The Ministry of New and Renewable Energy (MNRE) has issued draft guidelines for standards regarding the technical specifications for solar grid-tied inverters. The Ministry has invited comments and inputs from the public and stakeholders by April 30, 2020.

Solar inverters must be tested for safety, efficiency, environmental tests, and grid inter-connection aspects to ensure their quality and reliability. Keeping this in mind, the Ministry has introduced relevant standards covering safety, efficiency, environmental, and islanding prevention measures tests for utility-interconnected photovoltaic inverters.

Further, to make the process of testing simple and consistent, the focus has been laid on developing an inclusive standard for photovoltaic grid-tied inverters for complete performance evaluation for grid-interactive applications for quality and reliability assurance in the Indian conditions.

The draft has laid out a detailed interconnection between technical specifications and requirements along with environmental test specifications. The Ministry said that the purpose of the standards is to lay down the requirements for the interconnection of PV systems and inverters to the utility distribution system.

The standards also provide a test procedure to evaluate utility-interconnected PV power systems that operate in parallel with the utility and for utilizing static non-islanding inverters for the conversion of DC to AC. Islanding is the condition in which a distributed generation system continues to power a location even when grid power is not available. So, an anti-islanding inverter will cease to energize a utility system that is out of its regular operation specifications after a specified amount of time.

The draft added that the MNRE series guidelines should be referred to for selecting the samples from a single family of inverters. In August 2019, the MNRE had approved the series guidelines for grouping solar inverters. These guidelines were for conducting tests in laboratories for the implementation of quality control order that was introduced in 2017. As per the guidelines, the manufacturers will have to submit a declaration about the series of their products while submitting the samples of a particular series for testing.

The draft has proposed routine tests that should be performed by the manufacturer on all inverters, and a test report should be included with each inverter. These tests are:

• Protection against abnormal voltage
• Protection against abnormal frequency
• Response to utility recovery

These tests assume that the equipment has met the applicable requirements of this standard and may be conducted as a factory test or performed as part of a commissioning test, the draft guidelines added.

For the Harmonic test, the MNRE has suggested shifting from the Institute of Electrical and Electronics Engineers (IEEE) standard to the International Electrotechnical Commission (IEC) standard. Solar PV systems incorporate power electronic interfaces, which generate a level of harmonics. These harmonics have a great influence on the operational efficiency and reliability of the system.

Regarding the grid interconnection test, the draft states that the PV system will not inject DC higher than 0.5% of the continuous maximum rated inverter output current into the utility interface when tested at 25%, 50%, 75%, and 100% of rated output power.

“The requirement is not applicable for an inverter that interconnects through a line frequency isolation transformer located between the output of the inverter and the utility system,” the MNRE added.

Regarding the grid management, the MNRE has suggested that the PV system, which is connected to the low voltage (LV) and medium voltage (MV) lines, will be capable of remaining connected to the grid during low and high voltage conditions.

Previously, Mercom has written about the struggles of inverter manufacturers in gaining clarity on the ambiguous BIS certification process. The unavailability of labs, lack of testing facilities and workforce, unreasonable costs of testing, absence of series guidelines, and confusion regarding MNRE notifications were some of the issues that have made the compliance of the order “Solar Photovoltaics Systems, Devices and Component Goods Order 2017” extremely difficult. Through several interviews with inverter suppliers, Mercom found out that the cost of BIS certification is also a cause of concern for the inverter suppliers apart from the time-taking process.

In January 2020, the Ministry issued a notification extending the deadline for the self-certification of solar inverters by six months from December 31, 2019, to June 30, 2020. Realizing the need for quality components in solar projects, the government had mandated that laboratories must conduct the tests for compulsory registration with the Bureau of Indian Standards (BIS) for the implementation of the quality order. Considering various issues related to testing fees, and the lack of test labs available, the industry has been seeking more time for compliance since the introduction of the policy.