New energy storage technologies are surging into the market, as business leaders and policymakers seek to address climate change, support renewable energy, and create a more reliable and resilient grid. However, not all energy storage solutions are the same. The global economy faces multiple challenges in addition to climate change. To foster long-term sustainability at a holistic level, energy storage should support reliability and security while benefitting people and the planet, including historically disadvantaged communities.
Why energy storage matters
The technology behind wind turbines and solar panels is now more efficient and economically competitive than ever before, but nothing can change the essential nature of wind and solar power.
Wind speeds vary by the hour, day and season. Sunlight is absent all night, and cloudy weather can cut into solar panel performance during the day.
That’s where energy storage comes into play. Batteries can store enough electricity to fill the gaps when the output from wind turbines and solar panels shrinks.
Businesses can use energy storage to absorb excess wind or solar energy during low demand periods and discharge it strategically to avoid peak demand charges. They can also use energy storage in place of diesel or gas generators for emergency backup power and avoid longer outages with solar-plus-storage microgrids.
On a broader planning level, large-scale energy storage can be deployed to avoid costly new transmission infrastructure and peaker plants, supporting economic growth and better health outcomes in remote or underserved areas.
In addition to its bottom-line benefits, energy storage enhances a company’s reputation. Many businesses already pitch in with supplies and resources when emergencies strike their area. Onsite energy storage could enable them to add electricity to the list, without the noise and pollution associated with fossil-fueled emergency generators.
Beyond lithium-ion batteries
Lithium-ion is today’s most common energy storage technology. Once confined to cell phones, laptops and other portable rechargeable devices, lithium-ion batteries are now the technology of choice for most electric vehicle manufacturers.
Interest is also growing in expanding the use of lithium-ion batteries to store electricity for use onsite at buildings and industrial facilities, and to store and return power to the electric grid.
Here, however, a key shortcoming arises. Lithium-ion batteries only last a few hours. That can be sufficient in some circumstances, especially when combined with smart grid technology. But the four-hour limitation typical of conventional lithium-ion technology falls short in other cases. Longer-lasting batteries, with a duration of 10 hours or more, are needed to achieve a highly decarbonized electric grid that is resilient, reliable and stable.
In the energy storage field, water reigns supreme. Despite rapid growth in lithium-ion batteries, pumped hydropower reservoirs still account for 97 percent of large-scale energy storage in the U.S. According to the U.S. Energy Information Administration (EIA), the average hydropower facility stores about 500 megawatts of zero-emissions electricity for six to 20 hours, safely and securely, without fear of fire, toxic chemicals or end-of-life hazardous waste issues.
But hydro isn’t expected to be a large part of the energy storage solution going forward. The water resources needed for hydropower plants are geographically limited and the deployment timeline is many years. New project development is further curtailed by wildlife and habitat conservation concerns, as well as competing interests including river-based transportation, fisheries, recreation, and the rights of Native Americans. So the need for a breakthrough is clear.
In addition, the U.S. Department of Energy, grid planners and other stakeholders are coalescing around the idea that the future grid will not rely as heavily on large, centralized power plants, whether fueled by water or by fossil resources.
Instead, distributed energy resources, including rooftop solar arrays and small wind turbines, will play a more prominent role. To adapt to the grid of the future, long-duration energy storage technology must be scalable and flexible enough to be located just about anywhere.
The search for sustainable long-duration energy storage
Long-duration energy storage is a critical feature of the Energy Department’s plans for integrating more wind and solar onto the grid without sacrificing reliability and stability. Having recognized the four-hour limitation of conventional lithium-ion technology, the Energy Department defines long-duration energy storage as a device or system that can generate electricity for at least 10 hours, and preferably for multiple days lasting 100 hours or more.
The recently passed Senate infrastructure bill supports the Energy Department’s efforts in this area by including billions in funding for long-duration energy storage projects and domestic supply chain stimulus programs.
It is possible to link sets of lithium-ion battery arrays in a sequence that lasts longer than four hours. But the cost of such a system is often prohibitive, especially if the goal is to maintain power for multiple days.
In addition, the environmental and social impacts of over-reliance on lithium technology are beginning to come into view, and the picture is not pretty.
While the U.S. has large deposits of lithium to exploit, fossil energy stakeholders are among those pointing out that the local environmental impacts of lithium extraction and refining share characteristics with the impacts of coal, oil and gas operations.
Along with environmental and public health impacts, lithium mining can raise significant social, cultural and human rights issues. In the U.S., most lithium reserves are concentrated in western states, where the once-dormant domestic lithium mining industry has become a hotbed of activity, triggering new concerns over water resources and the use of public lands.
Native Americans in Nevada, for example, have allied with ranchers and conservationists to stave off at least one new lithium mine that was approved on federal land during the Trump administration. The impact of lithium mining on indigenous communities in other countries has also drawn media attention.
Researchers are working on lithium recovery methods that involve less surface destruction and eliminate the need for large evaporation ponds. However, the use of toxic substances in the refining process is an issue that has yet to be resolved, and disposing vast quantities of waste brine could raise issues similar to the notorious problem of fracking waste disposal.
The skyrocketing demand for lithium shows no sign of slowing down, as the growing number of stationary battery arrays competes for raw material resources with countless electronic devices. With millions of electric vehicles set to roll off assembly lines in the near future, both supply and end-of-life issues appear likely to increase.
More options for sustainable energy storage
A growing number of more sustainable long-duration energy storage options are on the horizon. One approach uses heavy blocks to substitute for water and hydropower turbines. When renewable energy is available, electric motors raise the blocks to the top of a tower. When more electricity is needed, gravity takes over. The blocks are allowed to fall gradually back down, and they generate electricity along the way.
The blocks themselves can be made of any material with optimal mass. That opens the door to new opportunities for recycling wind turbine blades and other materials that support the renewable energy transition.
Such recycling would represent a key advantage over lithium-ion technology. While lithium-ion batteries can be recycled, few if any recycling facilities exist today on a scale large enough to take in the quantities of spent batteries that will populate the globe in only a few years. And while scaling up the global lithium recycling industry is possible, it would involve additional environmental impacts related to transportation emissions and facility operations. It would also add new burdens to oversight of illegal recycling operations, which is already strained to the hilt by the global plastics crisis.
In terms of lifecycle sustainability, gravity-based energy storage is a better fit for the circular economy of the future. However, its application is limited to sites with sufficient space, and it is subject to zoning restrictions, competing uses, and aesthetic considerations due to the height of the towers.
Site limitations also come into play for other long-duration energy storage technologies that are beginning to emerge at the pilot and demonstration stage, such as compressed air systems.
In terms of a sustainable solution that can fit almost any use case, what is really needed is a sort of hydropower dam in a box – meaning a relatively compact system that uses little or no toxic chemicals, maximizes compatibility with the circular economy, and can store and deliver electricity for 10 hours or more.
Flow batteries are one such option. As the name suggests, flow batteries deploy two types of specially treated electrolyte to generate and store electricity. The electrical charge occurs when the electrolyte, pumped by electricity from the grid or a paired generator, flows across a membrane. When ions cross the membrane in one direction, the battery charges; when they cross in the other, the battery discharges.
Researchers have been perfecting flow batteries since the science was first confirmed in the 1970s. Only in recent years have flow batteries finally begun to cross the chasm separating promising laboratory technologies from successful commercial deployment. And today, the decades-long promise of long-duration, low-impact, and low-cost energy storage with flow batteries is finally upon us.
ESS Inc., based near Portland, Oregon, is one company that has been working on flow batteries for a decade and is now poised to shake up the storage sector. Founded in 2011, a year later ESS was awarded an Energy Department grant for its flow battery design that met the agency’s exacting standards for both cost and efficiency.
That initial investment and subsequent other funding have paid off. After years of development, the company has devised a safe, reliable new flow battery that delivers on duration and sustainability as well as cost and efficiency, with an electrolyte that uses earth-abundant iron, salt and water to generate and store electricity.
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