wagner: If you look globally, California has the means, has more of the political will, is actually quite blessed with natural resources, and has access to technology and innovation. California is one of the best-placed economies in the world to make the transition, so California should be a leader.

Jason Glickman: If you can’t do it here, where can you do it? There’s a big opportunity for us not only to improve things in our backyard, but to create a pathway for collective action globally.

Total Clean Electricity Resources GraphSource: 2021 SB 100 Joint Agency Report

In California’s fight against climate change, do you think 100 percent carbon-free electricity by 2045 was the right goal to set? How difficult will it be to reach?

Wagner:  You could say that it is actually relatively easy to get to 80 or 90 percent carbon-free electricity. We will. It’s that last 10 to 20 percent that becomes quite a bit more difficult. Part of what the [state] did there in terms of the rule—it’s carbon-free electricity but not renewable energy, specifically, to give some additional flexibility to keep some of the conventional generation. When people think of 100 percent carbon-free electricity, the vision is of solar and wind. In reality, it is helpful to keep conventional generators that you see today—for example, the natural gas generators—and allow them to sit around, largely unused, to be the backup for renewables, either burning carbon-free fuels or with small amounts of fossil fuel emissions offset by carbon capture.

The key is to understand why. That’s because while you were originally worried mostly about how you were going to deliver and produce energy, you start becoming much more concerned about the reliability of the system as you move into a carbon-free system. You need all those generators not running very many hours a year. But you need all those generators to turn on, or be able to be turned on, with stored fuel next to them, or you would need the batteries to turn on, whenever there is low sun, low wind, or a high-demand event.

The major sources of carbon-free power include solar, wind, hydro, nuclear, and geothermal. What are the challenges to fully harnessing the renewable power that’s available?

Glickman: One thing that’s really important here, when we talk about renewable energy goals, is we’re talking about an average over the course of the year. We’re talking about total production across all hours of the day for all days of the year. This is how California measures its progress in meeting its renewable energy goals.

California set a new record last year when, for a brief period, 100 percent of electricity on the grid came from clean, renewable energy. [According to California’s Independent System Operator, renewables generation reached 99.9 percent of demand on April 30, 2022; it topped that at 103.5 percent on May 8, 2022—still the record as of June 2023.]

We can choreograph the ramp up and ramp down of solar production on a typical spring, summer, or fall day very well. And just this year we added an extra several thousand megawatts of storage onto the California grid, which is a huge boon. We’re bullish on storage. We’re bullish on EVs to help absorb some of that solar production coming on and off. 

The problems that I start to worry about are the ones of reliability and resiliency. I worry about compounding climate events like we had in 2020, where there’s smoke from wildfires that were lightning-caused, a transmission line from the Pacific Northwest is down. It’s hot, and everyone’s using their air-conditioning to try to to filter the air. You get these compounding factors that traditional electric system probabilistic planning just does not account for.

Yi Cui: Clearly, the energy storage problem is huge right here—particularly the storage problem across the various time scales. Day to day, we probably know how to solve for variation. But when you get to weekly, monthly, or seasonal durations—this is challenging. This requires very low-cost storage because the number of times you use this storage becomes smaller—and then the cost, the capital investment, needs to be very low. Other than natural gas or coal, we don’t know what can get down to that low-cost, long-duration capability. That’s very, very hard.

Getting to 100 percent carbon-free electricity—we understand it’s super important. If you get there, very likely you’ve decarbonized 70 to 80 percent of the economy. Very likely we’ve still got to have some fuel-based generation system to provide reliability for the electric grid. If it’s a carbon-free fuel, fantastic! If it’s not carbon-free, then the carbon sequestration or capture idea or some sort of carbon-negative technology needs to come hand in hand. There’s already a lot of CO2 in the atmosphere. We actually want that number to go down, not just maintain the current level. 

Percent of Renewable and Zero Carbon Electricity Serving CaliforniaSource: California’s Clean Energy Transition Plan

On the topic of the grid and its infrastructure—what will be needed in terms of transmission capability? What are the sticking points that need to be resolved?

Glickman: We’ve been in a multidecade policy environment in California that said keeping electric demand kind of flattish through energy efficiency and other means is a good thing. The thing that has changed in the last two to three years is a policy objective to drive growth in electric demand [now that clean energy can be delivered that way]. It is a complete paradigm change in terms of the demand growth we’re expecting—call it 70 to 90 percent growth in demand over the next 20 years, when we’ve been basically flattish for the past 20 years, growing a percent to a percent and a half. We now have to find a way to get a lot more electricity into the demand centers over that timeframe, and our end-to-end process for planning for, siting, scoping and engineering, building, and energizing transmission, as a state—state agencies, permitting agencies, and utilities developers—is not yet geared up for that.

We were really encouraged by the governor saying, “I’m going to take some action on the parts that I can take action on from an executive perspective to try and clean up and streamline that process.”

Wagner: One baseline thing to know is how difficult it is to build transmission lines, since they run through all different types of land, with different ownership, different permitting requirements, different endangered species, or other critical [issues] that you have to take into account. But the lines have to go from point A to point B into order to work within the grid network.

It has typically taken at least 10 years to build a large transmission line in the state, and I have many examples where it’s 20. So the challenge there is going from spending of about $200 million over the past five years to a 10-year plan of $7.3 billion approved in the latest transmission investment plan. It’s an order-of-magnitude shift in a very challenging environment, where each of those transmission lines doesn’t necessarily get easier to build. It gets more challenging as you get into more constrained areas. There’s more activism around not wanting transmission lines “in my backyard.” People need to recognize this as a critical blockade.

Majumdar: And interstate is a little more challenging beyond that. There are lots of issues with building interstate transmission lines. Planning can be done, but the actual implementation in terms of business model—who takes the first capacity, who pays for it, how do you compensate if you go across a third state? These issues still have to be worked out line by line. There are jurisdictional elements—there’s local, state, and interstate. There is no universal model for this.

They’re trying to get a line from New Mexico through Arizona to Southern California. That, of course, makes a lot of sense—we could get a lot of solar that way. But just getting that approved for construction—the Department of Energy is involved in that right now. 

As difficult as it is to get a clean-energy project approved, built, and up and running, I think, what’s the use if you don’t have the transmission or the storage to use it?

Majumdar: Regulatory reform for siting and permitting should not be partisan issues in Congress. There was an attempt to make a bipartisan permitting reform bill. It hasn’t gone anywhere yet.

Wagner: Transmission requires a lot of central planning. It doesn’t have an easy market-forces kind of process. So the broader the net is cast on planning earlier, with more of the stakeholders in the tent, the more likely you are to have a plan that holds and can accelerate through some of the construction permitting processes. For example, it’s helpful to have some of the environmental stakeholders—like, say, the Nature Conservancy—in the planning process early, to understand what their critical issues are.

Let’s dig into the subject of grid-scale battery storage. First, how does such storage currently work? How will it need to work in the future? 

Cui: So, the storage is really serving multiple purposes, depending on the time scale. The common one is—look in California at the famous duck curve [which shows the difference between consumption and available solar and wind power, aka net load; see graph below]. Power consumption varies so much during the day. Starting at about 6 p.m. until 9 p.m., there’s a huge jump in consumption there. One purpose of storage is taking the solar made during the day for use in the evening. 

But energy storage can serve many purposes. Here’s another: Say your whole night should be powered by clean electricity. Then you need storage. Your storage baseload—you’re talking about 20 gigawatts to continue for 10 hours. You’re really looking into a gigantic battery—200 gigawatt-hour batteries. This 200 gigawatt-hour battery is 20 percent of the world’s yearly production of these batteries, just to power California. 

The cost of storage needs to be lower, and the safety needs to be outstanding. Recent events have shown that lithium-ion safety is far away from being able to meet our purposes. Once we have huge storage system distribution here and there, we do need to have low-cost, safer, much longer-lasting batteries.

Graph of California's Duck Curve, 2023Source: California Independent System Operator

What is a grid-scale battery? What kind of battery is it? What do they look like?

Glickman: They’re lithium-ion batteries. It’s the same cells you would see in your electric vehicle and, at a smaller scale, your consumer electronics.

I’ll give you a concrete example. If you go down to Moss Landing, there’s a major interconnection to the grid. We have there a mix of third-party-owned and PG&E-owned battery facilities. If you look at the third-party-owned ones, it literally looks like server racks. At another part of the footprint, we have about 180 megawatts worth of capacity of Tesla megapacks, which are not quite the size of shipping containers. A couple hundred of those units together comprise the full storage capability. In those instances, we took advantage of an existing site where there’s an existing power plant and high-capacity substation connected to the transmission system and a bunch of available land. In other cases, you would see it co-located potentially with a wind farm or solar farm.

Wagner: There are some historical storage systems that are still very important to the system today, like pumped storage facilities [stored hydro power], as well as direct hydro. Those create an amount of storage and flexibility for the grid. That was yet another California advantage—it already had some flexibility built into its system that made it easier for us to start with renewables. 

When we look at the goal the governor stated, where we’re trying to get to 52 gigawatts of storage by 2045, is the assumption that this is mostly large lithium-ion batteries at big sites? What are some of the other storage options that will come into play?

Cui: I don’t think you assume it’s lithium-ion. It’s open to all types of storage technologies. People use lithium-ion, lead acid, new types of flow batteries. Pumped hydro. There’s also the potential for heat storage. And gravity-based systems. Whatever makes sense in terms of cost, and the relevant performance in the [system’s] lifetime.

Wagner: When we think of long-duration energy storage, we break it up into four different types. There’s mechanical—that’s gravity-based, like lifting up large blocks and letting them down slowly—and then chemical, electrochemical, and thermal. Where you get more competitive on a cost-basis to lithium-ion is with longer-duration applications and technologies. Lithium-ion at the moment is very competitive on a price point for durations between two and eight hours. 

Majumdar: As your renewable penetration increases in the grid, the need for long-duration storage increases and the capital cost of storage has to come down. Lithium-ion batteries are fine for daily storage needs. But for longer-duration storage, which is needed for deeper penetration of renewables, lithium-ion batteries are too expensive, and we need cheaper alternatives, which are currently under development. 

What are the most exciting technology solutions on the horizon?

Glickman: I’ll offer one thought and then turn it over to the group. We’ve got to do things that are not as exciting within the 80 percent—things like, how do we make it easier to integrate electric vehicles or battery storage at the consumer premise without having to do an expensive panel upgrade in a world where we don’t have an infinite number of electricians? In industry, there’s always this focus on a technological-breakthrough panacea. We will need that on the last 20 percent, for sure. But I think we need to keep a lot of attention and energy on some things that don’t seem as technologically exciting: permitting process reform, good old-fashioned industrial technology in electrical panels, things like that.

Majumdar: I would agree with that. In addition, pumped hydro. There’s nothing sexy about it. It’s really cheap. The challenge is permitting. Trying to get a dam permitted for an existing hydro project to also do pumped hydro—you need to pump the water, and you need a pool—if those could be streamlined in some way, pumped hydro could be really cheap, in addition to what Jason is suggesting. And then there could be new technologies—Yi is the leading person in that.

Cui: I’ve worked on this for close to two decades. You need low-cost, extremely safe—working in all the temperature environments—technologies. I recently worked on one called metal hydrogen gas batteries that have a 30-year life span, 30,000 cycles, passing high safety standards, never catching fire no matter what you do—you can shoot a bullet at it, you can put it on fire, and it still doesn’t catch fire—and have high-energy efficiency. You can go down to 40 degrees Celsius, go up to 60 degrees Celsius. So very reliable. A system like that, having flexibility, allows you to run minute to minute, hour to hour, day to day, up to, maybe, 72 hours. Eventually, how long a timescale this type of technology can go depends on the cost.

Through the Doerr School, we just put out a proposal to the Department of Energy to see whether we can reinvent batteries to have 10 times lower cost compared with common lithium-ion batteries, having the scalability to go to 100 terawatt-hour scale. California only needs a few hundred gigawatt-hours, but the whole world needs 10,000 times more. We don’t have battery chemistry that can go to this scale. We don’t have pumped hydro that can go to this scale. What’s that storage mechanism we could utilize on a global scale? We need to think about that.

Graph of California's Growing Battery Storage CapacitySource: California’s Clean Energy Transition Plan

What closing thoughts would you all like to offer?

Wagner: I think that people often think of carbon capture and sequestration as outside of the realm of the electricity challenge. I think of them intertwined. That is partly because of those tail event [e.g., extreme weather] challenges. If you are able to have technology in carbon capture and storage that is safe, effective, and lower cost, it allows you to use your existing infrastructure in a much more effective and efficient way. Instead of building out for those tail events, you can actually use some of your existing infrastructure in a more productive way. But it requires innovation in carbon capture and sequestration, and it requires an acceptability of those technologies, which is actually a challenge in California in particular, because people would like to see more of a purist solution of renewable energy and battery storage.

Majumdar: Today’s grid was not designed to address the climate extremes that we are facing today, and we are likely to face even more in the future. The duration and the intensity and the frequency—as we go into 2035 goals of the United States, 2045 for California, I think that consideration of not how to manage today’s grid, but what the grid of the future ought to be, based on climate extremes, is a really important issue.

What do you think some of the key elements of the grid of the future should be?

Majumdar: If you have summer heat like the one we had in September of last year, some [excess] resource capacity is going to be super important. Sometimes if you discharge storage based on the market, that may not be the wisest choice to make because you may have a bigger peak later on that you’re not prepared for. 

I think the [transmission] capacity development—say, reconductoring some of the lines to increase the capacity of existing approved lines—may be critical. And new lines are critical if you’re going to integrate more solar and wind. 

One has to really look at it holistically, and one of the big challenges that we’re facing nationally, besides permitting, is workforce. There is a workforce shortage on power systems—engineering, construction, and all of that. If you have the permits, then you need the workforce to do something about it. But you also need the workforce to get the permitting done. 

Jill Patton, ’03, MA ’04, is the senior editor of Stanford. Email her at jillpatton@stanford.edu.

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