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BATTERY ENERGY STORAGE What are battery energy storage systems?

From Luke James

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As the need for power system flexibility has grown alongside the rapid decline in the cost of storage technologies, especially lithium-ion batteries, the interest in grid-scale battery energy storage has gained much prominence.

According to recent estimates, the global market for energy storage systems will grow at a compound annual growth rate of 32.8 percent from 2020 to 2025, rising from $2.9 billion in 2020 to $12.1 billion in 2025.
According to recent estimates, the global market for energy storage systems will grow at a compound annual growth rate of 32.8 percent from 2020 to 2025, rising from $2.9 billion in 2020 to $12.1 billion in 2025.
(Source: gemeinfrei / Unsplash)

As more researchers look into battery energy storage as a potential solution for cost-effective, grid-scale renewable energy storage, and governments seek to integrate it into their power systems to meet their carbon neutrality targets, it’s an area of technology that will grow exponentially in value.

In fact, from 2020 to 2025, the latest estimates predict that the global energy storage system market will achieve a compound annual growth rate of 32.8 percent, reaching US$12.1 billion by 2025 from USD$2.9 in 2020.

What is battery energy storage?

Battery energy storage systems are rechargeable battery systems - much like the battery found in your phone is rechargeable - that store energy from renewable sources or the power grid during periods when supply exceeds demand and provides that energy to end users when it’s needed.

Battery energy storage systems are so much more than your bog-standard Li-ion battery, though; they contain advanced technology that regular batteries do not. This allows them to perform tasks such as peak shaving and load shifting.

Generally speaking, the systems work like this:
1. Charging: During daylight hours (or when it’s windy in the case of wind farms) the battery storage system is charged by clean energy generated by the sun’s light.
2. Optimization: Intelligent technology and battery software use algorithms, data, and weather patterns to determine the best time for the stored energy to be used.
3. Discharge: Energy is discharged from the battery and sent to the grid during times of high usage when demand is high. This reduces energy demand charges.

Battery energy storage system applications

Battery energy storage systems have many applications, both commercial and residential. Commercial applications include load shifting, peak shaving, grid services, and emergency backup whereas residential applications also include powering off-grid homes and self-consumption.

Here’s a look at some of these applications in more detail:

Peak shaving
Peak shaving is regarded as one of the most important energy storage applications in commercial settings. For businesses on demand charge utility tariffs, roughly 30 to 70 percent of utility bills can be made up of demand charges, and this can get expensive. However, battery energy storage systems can guarantee that zero power above a pre-defined threshold will be drawn from the power grid during peak times. Instead, it’ll be taken from the battery system, avoiding expensive demand charges.

Load shifting
Battery energy storage systems enable commercial users to shift energy usage by charging batteries with renewable energy or when grid electricity is cheapest and then discharging the batteries when it’s more expensive.

Renewable integration
Battery storage can help to smooth out the output of cyclical renewable power generation sources, i.e., day vs. night, summer vs. winter, high wind vs. low winds. This allows renewable energy production to mimic the consistency and reliability of traditional fossil fuel energy sources.

Types of battery energy storage

Despite its dominance, there’s more to battery energy storage than Li-ion. There are many different battery technologies based on different chemical elements and reactions, including lead-acid and Nickel-Cadmium (Ni-Cd).

Lithium-ion (Li-ion)
Lithium is the lightest of all metals and provides the highest energy possibilities. Rechargeable batteries based on lithium metal anodes can provide huge energy densities, and this is why they’ve become so prolific. Other benefits of Li-ion include high capacity, low internal resistance, and reasonably short charge times.
There are some limitations, however. One of the biggest problems which we’ve covered before is the production of dendrites on the anode which can lead to short circuits and combustion. Li-ion batteries also degrade at high temperatures and when stored at high voltage.

Lead-acid batteries are more common than many people think. They’re based on a negative lead electrode and a positive electrode made of bi-oxide or lead, while the electrolyte is a water-based sulfuric acid solution. The main advantages of lead-acid batteries are low cost and technological maturity. They’ve also got a high specific power, low self-discharge, and perform well at both low and high temperatures.

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A car lead-acid battery after explosion showing brittle fracture in casing ends.
A car lead-acid battery after explosion showing brittle fracture in casing ends.
(Source: Wikimedia Commons)

Lead-acid batteries charge very slowly, requiring up to 16 hours to achieve a full charge. They must also be stored in a charged condition to prevent sulfating, they’re bad for the environment, and they have a limited life cycle which is degraded by repeated deep-cycling. There’s also an inherent risk of explosion due to ‘gassing’.

Nickel-Cadmium (Ni-Cd)
Ni-Cd batteries were the battery technology of choice for portable systems before the onset of Li-ion and other lithium battery technologies. Ni-Cd has strong power performance and can quickly be charged without stressing the system. It’s also got good low-temperature performance, good load performance, and can be stored in a discharged state without degradation.

However, Ni-Cd has a relatively low specific energy when compared with newer systems. It also has a low cell voltage of 1.20 V which means many cells are required in series to achieve high voltage. Cadmium is toxic, too, and it can’t be easily disposed of.