Technical requirements for grid connected rooftop PV systems

Government of India launched its National Solar Mission in January 2010 with a targeted installation of about 20 GW of solar electricity by 2022 under the Jawaharlal Nehru National Solar Mission (JNNSM). The first phase targets were of the order of 1000 MW by 2013, the second phase targets were set to be about 4000 MW by 2017, and in the third phase the targets were set to be of the order of 20000 MW. The first phase has observed a remarkable attention of and achieved installations of the order of 950 MW of solar electricity in the country. While there is a considerable interest in the utility scale grid connected solar power plants, roof top systems are  equally getting attention and the country has about 43 MW of roof top systems connected to the grid.  Rooftop PV systems find much more attractive due to the fact that these systems have potential to reduce transmission and distribution losses reduce additional burden of laying the T&D infrastructure. Connecting roof top solar PV systems to the grid is a great challenge, specially the rooftop systems which are in kW capacity, the utilities face tremendous challenge in terms handling the unstable sources of electricity at distributed level. While the PV system cost have come down considerably, roof top systems provide altogether a new market to the urban households who already has an inverter and battery storage systems as back up source in the event of grid unavailability.

Most of Indian households are not having electricity access due to grid unavailability and have to install inverters which charge batteries from the mains and use the same electricity during the periods of non availability of grid. The grid supply is generally not available from 30%-50% of time in the small towns and condition in villages is even worse where the electricity supply is available for a period of only 8hrs in a day. Often the grid supply is not even enough to charge these inverters to provide uninterrupted power supply. These inverters when under the charging mode create additional peak demand which at times makes the load relief measure undertaken by the Utility as irrelevant.  Integrating solar Photovoltaic with these existing home inverter system can provide relief to the households for additional charging option apart from normal grid charging of the storage batteries and will also reduce the system peak which create another set of problems to the utilities. In the event of non requirement of solar electricity at the household, these surplus electricity can be fed back to the grid as well.


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