Residential Energy Storage System: Structure, Working, BMS & Power Solution

1. Background of the Rise of Residential Energy Storage Systems

With the global emphasis on renewable energy and smart grids, as well as the advancement of initiatives like the United States’ “Million Solar Roofs Plan” and Germany’s “Energy Transition”,   have gradually come into the spotlight. Thanks to the government providing high subsidies for the private use of photovoltaic power, more and more households can achieve self-sufficiency in electricity and store excess electricity. This is particularly prominent in the residential energy storage market in Germany and Europe.
In today’s rapidly developing era of intelligence and information, global electricity demand is growing explosively, which has brought energy supply challenges, environmental pollution, and energy consumption issues. As a clean and green way of generating electricity, photovoltaic power generation is favored worldwide. Thanks to policy support and the reduction of power generation costs of photovoltaic energy storage technology, residential photovoltaic power generation and energy storage systems are entering thousands of households. It can not only help households achieve self-sufficiency in electricity and reduce dependence on traditional power grids but also store electricity for emergencies during peak periods of low power consumption.

Residential Energy Storage System

2. Basic Structure and Working Mode of Residential Energy Storage System

(1) Grid-connected Residential Energy Storage System
Components
Solar cell array: It is the core of the system and converts sunlight energy into DC power. Its conversion efficiency, durability, and maintenance cost are key considerations.
Grid-connected inverter: Converts DC power into AC power and is compatible with household electrical equipment. It also monitors and manages the operating status of the system to ensure safety and stability.
BMS management system: Monitors the status of the battery pack, including voltage, current, temperature, remaining power, etc., and balances charge and discharge to ensure battery safety and longevity.
Battery pack: Stores electrical energy. Its capacity, type, and performance affect energy storage capacity and service life. Commonly used batteries include lead-acid batteries, lithium-ion batteries, etc.
AC load: Household electrical equipment such as lamps, TVs, refrigerators, etc.
Working Mode
Mode 1: Photovoltaic provides energy storage and surplus electricity to the grid. When there is sufficient sunlight, part of the solar cell array’s power is used to meet household electricity needs, part is stored in the battery pack, and the excess power is sent to the public grid.
Mode 2: Photovoltaic provides energy storage and electricity for some users. Electric energy is first used to meet household needs, and excess energy is stored in the battery pack. When the battery pack is full, the excess energy is sent to the public grid.
Mode 3: Photovoltaics only provide partial energy storage. Electric energy mainly meets household electricity consumption and battery storage, and does not transmit power to the public grid.
(2) Off-grid Residential Energy Storage System
Main Components
Solar array: Converts solar energy into direct current.
Photovoltaic inverter: In an off-grid system, it not only converts DC power into AC power for home use but also manages the charging process of the battery pack.
BMS management system: Same as the grid-connected system, it manages the status of the battery pack.
Battery bank: Stores electricity for use in the home when the sun is not shining or when electricity demand is peak.
AC load: Household electrical equipment.
Working Mode
Mode 1: Photovoltaics provide energy storage and user electricity (sunny days). The solar array power is used directly by the home and charges the battery bank.
Mode 2: Photovoltaics and energy storage batteries provide users with electricity (on cloudy days). On cloudy days, solar energy production is reduced, and the battery pack releases stored electricity together with photovoltaic electricity for home use.
Mode 3: The energy storage battery provides users with electricity (in the evening and rainy days). Photovoltaics do not produce electricity when the sun sets or on rainy days, and they completely rely on the battery pack for power supply.
Off-grid residential energy storage systems are suitable for areas where the grid is unstable or cannot be connected to the grid, but it has higher requirements for battery pack capacity and management systems.

3. The Role of Battery Management System (BMS) in Residential Energy Storage Systems

The battery management system (BMS) is the “brain” of the residential energy storage system and is crucial.
Main Functions
Data collection and monitoring: Through real-time communication between the BCU (battery control unit) module and the BMU (battery management unit) module, key parameters such as single cell voltage, battery box temperature, and insulation resistance are collected. The charge and discharge current is also collected through the current sensor.
State estimation: Dynamically calculate the battery state of charge (SOC) based on collected data and evaluate the remaining battery power.
User interaction: The real-time battery status, historical data, warning information, etc. are displayed through user interfaces such as touch screens to facilitate user understanding.
System Intelligent Management
Intelligent interaction: BCU intelligently interacts with other system components through an independent CAN bus to ensure that the battery and other devices work together.
Safety control: BMS implements secondary protection of charge and discharge through relays. When abnormal, the power is cut off to prevent battery damage and safety accidents, ensuring the isolation of strong and weak electricity to meet system safety requirements.

4. The Core of Energy Storage System BMS Power Solution: Isolation Voltage Conversion

In the BMS of the energy storage system, the key to power solution design lies in safe and efficient isolation voltage conversion. Considering that the main control unit is based on a 24VDC system and the power requirement is less than 5W, a suitable power supply product can be used.
For example, a power supply product can output 5VDC voltage to power the isolation module and low-dropout linear regulator (LDO); the LDO converts the 5VDC voltage to 3.3V to power the microcontroller (MCU); multiple isolation modules are used in the system to The CAN communication module, voltage and insulation detection circuit, and current detection circuit provide power and isolate the power circuit from the signal circuit and communication module to reduce electromagnetic interference and improve system stability and reliability. In addition, similar automotive-grade power supplies are also widely used in vehicle BMS systems to provide support for vehicle battery management due to their excellent performance and stability.
In short, the residential energy storage system is an important link between the home and new energy. Its structure, working mode, and related battery management and power solutions all play a key role in achieving efficient utilization, stable supply, and sustainable development of home energy. With the continuous advancement of technology and the promotion of applications, residential energy storage systems are expected to play greater value in the future energy field.