Home energy storage is usually used in conjunction with household photovoltaic power, and the installed capacity has ushered in a rapid growth. Home energy storage system, also known as battery energy storage system, its core is rechargeable energy storage battery, usually based on lithium ion or lead acid batteries, controlled by the computer, and realize the charging and discharge cycle under the coordination of other intelligent hardware and software. Home energy storage systems can usually be combined with distributed photovoltaic power generation to form home light storage systems. From the user side, the home light storage system can eliminate the adverse impact of power failure on normal life. From the power grid side, the home energy storage equipment supporting unified scheduling can relieve the power shortage during peak hours and provide frequency correction for the power grid.
According to the different coupling modes of photovoltaic and energy storage systems, it is divided into DC coupling system and AC coupling system, which are suitable for the incremental market of newly installed photovoltaic systems and the stock market of installed photovoltaic systems, respectively. Greater incremental market space is the main driving force for future market growth:
(1) Incremental market (newly installed photovoltaic + energy storage system for target homes): DC-coupled products are generally used. The DC-coupled energy storage system includes a battery system and a hybrid inverter, which is used as both a photovoltaic grid-connected inverter and an energy storage converter. The advantage of DC coupling is that both photovoltaic and energy storage batteries complete the converter through hybrid inverters, without the need to install additional photovoltaic grid-connected inverters, higher system integration, installation and after-sales service are more convenient, and convenient for intelligent monitoring and control. Some families that have installed photovoltaic systems choose to remove the original grid-connected inverters and install new hybrid inverters.
(2) Stock market (the target home has installed photovoltaic, and added a new energy storage system), and AC coupled products are generally used. Just add the battery and the energy storage converter, the original photovoltaic system will not be affected, and the design of the energy storage system is not directly related to the photovoltaic system in principle, and can be determined according to the demand. The advantage of AC coupling lies in high safety: under the AC coupling mode, the energy is collected at the AC terminal, which can be directly provided to the load or sent to the power grid, or directly charged to the battery through the bidirectional converter. Low voltage PV and low voltage battery can be selected to eliminate the risk of DC high voltage in the energy storage system.
According to whether the system is integrated into the grid, the home energy storage system can be divided into grid-connected system and off-grid system. The core difference is whether it is connected to the grid. At present, most areas use the off-grid all-in-one machine system.
(1) Grid-connected system, photovoltaic and energy storage system can be connected to the power grid, and electricity can be purchased from the power grid when the photovoltaic or battery power is insufficient. Suitable for areas with stable power system and relatively low electricity price.
(2) The off-grid system is suitable for desert, islands and other areas without the power grid or areas where the power grid is unstable and needs self-use. Using off-grid energy storage converters, usually with diesel generator interfaces, to replenish power when battery power is insufficient at night.
(3) Off-grid all-in-one machine, with the function of off-grid switching or grid-connected mode integrated into one machine, can switch into off-grid mode during power failure, which is suitable for areas with unstable power system and frequent power failure.