J. ROWELL and J. CRISTIANI, Victaulic, Raleigh, North Carolina; F. Jakob, Victaulic, Overland Park, Kansas
Aggressive decarbonization and sustainability goals are driving unprecedented amounts of renewable energy onto the grid as the world scrambles to move toward low-carbon and zero-carbon generation, with negative-carbon goals not too far behind. Throughout 2021, renewable energy capacity additions in the U.S.—led by solar power, with an increasing growth of wind and hydropower generation—reached record highs. Building on these trends, U.S. federal estimates forecast that renewable energy will provide 75% of U.S. electricity by 2035 and 90% by 2050.
However, the full-scale adoption of carbon-free electricity still hinges on successfully overcoming the notorious “v” word: variability. Since the powers of nature are not always aligned with the hourly demands of our global electricity needs, variability issues remain a constant threat. Simply put, wind and solar produce energy on a schedule that is out of sync with consumer demand. While solar supply peaks at noon and onshore wind turbines peak in the middle of the night, consumers tend to use the most electricity in the mornings and evenings as they start and end their day—thus introducing the need for energy storage.
Lithium-ion batteries represent the primary focus for most consumer-level battery storage solutions such as portable electronics, automobiles and residential storage. Lithium-ion batteries support the day-shifting of energy, charging and discharging rapidly following variable renewable generation to offer 4 hr–8 hr of grid-deployable power.
However, the physical limitations of lithium-ion chemistry cannot extend past 8 hr of storage discharging at rated power—this is not particularly helpful when the power cuts out and consumers are left without electricity for days, or when market economics encourage seasonal shifting (such as energy storage that would enable the use of electricity generated in warm, sunny July during the cold, dark months of February).
To unlock the full potential of renewable energy to cut carbon emissions, cost-effective, utility-scale and long-duration energy storage systems are needed. While the U.S. Department of Energy (DOE) defines these systems as anything that can hold more than 10 hr of storage, consumers require systems that can store days’ worth of capacity.
Unfortunately, there is one tiny roadblock to achieving sufficient energy storage—there are few commercially feasible, economically viable and technically scalable long-duration energy storage technologies on the market. Pumped hydroelectric storage is currently the only solution, but this type of energy storage remains constrained by geography and access to water, and can take many years to design, permit and construct.
In recent decades, power providers have turned to natural gas as the standby/backup fuel of choice. With hydraulic fracturing technology, natural gas is low-cost and abundant, and lower in carbon than alternatives (oil, coal and wood). Additionally, natural gas already has a developed infrastructure for transportation (including pipelines for its gaseous form, underground salt caverns for its compressed form and tanks for its liquefied form). California—which increasingly struggles to meet its energy needs and is forced to curtail huge amounts of solar power when generation exceeds demand—is fast-tracking the development of gas-fueled generators to obtain more power on the grid, even as it continues its efforts to achieve the state’s net-zero-carbon goal by 2045.
H2 production. In the zero-carbon future, a zero-carbon fuel is a solution—and H2 is that fuel. H2 does not occur by itself on earth the way natural gas (methane) does. H2 must be manufactured from either hydrocarbon fuels (which is the current pathway, but this method emits carbon dioxide)—or it can be extracted from water (the future pathway), involving no carbon emissions.
Therefore, power-to-gas (P2G) technology uses renewable electricity to decompose water into its elemental constituents that can be stored, transported and combusted to produce power as compressed gas or as liquid ammonia by combining H2 with the nitrogen in the air to produce ammonia. H2, either as a compressed gas or as liquid ammonia, can be used as a zero-carbon pathway to bridge the future gaps between supply and demand.
Decarbonization targets aside, S&P Global reported that the economics around natural gas are not necessarily working out anymore: “At an all-in electricity production cost of $132/MWh, a 4-hr utility-scale battery is now priced below the global gas-peaker plant average at $173/MWh.” Also, it is important to note that “levelized cost of electricity” is typically $/MWh of electricity produced over the life of a facility. This makes natural gas far less attractive than it used to be, particularly since accessibility and duration are not factored into the cost comparison.
Advanced battery technologies. Lithium-ion batteries are the most popular energy storage option today, controlling more than 90% of the global grid battery storage market. However, other battery technologies—particularly those built with low-cost and abundant materials like iron, zinc and sodium—are coming into the market.
In early 2022, Massachusetts-based startup Form Energy announced that it would collaborate with Georgia Power to deploy an energy storage project of up to 15 MW/1,500 MWh, using an iron-air battery that the company says can offer up to 100 hr of electricity storage. This is 15 times larger than the first pilot project announced in 2020 by Minnesota utility Great River Energy, which promised 1 MW/100 MWh.
This latest project marks a tremendous leap forward from current storage projects and would provide backup power to cover more than 99% of all localized grid outages. However, 100 hr is only about 1 wk, and this is still not nearly enough to enable monthly or seasonal energy shifting.
These iron-air batteries promise to store multiple days’ worth of energy. They will not degrade or catch on fire and are more attractive against the rising raw-material cost of lithium-ion battery cells (there is even a battery chemistry based on antimony, another low-cost element).
A surge in funding for research and development has helped overcome many challenges around iron and zinc batteries, with promising advancements. For example, ZAF Energy Systems is exploring nickel zinc batteries to support data centers (one of the fastest-growing markets for energy storage), pushing beyond what was traditionally driven by lead-acid and lithium-ion energy storage.
Iron-air batteries derive their power from the interaction of iron and oxygen, which causes oxidation. AZO Materials reports that iron-air batteries save more energy than lithium-ion batteries—1,200 Wh/kg vs. 600 Wh/kg. In addition, they are extremely durable, capable of withstanding more than 10,000 full cycles from fully charged to completely discharged and back again (the charge life of lithium-ion batteries is only 3,000 cycles–5,000 cycles).
Zinc batteries rely on a water-based electrolyte to charge and discharge, making them safer than potentially flammable lithium-ion batteries. Additionally, according to a 2020 scientific paper, zinc batteries offer an energy density of up to 1,350 Wh/kg, and the production costs are much lower than lithium-ion batteries. Canadian-based startup Zinc8 reports that the capital cost of its 8-hr storage product is about $250/kWh, declining to $100/kWh for a 32-hr system and $60/kWh for 100 hr. By contrast, lithium-ion projects cost about $300/kWh for any duration over 8 hr.
However, the downside is that these iron and zinc batteries still do not achieve very long-duration energy storage. While 100 hr is a huge improvement over lithium-ion’s 8 hr, it is still not enough to enable that critical seasonal shifting. In addition, the amount of storage capacity is directly tied to the size of the unit. Increasing storage capacity would require increasing the size of the unit, making it more site constrained.
Traditional battery energy storage is extremely mineral intensive. According to an article from Canary Media, batteries require the mining of 11 different mineral ores, from which everything from aluminum to zinc are refined. The article states, “Of all the clean-energy technologies set to boom in coming decades, none will put a strain on minerals supply like batteries. They account for about half of the projected growth in minerals demand over the next two decades in a rapid decarbonization scenario.”
H2: A step toward long-duration energy storage. Advanced energy storage technology is where H2 comes in. Bringing batteries and H2 together can solve the energy storage issue in a fast, potentially economical manner. H2, as a form of chemical energy storage, can both complement and serve as a reliable alternative to batteries, particularly when considering that H2 prices will become more competitive in the future. Also, green H2—which is produced through electrolysis of water, powered by renewable energy—takes it one step further by offering a carbon-free solution. To be economical, batteries must be charged and discharged daily, discharging for a few hours. Conversely, H2 can be produced continuously and stored, providing storage systems of very long durations—such as seasonal storage that can be used for backup power, limited only by storage volume capacity.
In tandem with batteries, H2 can be deployed when it is needed, much like the natural gas or diesel backups in use today. This flexibility and its features as a carbon-free, mineral-free electricity generator provide premium benefits that offset the conversion losses as H2 is extracted from water, stored, and then used in backup turbines or engines that are the conventional power equipment sources that produce electricity.
Small amounts of H2 (up to a few MWh) can be compressed and stored in pressure vessels or, with new technology, adsorbed by solid metal hydrides or even advanced nanotubes. Very large amounts of H2 can be stored in underground salt caverns of up to 500,000 m3 at 2,900 psi, which would mean about 100 GWh of stored electricity, according to the U.S. Energy Storage Association.
H2 can also be converted into green ammonia, a liquid chemical consisting of nitrogen and hydrogen that can be produced using 100% carbon-free renewable energy. Being a liquid makes green ammonia easier to transport and store, especially when using existing liquefied natural gas (LNG) infrastructure. This ammonia can then serve as an energy storage medium, and it can even be burned directly as a carbon-free/emissions-free energy source—or, since it is composed of one nitrogen and three H2 atoms, it can be cracked to convert it back into H2, then used as described previously.
The H2 can then produce the electricity used in engines, combined-cycle gas power plants and even in fuel cells that would use the H2 directly with the oxygen in air to produce electricity and heat, emitting only water vapor.
After touching on the mineral intensity of traditional battery energy storage, it must be said that while H2 energy storage would still require minerals to build the electrolyzers that split water into H2, that capital is a sunk cost. Once the electrolyzer is built, it can process huge amounts of H2 for long periods of time (decades), unlike lithium, iron and zinc batteries, which would require an ongoing feed of minerals, considering their shorter lifetimes.
Cost does remain an issue for H2. Although H2 offers several benefits vs. traditional battery energy storage, iron and zinc do win out when it comes to capital cost requirements. H2 has not yet reached the economies of scale that will bring costs down.
Further, there is an impact on energy efficiency at every stage of H2’s journey from conversion from water to H2 gasification and storage, and back to water when burned to produce power. However, this is not uncommon for energy carriers (e.g., gasoline, diesel, jet fuel, batteries and elemental H2). In each case, energy must be expended to produce an end product, even if the end product is an energy or fuel source. Even solar photovoltaic (PV) power generation—roughly 20% efficient now—required advances in technology, engineering and manufacturing to get to a price point in the 2010s that would make solar PV systems cost-competitive with fossil resources. That is the path for H2 to follow.
Another capability H2 offers that is unique to other storage technologies is its potential for direct uses—e.g., as a feedstock in the hard-to-carbon-abate cement, steel, chemical and petrochemical industries; as a zero-carbon fuel in fuel-cell vehicles; and in the creation of synthetic fuels (i.e., “efuels”) ranging from methanol to gasoline to sustainable aviation fuel. This makes H2 even more valuable by enabling multiple revenue streams. It could be that, by mid-century, H2 will be as ubiquitous in society as potable water, electricity and the internet.
Intermountain Power Agency project. In Utah (U.S.), the Intermountain Power Agency’s (IPA’s) Intermountain Power Project (IPP) Renewal Project stands as a potential case study for a long-duration H2 energy storage project. In 2020, the IPA selected the author’s company to serve as the owner’s engineer on the project, which stands as one of the earliest installations of combustion-turbine technology designed to use a high percentage of green H2.
The IPP Renewal Project involves retiring IPA’s original coal-fueled facility, which the author’s company designed in the early 1980s, and replacing it with an 840-MW natural-gas-fueled combined-cycle power plant by 2025. The project’s two single-shaft, advanced-class, combustion turbine combined-cycle units will be capable of blending 30% green H2 at startup, with plans to increase H2 utilization to 100% H2 by 2045.
Perhaps more intriguing is that the IPP Renewal Project envisions the development of long-duration H2 storage in geological salt caverns that are adjacent to the power plant, which would result in a fully dispatchable resource capable of providing highly reliable and resilient power on demand.
Making H2 energy storage a reality. Now that it has been determined that iron and zinc batteries offer good medium-duration energy storage (up to 100 hr) and that H2 can offer the potential for unlimited amounts of long-duration energy storage, the question comes down to this: What needs to happen to move H2 energy storage technologies forward?
First and foremost, H2 energy storage projects must be demonstrated and then scaled, ultimately with the support of power utilities and power generation providers. Demonstrating that H2 technology can scale will help move it forward and, thus, lower the cost. The green H2 hub at the Advanced Clean Energy Storage Project in Delta, Utah, will be a true test of this in the marketplace. The project would interconnect green H2 production, storage and distribution in the western U.S., helping to decarbonize multiple industries, including power, transportation and manufacturing.
True adoption will also require regulatory changes and government incentives. The more the U.S. government can incentivize utilities to start a clean transition to long-duration energy storage, the more successful the transition will be. This is already happening with renewable energy. According to the author’s company’s 2021 Electric Report, which is backed by a survey of nearly 500 U.S. power sector stakeholders, 56% of respondents said that government incentives or policies are driving renewable energy investments in their region. The same will likely hold true for long-duration energy storage.
Efforts to advance long-duration energy storage are underway. The U.S. DOE is actively working on advancing long-duration energy storage technologies. In 2021, the agency launched its Energy Earthshots Initiative, which is designed to accelerate breakthroughs of more abundant, affordable and reliable clean energy solutions within the decade.
The first two Energy Earthshots projects seek to lower the costs of two promising clean energy technologies within the next decade: the Hydrogen Shot project seeks to lower the cost of clean H2 by 80% to $1/kg, while the Long-Duration Storage Shot project aims to cut the cost of grid-scale, long-duration energy storage by 90%. Programs such as these will be critical in helping to advance long-duration energy storage.
The path forward. The global energy marketplace is hungry for long-duration energy storage technologies as renewables continue to grow and become the leading contributor to electricity generation. While the headlines make it sound as though these technologies are ready to go tomorrow, the industry is still in a period of exploration and development as the market tries to understand where the technology stands today. It is also working to corral the rollercoaster of expectations around energy storage options, which are many.
H2 is not a “today” technology, but it is coming down the pike, and when it does, the entire energy game will change. With viable medium-duration energy storage options (such as iron and zinc batteries) on the table right now, stakeholders would be wise to be looking at methods to create flexible, complementary systems that can evolve as technologies advance.
In the next 5 yr–7 yr, expect to see a rapid increase in the viability, scalability and availability of medium- and long-duration storage solutions if the market remembers to avoid the worst mistake possible: getting enamored by one technology and not considering alternative and successor technologies.
Long-duration energy storage is a key that will help unlock global decarbonization. With traditional and emerging battery energy storage on the table (including H2 energy storage), society will soon arrive in a future where electricity can be both generated and stored, and then balanced and managed according to demand—thus enabling tomorrow’s net-zero future.H2T
JASON ROWELL is an Associate Vice President for Black & Veatch who leads the company’s new energy solutions.
JONATHAN CRISTIANI is a Bioenergy and H2 Technology Manager at Black & Veatch.
FRANK JAKOB is the Director of Advanced Energy Storage Solutions at Black & Veatch.