Solar electric systems also called PV systems, use sunlight to produce electricity. Heres how:
In grid connected rooftop or small SPV system, the DC power generated from SPV panel is converted to AC power using power conditioning unit and is fed to the grid either of 33 kV/11 kV three phase lines or of 440V/220V three/single phase line depending on the local technical and legal requirements.
These systems generate power during the day time which is utilized by powering captive loads and feed excess power to the grid. In case, when power generated is not sufficient, the captive loads are served by drawing power from the grid The concept of rooftop solar is based on the scale of the PV plant rather than the fact whether it is situated on a roof/terrace or not. Hence, the definition of RTS also includes small solar plant on the ground.
Net metering systems are primarily aimed at providing an opportunity to consumers to offset their electricity bills, wherein a single meter records both import of conventional energy from distribution grid and export of solar energy into distribution grid. Thus, net metering allows the final user to credit produced energy in the grid and is also promoted as a preferred option.
Gross metering systems are aimed at rooftop owners/third party investors who would like to sell energy to the DISCOM by using roofs owned by them or another party. It is also known as feed-in metering wherein, all the energy generated from the system is exported to the grid and is separately recorded through a different ‘feed-in meter’. The developer exports the solar energy to the utility at a predetermined feed-in-tariff (FiT) approved by the regulator, and the third party investors/RESCO developers enter into a long term Power Purchase Agreement (PPA) with the utility. Only grid-connected PV systems can be gross-metered.