Islanding occurs when a solar rooftop system continues to supply to a load even when the grid is down; this can be very dangerous. Therefore, when the grid is down, the inverter, used in the rooftop system solar power plant for generating solar energy for home/industrial/commercial roof top, stops supplying power. This is a technical requirement for inverters strictly mandated by CEA and MNRE. However, in view of frequent grid outages in most States, particularly in industry, commercial and institutional establishments, the rooftop system should be able to disconnect from the grid and continue to supply solar power to the loads of such establishments using a battery storage system or in synergy with the backup diesel generator, else the solar power will be wasted. This is possible through additional advanced features to be provided in inverters – the hybrid inverter which could work in the off-grid mode and continue to charge batteries which power certain loads, or the inverter can continue to function in grid-tied mode in synergy with the larger backup diesel generator. For most industrial, commercial and institutional establishments, the second option is more feasible as they have large existing backup diesel generators for their loads. Such backup facilities already have the required safety features which prevent reverse flow to the grid. Rooftop solar with the right type of inverter is, therefore, technically feasible even when the grid is down, and can also be more cost-effective compared to costlier diesel generation. For harnessing the full potential of rooftop solar as envisioned by Government, CEA and MNRE should consider allowing such ‘intentional islanding' in rooftop projects and formulate technical specifications of inverters with such additional advanced features for automatic and safe operation.
Ref: Grid Integration of Distributed Solar Photovoltaics (PV) in India, Prayas Energy Group, 2014