By Sustainability Research Fellow Katie Koenig
Part 1: Renewable Energy Storage
Introducing Power Plants
Electricity acts like the air that we breathe, or the water we drink—it’s that important to our day-to-day lives. Even a short blackout can send entire communities into haywire. Power plants, by extension, are vital to the functioning of our lives. We rely so heavily on them, even if we don’t think about exactly how they work to provide us electricity every time we flip a lightswitch. They work, we get power, and we move on with our lives.
Still, here are two facts you should keep in mind about power plants: one, Homer Simpson works at one. Two, they don’t blow up nearly as much as they do in the movies.
Power plants are very intricate systems that generally rely on fossil fuels to produce the electricity needed to power energy grids. As an industry, in 2022, electricity generation accounted for a third of all U.S. greenhouse gas emissions.1 As such, solutions into alternative renewable energy sources for the national power grid will greatly reduce U.S. emissions, helping us achieve our national goal of being net zero by 2050.
Renewable energy isn’t the issue, of course—wind and solar has existed and been implemented for years. The problem arises with electricity needs when there isn’t any wind or sun, like at night when people tend to use more electricity to keep their lights on, their homes warm, and their devices powered. Power plants work in such a way that they generate only the amount of electricity estimated to be needed during certain times of the day, so that they don’t produce too much or too little electricity that might result in a power outage.
Renewable energy simply can’t meet energy demands to fully switch plants off of fossil fuels.2 In order to make up for lacking power, power plants continuously burn fossil fuels to fulfill electricity demands in order to prevent an imbalance in the system between demands and production.Conversely, renewables can occasionally generate too much electricity compared to demands. If stored, that surplus energy could make up for energy deficits at other times.3
Storing Electricity
Storage, however, isn’t as easy as it may first appear. Electricity is just moving electrons—there’s nothing to store.4 It technically isn’t even renewable or nonrenewable. What is, however, are the sources of electricity: sunlight, wind, water, coal, oil, etc. Renewable energy sources like the wind obviously also can’t be stored, whereas nonrenewables like coal can be stockpiled.
The solution is to store electricity as different forms of energy, like potential energy or chemical energy, that’s generated from renewable sources. I’ll provide a brief description of each, along with examples of each that are currently being tested and, in some cases, implemented in the power industry.
Potential Energy
Unless you remember your physics or chem classes from high school, you probably don’t know what potential energy is. Simply put, it’s the potential for an object to produce energy. There are a few different types, but the most important thing to know is that it’s the possibility for movement, in this case either the movement of atoms or movement that can be used to generate electricity. Think of a box, put high on a shelf, teetering on the edge—that has potential energy, because it has the potential to develop energy (through physical movement) as it falls.
For practical purposes, one specific strategy is to use the additional renewable generated energy to compress air. When that energy is required to fill a lack of electricity in a plant, say, during a storm, the compressed air is decompressed through a turbine, which, as it turns, generates electricity like a wind turbine.5
There is also potential energy stored in phase-change materials. The idea behind it is that, by adding or removing energy (electrons) to a material, you can change it from one form of matter to another. An example of this is liquid-to-air transition energy storage. Surplus grid electricity chills ambient air until it cools enough to become a liquid, and when electricity is needed, it’s reheated and the released energy provides additional energy, not to mention that the air can be reheated again into a turbine as a form of wind for more electricity.5
Chemical Energy
This is simultaneously a simpler and more complex topic to explain. The simple part is that everyone interacts with stored forms of chemical energy, namely, batteries. Batteries are convenient and already proven to be able to be recharged with additional electricity—how many times have you used rechargeable batteries recently? However, on such a large scale as is necessary with power plants, it’s hard to scale up batteries’ size, it takes up a lot of space, and in certain cases it’s also costly.2
Ongoing research on longer lasting and cheaper rechargeable batteries makes this one of the most implementable solutions to store renewable energy in the power industry, however. The largest battery energy storage system actually exists in the U.S. It is the Moss Landing Energy Storage Facility in California that currently has 300-megawatt lithium-ion battery capacity, and started its operations in 2021.3
Part 2: Rechargeable Batteries
Briefly, a few different types of batteries that have the potential to be used in the power industry are lithium-ion batteries (which already exist on the market for individual use), flow batteries, and iron-air batteries.
Lithium-ion Rechargeable Batteries
First, to explain how a battery works, they each have two ends, a cathode and an anode separated by electrolyte, a liquid. When electrons move through the battery as a part of an external circuit (like it’s attached to a lightbulb with wires), ions (atoms with an electrical charge, basically with an atypical number of electrons) move through the electrolyte to the opposite end. Oppositely charged ions (either positively charged, so they have one less electron, or negatively charged, so they have one more) move through the electrolyte to balance the charge of electrons moving through the external circuit.6
The only important thing to note in that description is that, when electricity runs through the circuit (like to light a lightbulb), ions also move through the battery. Rechargeable batteries differ only in that these ions can move in either direction.6
Lithium-ion batteries have a longer shelf-life, they charge better, and have higher voltages than other batteries available to buy for individual use, although they might be more expensive than other kinds. Other kinds of batteries’ charge capacity degrades much faster than lithium-ion batteries, and one kind, nickel-metal hydride batteries, actually suffer from a ‘memory effect,’ so that, if some of the energy is still left when it’s recharged, it loses a lot of its charge capacity.7
When scaled up for industrial use to store renewable energy, lithium-ion batteries can end up being too costly to justify their implementation.4 They also still degrade over time at a noticeable rate, and present unique fire risks that require intricate management.3 However, they are still convenient and proven usable.
Flow Batteries
Flow batteries work a little differently from traditional batteries. Electrical charges are stored in tanks of liquid electrolyte. In order to use the stored energy, the electrolyte is pumped through electrodes to extract the electrons and the used liquid is returned to a tank. It is recharged by using the electrodes to add excess renewable energy, for example, back into the electrolyte to be stored. The electrolyte is a composite of materials that went through a chemical reaction as a liquid, and vanadium, a metal, and iron are current researched electrolyte components.3
Iron-Air Batteries
Iron-air batteries work a little differently from either of the previous two types. They take advantage of the process of rusting and use water, oxygen, and iron, which naturally releases energy that batteries capture and turn into an electrical current.4
It’s recharged by “unrusting” the iron back into its original metallic form. Essentially, by adding electrons to the rust, it breaks the rust back into its oxygen and iron components. This is difficult, however, because the process can degrade these components, although the process already exists in large-scale uses. One such use is by running very low electrical currents through metal bridges to prevent corrosion and rusting.4
NASA did try using iron-air batteries to store renewable energy in the 1960s, but the process was too slow, the materials too heavy, and overall there were too many difficulties for implementation. Now that additional research has been conducted, iron-air batteries do present as a legitimate possibility for renewable energy storage.4
Policies
The U.S. Department of Energy has declared this year that it will invest over three hundred million dollars into the development and implementation of new battery types in the power industry. This investment will span across fifteen distinct projects, seventeen states and the Red Lake Nation, a North American tribe in Minnesota.8
The DOE has declared that the purpose is to provide more reliable and affordable renewable energy to power grids at these sites, and is based on the bipartisan infrastructure law from 2021.8 The DOE’s specific energy innovation hub is the Joint Center for Energy Storage Research.6
The 2022 Inflation Reduction Act (IRA) provides support to energy storage through the extension of the Investment Tax Credit (ITC). The ITC allows businesses to deduct costs associated with certain renewable energy systems, including storage technology, from their federal taxes.
Learn More
To look specifically into the Joint Center for Energy Storage Research, this is their webpage. More in-depth examples of kinds of energy storage are also available through National Grid.