Preface

At the outset of the 15th Five-Year Plan, the state has set a clear target: by 2030, installed capacity for new‑type energy storage will more than double, rising from 136 million kilowatts to 300 million kilowatts. Over the next five years, annual additions are expected to exceed 30 million kilowatts, signaling that energy storage has evolved from an optional ancillary measure into an essential standard configuration.

The industry is booming, but breaking in isn’t easy. Battery‑cell specifications evolve annually, with a wide array of competing technological pathways; add to that acronyms like SOC, SOH, DOD, BMS, PCS, EMS, and more, and newcomers can quickly find themselves in the frustrating situation of recognizing every individual term yet being unable to make sense of the whole.

This article covers four key sections: battery cell specifications, application scenarios, core systems, and technological roadmaps. Whether you’re a newcomer to the industry or a professional tasked with educating clients, it’s well worth bookmarking.

I. Six Key Parameters of a Battery Cell

1. Cell Capacity (Ah) — How much “capacity” does a single cell have?

Cell capacity is expressed in ampere-hours (Ah), which can be thought of as the battery’s “fuel tank volume.” With a nominal voltage of 3.2 V, the amount of charge stored in a single cell is approximately:

Capacity (Ah) × 3.2 V = Energy (Wh)

Taking a 314 Ah battery cell as an example: 314 Ah × 3.2 V ≈ 1 kWh. With ongoing technological advancements, higher-capacity cells have also entered mass production, with individual cells capable of storing roughly 2 kWh or more.

The direct benefit of increased capacity is that the same number of cells can store more energy, while system integration and cost-effectiveness are significantly improved.

2. SOC (State of Charge) — the battery’s “fuel gauge”

SOC, or State of Charge, represents the battery’s remaining capacity as a percentage.

100% = Fully charged

0% = Empty battery

It follows the exact same logic as the battery‑level indicator in the upper‑right corner of your phone.

3. SOH (State of Health) — the battery’s “physical age”

SOH, or State of Health, reflects the degree of aging of a battery relative to its condition at the time of manufacture.

The SOH of the new battery is 100%.

As the number of charge–discharge cycles increases, the SOH gradually declines.

The industry regards a SOH of 80% as the reference threshold for battery life.

⚠️ Note: A SOH drop to 80% indicates that the battery cells no longer meet the design and operational requirements of the energy storage power station. In project economic assessments, reaching an SOH of 80% marks the end point of the full‑life‑cycle revenue model.

4. DOD (Depth of Discharge) — How much battery capacity is used each time?

DOD stands for Depth of Discharge, which refers to the ratio of the amount of energy discharged during a single cycle to the battery’s total capacity.

For example:

After a full charge, discharge until 10% remains → DOD = 90%

Discharge until 50% remaining, then stop → DOD = 50%

5. Cycle Life — How many charge–discharge cycles can the battery endure?

Cycle life refers to the number of complete charge–discharge cycles a battery can undergo under specified conditions before its state of health (SOH) declines from 100% to 80%.

A few key facts:

Currently, mainstream lithium iron phosphate cells used in energy storage applications are required to have a cycle life of no less than 8,000 cycles at the large‑scale energy storage cell level.

However, in actual operation, due to temperature fluctuations, changes in operating conditions, and cell‑to‑cell consistency, the system‑level cycle life typically falls short of the cell‑level nominal value. Industry standards stipulate that the system level must achieve at least 6,000 cycles.

Achieving 6,000 to 7,000 effective full cycles already represents the system-level benchmark of leading manufacturers.

6. Energy density — How much electricity can be stored per unit volume?

Energy density refers to the amount of energy a battery can store per unit mass or per unit volume.

As battery cell technology continues to evolve, energy density has steadily increased. The capacity of a 20-foot energy storage container has risen from an early 3.44 MWh to over 6.25 MWh.

II. Three Mainstream Monetization Models for Energy Storage

1. Peak–Valley Arbitrage — The Most Fundamental Source of Returns

By leveraging time-of-use pricing, charge during off-peak hours and discharge during peak hours:

Charging and energy storage during low‑price periods (e.g., noon or late night)

Peak electricity price periods (e.g., morning/evening) → discharge for use or sell electricity

This is currently the most fundamental and core source of revenue for commercial and industrial energy storage projects. The level of returns depends on the peak‑to‑valley price spread: the wider the spread, the faster the investment can be recouped.

2. Frequency Regulation — The “Emergency Response Team” of the Power Grid

The frequency of the power system must remain stable at 50 Hz. In the event of a sudden disturbance, such as the tripping of a large generating unit, the frequency can drop rapidly within a few seconds.

The advantages of energy storage lie in its response time, which can reach the millisecond level—typically less than 200 milliseconds—enabling it to instantaneously inject or absorb power before thermal power units can react, thereby providing rapid support to the grid.

3. Source–Grid–Load–Storage Integration — The Ultimate Form of the New Power System

Integrate the power supply, grid, load, and energy storage into a unified system for coordinated planning and operation.

In simple terms: By leveraging power forecasting and optimized dispatch, we achieve precise alignment between the amount of electricity generated and the amount consumed.

When photovoltaic or wind power generation is at a high output → energy storage charges to absorb the excess power.

During peak electricity demand → Energy storage discharges to provide supplemental power.

This is the typical architecture of the new‑generation power system and also the direction of future large‑scale grid development.

III. The Four Core Subsystems of Energy Storage

1. BMS (Battery Management System) — the “personal bodyguard” of the battery cells

The BMS is responsible for real-time monitoring and protection of each cell’s voltage, temperature, and state of charge.

One of its most essential functions is state-of-charge balancing—coordinating the conditions of each battery cell to prevent any single cell from overcharging or overdischarging. You can think of it as a classroom teacher, ensuring that every student (battery cell) keeps up with the pace, neither falling behind nor rushing ahead.

New challenge: High-capacity battery cells generate more heat and exhibit more complex internal current distribution, placing higher demands on the BMS’s monitoring accuracy and balancing capabilities.

2. PCS (Power Conversion System) — the “translator” between AC and DC

Batteries store direct current (DC), while the power grid transmits and uses alternating current (AC). A conversion between the two is required, and this function is performed by the power conversion system (PCS).

PCS achieves bidirectional conversion:

During charging: AC → DC (electricity from the grid is stored in the battery)

During discharge: DC → AC (the battery’s electricity is supplied to the grid or to a load).

The performance of the PCS directly determines the grid‑connection quality and response speed of the system, making it the core power component of the energy storage system.

3. EMS (Energy Management System) — the “brain” of the entire power plant

EMS serves as the dispatching hub for energy storage power stations.

It automatically formulates charging and discharging strategies based on the following information:

Electricity price signals (when prices are high and when they are low)

Load forecasting (what will electricity demand be in the future)

Equipment status (health information reported by the BMS and PCS)

The ultimate goal is to determine the optimal timing for energy storage and release, thereby maximizing returns. At the same time, the EMS provides comprehensive oversight of safe equipment operation, serving as the central decision-making layer that ensures both profitability and safety for the energy storage system.

4. Liquid Cooling and Air Cooling — The Battery’s “Air Conditioning System”

Significant heat is generated during battery charging and discharging, necessitating the installation of a thermal management system.

Air cooling: Heat dissipation through air convection.

Advantages: simple structure, low cost

Drawbacks: Cooling uniformity is relatively poor, and the temperature difference between cells is significant.

Liquid cooling: dissipates heat through the circulation of a coolant.

Advantages: Fast cooling rate; temperature differences between cells can be kept within 2–2.5°C.

Drawbacks: Higher cost and the risk of coolant leakage (requiring an electrical–water isolation design).

For high-capacity battery cells with more concentrated heat generation, liquid cooling has become the mainstream solution, with its penetration rate exceeding 75% in large-scale grid‑side energy storage projects. Air cooling is now reserved for only a few low‑power applications or scenarios where cost sensitivity is extremely high.

In addition to temperature control, another critical subsystem that cannot be overlooked is the fire‑protection system. The “Design Standard for Electrochemical Energy Storage Power Stations” (GB/T 51048‑2025), which came into effect in April 2026, explicitly mandates that lithium‑ion battery rooms and prefabricated modules must be equipped with automatic fire‑extinguishing systems—this constitutes a stringent prerequisite for passing safety inspections and obtaining operational approval.

IV. Two Major Technological Approaches

1. Lithium Iron Phosphate (LFP) — The Clear Market Leader

Currently, battery technologies hold an overwhelming dominant position in the electrochemical energy storage sector, accounting for approximately 82% of the market share and continuing to grow.

On what grounds?

Cost control: Mature raw material supply chain

Good safety: high thermal runaway temperature, unlikely to catch fire.

Long cycle life: The system‑level effective full‑cycle life typically ranges from 6,000 to 7,000 cycles. Based on an average of one charge–discharge per day, this translates to a practical service life of 16 to 19 years, comfortably exceeding the 15–20‑year design lifespan of energy storage power stations.

Lithium iron phosphate is the cornerstone of current technological advancement. The key challenge in its evolution lies in the fact that, as capacity increases, achieving uniform distribution of current and temperature within the cell becomes increasingly difficult, necessitating continuous breakthroughs in material formulation and electrode design.

2. Sodium-ion batteries — an important complementary technology

It is regarded as an important complementary pathway to lithium iron phosphate batteries, rather than a substitute.

Advantages of sodium:

Excellent low-temperature performance: maintains high capacity even in environments as cold as −20°C.

High safety: The risk of thermal runaway is significantly lower than that of lithium batteries.

Current limitations:

Its energy density remains slightly lower than that of mainstream lithium iron phosphate, resulting in a larger battery pack volume for the same capacity.

Mass-production volumes are still ramping up, and the supply chain’s level of maturity lags behind that of lithium iron phosphate.