Currently, the regions with the largest installed capacity of household energy storage lithium battery systems in the world such as the United States, Germany, Japan, and Australia, where all have the following things in common. Firstly, the marketization degree of electricity prices is high, and the peak-to-valley electricity price difference range is at the forefront of the world, providing huge profit margins for peak-to-valley arbitrage. Secondly, there is a good foundation for the household photovoltaic development, and there are a large number of single-family residential buildings suitable for laying photovoltaic panels. Thirdly, the stability of energy supply is poor, and the demand for distributed energy products for self-use is high. For example, the stability of power grids in the United States and Australia is poor, and power outages caused by natural disasters occur frequently, while residents have a rigid demand for emergency backup power.
Household energy storage is used for small household backup applications, with general capacities of 5 to 20kWh. In terms of product requirements, on the premise that the electrical and mechanical safety of home batteries are met, the performance requirements focus on long cycle life, wide temperature conditions, high charge and discharge rates, and high energy density. The high voltage of product platforms is an important trend in the development of battery backup for home. The high voltage can reduce the current, thereby reducing the heat generation, and improving the discharge efficiency and safety. With the global popularity of electric vehicles and the continuous increase in the cost of electricity prices for residents, the capacity of home batteries is gradually increasing. The system capacity is expected to gradually increase from 5kWh to more than 15kWh, and the power of household inverter will also increase from 3kW, 5kW to 8kW or even three-phase 10kW or above. Such systems would cover most emergency backup power.
In terms of household battery storage system solutions, many companies are launching battery-inverter all-in-one solutions. Compared with the split-type (battery system and inverter are separated) solution, the all-in-one battery system has the following advantages.
Firstly, the inverter and the battery system are provided by the same supplier, which saves a lot of time and labor costs. Secondly, high degree of integration means easy to plug and play and more friendly to end users, and conducive to system product standardization and large-scale promotion. Thirdly, the battery and inverter can be made into a closed system, that can increase the profit relying on its own brand channel. However, the all-in-one battery system also has difficulties such as low compatibility and difficult design, and dealer acceptance is not as good as the split solutions, and further innovation and improvement are still needed in the future.
In terms of battery solutions, there are various technical solutions for home batteries, including the NMC cylindrical 21700 used in the Tesla Powerwall series, and the LiFePO4 prismatic cells, usually with 50Ah or 100Ah capacity. From the perspective of safety and cost, the short-to-medium term lithium iron phosphate material system is expected to further increase the proportion of household battery storage in the world, but the rapid rise of new materials such as sodium ions will also bring about cost reduction and efficiency increase for household battery storage in the next five years. With new development ideas, the future household battery storage core materials are expected to be a multi-variety coexistence situation.
In terms of inverter solutions, distributed photovoltaic installation is the general direction of household storage applications in the future, and it needs to meet the trend of high-voltage household storage platforms. In this way, the inverter needs to develop in the direction of high-power hybrid (such as three-phase 10-15kW) to meet the multi-functional services of grid connection and energy storage, so as to improve the installation efficiency of home energy storage systems.