Home energy storage is usually used in conjunction with household photovoltaics, and the installed capacity has ushered in rapid growth. Home energy storage system, also known as battery energy storage system, its core is a rechargeable energy storage battery, usually based on lithium-ion or lead-acid batteries, controlled by a computer, and realizes charging and discharging under the coordination of other intelligent hardware and software. cycle. The home energy storage system can usually be combined with distributed photovoltaic power generation to form a home solar energy storage system. From the user side, the home solar energy storage system can reduce the electricity bill while eliminating the adverse impact of power outages on normal life; from the grid side, the home energy storage equipment that supports unified dispatching can alleviate the power shortage during peak hours and save energy. The grid provides frequency correction.
According to the different coupling methods of photovoltaic and energy storage systems, it is divided into DC coupling system and AC coupling system, which are respectively suitable for the incremental market of newly installed photovoltaic systems and the stock market of installed photovoltaic systems.
The larger incremental market space is the main driving force for future market growth:
(1) Incremental market (newly installed photovoltaic + energy storage systems in target households): DC-coupled products are generally used. The DC-coupled energy storage system includes a battery system and a hybrid inverter, which combines the functions of a photovoltaic grid-connected inverter and an energy storage converter. The advantage of DC coupling is that both photovoltaic and energy storage batteries are converted through hybrid inverters, and there is no need to install additional photovoltaic grid-connected inverters. The system integration is higher, installation and after-sales service are more convenient, and it is convenient for intelligent monitoring. and control. Some households that have already installed photovoltaic systems choose to remove the original photovoltaic grid-connected inverter and install a new hybrid inverter.
(2) In the stock market (target households have installed photovoltaics and newly added energy storage systems), AC-coupled products are generally used. It only needs to install batteries and energy storage converters without affecting the original photovoltaic system, and the design of the energy storage system is not directly related to the photovoltaic system in principle, and can be determined according to needs. The advantage of AC coupling is high safety: in AC coupling mode, energy is collected at the AC side, which can be directly supplied to the load or sent to the power grid, or can be directly charged to the battery through the bidirectional converter, and low-voltage PV and low-voltage batteries can be selected. , eliminating the risk of DC high voltage in the energy storage system.
Depending on whether the system is integrated into the grid, home energy storage systems can be divided into grid-connected systems and off-grid systems. The core difference lies in whether they are connected to the grid. Currently, most areas use grid-connected and off-grid integrated systems.
(1) Grid-connected system, photovoltaic and energy storage systems can be connected to the grid, and electricity can be purchased from the grid when the power of photovoltaics or batteries is insufficient. It is suitable for areas with stable power system and relatively low electricity price.
(2) The off-grid system is suitable for areas such as deserts and islands without power grids or areas where the power grid is unstable and needs to be used by itself. Use off-grid energy storage converters, usually with a diesel generator interface, to supplement power when the battery power is insufficient at night. (3) On-grid and off-grid all-in-one machine, with on-grid and off-grid switching function or integrating grid-connected and off-grid modes in one machine, it can switch to off-grid mode during power outage, suitable for unstable power systems and frequent power outages. area.
The core hardware equipment of the home energy storage system includes batteries and converters. According to the degree of integration of the products, there are mainly two modes: all-in-one machine and split machine.
The current market is dominated by split machines, but all-in-one machines are the development trend of the high-end market. :
(1) Split machine, some AC coupling products and DC coupling products adopt the split machine mode, the battery system and the inverter system are provided by the pack manufacturer and the inverter manufacturer respectively, and then through the integrators, distributors, installers Channels reach end users.
(2) All-in-one machine, the product is an all-in-one system including a battery and an inverter, usually an AC-coupled product. Upstream battery systems and inverters provide products as suppliers, usually in the OEM mode. The supplier‘s brand is not displayed in the final product, and the sales and after-sales of the products are all borne by the brand owner.
According to the voltage of the battery pack, it can be divided into high-voltage energy storage batteries and low-voltage energy storage batteries. The industry shows a trend of switching to high-voltage batteries. The main purpose is to improve efficiency and simplify system design, but at the same time, it requires higher cell consistency and BMS management capabilities. High-voltage energy storage batteries usually have a battery pack voltage of more than 48V, and can achieve high-voltage at the battery pack level by connecting multiple cells in series. In terms of efficiency, using batteries of the same capacity, the battery current of the high-voltage energy storage system is smaller, the interference to the system is smaller, and the efficiency of the high-voltage energy storage system is higher; in terms of system design, the circuit topology of the high-voltage hybrid inverter is simpler , smaller size, lighter weight and more reliable. However, high-voltage batteries are composed of multiple cells in series and parallel. The higher the voltage, the more batteries connected in series, and the higher the requirements for the consistency of the cells. At the same time, it needs to cooperate with an efficient BMS management system, otherwise it is prone to failure.
