Home storage products: towards all-in-one machine and higher charging capacity
Product: supporting demand for stock and incremental household PV market
Household energy storage is usually used in combination with household photovoltaic, and the installed capacity is experiencing rapid growth. The core of the household energy storage system, also known as battery energy storage system, is a rechargeable energy storage battery, which is usually based on lithium ion or lead-acid batteries, controlled by a computer, and realizes charging and discharging cycles under the coordination of other intelligent hardware and software.
The home energy storage system can usually be combined with distributed photovoltaic power generation to form a home optical storage system. From the user side, the home optical storage system can eliminate the negative impact of power failure on normal life while reducing the electricity bill; From the grid side, the household energy storage equipment supporting unified dispatching can alleviate the power shortage during peak hours and provide frequency correction for the grid.
According to the different coupling modes of photovoltaic and energy storage systems, they are divided into DC coupling systems and AC coupling systems, which are respectively suitable for the incremental market of newly installed photovoltaic systems and the stock market of installed photovoltaic systems. Greater space for incremental market is the main driving force for future market growth:
(1) Incremental market (photovoltaic+energy storage system newly installed in target households): generally, DC coupled products are used. The DC coupled energy storage system includes a battery system and a hybrid inverter. The hybrid inverter has the functions of both photovoltaic grid connected inverter and energy storage converter. The advantage of DC coupling is that both photovoltaic and energy storage batteries are converted through hybrid inverters, and no additional photovoltaic grid connected inverter is required. The system integration is higher, installation and after-sales service are more convenient, and intelligent monitoring and control are also convenient. Some families that have installed PV systems choose to remove the original PV grid connected inverter and install a new hybrid inverter.
(2) In the stock market (the target households have installed photovoltaic and newly added energy storage systems), AC coupling products are generally used. Only batteries and energy storage converters need to be installed, which will not affect the original photovoltaic system. In principle, the design of the energy storage system is not directly related to the photovoltaic system, which can be determined according to the needs. The advantage of AC coupling lies in high safety: in the AC coupling mode, the energy is gathered at the AC terminal, which can not only be directly provided to the load or sent to the power grid, but also can be directly charged to the battery through the bidirectional converter. Low voltage PV and low-voltage batteries can be selected to eliminate the DC high-voltage risk in the energy storage system.
According to whether the system is connected to the power grid, the household energy storage system can be divided into grid connected system and off grid system. The core difference lies in whether the system is connected to the power grid. At present, most regions use the parallel off grid integrated system.
(1) Grid connected systems, photovoltaic and energy storage systems can be connected to the grid, and power can be purchased from the grid when photovoltaic or battery power is insufficient. It is suitable for areas with stable power system and relatively low electricity price.
(2) Off grid system is suitable for desert, island and other areas without power grid or areas where the power grid is unstable and needs self use. The off grid energy storage converter is usually equipped with a diesel generator interface to supplement power when the battery power supply is insufficient at night.
(3) The parallel and off grid integrated machine has the parallel and off grid switching function or integrates the parallel and off grid modes into one machine, which can complete the switching into the off grid mode in case of power failure. It is suitable for areas with unstable power systems and frequent power outages.
The core hardware equipment of the household energy storage system includes batteries and converters. According to the degree of product integration, there are mainly two modes: integrated machine and split machine. The current market is dominated by split machine, but the integrated machine is the development trend of the high-end market:
(1) Split machine is adopted for some AC coupling products and DC coupling products. The battery system and inverter system are provided by pack manufacturers and inverter manufacturers respectively, and then reach the end users through the channels of integrators, dealers and installers.
(2) All in one machine, the product is an all in one machine system including battery and inverter, usually an AC coupling product. The upstream battery system and inverter, as suppliers, usually adopt the OEM mode. The final product does not show the supplier's brand, and the product sales and after-sales are all undertaken by the brand.
According to the voltage of the battery pack, it can be divided into high-voltage batteries and low-voltage batteries. The industry has shown 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 batteries usually have a battery pack voltage of more than 48V, which can be achieved by connecting multiple cells in series. In terms of efficiency, with the same capacity of batteries, the battery current of the high-voltage energy storage system is small, and the interference to the system is small. 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, lighter and more reliable. However, the high-voltage battery is composed of multiple cells in series and parallel. The higher the voltage, the more batteries in series, and the higher the requirement on the consistency of the cells. At the same time, it needs to cooperate with the efficient BMS management system, otherwise it is easy to have failures.