Energy Storage Systems

Energy Storage Systems

A review of technologies available for Grid integration of Renewable Energies

As recently as 2010 it was assumed the only way to deal with the intermittency problem posed to the grid by renewable energy was to vastly over build the generation potential to ensure adequate production during low wind speed or low light conditions. However today it is becoming increasingly accepted that Battery Energy Storage Systems (BESS) when used in conjunction with renewable energy sources can overcome the intermittency problems and greatly improve the efficiency and output of wind or solar generation.

In this article we discuss a number of different Energy Storage Systems (ESS) starting with firstly Mechanical Energy storage systems:

1.    Pumped Hydropower Storage (PHS)

2.    Compressed Air Energy Storage (CAES)

3.    Flywheel Energy Storage System (FESS)

4.    Gravity Energy Storage System (GES)

Then the Chemical Energy Storage Systems, the real battery systems, being:

1.    Lithium-Ion (Li-Ion)                            

2.    Sodium-Sulphur                                

3.    Sodium-ion                                

4.    Lead Acid batteries                                

5.    Zinc Bromine Battery                    

And lastly the Redox Flow Batteries

1.    Vanadium Redox Flow Batteries (VRFBs)

2.    Zinc Bromine Battery

3.    Organic Flow batteries

Finally, are the links for further reading or research.


Abbreviations

AC – alternating current

ACB – air circuit breaker

BESS – battery energy storage system

BMS – battery management system

CAES – compressed air energy storage

CB – circuit breaker

C&I – commercial and industrial

COD – commercial operation date

EFR – enhanced frequency response

EIS – electric insulation switchgear

EMS – energy management system

EPC – engineering, procurement, and construction

ESCO – energy Service Company

ESS – energy storage system

EV – electric vehicle

FES – flywheel energy storage

GES- Gravity Energy Storage

KW – kilowatt

KWh – kilowatt–hour

LA – lead–acid

LCOS – levelized cost of energy storage

LFP – lithium–iron–phosphate

LMO – lithium–manganese oxide

LPMS – local power management system

LSE – load-serving entity

LTO – lithium–titanate

MW – megawatt

NCA – nickel–cobalt–aluminium oxide

PCC – point of common coupling

PCS – power conversion system

PHS - Pumped Hydropower storage

PMS – power management system

PV – photovoltaic

SCS – supervisory control system

SOC – state of charge

SOH – state of heath

UPS – uninterruptible power supply

VRFB – vanadium redox flow battery

VRLA – valve-regulated lead–acid

W – Watt

WTG – Wind Turbine Generator

ZBFB – zinc–bromine flow battery


Background

A 2012 article in Scientific American (SA) written by Nathanial Massey and Climatewire stated; 

“By 2030, scaled-up green power could meet the demands of a large grid 99.9 percent of the time, according to new research from the University of Delaware.” 1 

Although that figure might look somewhat unlikely today the SA article, titled “Solution to Renewable Energy’s Intermittency Problem: More Renewable Energy” went on to suggest that despite the challenges of intermittency; “A mix of offshore and onshore wind, along with contributions from solar power, could provide reliable power flow during all but a handful of days in the hypothetical four-year period under study.”

Inconsistent production of electrical energy; which can be either to little or too much, leads to strains within the power supply grid as other sources look to take up the shortage or curtail production (dump excess power) either state leads to voltage fluctuations within the grid. 

Remarkably Massey continued; “researchers found that scaling up renewable generation capacity to seemingly excessive levels – more than three times the needed load, in some instances – [is the only way to economically deal with intermittency] due to the high systems costs associated with storage technology”. 

Willett Kempton, a professor in the School of Marine Science and Policy at the University of Delaware and a co-author of the study acknowledged “That’s a lot of overbuilding,” [and] much of that excess capacity would be underused during all but a few days a year,”. 

By 2021 the story had some what changed, in December of 2021 the IEA reported that “demand for Global installed storage capacity is forecast to expand by 56% in the next five years to reach over 270 GW by 2026”2 and although intermittency, the intermittent nature of renewable sources (solar or wind) is still considered a significant drawback, the extent of the problem is now considered manageable with articles such as “Renewable Energy’s Intermittency is Not a Showstopper” 3 claiming “The intermittency of renewable energy has raised concerns over potential supply shortages, but technological solutions exist to keep the electricity grid stable.” 

Today batteries have become a commercially viable energy storage technology in most part because the increased use of lithium-ion batteries in consumer electronics and electric vehicles has led to an expansion in global manufacturing capacity which has resulted in a significant cost decrease that is expected to continue over the next few years. The low cost and high efficiency of lithium-ion batteries has been instrumental in a wave of BESS deployments in recent years for large-scale, grid-level deployments that are supplied as modular systems often deployed in standard shipping containers.


History

Traditional electricity supply has been via fossil fuel consumption, primarily coal providing a base load requirement and gas or diesel generation being used to increase supply during peak demand.  Latterly Nuclear power has been used to produce base load power where, similar to coal the nuclear reaction produces heat that is in turn used to turn water into steam that is then used to power turbines which in turn drive generators. Neither of these methods are particularly responsive, that is they cannot react to fluctuations in demand and so excess of energy is consistently produced to absorb low level fluctuations, this practice leads to significant inefficiency in production. In times of increased demand responsive gas or diesel generators “kick in” to provide energy for the peak or increased demand above that being provided by the base load generators. These problems with matching supply with demand have been exacerbated by the introduction of renewable energy into the mix, as they do not produce a regular base load but fluctuate with the power of the wind or the sun, known as intermittency.

As a green alternative to generators, and as a response to intermittency a number of different energy storage systems (ESS) are being developed, the most obvious being batteries. But as well as batteries there are a number of mechanical solutions that have been developed as well.


Mechanical Energy Storage Systems

      1. Pumped Hydropower Storage (PHS)

The most well-known mechanical system is probably pumped water storage or pumped hydropower storage (PHS) as it has been around for many years.  According to the EIA (2023) they are “a type of hydroelectric storage system where water is pumped from a water source up to a storage reservoir at a higher elevation. … They usually pump water to storage when electricity demand … [is] relatively low, and release the stored water to generate electricity during peak electricity demand periods ….”

  

Fig 1a Pumped storage system found at https://blog.yesenergy.com/yeblog/what-is-pumped-hydro-storage-and-how-does-it-work

The first known use cases of PHS were found in Italy and Switzerland in the 1890s, and PSH was first used in the United States in 1930.6 There are two basic systems of PHS, open-loop or closed-loop. Open-loop PHS has an ongoing hydrologic connection to a natural body of water. With closed-loop PHS, reservoirs are not connected to an outside body of water, but with both systems the basics are the same, pumping water up to a holding tank or reservoir for storage and releasing back down to drive a turbine when energy is required. 

This PHS solution is limited by geography; it is only possible where water storage in volume at height is possible, but that has not stopped China moving ahead, building and planning 89GW of installations as shown in Fig 1b.

      2. Compressed Air Energy Storage (CAES)

As early as 1896 compressed air was used in Paris (France) to power homes and industry (U.S. Department of Energy (DoE) 2023) although it was 1978 before the first utility-scale compressed air energy storage (CAES) was built in Germany.7 Similar to pumped water, this solution is limited by geography and the empty subterranean caverns or cisterns that can be used for storage (depleted salt mines, gas wells or similar) where it is compressed for future release again through a turbine to produce energy at a later date.

 

Fig 2 a simplified compressed air system found at https://www.mdpi.com/1996-1073/10/7/991

Compressed air energy storage works by compressing air to high pressure using compressors during the periods of low electric energy demand and then the stored compressed air is released to drive an expander for electricity generation to meet high load demand during the peak time periods.8

There is the potential for compressed air storage underwater in tanks with a constant pressure and variable volume however neither system is discussed here.*

* NB: the description of the CAES compression train and an expander train process is more complicated and involves a number of processes not mentioned here.

It should be noted that both of the PHS and the CAES solutions rely on geographical features to be feasible and so their potential is limited accordingly.

There are 2 other mechanical systems that should also be mentioned, firstly flywheels, and secondly gravity systems.

     3. Flywheel Energy Storage System (FESS)

Flywheel as energy storage device is an age-old concept for storing potential energy and have been used to smooth out the “intermittency” within reciprocating engines and stabilise torque output from at least the early days of steam (circa 1750). An age-old example is the Potter’s wheel where, like the previous example, it uses the inertia of the [fly] wheel and once started keeps on rotating with minimum effort.9 

In the context of renewable energy storage today, “flywheel energy storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy” (Wikipedia 2024) and have great potential for rapid response, short duration, high cycle applications.

 

Fig 3 Flywheel storage system (FES) found at https://electricalfundablog.com/flywheel-energy-storage-calculations-rotor/

The speed of the flywheel increases and slows down as it stores energy and gets discharged, respectively. An M/G (motor/Generator) is responsible for exchanging energy in the two different forms, to and from the rotating flywheel. 11

The flywheels used for energy storage have become increasingly sophisticated than their forebears, with the flywheels rotating in a vacuum to remove air resistance and the generator rotor often taking the place of the actual wheel, but the scientific basis is still the same, inertia of a heavy wheel revolving at speed. FES can be used alone or combined into an “Innovative hybrid system [that] combines a large battery storage system with flywheels to keep the grid frequency stable” (ABB 2022).

     4. Gravity Energy Storage System (GES)

The Gravity Energy System (GES), is an innovative technology to store electricity using the potential energy stored in solid weights lifted against the Earth's gravity force. where the lifting of weights to a significant height is used to store energy and then releasing them when extra energy generation is required.

 

Fig 4 Gravity Storage system, the weights can be lifted into the air or be suspended in old mine shafts below ground. Found at https://www.thermopedia.com/content/10359/

Mechanical ESS (electrical storage systems) are becoming increasingly efficient and today have their place in the energy mix of renewable sources, and are able to contribute to a smooth and provide a stable energy supply.


Chemical Energy Storage Systems

Today by far the most widely used system for commercial (utility scale) energy production are battery based, collectively known as BESS (battery energy storage systems), 

According to the National Grid [UK] “Battery storage technologies are essential to speeding up the replacement of fossil fuels with renewable energy. Energy storage systems will play an increasingly pivotal role between green energy supplies and responding to electricity demands.

 

Fig 5 BESS central to the successful integration and operation of the future electricity grid https://www.siemens-energy.com/global/en/home/products-services/product/battery-energy-storage.html


Battery Solutions

It is likely that utility-scale BESS solution, which already accounts for the bulk of new annual capacity, to grow around 29 percent per year for the rest of this decade,15 as shown in Fig 6. 

A battery energy storage system (BESS) captures energy from renewable and non-renewable sources and stores it in rechargeable batteries for later use. A battery is a Direct Current (DC) device and when needed, the electrochemical energy is discharged from the battery to meet electrical demand to reduce any imbalance between energy demand and energy generation. 

The increase in renewable energy sources and drive to achieve net zero carbon make BESS an essential technology for many commercial and industrial organisations, this expected growth in volume and value is driving innovation within the industry.

    1. Lithium-Ion (Li-Ion)

There are a number of Lithium-Ion batteries, of these “Lithium iron phosphate (LFP) and lithium nickel manganese cobalt oxide (NMC) are the two most common and popular Li-ion battery chemistries for battery energy applications.

Li-ion batteries are small, lightweight and have a high capacity, for BESS applications batteries  safety, charge and discharge performance, efficiency, life cycle, cost and maintenance issues are the points of interest when comparing the different technologies, for most BESS applications the energy density advantage of Lithium batteries is of lesser concern than for example in mobile applications.

Five of the most used Lithium based battery technologies are:

• Lithium Iron Phosphate (LiFePO4) — LFP

• Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) — NMC

• Lithium Nickel Cobalt Aluminium (LiNiCoAlO2) — NCA

• Lithium Manganese Oxide (LiNiMnCoO2) — LMO

• Lithium Cobalt Oxide (LiCoO2) — LCO

 

Fig 7 A comparison between the technologies https://www.efore.com/content/uploads/2020/12/Comparison_of_lithium_batteries_20201209.pdf

Of these technologies, 3 are the primary technologies within residential, commercial and utility BESS units,


Li-ion Chemistry

Description

Lithium Iron Phosphate (LFP)

LFP batteries are designed to handle utility-scale renewable power generation and energy storage capacities up to several hundred megawatt-hours. Without nickel or cobalt, LFP devices are less dense and cheaper to manufacture than NMC and NCA batteries, making them best suited for large installations, see Fig 3.

Lithium Nickel Manganese Cobalt Oxide (NMC)

As can be seen in Fig 3 it is more energy dense than LFP, NMC batteries are frequently used in home solar systems, power tools, and electric vehicles (EVs) as well as utility-level storage.

Lithium Nickel Cobalt  Aluminium Oxide (NCA)

Even denser than NMC chemistry, NCA batteries are typically found in higher-end performance EVs like the Tesla Model X. However it is also the most expensive solution as shown in Fig 3


Fig 8 Most often used Li-ion Chemistry used within differing BESS solutions Based upon the Flexigen (2023) White paper An Introduction to battery Energy Storage Systems (BESS)

“Lithium-ion batteries, which are used in mobile phones and electric cars, are currently the dominant storage technology for large scale plants to help electricity grids ensure a reliable supply of renewable energy.” and are expected to remain the dominant energy storage technology in the short-term.

Of the Li-ion batteries, Lithium Iron Phosphate (LFP) battery delivers the best all round performance for a BESS unit (see Fig 7 and Fig 8) however there are alternatives both chemical and mechanical solutions, some of which are fast becoming an effective alternative.

        2. Sodium-Sulphur (Na-S)

A sodium-sulphur battery is a molten salt-based device. Na-S batteries have several advantages, including high energy and power density, a long lifespan, and reliable operation however a major disadvantage is they must be kept in extreme 300 to 350 degrees Celsius temperatures.

Currently research is underway to reduce the operating temperature with the ultimate goal of room temperature operation.17

This research appears progressing and helping to define sodium as a possible low-cost alternative for the future, with lithium’s sustainability in question and a growing demand for expansive energy storage, the 21st century has marked a return to sodium.

        3. Sodium-ion

Sodium-ion technology is gaining traction, promising sustainability and affordability, especially when contrasted with the widely-used Lithium-Ion (Li-ion) batteries. Sodium-Ion (Na-ion) batteries, much like their Lithium-Ion (Li-ion) counterparts, operate on the principles of electrochemistry. The fundamental process involves the movement of sodium ions between the battery’s two main electrodes: the anode and the cathode. 

In November 2024 Energy Storage news reported that “BYD launches sodium-ion grid-scale BESS product” and announced “Chinese EV giant BYD has launched what an executive claimed is the ‘world’s first high-performance’ sodium-ion BESS product, using its proprietary form factor Long Blade Battery cell.”18

Both India and China are making advances in sodium-ion may be best summed up by Xiaoying You, writing for the BBC; “Even as the rest of the world tries to close its gap with China in the race to make cheap, safe and efficient lithium-ion batteries, Chinese companies have already taken a head-start towards mass producing sodium-ion batteries, an alternative that could help the industry reduce its dependence on key raw minerals.”16 

It is not only China and India, Natron Energy in the USA have entered the sodium-ion space too, they state “[our] batteries and systems outperform lithium-ion and lead acid batteries in power density, recharging speed, and expected lifecycle thanks to our unique sodium-ion battery technology.”17 Founded in 2012, Natron was the first U.S. company to commercially produce sodium-ion batteries, beginning manufacturing in Michigan, USA in 2024.

        4. Lead-Acid (PbA)

Lead-Acid batteries are well-proven within the automotive industry and behind-the-meter grid and UPS applications. PbA batteries are widely available, low cost, widely recyclable, and can perform effectively at both hot and cold temperatures18 and recently have adopted innovations so that today there are number of different battery technologies generally known as valve regulated lead-acid batteries, 3 notable types are: 

 1. lead-gel batteries, 

 2. lead-fleece batteries and 

 3. pure lead batteries

all designed to improve energy density and storage and maintenance requirements.


Lead-gel batteries

Lead-gel batteries use liquid sulfuric acid as the electrolyte, which is bound with silica and equipped with a valve to prevent and electrolyte escaping; because of this sealing they can be used in enclosed spaces and are also effectively maintenance free. These batteries are designed for continuous operation and are suitable for emergency power systems as well as telephone and solar systems. 

Lead-fleece batteries

Lead-fleece batteries, also known as Absorbent Glass Mat (AGM) battery, thanks to the glass fibre fleece, this battery is leak-proof and maintenance-free these batteries are often used where a large amount of energy needs to be stored for a long time, for example, in an emergency power supply. (Reichelt 2022)

 Pure Lead battery

Pure lead batteries are also sealed and use a compound of lead and tin (TPPL) as the electrode inside the battery that results in both a higher cell voltage and increased resistance to high short-circuit currents and are the ideal solution for high-current applications.

All versions of the valve regulated lead-acid batteries function reliably and are known for their long service life. For example, a lead-acid battery used as a storage battery can last between 5 and 15 years, depending on its quality and usage (they are sensitive to deep discharge and so should always be charged to at least 20 percent). The advances in Li-ion battery technology have highlighted the low energy density and slow charge rate of lead batteries, and so they are not often used on a commercial (utility) scale for energy storage.

Specifications

Lead Acid

LFP

NMC

NCA

Nominal voltage (V)

2

3.2

3.6-3.7

3.6-3.7

Typical operating range (V/cell)

1.6 - 2.4

2.5 - 3.6

2.5 - 4.2

2.5 - 4.2

Specific energy (Wh/kg)

30 - 50

90 - 150

150 - 220

150 - 260

Typical charge rate

0.2C

0.5C

0.5C

0.5C

Typical discharge rate

0.1 - 0.5C

1 - 2C

1 - 2C

1 - 2C

Charge temperature (°C)

-20 - 50

0 - 55

0 - 50

0 - 50

Discharge temperature (°C)

-20 - 50

-20 - 55

-20 - 50

-20 - 50

Cycle life (100%DOD)

200 - 300

1000-4000

500 - 2000

500 - 2000

Thermal runaway temp (°C)

100 - 150

270

210

150

Comments

Plastic container softens or melts

Very safe even
if fully
charged

High charge
promotes thermal
runaway

High charge
promotes thermal
runaway

Fig 10 Comparison between the 3 most commonly used Lithium based batteries and 

conventional Lead-Acid batteries

Taken from Comparison of Lithium-ion batteries (white paper) https://www.efore.com/content/uploads/2020/12/Comparison_of_lithium_batteries_20201209.pdf

        5. Zinc Bromine Battery

A zinc-bromine battery is a rechargeable battery that uses the reaction between bromine and zinc metal to produce an electric current with an electrolyte composed of an aqueous solution of zinc bromide. According to research carried by Asif, Zhi, and Chen (2023) “Zinc-bromine batteries (ZBBs) have recently gained significant attention as inexpensive and safer alternatives to potentially flammable lithium-ion batteries.” In 2021 PV Magazine reported the launch of a non-flow zinc-bromide battery based on a stable gel replacing a flowing electrolyte in Australia.

 

Fig 10 Gelion’s redesigned and trademarked non-flow zinc-bromide (ZnBr2) “Endure” batteries produced in Battery Energy’s facility in Sydney

https://www.pv-magazine.com/2021/11/03/zinc-bromide-battery-for-stationary-energy-storage-from-australia/ however most research and commercial success to date has been in the flow battery format.

6. Redox Flow Batteries

Redox Flow Batteries (RFBs) are rapidly emerging as a top choice for energy suppliers, particularly those in the renewable sector. With the increasing awareness of the environmental crisis and the need for sustainable and cost-effective energy storage the use of more abundant materials not only enhances the economic feasibility of redox flow batteries but also reduces the reliance on less abundant resources, creating a truly sustainable energy storage solution.

Flow batteries store energy in liquid electrolyte solutions, but unlike any traditional batteries; the solutions flow between storage tanks with the aid of pumps as shown Fig 11.

Because the redox flow battery stores energy in the solutions, the capacity of the system is determined by the size of the electrolyte tanks, while the system power is determined by the size of the cell stacks as shown in Fig 11 and described by Arévalo-Cid, Dias, Mendes & Azevedo (2021) as “Redox reactions take place inside the cell (marked with a blue dashed rectangle) on the surface of the electrodes (black rectangle). The electrolyte is continuously renewed by pumping the solution from the tanks. The direction of electron flow (charge or discharge) is managed by the electrical components, acting as a power source or loading the energy from the battery.” 

 

Fig 11 General scheme of a Redox Flow battery Retrieved from: https://pubs.rsc.org/en/content/articlelanding/2021/se/d1se00839k#!

6.1. Vanadium Redox Flow Batteries (VRFBs)

The Vanadium Redox Flow Battery is the most prevalent flow battery type and are considered to have a number of advantages over other systems. “These include scalability, long lifespan, instant energy release, superior charge retention, and the ability to discharge fully without incurring any damage.”23

They go on to report that other materials and chemistries are under development too, “with the all-iron systems demonstrating robust performance, durability, and safety.”

RFB systems are already available and have been deployed in the field in commercial conditions, in September 2021 Dr. P. Fischer, reported at the Summer Symposium of the International Flow

Battery Forum, that “there are 41 known, actively operating flow battery manufacturers,” (fig 8) and that some 65% of them were developing VRFB solutions.

 

Fig 12 the number of companies worldwide developing different RFB solutions

Source: https://www.sonar-redox.eu/content/dam/scai/sonar-redox/documents/FLORES-Policy-Brief_October-2021.pdf

In 2021 the largest VRFB project under development was the 200 MW 800 MWh Storage Station designed by Rongke Power of China (Sánchez-Díez et al., 2021)24 the first phase of which (100MW 400MWh)  was connected in September 2022 (Santos 2022).

The Dalian vanadium flow battery station 

Fig 14 The world's largest VRFB, 100MW of power and a capacity of 400MWh. Source: https://www.abc.net.au/news/science/2023-02-02/vanadium-redox-flow-battery-and-future-of-grid-energy-storage/101911604

“The maturity level of VRFBs has resulted in the deployment of this technology all over the world and research is on a good track to improve the performance of this system” (Sánchez-Díez et al., 2021). Currently Redox flow batteries are very large and as such only really of use for major utility integration (Fig 9) and are not envisioned as being used in their present form as residential power sources.

6.2. Zinc Bromine Battery

As touched upon earlier, Zinc Bromine is not only a solid-state battery but also a flow contender. “Zinc–bromine rechargeable batteries (ZBRBs) are one of the most powerful candidates for next-generation energy storage due to their potentially lower material cost, deep discharge capability, non-flammable electrolytes, relatively long lifetime and good reversibility” (Alghamdi et al., 2023)

A number of zinc-based chemistries have been proposed for Redox flow or hybrid flow batteries, some of which have been scaled-up into industrial systems. The ZBRBs flow batteries have been developed like all flow batteries as an alternative to lithium-ion batteries for grid-scale stationary power applications due to their long lifecycle, high safety, sustainability, high theoretical energy density, low cost and the wide availability of active materials.

6.3. Organic Flow batteries

The third class of Redox Flow Batteries noted in Fig 12 are classed as Organic.  “The redox-active organic molecules have leaped to the more important electrolytes than conventional inorganic species because of their structural diversity, tailor ability, and potential low cost” (Cao, Tian, Xu & Wang. 2020) they go on to say that “much research work was conducted on organic electrolytes for designing high-performance aqueous flow batteries.”

For the purposes of this report the different types of RFB have been highlighted purely to make the reader aware of the amount of research currently ongoing and that advances have already been achieved and commercial alternatives to Lithium based batteries are already available. Flow batteries utilize chemical reactions to store and release energy, making them ideal for renewable energy integration, grid-scale storage, and load management.


Conclusion

The greatest question facing the world during the transition away from traditional fuels to 100% clean, renewable energy is whether we can keep the electricity grid stable every minute of every day given the variability of wind and sunlight. This means that grids must become more flexible and resilient and it is the flexibility and resilience that a BESS provides that make it integral to applications during curtailment and providing reserve power when needed.

With BESS units becoming an accepted way of overcoming the intermittency problems of renewable energy sources within a grid ecosystem the systems and materials are developing rapidly. Whereas once it was lithium or nothing (except pumped water in a few geographic locations) now there are a large array of alternatives many of which are gaining in energy density, charging speed, reliability and material sustainability.

Lithium-ion batteries are currently still the most widely used battery solution, however, they come with notable drawbacks. Lithium-ion batteries are prone to overheating and, in extreme cases, can explode and still have the problem of degradation over time, plus ultimately, the source of new lithium for more batteries. 

Lithium-sulphur batteries have been touted as the next-generation energy storage systems with higher energy density, lower production costs, and reduced environmental impact compared to traditional lithium-ion batteries; however they still suffer rapid capacity degradation after 300 cycles.

Sodium-ion batteries are rapidly becoming the alternative to lithium-ion batteries, driven by the abundant and low-cost availability of sodium. Although they do not yet match the energy density of Li-ion batteries, their cost-effectiveness and sustainability make them attractive for grid storage and other large-scale energy applications where being larger and heavier and requiring more space than lithium batteries is not a disadvantage.

Then there are the various Redox Flow Batteries that show great potential especially where the BESS footprint is not of concern. To date the all-vanadium redox flow battery (VRFB) stands out as one of the most advanced RFBs due to its low capital cost, high-energy efficiency (EE) and reliability. Other advantages; it retains its charge over time and does not degrade with use, given the right maintenance they are expected to last many tens of years. It is not only chemistry that is being improved but Electrode and Membrane Innovations are also being made. Researchers have developed graphene-based electrodes for VRFBs using rapid low-pressure combined gas plasma treatments. These electrodes exhibit high catalytic activity, leading to energy efficiencies up to 93.9% at 25 mA/cm². The approach is cost-competitive, this may be good news for Zinc RFBs where membrane degradation remains an area of ongoing research. As mentioned in the text several other promising configurations are being pursued as more and more VRFBs are installed around the world. 

This small research article is meant to make the reader aware that there are alternatives to lithium and that it maybe that one of these alternatives will better suit their application.


Storage news for 2025

Utility size storage is being installed all around the world, including in Switzerland the largest VRFB battery to date, with a total capacity of more than 1.6 GWh and an output of over 800 MW28, a few other notable examples of the scale of investment are:

Australia, investment in large-scale batteries surged, with $2.4 billion committed in early 2025. Six new projects totalling 1.5 GW reached financial close, reflecting the country's commitment to renewable energy integration.

Saudi Arabia awarded contracts for BESS facilities totalling up to 2,500 MW (10,000 MWh), aiming to enhance grid stability and support renewable energy adoption. 

The USA Texas & California: ENGIE North America, in partnership with CBRE Investment Management, is developing 31 BESS projects across Texas and California, adding 2.4GW of capacity to bolster grid resilience.

Recently Kazakhstan has taken significant steps to support the integration of renewables into the local grid by installing storage; Total Energy and Masdar (UAE) are both in the process of developing 1GW wind farms with 600MW of energy storage, and on May 14th it was reported that “UAE, Kazakhstan commit to 2 GW battery storage in wider renewable energy agreement” 29

On May 28th Nazarbayev University hosted a International Business Conference, “The Role of Energy Storage Systems BESS in the energy sector of Kazakhstan” where a white paper was presented, “Application of Battery Energy Storage Systems (BESS) in the Unified Power System of the Republic of Kazakhstan” that “outlines modern BESS technologies, their market costs, international standards applied in BESS project implementation, technical requirements recommended by domestic and foreign experts, as well as recommendations for the regulatory framework governing these technologies in Kazakhstan’s legislation.” it might herald the beginning of an energy storage boom in the country.

Links and further reading

1

SA (2012)

N. Massey & Climatewire (2012). Solution to Renewable Energy's Intermittency Problem: More Renewable Energy. Retrieved 12th February, 2024, from https://www.scientificamerican.com/article/solution-to-renewable-energy-more-renewable-energy/

2

(IEA 2021)

International Energy Asociation (2021) retrieved 16th February, 2024, from  https://www.iea.org/articles/how-rapidly-will-the-global-electricity-storage-market-grow-by-2026

3

 (M. Jacobson 2022)

Mark Z. Jacobson (2022) Renewable Energy’s Intermittency is Not a Showstopper, retrieved from https://physics.aps.org/articles/v15/54

4

(ADB 2018)

Asian Development Bank. (2019). Handbook on Battery Energy Storage System. Retrieved 15th February, 2024, from https://www.adb.org/sites/default/files/publication/479891/handbook-battery-energy-storage-system.pdf

5

EIA (2023) 

 https://www.iea.org/articles/how-rapidly-will-the-global-electricity-storage-market-grow-by-2026

6

DoE 2022

Pumped Storage Hydropower, found at; https://www.energy.gov/eere/water/pumped-storage-hydropower

7

DoE 2023

About Storage Innovations 2030, found at https://www.energy.gov/sites/default/files/2023-07/Technology%20Strategy%20Assessment%20-%20Compressed%20Air%20Energy%20Storage_0.pdf

8

MDPI (2017)

Overview of Compressed Air Energy Storage and Technology Development. Found at https://www.mdpi.com/1996-1073/10/7/991

9

Ratna

Flywheel as Energy Storage Device, found at https://electricalfundablog.com/flywheel-energy-storage-calculations-rotor/

10

Wikipedia 2024

Flywheel energy storage Retrieved 02 March 2024 from https://en.wikipedia.org/wiki/Flywheel_energy_storage

11

Choudhury 2021

Subhashree Choudhury 2021 Flywheel energy storage systems: A critical review on technologies, applications, and future prospects Retrieved 02 March 2024 from https://onlinelibrary.wiley.com/doi/full/10.1002/2050-7038.13024

12

(ABB 2022)

Regenerative drives and motors unlock the power of flywheel energy storage to stabilize Europe’s grids. Retrieved 22nd February 2024 from https://new.abb.com/news/detail/93092/regenerative-drives-and-motors-unlock-the-power-of-flywheel-energy-storage-to-stabilize-europes-grids

13

Thermopedia

Gravity Energy Storage Systems with Weight Lifting found at https://www.thermopedia.com/content/10359/

14

National Grid 2023

What is battery storage? Retrieved 22nd February 2024 from https://www.nationalgrid.com/stories/energy-explained/what-is-battery-storage 

16

Edina 2024

Battery Energy Storage System (BESS). Retrieved 23rd February 2024 from https://www.edina.eu/power/battery-energy-storage-system-bess

17

Lie Wang et. al., 2022

Lei Wang, Tao Wang, Lele Peng, Yiliu Wang, Meng Zhang, Jian Zhou, Maoxin Chen, Jinhui Cao, Huilong Fei, Xidong Duan, Jian Zhu, Xiangfeng Duan, The promises, challenges and pathways to room-temperature sodium-sulfur batteries, National Science Review, Volume 9, Issue 3, March 2022, nwab050, https://doi.org/10.1093/nsr/nwab050

15

Energy Storage news 

Cameron M. 2024. BYD launches sodium-ion grid-scale BESS product found at https://www.energy-storage.news/byd-launches-sodium-ion-grid-scale-bess-product/

16

BBC 2025

Xiaoying You; How electric scooters are driving China's salt battery push, found at https://www.bbc.com/future/article/20250530-how-electric-scooters-are-driving-chinas-salt-battery-push

17

Natron 2025

Natron Energy website, found at https://natron.energy/products

18

Edina 2024

Battery Energy Storage System (BESS) Types of Battery Chemistry Found at https://www.edina.eu/power/battery-energy-storage-system-bess

19

Reichelt 2022

Reichelt elektronik magazine 2022. Everything You Need to Know about lead-Acid batteries. Retrieved 26th February 2024 from, https://www.reichelt.com/magazin/en/guide/everything-you-need-to-know-about-lead-acid-batteries/

20

Asif, Zhi, and Chen 2023

Asif Mahmood, Zhi Zheng, Yuan Chen. 2023 Zinc–Bromine Batteries: Challenges, Prospective Solutions, and Future

21

PV Magazine 2021

Zinc-bromide battery for stationary energy storage from Australia. Retrieved 27th February 2024 from https://www.pv-magazine.com/2021/11/03/zinc-bromide-battery-for-stationary-energy-storage-from-australia/

22

Arévalo-Cid et al., 2021

P.Arévalo-Cid, P.Dias, A.Mendes and J.Azevedo (2021) Redox flow batteries: a new frontier on energy storage. Retrieved February 29th 2024 from https://doi.org/10.1039/D1SE00839K 

23

Nockemann Lab (2019)

Peter Nockemann Research Group. (2019) Redox Flow Battery Research. Retrieved 27th February 2024 from https://www.nockemann-lab.org/research/redox-flow-battery-research/

24

Sánchez-Díez et al., 2021

Eduardo Sánchez-Díez, Edgar Ventosa, Massimo Guarnieri, Andrea Trovò, Cristina Flox, Rebeca Marcilla, Francesca Soavi, Petr Mazur, Estibaliz Aranzabe, Raquel Ferret, Redox flow batteries: Status and perspective towards sustainable stationary energy storage 2021 Journal of Power Sources, Volume 481, 2021, doi.org/10.1016/j.jpowsour.2020.228804.

25

Santos 2022

Beatriz Santos September 29 2022. China connects world’s largest redox flow battery system to grid Retrieved 29th February 2024 from https://www.pv-magazine.com/2022/09/29/china-connects-worlds-largest-redox-flow-battery-system-to-grid/