The typical power output of a solar PV inverter is in the range of 330-460V and frequency in the range of 47-52HZ .The output of PV inverter should be stepped up to the required voltage level of the grid to export electricity to the grid. It also needs to replace the existing meter by a export-import meter so that the net metering can take place. Currently there are no clear guidelines for net metering for different states which makes little confusing how to connect solar PV system with grid as well as the typical captive loads . It also needs to synchronize with grid and in absence of grid it needs to synchronize with DG sets as can we seen from following figure .The typical grid interactive PV system is connected through the LT consumer panel ,where in the consumer AC loads are also connected . The LT panel is also connected to utility side through a grid meter . In case the consumer AC load more than the electricity produced by solar PV . The electricity produced by solar is consumed by the loads. However in case the consumer load is less than the electricity produced by solar PV the surplus electricity can be fed back to the grid through a grid meter which is typically export import meter . In case the consumer has the DG set ,it can also be connected to the same LT panel and the electricity can be fed by DG set along with solar PV in the absence of grid electricity. It may be noted that through net metering you are only nullifying your electricity consumption and not selling electricity to grid. Through net metering the import export meter run in both directions .
Hence when you are generating surplus electricity it feeds the same to the grid reduces the total electricity consumed during the month. Net metering provisions do not require any wheeling and banking agreement or a PPA with the grid as the consumer is not being paid for his surplus electricity to the utility grid. In such type of provision consumer is also not eligible for REC benefits.This is the reason many of the home owners having large rooftop area are not inclined to have rooftop system on there roof. May be in future if government considers the electricity generated by solar PV under net metering provision eligible for REC benefits ,it will make the roof top segment attractive proposition for the investments.
Dr Sanjay Vashishtha & Rishikesh Muthyal