1. The Composition of Off-grid PV System
Figure 1 is the schematic diagram of a typical off-grid PV system.
Figure 1. Composition of Off-grid PV System
2. Major Components of Off-grid PV System
1). Solar-cell Array. It is the core component of the system, convert solar energy into electric energy. The solar cell modules are installed in series or in parallel in accordance with the requirements of different systems.
2). Battery. Store the electric energy generated by solar-cell array so as to supply power at the following conditions: light deficient conditions, nights, or when load demand is higher than power supply of the array. The most widely applied batteries in PV systems are lead acid batteries.
3). PV Controller. It is the core control section of the whole system, controlling the charge/discharge of batteries and the electrical power output of the array and battery pack. Currently, there are mainly two widely applied control modes: PWM and MPPT. The PWM has higher control efficiency but relatively lower utilization rate to solar modules; while MPPT has relatively lower control efficiency but higher utilization rate to solar modules. In most cases, PWM mode is applied in system with smaller power, and MPPT mode is applied in system with lager power, especially when system power is higher than KW level.
4). Inverter. If AC Load is included in the system, inverter is needed to concert direct current from solar-cell array or battery pack into needed alternate current.
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