For Cleaner, Greener Power, Expand the Definition of “Batteries”
Intermittent power sources like wind and solar will require supporting the grid with long-duration storage—a concept we are just beginning to explore.
As California and other municipalities set off on the path to zero-carbon energy economies, there is a worldwide search for ways to provide clean, ever-ready power to the grid to balance intermittent sources of renewable electricity such as wind and solar. In general, there are three ways to provide what is being described as “clean firm power” to balance the load: (1) create methods of storing solar and wind power for long periods, (2) produce clean power from nuclear or geothermal generation, or (3) retrofit existing fossil fuel power plants to capture the carbon they produce.
Recently, the energy and climate scientist Jane C. S. Long and others argued for investment in clean firm power production rather than long-duration storage, saying “Long-duration storage may provide another useful arrow in the quiver, but systems with clean firm power remain meaningfully less expensive.” Based on the current pace of innovation in technology and pricing, as well as our ongoing work funded by the California Energy Commission, we disagree with that assessment and encourage decisionmakers to broaden their research and deployment agenda rather than picking winners at this point.
When coupled with solar and wind electricity, we believe that long-duration storage technology has the potential to provide clean firm power at a competitive price. History shows a poor track record of picking winning technologies. Solar electricity was long predicted to be too expensive to be practical, but is now considered to be the lowest-cost source of electricity in some locations. Similarly, oil production was predicted to peak as sources of easily recovered oil were exhausted, but technology advancements enabled the United States to increase oil production considerably over the past decade.
Energy storage technologies are now declining in cost and expanding their physical and economic performance on par with the advancement of solar and wind technologies. Recent work examines technology learning rates for battery storage ranging from 16% to 31% with every cumulative doubling of capacity, demonstrating rapid progress akin to the learning rates previously seen in both solar (20%) and wind (7%).
It is much too early to lock in investment on a narrow path that excludes long-term storage technologies, particularly in light of the potential health and climate impacts and technological limits of carbon capture and thermal electricity generation (e.g., natural gas and coal). Fossil fuel plants have been the source of air pollution, fuel leaks, and poor waste disposal—all creating environmental injustices that increase the social and environmental burdens borne by surrounding communities.
By contrast, with a thoughtful strategy for innovation and adoption, long-duration storage could blossom into a complementary technology that enables higher shares of pollution-free solar and wind to power electricity grids across the world. A research agenda with a broad vision can spur this innovation and uncover opportunities that might be missed if winners are chosen too early.
Although experts often talk about long-duration storage technology as if it were simply a scaled-up version of the batteries in laptops and vehicles, there are in fact many potential storage mediums, configurations, and business models that could use this technology in productive ways.
Among many unknowns regarding storage capacity is how much will be required for a future zero-carbon grid, but simply exploring the question reveals myriad potential ways to profitably and efficiently store energy. The question generally posed for solar- and wind-powered grids of the future is whether the need for energy storage will be greater or less than it is now. Some experts have built a case suggesting that the variability of solar and wind power will require significantly more storage capacity, while other researchers believe that less total storage capacity will be necessary because consumers will not require protection from disruptions of foreign oil or fuel imports.
Today’s grid technology already relies on huge stores of fossil fuels to enable conventional power plants—often called peaker plants—to provide firm, reliable power. As shown in Figure 1, today’s fossil fuel storage reservoirs collectively contain enough energy to run the country for months. Some of this is stored to meet seasonal needs, some is stored simply as a matter of practicality or speculation, and some is stored for national security purposes. Looming large among these storage schemes is the Strategic Petroleum Reserve, which was created by the federal government to protect domestic consumers from disruptions of oil imports and has been maintained for decades at considerable expense. But not all energy storage is large scale: some energy is stored at the site where it will be used, such as a vehicle’s gas tank.
As we envision the energy system of the future, we can anticipate that we will change not only the sources of energy we use, but how we use it across many sectors. Electric vehicles are already replacing internal combustion engine vehicles and heat pumps are replacing natural gas furnaces. Together, electric vehicles, electrified water tanks, and thermal mass associated with space heating are forms of storage. They can assist in the transition toward zero emissions by participating in power company initiatives such as demand response programs, which encourage use during specific times of the day that can support the grid. Already, these three technologies effectively support grid stability, reliability, and resiliency.
We simply don’t know the full potential for technologies that manage demand. The innovations needed are not only technological, but also financial. The Federal Energy Regulatory Commission just last year allowed participation of such distributed energy resources in the wholesale electric power markets with Order 2222, potentially opening the field for new players and the design of new regulation and markets.
Another potential disruptor in this space is hydrogen, which can be produced from excess power, stored, and then used to generate power. This field is rapidly scaling up, with some companies, such as LAVO in Australia, now even offering hybrid solar battery–hydrogen home solutions. These systems can store energy at big central locations, or distribute the energy across many different places where it will be used. This potentially changes the shape and form of the power grid away from today’s linear, centralized grid—which sends energy from a power plant through a transmission system directly to people’s homes—toward a grid with bidirectional power flow.
As seen in Figure 1, tomorrow’s energy storage capacity will need to provide energy security for not only the power sector, but also for the transportation, industrial, and other energy-consuming sectors. As we explore options for storage to keep the power grid running, there is value in considering how energy storage can support other sectors.
As power shifts across sectors, new synergies will arise. For example, if heavy-duty vehicles use hydrogen-powered fuel cells, a robust infrastructure will develop for distributing hydrogen, making it more available for use in generating electrical power as well. Fuel cell–powered vehicles could convert hydrogen to electricity for the grid when the vehicle is parked. Could tomorrow’s fuel cell–powered trucks effectively become “peaker plants on wheels”? Such a concept may seem far off today, but innovations across the technical, business, and regulatory arenas may uncover opportunities for the transportation and power sectors to support each other.
For example, because we currently see power generation and building-based heating and cooling technologies as entirely separate categories, we miss the opportunities they present for cross-sector innovation. When looking for low-cost storage options, it’s hard to beat the fleet of hot and chilled water tanks that already exist in buildings across the country. Some large buildings currently chill a tank of water during the night to use for air conditioning during the day. When renewable electricity is plentiful and electricity is cheap, the chiller can be programmed to chill at any time, effectively turning the water tank into a type of battery. Collectively, the storage capacity of both cold and hot water tanks in the United States represents about 1 terawatt hour (TWh)—enough to supply about 90% of the US electricity demand for an hour. Lithium-ion battery systems supplying 1 TWh of storage would currently cost hundreds of billions of dollars. And although most current systems are designed only for diurnal storage cycles, some communities are developing seasonal thermal storage to capture heat during the summer to use for heating buildings during the winter when there is less sunlight available.
The power sector may also find synergies with the chemical industry. Innovations have allowed for solar- and wind-based electricity to produce cleaner “green” hydrogen—that is, hydrogen made by electrolysis using renewable electricity. If green hydrogen could achieve the cost reductions that combinations of solar, wind, and batteries are demonstrating, surplus electricity from solar and wind farms could be used to supply hydrogen for making fertilizer, steel, and chemicals. These chemicals may be more efficiently and easily stored than electrical energy, to be spread on fields, transferred into cars, or made into plastic at the right moment. While many manufacturers prefer to obtain supplies as needed, access to low-cost surplus electricity may offset the added cost of a warehouse for those that prefer to maintain a stock of supplies for anticipated needs. Perhaps tomorrow’s version of Figure 1 will include wedges for hydrogen, ammonia, and a range of other renewable chemicals.
Finding ways to commercialize energy transformations for the purpose of steadying the power grid may also create synergies in other industries that are generally considered as being entirely separate, such as agriculture and waste disposal. Today, in addition to selling milk, dairy farms are offering biogas made from cow manure. Wastewater treatment plants use their digesters to not only generate biogas from the wastewater, but also to process fat, oil, and grease, providing a useful waste-disposal process while also supplying a storable fuel (biogas). Although most studies conclude that waste-to-power processes will be unable to make a big enough dent in our energy needs to be considered an effective solution, waste-to-power innovations might prove valuable to society by providing local solutions for waste disposal and energy needs at the same time. California’s Low Carbon Fuel Standard has motivated increased investment in biogas: the state generates 3% of its electricity from a range of projects, including wastewater treatment, dairies, and organic waste in or diverted from landfills.
We recommend that policymakers, regulators, entrepreneurs, and the scientific community continue pushing the frontiers of knowledge by developing inter-sectoral models and scenarios to better understand and quantify potential benefits of synergies among different ways of storing energy across the economy. To maximize social benefits, investments should not be confined only to clean firm power and long-duration storage technologies for the power sector, but expand to technologies that enable energy storage across many sectors.
Locking investment into a specific and narrow definition of clean firm power disincentivizes the very sort of innovation that has brought zero-carbon electricity goals within reach. Given the urgency of climate change and need to create low-cost solutions, regulatory openness and financial incentives to spur projects that challenge the existing energy system are needed for US leadership on clean technology. Further research and investment to open cross-sector collaborations could foster more dramatic innovations that can lead to better long-term outcomes for society.
There is no question the world will soon use solar and wind power to generate a substantial fraction of our electricity. And although the precise portfolio of long-duration storage and clean firm power technologies is not yet clear, we can assume that further innovations will lead to technology advances that will surprise us. In the year 2000, almost no one was predicting a huge growth in solar power generation, nor was anyone predicting that the United States would today be a net exporter of oil. As we explore options for tomorrow’s energy system, keeping the door open to all solutions—and particularly not-yet-commercialized long-duration storage technologies—could give us the best chance of quickly reaching low-cost, net-zero carbon energy.