Long Duration Storage is Essential to a Clean Energy Future: How California is Leading the Way

Under the 2015 Paris Agreement, the average global temperature must be held to no more than 1.5 degrees Celsius above pre-industrial levels by the end of the 21st century. That means, according to the United Nations, global emissions of greenhouse gasses must come down by 45 percent by the year 2030.

At present, California has 289 operational storage facilities on its power grid—more than any other state by a long shot. Only four other states (Massachusetts, New York, Pennsylvania, and Texas) have more than 20. 

Meeting that goal is going to be difficult, to say the least. According to the U.N., even if all of the treaty’s 196 signatory countries stick to their current climate plans, global emissions will, in fact, increase by 9 percent by the end of this decade. 

But the solution may be right in front of our faces, at least according to an extensive report by the nonprofit Long Duration Energy Storage Council. The report, issued in November 2023, asserts that using LDES technologies combined with renewable energy sources would cut industrial greenhouse gas emissions by 65 percent. 

Industrial emissions do not include emissions from transportation, which account for about 25 percent of global warming pollution according to the U.N. Sustainable Transport Conference. Nonetheless, according to the LDES report, industrial processes that generate electricity, or that produce relatively low amounts of heat (500 degrees Celsius or less) account for 65 percent of all industrial emissions. That’s almost 8 billion tons of carbon dioxide that could be eliminated using currently available technologies if the world’s industries switched to renewable energy and long duration energy storage.

Of course, as the report notes, making that conversion isn’t going to be simple. “Policy and market support is required to ensure that these reductions can be achieved,” the report says. In other words, legislatures, businesses and consumers need to get with the program. When it comes to energy storage, though there's more to be done, California is with the program to a greater degree than any other state. 

According to the Center for Sustainable Systems (CSS) at the University of Michigan, California was not the first state to deploy a large energy storage facility. Connecticut was the first to do so—way back in 1929—when it opened the Rocky River Pumped Storage plant on the Housatonic River  in 1929. With pumped storage, water is stored in a reservoir then released into a second, lower reservoir, and later pumped back up again. 

But California has done more than catch up in the ensuing century. At present, according to CSS, California has 289 operational storage facilities on its power grid—more than any other state by a long shot. Only four other states (Massachusetts, New York, Pennsylvania, and Texas) have more than 20. 

Are We Just Talking About Batteries Here?

A persistent myth about renewable energy is that because sources such as solar and wind are intermittent, they are fundamentally unreliable. Some opponents of renewable energy even claimed that rolling blackouts during the 2020 California heat wave were due to the “intermittent nature” of renewable energy. In other words, the sun isn’t out at night, and sometimes the wind dies down—so those things are not reliable sources of energy.

In 2019, the California had 136.1 megawatts of battery storage, less than one-tenth of one gigawatt. By 2023, California had just over 5,000 megawatts, or five gigawatts.

This argument, made popular by Donald Trump, ignores the fact that energy variability is something power grids always have to deal with, and no power plant of any kind is online all the time. The reality is renewable can be the basis of reliable power grids. Renewable energy sources only become truly reliable when the energy can be stored and distributed when it is needed.

Batteries are the most common and best-known way to store energy for long periods of time, but they are not the only way. Most of California’s storage capacity is in batteries, and that capacity has skyrocketed since 2020. 

In 2019, the state had 136.1 megawatts of battery storage, less than one-tenth of one gigawatt, according to California Independent System Operator (CAISO), the nonprofit organization that manages the state’s power grid. By 2023, California had just over 5,000 megawatts, or five gigawatts. The steep growth needs to continue, and even accelerate. According to CAISO, to meet the greenhouse gas reduction goal set for 2045, the grid needs 45 gigawatts of battery storage.

Again, batteries are not the only type of long duration energy storage. Thermal storage is a system in which a substance—often but not always water—is heated and then the heat is released as energy at a later time. 

How California Leads in Energy Storage

Energy can also be stored by various mechanical means. In fact, the vast majority of energy storage in the United States is pumped hydro storage as pioneered in 1929 on the the Housatonic River in Connecticut. This practice accounts for 93 percent of the country’s energy storage, according to the U.S Department of Energy. California has more pumped storage capacity than any other state, 3.9 gigawatts, which accounts for 17 percent of the total nationwide.

The term “Long duration” storage refers to the amount of time that a storage system can continuously deliver its stored energy. While there’s no set definition for what constitutes “long duration,” it is generally taken to mean a storage facility that can generate energy for at least 10 uninterrupted hours

With compressed air energy storage (CAES), air is liquified at temperatures lower than 150 degrees below zero Celsius, then warmed and released as gas, and magnetic flywheels are all used to store energy for later use. As of this writing, two major CAES projects were in the works in California, either of which would instantly become the world’s largest energy storage system outside of pumped hydro. The Willow Rock Energy Storage Center in Kern County was slated to come online with 4 GW of capacity in 2028, though as of July 2023 it looked like 2030 might be a more likely target. 

The second project, the Pecho Energy Storage Center in San Luis Obispo County, near Morro Bay, appeared dead as of October, 2023, after the California Coastal Commission blocked test drilling on the proposed site.  

Finally, energy can be stored in chemicals, in particular, hydrogen. The process of electrolysis produces hydrogen from water. The hydrogen can then be stored in liquid form, which requires extremely low temperatures (below -423 degrees Fahrenheit), or as a compressed gas. 

Hydrogen produces no carbon dioxide when it burns, but hydrogen itself is a greenhouse gas. So preventing leaks into the atmosphere during transportation and storage would have to be a priority for any such system.

The federal Infrastructure, Investment and Jobs Act of 2021 (aka the Bipartisan Infrastructure Bill) allocated $9.5 billion for hydrogen development. California will receive $1.2 billion of that cash after being picked by the Biden administration to become one of seven regional hydrogen hubs in the country. 

No Clean Energy Without Long-Duration Storage

There are other types of energy storage, all of which are important for the seamless integration of renewables into the grid. “Long term storage” refers to systems that can hold onto energy for months at a time, so for example, energy generated in the winter can be saved and used in the summer when demand peaks. 

Because they allow renewable energy sources to work at full capacity without overloading the grid, and using that energy to keep power flowing when the grid otherwise couldn’t keep up, long duration storage systems are essential to a future based on renewables. 

The term “long duration” storage refers to the amount of time that a storage system can continuously deliver its stored energy. While there’s no set definition for what constitutes “long duration,” it is generally taken to mean a storage facility that can generate energy for at least 10 uninterrupted hours—though some systems can go as long as 100 hours. On the other hand, some chemical batteries discharge all of their available energy in just two hours.

One of the most important problems with renewable energy sources such as sun and wind is that they generally produce most of their energy in times of relatively mild weather. 

“In the spring and early summer, abundant sunshine, blustery winds, and rushing rivers all coalesce to produce ample amounts of renewable electricity,” wrote energy analyst Mark Specht of the Union of Concerned Scientists. “But all this happens at a time when mild temperatures mean that people aren’t using much electricity in the first place (You don’t usually need to crank the AC in the spring).”

Because the grid must always remain “balanced,” that is, with energy consumption equalling the amount of energy generated, renewable sources must be what energy experts call “curtailed” at the very times they’re doing their best work. A lot of clean energy potential is just wasted.

If that excess energy, instead of being throttled, can be channeled into storage, it can be used later, such as during summer heat waves—which are now three times more frequent than they were five decades ago, thanks to climate change. 

“A long-duration energy-storage market with government support would enable the energy system to function smoothly with a large share of power coming from renewables, and would thus make a substantial contribution to decarbonizing the economy,” according to a 2019 report by the LDES and the consulting firm McKinsey.

Because they allow renewable energy sources to work at full capacity without overloading the grid, using that energy to keep power flowing when the grid otherwise couldn’t keep up, long duration storage systems are essential to a future based on renewables. 

“Renewable energy sources, primarily wind and solar power, are set to account for the majority of growth within the power sector over the coming years,” wrote research analyst Madeline Ruid of the investment advisory firm Global X.  “But to take full advantage of this potential growth requires reliable energy storage systems that can bolster energy grids already under pressure from increasing variability and climate change.”