Net Metering and Grid Interconnection
Net Metering and Grid Interconnection
This domain tests how a grid-connected PV system safely parallels with the utility and how net metering credits import and export.
Core rules
- Grid-tie inverter must synchronise voltage, frequency and phase with the grid before connecting.
- Anti-islanding protection disconnects the inverter when the grid fails, protecting utility workers.
- A bi-directional or net meter records import and export separately; net energy = import − export, subject to tariff rules and caps.
- Interconnection requires approved inverter, isolation device, protection settings, and compliance with the utility's voltage/frequency window.
- Local loads are supplied first; surplus export is credited, but exported units may be settled at a lower rate than retail import.
Worked example
A rooftop system imports 300 kWh and exports 200 kWh in a month. Net import = 100 kWh. If the retail tariff is ₹7/kWh, the energy charge is 100 × 7 = ₹700, plus fixed charges and taxes. The 200 kWh export does not necessarily save 200 × 7 if the utility applies a separate feed-in or settlement rate.
Traps that cost marks
Assuming export is always credited at retail tariff; ignoring fixed charges; connecting a grid-tie inverter without anti-islanding; setting the inverter outside the allowed voltage/frequency range; confusing gross metering with net metering.