A battery energy storage system (BESS) is more than just a passive store of electricity. Its true value and power lies in its intelligent operation—a precisely controlled charging and discharging cycle that delivers maximum economic and operational benefits to the business.
See also: What is a Battery Energy Storage System (BESS)?
So how does a BESS know when to “charge” and when to “discharge”? The secret lies in exploiting the cost differential and variability of energy supply. This article will explain the two core operating scenarios in detail, helping you understand how BESS works to optimize efficiency.
1. The “Brain” that Controls Operations – Energy Management System (EMS)
Before going into specific scenarios, it is important to understand that all charging and discharging operations of the BESS are automated and controlled by Energy Management System (EMS).
The EMS acts as the central brain, continuously collecting and analyzing real-time data from multiple sources: grid electricity tariffs, solar power system output, and the plant's electricity consumption needs. Based on advanced algorithms, the EMS will make the most optimal decision: charge, discharge, or maintain the state to achieve the pre-programmed target.
2. Combined with the Electricity Grid – “Business” of Electricity Price Difference (Energy Arbitrage)
This is the basic operating principle and brings the most direct financial benefits to businesses using the national grid, especially with the 3-level electricity price list (off-peak - normal - peak) in Vietnam.
CHARGE Phase: Cheap Energy Storage
- When? During off-peak hours, typically between 22pm and 4am the following morning.
- Why? This is the time when the social demand for electricity is at its lowest, so the electricity price is also the cheapest.
- Work: The EMS system will automatically command the BESS to charge from the grid and fully charge the battery packs.
DISCHARGE Phase: Providing energy in lieu of high-cost grid electricity
- When? During peak hours, usually morning (9:30 – 11:30) and afternoon (17:00 – 20:00).
- Why? This is when the demand for electricity from both factories and society as a whole skyrockets, leading to the highest electricity prices.
- Work: Instead of having to buy expensive electricity from the grid, EMS will control BESS to release the energy stored at night to supply production activities.
Result: By purchasing cheap electricity and using it instead of expensive electricity, businesses can significantly reduce the cost of their monthly electricity bills. This strategy, called “load shifting,” helps smooth out the electricity consumption curve and reduce pressure on the national grid.
3. Integration with Renewable Energy – Maximizing Investment Efficiency
For businesses that have installed rooftop solar power systems, BESS acts as the “missing piece”, solving the inherent problem of incompatibility between generation time and usage time.
CHARGE phase: Store “pure gold” of solar energy
- When? At noon, especially on sunny days.
- Why? This is the time when the solar power system reaches its peak output, but the plant’s consumption demand may not be as high, resulting in a large amount of excess electricity. Without a BESS, this electricity may be wasted or sent back to the grid at a low price (or with limited output).
- Work: EMS will detect excess solar power and immediately redirect this energy flow to charge the BESS system.
DISCHARGE Phase: Use solar energy 24/7
- When? In the evening, at night, or on cloudy, less sunny days.
- Why? This is when the solar system no longer produces electricity, and the business must return to using grid power.
- Work: EMS will mobilize clean solar energy that has been "stored" in BESS during the day to supply to the loads.
Result: BESS helps businesses make the most of every kWh of solar power generated, increasing their energy self-sufficiency and maximizing the efficiency of their renewable energy system investments. This reduces their dependence on the grid and moves them closer to a sustainable operating model.
4. Technical Connection Method
Technically, the integration of BESS with existing solar power systems can be done in two main ways:
- AC Coupling: The BESS system is connected to the alternating current (AC) side of the power system, operating independently of the solar power system. This solution is very flexible and can be easily installed as an addition to existing solar power systems.
- DC Coupling: The BESS system and solar panels are connected to the DC side and share the same inverter. This solution is often more efficient due to the reduced number of energy conversions and is suitable for new installation projects.
Which option you choose will depend on your current system configuration and your business goals.
The operating principle of BESS is not complicated but extremely effective. By charging and discharging energy strategically, controlled by an intelligent management system, BESS turns energy into a flexible asset. It allows businesses to proactively “buy low, use high” with grid electricity and “store for later” with solar energy.
Understanding this principle is the first step to realizing the huge potential that BESS can bring, not only helping to save costs but also increasing the stability and sustainability of production and business operations.
See more: Detailed Structure of a BESS Container System: What's Inside?
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