Introduction

The Solar Net-Metering policy was announced in the state of Delhi in September 2014. Under this policy, consumers planning to install grid-connected solar PV systems are eligible to apply for solar net-metering.

The Solar net-metering is usually useful for Consumers whose energy consumption on certain days in a week or certain months in a year is nil or quite low as compared to other week days. The solar energy generated during these days is net-metered to the grid/ DISCOM and therefore, the Consumer gets the full benefit from his/ her solar PV system.

How Solar Net-Metering works?

In grid-connected Solar PV systems, the DC output generated by the solar panels is converted into AC (alternating current) output by a solar inverter. This output, from the solar inverter, called solar energy, is connected to the distribution board or switch board of the building or the home and is then consumed by the electrical appliances. If the solar energy produced is more than what the loads in the building or home consume, the surplus solar energy is automatically exported (energy export) to the DISCOM distribution network (the grid) with the help of a two-way meter. If the solar energy produced is less than the total energy required in the building, then the shortfall energy is automatically supplied by the grid (energy import).

Bidirectional energy meter

In order to implement net-metering, your existing energy meter would need to be replaced with a bidirectional (two-way) energy meter. This bidirectional energy meter can measure both, energy import (from the grid to the consumer) and energy export (from the consumer to the grid). These meters are also called import-export energy meters.

Electricity Bill with Solar net-metering

Under solar net-metering, the Consumer only pays for the difference in energy imported and the energy exported. If a Consumer imports 1000 kWh in June billing period and exports 600 kWh in the same period, the Consumer will be charged for only 400kWh. If the import energy in the July period is 500 kWh and the export again is 600kWh, then the excess 100kWh will be carried over to the next month's bill or next billing cycle and adjusted there. At the end of the Settlement period (usually 12 months period), any balance and unadjusted carried forward excess export will be paid to the Consumer at a pre-defined tariff (rate/kWh), which will be notified time to time by the relevant authorities.

Illustration

(A case for a Delhi-based School open 6 days/week having monthly electricity bill of Rs 2 lacs sets up a 60kW Solar PV system)

(A)	Monthly Energy consumption (Import from Grid)	: 16,500 units (kWh)
(B)	Monthly Solar energy generation(Solar energy consumed by School	: 7,800 units
(C)	Solar energy consumed by School	: 6,685 units
(D)	Balance solar energy (Exported to Grid)	: 1,115 units (7,800 - 6,685)
(E)	New Monthly import from grid	: 9,815 units (16,500 - 6,685)

As the net import export, the net billable units = 8,700 (16,500 - 6,685 - 1,115) leading to a reduced monthly energy bill of Rs. 1,13,030, which is a saving of Rs. 86,970 per month.

Had export been greater than the import, the difference would have been carried forward to the next billing cycle. Any unadjusted units are paid only at the end of the settlement period at the APPC rate, which currently is Rs. 4.30 for Delhi.

Additionally, this Delhi school is also entitled to be paid an incentive for the monthly solar generation at a rate of Rs 2 per unit under the Generation Based Incentive scheme, which would mean another reduction of Rs 15,600, effectively reducing the monthly energy bill to Rs 97,430 from the current number of Rs 2,00,000.

Category	Existing Electricity Connection	With Solar Net Metering
Monthly Import from grid (units or kWh)	16,500	9,815
Net billable units	16,500	8,700
Grid Electricity Bill	2,00,000	1,13,030
Generation Based Incentive* (Rs)	N.A.	15,600
Grid Electricity Bill after Incentive (Rs)	2,00,000	97,430