Not all rooftop solar plants generate power during a power failure. This comes as a surprise to many of our clients, but solar plants have different designs for different purposes, and some designs benefit from the plant not generating power during a power failure.
There are two important reasons why some solar plants shut down during a power failure
As the amount of sunlight falling on the panels varies during the day (due to clouds, etc.), the power output from the panels also varies. As this variation could damage equipment that is powered by solar, the inverter continuously matches the PV plant’s output to another source of steady power. Therefore a rooftop solar PV that generates AC power will always needs another source of power (whether the grid or diesel generator or batteries) to provide a reference voltage in order to function. If the inverter is designed to use only grid power as a reference voltage, the plant will not generate power even if there is ample sunlight.
When a power failure occurs, a portion of the grid isn’t energised. This non-energised portion of the grid is known as an island. If the solar plant is pumping electricity into this non-energised portion of the grid during a power failure, it might cause utility personnel who are working on the grid to be electrocuted. To eliminate this risk, the inverter in the solar power system turns off the power from the plant.
As it is the inverter that determines whether the plant continues to function or not during a power cut, we need to only understand the different kinds of inverters to ensure we have a rooftop solar plant that generates electricity even during power cuts. There are 4 kinds of inverters
|Hybrid inverters (also known as bidirectional or magical inverters) are a one system solution for a complete solar PV system. They can automatically manage between 2 or more different
sources of power (grid, diesel, solar). They have inbuilt charge controllers, MPPT controller, Anti Islanding solutions, DC and AC disconnects and other features like automatic turning on/off of the diesel generator, automatic data logging, and various kinds of protection for the different components of the system, making them ideally suited for applications that require management of power from different sources
It is therefore critical to understand the purpose the rooftop solar PV plant is to fulfil before selecting the inverter. As vendors use various terms to refer to different components we urge you to verify if the inverter will supply power during power failure by specifically discussing this issue with the vendor, rather than going by any label assigned to the product.