Utility-Scale Energy Storage

Exploring Future Technologies

Lithium-ion Storage Limitations

Lithium-ion batteries have revolutionized portable electronics and electric vehicles due to their high energy density and long cycle life. However, when it comes to utility-scale energy storage, they do have some limitations that need to be considered.

  • Limited Energy Density: While lithium-ion batteries have higher energy density compared to many other battery technologies, their density is still limited when it comes to utility-scale storage demands. This means that storing large amounts of energy for extended periods may require significant physical space, which can become impractical in certain situations.
  • High Cost: Lithium-ion batteries can be costly to manufacture, and the financial investment becomes even more pronounced when scaling up for utility applications. For large-scale energy storage, the overall expense can be a significant barrier to adoption, making it less economically viable compared to other energy storage technologies.
  • Limited Cycle Life: Lithium-ion batteries degrade over time, losing capacity as they undergo charge and discharge cycles. While this might not be a significant concern for small-scale applications like smartphones, for utility-scale storage where frequent cycling occurs, the reduced lifespan can be a deterrent. Replacing large battery systems frequently adds significantly to the overall cost.
  • Safety Concerns: Lithium-ion batteries are not immune to safety risks. Rare instances of thermal runaway or fires have been reported, particularly when the batteries are not properly designed, manufactured, or maintained. This poses a challenge for utility-scale installations, where the possibilities of incidents affecting a larger area are more significant.
  • Limited Charge/Discharge Rates: The rate at which lithium-ion batteries can charge and discharge is limited. In some utility applications, rapid charging or discharging may be necessary to balance the grid or respond to sudden changes in energy demand, and lithium-ion batteries may not always meet these high-power requirements efficiently.
  • Environmental Impact: While lithium-ion batteries are more environmentally friendly compared to some older battery technologies (e.g., lead-acid batteries), they still raise concerns about the extraction and disposal of lithium, cobalt and other rare materials used in their production. Proper recycling and disposal practices need to be implemented to minimize the environmental impact.
  • Capacity Fade: Lithium-ion batteries experience capacity fade over time, meaning that their ability to hold a charge diminishes even when they are not used. This can become an issue in utility storage applications, where consistent performance over a long duration is essential.

Due to these limitations, utility-scale energy storage applications often require other technologies like flow batteries, pumped hydro storage, compressed air energy storage (CAES) and advanced lead-acid batteries, which may be better suited for certain use cases.

Research and development efforts are ongoing to address the limitations of lithium-ion batteries and make them more viable for utility-scale energy storage in the future.

Meanwhile, there also continues to be significant investment in research of alternative technologies for energy storage.

During the recent CLEANPOWER Conference, held in New Orleans, Louisiana in May 2023, four of these technologies were presented.

Four Technologies on the Forefront

1. Reversible Rust Battery

A “reversible rust battery,” or more technically an iron-air battery, is a type of rechargeable battery that uses the oxidation and reduction of iron to store and release energy. The name “reversible rust” comes from the fact that when iron oxidizes, it forms iron oxide, or what we commonly refer to as rust. This is why it’s called a “reversible rust” battery. The process harnesses energy from the formation of rust (iron oxide), then returns the byproduct back to iron.

Here’s a simplified explanation of how an iron-air battery works:

  • During discharge — when the battery is providing energy — iron (Fe) reacts with oxygen (O2) in the air to form iron oxide (Fe2O3), also known as rust. This reaction releases electrons, which can be used to provide electrical energy.
  • During charging — when energy is stored in the battery — an external energy source is used to reverse this reaction. The iron oxide is reduced back to iron and oxygen. The oxygen is released back into the air, and the iron is ready to be oxidized again, allowing the cycle to continue.

Iron Air Technology

Iron-air batteries have several potential advantages for utility-scale use.

  • Abundance of Materials: Iron is one of the most abundant elements on earth and is environmentally benign. Air, obviously, is also readily available. This makes iron-air batteries potentially very cheap and environmentally friendly.
  • Energy Density: In theory, iron-air batteries can have a high energy density — potentially higher than that of lithium-ion batteries. This makes them attractive for applications that require long-duration storage.
  • Safety: Iron-air batteries operate at ambient temperatures and pressures, and the materials involved are non-toxic and non-flammable, presenting fewer hazard risks than other types of batteries.

Challenges include efficiency (not all the energy put into the battery can be retrieved), lifespan (the iron electrodes can degrade over time) and power density (the rate at which energy can be discharged is lower than some other types of batteries). Research is ongoing to overcome these and other technical challenges.

2. Thermal Energy Storage

Thermal energy storage (TES) is not exactly a battery in the traditional sense. It’s a technology that stocks thermal energy by heating or cooling a storage medium so that the stored energy can be used later for heating and cooling applications and power generation.

Thermal energy storage can be implemented at large scales, making it useful for industrial applications or city-wide heating and cooling systems. It can also help to balance supply and demand on the power grid, especially with respect to renewable but intermittent energy sources such as wind and solar.

There are three main types of thermal energy storage:

  • Sensible Heat Storage: This is the most common type of TES and involves heating or cooling a material — most commonly water, rocks, or molten salt — and then either extracting or adding heat when needed. For example, during periods of low energy demand, excess electricity can be used to heat water or another substance, which can then be insulated to prevent heat loss. When energy is needed, this stored heat can be used directly or converted back into electricity.
  • Latent Heat Storage: This type of storage relies on the heat absorbed or released when a storage medium changes phase, most commonly from solid to liquid or vice versa. The energy is stored in the form of latent heat as long as the material remains in its new phase. Latent heat storage has a higher energy storage density than sensible heat storage.
  • Thermochemical Storage: This involves the use of chemical reactions to store and release heat. In these systems, heat causes a chemical reaction that can be reversed when the heat is needed. This type of storage can theoretically store energy for much longer periods without loss compared to sensible or latent heat storage, but it’s also the most complex and least commercially developed.

In all three TES options, the stored thermal energy can be used directly for heating or cooling, or can be converted back into electrical energy using a variety of technologies. For example, in a concentrated solar power (CSP) plant, molten salt may be used as the storage medium. The heat stored in the molten salt is used to produce steam that drives a turbine to generate electricity.

3. Iron Flow Batteries

Iron flow batteries are a type of flow battery that uses iron, one of the most abundant, safe, and environmentally friendly elements on the planet, as an active ingredient.

Flow batteries are different from conventional batteries like lithium-ion or lead-acid. In traditional batteries, the energy storage medium — the electrolyte — is stored inside the cell. In contrast, flow batteries store their electrolyte externally in large tanks. The electrolyte is then pumped into a cell where the chemical reaction takes place across a membrane, and electricity is either stored or generated.

In an iron flow battery, the electrolyte is typically an iron salt solution. During discharge when the battery is delivering energy, iron in the electrolyte is oxidized at the negative electrode, and electrons are produced. These electrons travel through an external circuit to the positive electrode where a reduction reaction takes place.

During recharge, when energy is being stored in the battery, an external energy source is used to reverse this process, reducing the iron and forcing the oxidation reaction at the positive electrode.

A Typical Flow Battery

There are several key advantages of iron-flow batteries.

  • Scalability: Because the energy stored in a flow battery is largely determined by the volume of the electrolyte, iron-flow batteries can be scaled to meet a wide range of energy storage needs.
  • Safety and Environmental Impact: Iron is non-toxic, plentiful, and cheap. The use of an iron salt solution also means that the battery doesn’t rely on scarce or conflict minerals.
  • Longevity and Durability: Flow batteries, in general, have the potential for long operational lives (many thousands of cycles) and can be fully discharged without harm, unlike some other battery technologies.

Iron-flow batteries do come with some challenges. These may include lower energy density compared to other technologies like lithium-ion batteries, complexity of design and the need for careful balance and management of the electrolyte solutions to maintain efficiency.

4. Hydrogen and Green Hydrogen

Hydrogen is a versatile energy carrier that can play a significant role in renewable energy storage. It can be produced from various sources including natural gas, nuclear power, biomass and renewable power like solar and wind. Once produced, hydrogen can be stored and then converted back to electricity when needed. And the process relies on access to the most abundant substance on the planet — water.

  • Production: Hydrogen can be produced from renewable energy sources using a process known as electrolysis in which an electric current is passed through water to split it into hydrogen and oxygen.
  • Storage: Hydrogen is an energy-dense fuel and can be stored in large volumes. It can be stored in pressurized tanks, metal hydrides or in underground geological formations. This means that excess renewable energy that’s produced when demand is low (like solar energy during the day) can be stored and then used when demand is higher, or supply is lower (like at night).
  • Usage: When energy is needed, the stored hydrogen can be used in a few different ways. It can be burned directly for heat or to power an internal combustion engine. It can also be used in a fuel cell to produce electricity. In a fuel cell, hydrogen and oxygen are combined to create electricity, with water as a byproduct.

This ability to store large amounts of energy for long periods of time and then convert it back to electricity makes hydrogen a potentially valuable tool for integrating more renewable energy into the power grid. It can help to balance supply and demand and make renewable energy more reliable and accessible. It’s worth noting that, while promising, hydrogen energy storage still faces some challenges including the efficiency of the electrolysis process, the cost and availability of renewable energy to produce “green” hydrogen and the infrastructure for storing and transporting hydrogen.

What is Green Hydrogen?

Green hydrogen is a type of hydrogen fuel that is produced using renewable energy sources. The term “green” is used to differentiate it from other forms of hydrogen that are produced using fossil fuels.

  • Production: The process of creating green hydrogen does not emit any carbon dioxide. When the electricity that is used to split water into hydrogen and oxygen via electrolysis comes from renewable sources, such as wind or solar power, the resulting hydrogen is considered “green.”
  • Usage: Green hydrogen can be used in a variety of applications, like fuel cells to generate electricity that can power everything from vehicles to large power plants. It can also be used directly as a fuel or as a feedstock in various industrial processes, such as the production of ammonia for fertilizers. Green hydrogen can even be injected into the natural gas grid to reduce carbon emissions from heating and cooking.

Green Hydrogen Fuel Cell Energy

  • Benefits and Challenges: The main advantage of green hydrogen is that it is a clean energy carrier. It doesn’t emit any carbon dioxide when used, and if produced using renewable energy, it doesn’t emit any carbon dioxide during production. This makes it a potentially important tool in efforts to reduce greenhouse gas emissions and combat climate change.

    However, there are also challenges to using green hydrogen. As of my last update in September 2021, green hydrogen was typically more expensive to produce than hydrogen made from natural gas, due to the costs of electrolyzes and renewable electricity. Additionally, storing and transporting hydrogen can be challenging due to its low density.

Despite its challenges, there’s a lot of interest and investment in green hydrogen, and advancements are being made that could make it a key part of a sustainable energy future.


These are just four potential solutions for utility-scale energy storage. It is highly probable that there won’t be a single definitive winner among them.

At c3controls, we are prepared to fulfill the requirements of energy storage system (ESS) original equipment manufacturers (OEMs) by providing top tier electrical control products.

The c3controls product line can ensure efficient management of electricity flow from sustainable sources to energy storage systems and further distribute power to the grid or wherever it is needed. Rest assured, the reliable and guaranteed products available through c3controls are engineered and manufactured by experts who understand what it takes to support the seamless integration of utility-scale energy storage solutions.


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