Beyond Lithium-Ion Batteries: How can we store clean energy cleanly?
By Hailey Hurd
Clean energy has become cheaper and more efficient over the past few decades, but many sources of renewable energy, including solar and wind power, aren’t consistent enough to support our energy needs directly. So, we need to store the excess energy that isn’t used immediately after collection for later use–but where does all that energy go?
Lithium-Ion Batteries:
The current standard for energy storage is lithium-ion batteries: they have a high energy density (100-265 Wh/kg) and voltage (up to 3.6 V) and you’ll find them in your devices, in electric vehicles, and even in some technologically-advanced homes. Some movements are being made towards scaling the technology up to an energy-grid-level capacity. Following blackouts in 2016, Tesla built a $66 million, 129 MWh lithium-ion battery plant in South Australia, powered by an adjacent wind farm.
However, lithium-ion batteries won’t be able to scale up to the level of power grids for a few reasons. The primary reason is the price and risks associated with mining lithium. Lithium primarily comes from ore mining in Australia and salars (salt deserts) in Chile and Argentina, among other sources in China, and the world’s total reserves are estimated to be about 14 million tons. There have been some reports of droughts surrounding salar sites in Chile and Argentina, and more research is needed to determine the exact impact. Obtaining lithium is also cost-ineffective, and so while lithium-ion batteries are very useful on a small scale, they won’t be able to support entire countries’ energy needs.
So what do we do about it?
A CNBC video sheds some light on recent research into other options for clean energy storage. One option is using flow batteries, which are analogous to lithium-ion batteries but work in an aqueous system where electrolytes are stored externally rather than internally like they are in lithium-ion batteries. This system has some advantages over lithium-ion batteries, such as a lower fire risk and slowed depletion over time, but they are not more cost-effective than lithium-batteries are, so they could be used as a supplement but not as a replacement.
Thermal energy storage systems are another alternative but they often lose significant amounts of energy in transition, but one group called Antora Energy is working on a more efficient way to store and release power. Thermophotovoltaic heat engines work by heating blocks of carbon with excess energy and recapturing that heat later using similar technology to solar cells. Energy can also be stored in gravitational potential energy, which is accomplished by using excess energy to move heavy masses up high and harvesting the energy from lowering them later. Pumped hydro accomplishes this by pumping water to a higher-up reservoir and then letting it fall over turbines later on, but this method can only be used in certain geographies and carries the same environmental risks as hydropower. A company called Energy Vault is harnessing gravitational energy with literal weights that are raised and lowered, which makes for a very clean storage system with a very large physical footprint. Other methods can include compressed air, cryogenics, and a current frontier of research, hydrogen energy storage.
Hydrogen Energy Storage Systems:
In a hydrogen energy storage system, surplus energy powers electrolysis to isolate hydrogen which can then be stored in a hydrogen fuel cell. The hydrogen can be later re-electrified with an efficiency of up to 50%, and if you took general chemistry, you might then remember that this process is clean and produces a byproduct of water. Making this process efficient is difficult: “hydrogen has the highest energy per mass of any fuel; however, its low ambient temperature density results in a low energy per unit volume, therefore requiring the development of advanced storage methods that have potential for higher energy density.” Finding new ways to store hydrogen, then, is a current research frontier in chemistry and physics. Some of the ideas in discussion are described in the below graphic from the U.S. Office of Energy Efficiency and Renewable Energy:
The state of Utah could very soon be a hub of hydrogen energy storage for the Western United States. Mitsubishi Hitachi Power Systems (MHPS) and Magnum Developers have signed a mutual agreement to build the “world’s largest green hydrogen storage facility” in Delta, Utah. The project received a $504.4 million federal loan this past June, and will make use of Utah’s underground salt caverns to store energy. The project plans to start with a 30% green hydrogen and 70% natural gas mix, with the intention of moving to 100% green hydrogen by 2045. Utah is uniquely situated to produce large amounts of solar, wind, and geothermal energy, which makes Delta an ideal location for this project. The facility is set to open in 2025 and will hopefully provide jobs and tax revenue for the local community as well as a good source of clean energy for surrounding states.
Conclusions:
Clean energy storage at the moment is ripe for innovation. Similarly to clean and renewable energy production, there probably will not be a single right answer to how we should store energy. Different methods will be suitable for different locations and purposes, taking to account for example physical footprint and topological requirements. While most of these project have a high upfront cost barrier, if the U.S. government subsidizes and supports these efforts, the U.S. will hopefully reach a point of full decarbonization.