Understanding the Zero feed or Export Cutoff
We know that solar plants have the character to feed in the excess power into the grid. Which means when there is a solar plant on your roof then the power from solar first satisfies all your loads and the remaining power is pushed into the grid. We call this as a feed in power and in some countries, we have the privilege of getting paid for this amount of power sent into the grid, this is called the feed in tariff. And there are countries which does not allow any power to get fed into the grid. This is where the export cutoff/ zero feed concept is required.
The solar inverter is only capable of converting DC to usable AC it does not know if the power is used by our loads or the power is fed into the grid. We should make the inverter know when the power is getting fed into grid. For this we employ a energy meter. This energy meter is a special meter it should be a bidirectional meter and it will be fitted at the entry point of the grid and should be capable of communicating via MODBUS protocol.
Now what this energy meter organizes is, whenever the loads are satisfied and the power from the inverter tries to escape into the grid, the energy meter senses it and communicates the message to the inverter, by taking this feedback the inverter reduces its generation thereby no power is exported into the grid.
- Critical points to be taken care during this installation
- Energy meter must be installed at the point of entry of the grid
- Energy meter can communicate via MODBUS protocol which is understandable by the inverter.
- Some inverters have their own energy meters and they can communicate only with them.
- Inverter must be equipped with Active power control Feature.
- The other amateur way of doing this, is by installing a reverse power Relay and I will surely not recommend this for your solar plant for two main reasons,
- It will trip the inverter very often which is not good for the inverters health.
- By doing this you shut down the plant completely thereby not making fullest use of solar.