PV modules, off-grid inverters (including PV controllers/inverters), energy storage cells (lead-acid/colloid/lead-carbon/ternary lithium/lithium iron phosphate, etc.), PV brackets, cables, and distribution boxes, etc., are all important parts of PV off-grid systems.
The biggest difference between an off-grid system and a grid-connected system is whether the PV system is connected to the grid. Grid-connected systems use investment income as the calculation premise, while off-grid systems use rigid demand power supply as the basic requirement, so they will have a different focus when selecting components.
At the earliest, PV modules were only used in some off-grid systems and small PV systems. Later, with the large-scale development of grid-connected PV applications and the annual update of PV module technology, the conversion efficiency of modules has been greatly improved. Especially for some grid-connected power stations, due to the need to make full use of site resources, more efficient components are especially needed to increase the investment return ratio. Of course, because the general off-grid system has relatively large installation scenarios, it does not have too high requirements on the component conversion efficiency. Therefore, conventional components are often the first consideration in selecting components during system design.
Consider the AC load. General loads are divided into three categories: group loads (lights, heaters, etc.), inductive loads (air conditioners, motors, etc.), capacitive loads (computer mainframe, power supplies, etc.). Among them, since the inductive load requires 3 to 5 times the rated current when starting, and the short-time overload capacity of general off-grid inverters of 150% to 200% cannot meet the requirements, so in terms of inductive loads the capacity expansion design of inverters should be taken into account specially (when the off-grid inverter is connected to an inductive load, at least a system design with at least 2 times the inductive load is required).
1. Lead-acid/gel cell: Energy storage systems generally adopt maintenance-free sealed lead-acid cells, which have excellent self-discharge performance, excellent resistance to vulcanization, and strong resistance to overshoot.
2. Lead-carbon cell: A technology evolved from the traditional lead-acid cell. It can significantly increase the service life of the lead-acid cell by adding activated carbon to the negative electrode of the lead-acid cell. The cell also can be instantly charged with a large capacity. However, as a technological update of lead-acid cells, its cost is slightly high;
3. Ternary lithium/lithium iron phosphate cell: Compared with the above two types of energy storage cells, lithium-ion cells have the characteristics of higher power density, more charge and discharge cycles, and better depth of discharge.
The above is the brief introduction to some basic applications of PV energy storage systems: PV off-grid systems, and to some suggestions on the selection of basic equipment configuration for the PV industry personnel to understand and refer to.