Gross Metering system for solar PV plants

All energy consumed in the household is imported at the electricity retailer's rate (let's say 25c per kWh).

All solar energy produced is exported to the grid at 60c or 20c per kWh.

For many of you, the total value of the electricity being sold to the grid is greater than the total cost of your electricity, so the electricity retailer pays you the difference. Nice.

To maximise your refund paid by your electricity retailer, you need to reduce your overall electricity consumption so you import as little as possible, and export as much as possible from your solar to the grid.

Let’s say you have a rooftop solar system. It generates 10 units (kWh) of electricity during the day, but you only consume 8 units for powering your various devices/appliances. You are left with 2 excess units. What do you do with them?

You can either let them go waste, store them for future use (using a battery backup system), or feed them into the grid.

At night, without the sun powering your rooftop system, you again need electricity. You can either get that from your battery backup system (if you have one), or from the central grid, or from both of them combined.

Let’s say you fed the 2 excess units during the daytime into the grid and then consumed 2 units from the grid at night. Your day’s grid electricity balance would have been 0.

figure shows the actual site for PV installation

A bi-directional meter

the above figure shows the single line diagram for gross metering system

Net metering allows you to do that. It adjusts what you feed into the grid against what you take from the grid and only charges your for the difference. Nice, isn’t it? In some cases, if you supply more power to the grid than you draw from it, you can even earn money this way.

Net Metering vs. Gross Metering

In another case, let’s say that you choose to feed in all of the electricity that your rooftop solar systemgenerates (10 units in this example) directly into the central grid without consuming any of it at your house. Instead, both at night and the day, you consume electricity from the grid.

At the end of the day, you will have had a cumulative electricity consumption from the grid, as well as having fed electricity into the grid. You will be billed for your cumulative consumption, AND you will be paid for the “gross amount of electricity” you pumped into the grid. These are two entirely separate billing processes. This payment mechanism is called gross metering.

Therefore the essential difference between net metering and gross metering is that under the former, you are billed only for your “net electricity consumption”, while under the latter, you are paid for the “gross amount” of electricity you feed into the grid, while being charged in full for your grid electricity consumption.

click on this video to get the complete idea of the project