Bridge India

Intentional islanding functionality of solar PV inverters – what it is and why it can help the Indian grid

The current regulations for distributed solar PV generation in India are issued by the Central Electricity Authority (CEA). Currently, the regulations do not allow intentional islanding of inverters. Islanding is a mode of the inverter that allows it to operate independently of the grid. This is frequently used when the grid goes down and one requires the solar system to cater to the local loads. As of the now, the CEA mandates anti-islanding, which means that the inverter must automatically switch off, when the grid goes down.

  • Anti-islanding is an important safety feature, especially for the Indian grid, which experiences frequent down-times. This feature shuts off the inverter to prevent the solar system from energizing the grid.
  • Given India’s grid reliability, it would make sense for most owners of solar plants to run their systems as a back-up source of energy. Under current CEA regulations, this is not allowed
  • Intentional islanding allows the inverter to safely operate independent of the grid, during times of a blackout. This provides energy to consumers during a power cut and also ensures that safety is not compromised

 A recently concluded collaborative research project by BRIDGE TO INDIA, the National Center for Photovoltaic Research and Education (NCPRE) based in I.I.T. Bombay, Prayas Energy Group and the University of California, Berkeley has recommended that the intentional islanding feature be allowed under the current regulations (download the report here). The aim of this research project was to understand if the Indian grid is prepared for the impending distributed energy boom and make specific recommendations on the current regulations on distributed generation by comparing them with similar international standards.

 The study showed that the CEA could allow intentional islanding of PV inverters when there is a power failure. It makes sense to have the anti-islanding feature in countries with stable grids (USA, Germany). When the grid goes down in these countries, it is generally because of a fault. In such an event, you would want the inverter to be disconnected from the grid to allow safe repair works. However, the context in India is very different. Grid outages called “load shedding” (due to unavailability to adequate power to cater to the demand) are very common – especially during summer months. Almost all establishments use some form of back up (usually polluting diesel generator sets). As the prices of diesel rise and solar components fall, there suddenly is a business case for consumers to add solar PV into their energy mix. Such a system is known as a hybrid system and is used primarily as a source of backup when the grid fails.

 blog 2 prayas

Image source: sma-sunny.com

When the grid does fail due to “load shedding”, consumers want their hybrid systems to be running. Under the current regulations, the inverters must shutdown. This is unproductive and defeats the purpose of these hybrid systems. Therefore the study recommends that the systems stay connected in an ‘intentional islanding’ mode. In this mode, the inverters continue to form an island and cater to the local loads only. Under no circumstance is power fed back into the grid. Such a mode ensures safety for any personnel who might be working on the grid at the time of “load shedding”.

 Allowing intentional islanding will further open up the market for solar hybrid systems, reduce the levelized cost of electricity for consumers and significantly reduce carbon emissions from diesel generators. That is a win-win for everybody.

Akhilesh Magal is a Consultant at BRIDGE TO INDIA

4 comments

  • An important footnote to mention, that the blog and the report misses out on, is the inverter capacity. This argument holds good for smaller systems catering to a particular load. However, anti- islanding is very much required for utility scale power plants.

    Also, a clear bifurcation needs to be made between grid-tie inverters and hybrid inverters as they are quite different in handling this issue.

    But all in all, great work!

  • Idea of intetional islanding is not bad. But there is always mix of trippings and shedding in our grid system. More-so, at end grid there is problem of high & low voltages. Inverter design has to be robust and sound with such protections. Further if the load of grid is higher how this will be managed if there is sudden outage /shedding. All this needs to be studied by CEA in larger Indian prospective. As I understand Power Regulators do not take into account such availibility factor while determining levelized cost of electricity.