ESS: Everything About the Giant Battery That Stores Electricity

The Principles, Cases, and Future Prospects of Energy Storage Technology That Changes the World

• Understand why ESS (Energy Storage System) is essential in the renewable energy era.
• Confirm the economic and technical effects through real ESS use cases in Australia and South Korea.
• Compare various ESS technologies such as pumped hydro and flow batteries beyond lithium-ion batteries.

What is ESS? The Emergence of a Giant Auxiliary Battery

Think of a ‘power bank’ that saves us when our smartphone battery runs low. Now imagine scaling that power bank up so large it can light up an entire city. This sci-fi-like idea is the core of the Energy Storage System (ESS). ESS is literally a huge warehouse and auxiliary battery that stores produced energy.

Electricity is a tricky energy form that disappears if not consumed immediately upon production. In the fossil fuel era, power plants adjusted output as needed to solve this, but renewable energies like solar and wind introduced new challenges.

Solar power generates large amounts of electricity only during bright midday, and wind power only on windy days. However, peak electricity demand usually occurs in the evening after sunset. This mismatch between surplus energy times and demand times was the biggest weakness of renewable energy.

This is where ESS steps in as the savior. ESS stores the surplus energy gifted by sunlight and wind and reliably supplies it during peak demand times. This transforms the erratic output of renewables into a dependable 24-hour energy source.

Beyond simply ‘storing’ energy, ESS innovates the ’time value’ of electricity. For example, solar power during midday has low value due to oversupply, but if ESS stores this energy and supplies it during evening peak demand, it becomes high-value energy. ESS is thus an alchemist turning wasted energy into gold and the key to the renewable energy era.

Case Study: Tesla ESS Battery That Saved Australia

In 2016, South Australia faced a severe energy crisis due to a large-scale blackout. At that moment, Elon Musk made a bold promise on Twitter:

“If we don’t build a 100MW battery storage facility within 100 days, we won’t charge a cent.”

This provocative offer became reality. Tesla completed construction in just 63 days, creating the ‘Hornsdale Power Reserve (HPR)’. Located next to the Hornsdale wind farm, this massive lithium-ion battery was the world’s largest at the time and immediately became a ‘game changer’ for Australia’s power grid.

HPR’s main mission was to stabilize grid frequency. When a nearby coal plant unexpectedly shut down, HPR responded in less than 0.1 seconds, supplying 7.3MW of power and preventing a blackout. Compared to gas plants that take minutes to respond, this was revolutionary.

Even more impressive were the economic effects. Since HPR’s launch, frequency control service costs in South Australia dropped by 91%, and consumers saved over AUD 150 million (about KRW 130 billion) in the first two years.

Game-Changing Impact of Hornsdale Power Reserve (HPR)

The HPR project not only resolved South Australia’s energy crisis but also proved ESS’s economic value globally.

ESS Usage in South Korea: From Factories to EV Charging Stations

Does Australia’s story feel distant? ESS is already quietly but powerfully changing our daily lives.

A. Smart Factories’ Secret to Reducing Electricity Bills: Peak Shaving

Factory electricity bills are based on the highest instantaneous power usage (‘peak demand’). Even a brief spike can lead to high annual fees.

ESS installed in ‘Smart Green Industrial Complexes’ in Changwon and Gumi performs ‘peak shaving’ by charging at cheap nighttime rates and discharging during expensive daytime peaks. This reduces grid power draw, lowers peaks, and cuts electricity costs.

Changwon National Industrial Complex linked ESS with Factory Energy Management Systems (FEMS), achieving 6–7% average energy cost savings, with some companies saving over 20%.

B. AI-Enabled Public Buildings: Smart Energy Managers

Gyeonggi Province is installing AI-powered advanced ESS in six public buildings across five cities including Goyang and Ansan.

The AI analyzes building power usage patterns, weather forecasts, and real-time electricity prices to autonomously determine the most economical charging and discharging times. AI-based ESS not only maximizes energy efficiency but also monitors battery health in real time to detect fire risks and other anomalies, greatly enhancing safety.

C. ESS Unlocks Uninterrupted Ultra-Fast EV Charging

Ultra-fast chargers, which draw massive instantaneous power, strain existing grids and hinder EV adoption.

Korean startup ‘Standard Energy’ introduced a 100% standalone ultra-fast charging station disconnected from the grid. It stores solar power in a vanadium-ion battery (VIB)-based ESS and releases large power bursts on demand for ultra-fast EV charging.

This is possible thanks to ESS’s ‘grid-forming’ technology, which actively creates stable voltage and frequency, forming a ‘microgrid’. ESS thus acts as an active power source, not just passive storage. The vanadium-ion battery uses water-based electrolyte, making it structurally fire-safe and ideal for urban charging stations.

Beyond Batteries: The World of Various ESS Technologies

When we think of ESS, lithium-ion batteries come to mind, but energy storage methods are far more diverse. Initially, I thought of ESS simply as a ’large power bank,’ but the deeper I looked, the more it seemed a paradigm-shifting innovation.

A. Giant Water Battery on a Mountain: Pumped Hydro Storage (PHS)

Pumped Hydro Storage is the oldest and most widely used large-scale energy storage, accounting for about 66.5% of global ESS capacity.

The principle is simple: at night when power use is low, surplus electricity pumps water from a lower reservoir to an upper reservoir, storing potential energy. When demand spikes, water is released to spin turbines and generate electricity. It’s a huge gravitational battery. Advantages include massive capacity and decades-long lifespan, but drawbacks are high construction costs and limited suitable locations.

B. Underground Air Battery: Compressed Air Energy Storage (CAES)

CAES stores energy by compressing air into underground spaces like abandoned mines or salt caverns. Surplus power compresses air stored underground, which is later released to drive turbines when needed. It allows large-scale storage but has low energy density and requires specific geological conditions.

C. Fire-Safe Liquid Battery: Flow Battery

Flow batteries are gaining attention as a safer alternative to lithium-ion batteries. The representative vanadium redox flow battery (VRFB) stores energy in liquid electrolytes held in external tanks.

Their greatest strengths are safety and lifespan. The water-based electrolyte is inherently non-flammable, and the batteries can last over 20 years with more than 20,000 charge-discharge cycles. If lithium-ion batteries are sprinters excelling at speed, pumped hydro and flow batteries are marathoners specialized in long-duration energy supply. The coexistence of these diverse technologies will define the future energy market.

Conclusion

Today, we journeyed through the world of ESS, the giant auxiliary battery that stores electricity. From this, we confirmed several key facts about ESS:

• Essential Link in the Renewable Energy Era: ESS is the core technology that makes the unpredictable natural energy usable 24/7. True carbon neutrality is impossible without ESS.
• Proven Economic Value: ESS not only stores energy but stabilizes grids, reduces consumer costs, and enhances corporate competitiveness, creating real economic value.
• Technological Evolution and Diversity: ESS is evolving beyond lithium-ion batteries into pumped hydro, compressed air, flow batteries, and more. Each technology offers optimal solutions for different purposes and environments, ushering in an era of ’energy storage technology mix.’

ESS is no longer a distant future technology. It is the key to a cleaner, safer, and more sustainable energy future we dream of. What energy transition efforts are happening in your area? Why not take an interest in your community’s energy self-sufficiency plans?