PV energy storage system, generally refers to applications with PV modules, including energy storage batteries and other related equipment in the system. According to whether the stored energy needs to be sold on the grid, PV energy storage system can be divided into PV off-grid system and PV on/off-grid hybrid system. Here, we mainly focus on the PV off-grid system to make a brief introduction.
PV off-grid system components:
PV modules, off-grid inverters (including PV chargers/inverters), energy storage batteries (lead-acid/colloid/lead-carbon/tertiary lithium/ lithium iron phosphate, etc.), PV mounts, cables, and distribution boxes are all important components of off-grid PV systems.
Modules:
In the early days, PV modules were only used in some off-grid systems and small PV systems. Later, along with the wide range of grid-connected PV applications, as well as PV module technology updates year by year, module conversion efficiency has been greatly improved. Especially for grid-connected power plants, more efficient modules are needed to improve the ROI ratio because of the need to make full use of site resources. Of course, generally off-grid systems are not too demanding on module conversion efficiency due to the relatively large sites, so conventional modules are often the first consideration when choosing modules for system design.
Off-grid inverter:
1.Take AC load as the point of consideration. Generally, there are three types of loads: group loads (lights, heaters, etc.), inductive loads (air conditioners, motors, etc.), and capacitive loads (computer mainframe power supplies, etc.). Among them, since the current required for inductive loads to start is 3~5 times of the rated time, and the short-time overload capacity of 150%-200% of general off-grid inverters does not meet the requirements, inductive loads need special consideration for inverter capacity expansion design (when off-grid inverters are connected to inductive loads, at least 2 times more system design is required for inductive loads).
2.Take the DC side as a point of consideration. Off-grid inverters have built-in PV chargers, generally of two types, MPPT and PWM. As technology updates, PWM chargers are being phased out and MPPT chargers are becoming the preferred choice for off-grid inverters.
Energy storage batteries:
1.Lead-acid/colloid batteries: Energy storage systems generally choose maintenance-free sealed lead-acid batteries to reduce later maintenance. After 150 years of development, lead-acid batteries have significant advantages in terms of stability, safety and price, and they are both the battery type with the highest percentage of energy storage battery applications and the preferred energy storage battery type for off-grid PV systems.
2.Ternary lithium / lithium iron phosphate batteries: lithium-ion batteries have higher power density, more cycles of charge and discharge, better depth of discharge and other characteristics. However, due to the need for additional battery management technology (BMS), the system cost of ternary lithium / lithium iron phosphate batteries, generally 2-3 times more than lead-acid batteries. In addition, compared to lead-acid, its thermal stability is also slightly less, so the proportion of applications in the PV off-grid system is not high.