Off grid solar PV system can be a DC power source connected to directly to a DC load. The DC power can also be stored in battery and fed to the load i.e. a DC electric fan or a DC water pump. While connecting solar PV system with a DC load it is important to have a DC/DC converter which brings the solar PV output in line to the DC load requirement.
If the load requirement is of AC type, a DC/AC converter (inverter) is used which has inbuilt charge controller to control the battery charging. There are various algorithms used for operating the inverters at MPPT (maximum power point tracking).d
Battery is the weakest link in an off grid solar PV system as it has limited life and also leave to charging and discharging losses. There are intelligent charge controller which recognise the variation in battery charge voltage and align themselves these are typically known as battery charge equalizers. In many off grid systems battery can be avoided and variation in current & voltage can be controlled in a solar PV output through installation of variable frequency drive (VFD). A typical example of VFD system is running of an existing water pump through an inverter with VFD. The variation of voltage & current in solar PV output due to variability of solar radiation are absorb through variation of frequency in VFD & the output of VFD is relatively constant voltage & current at a variable frequency.
Article By: Dr. Sanjay Vashiahtha & Kapil Dev SHarma