Harnessing Solar energy, Options for India

Appendix - 2
Grid Integration in Urban India: Establishment of Standards
and Technical Challenges
Insufficient generation of power in India has led to widespread load shedding. Consequently,
establishments turn to economically and environmentally expensive diesel generators to meet their
needs. Distributed generation provides a very attractive solution. This could also save millions of
kilowatts of power lost in transmission in the Indian grid system. However, there is insufficient
clarity on the technical standards for proposed projects of grid-connected systems rated for less
than 100 kW at low voltage/tension (LT) level (400 V for three phases and 230 V for single phase).
Some major issues to be considered are:
1. Power quality issues: The quality of power provided by a photovoltaic (PV) system for onsite
alternating current (AC) loads and for delivery to the utility distribution grid should be within a
certain range with regards to voltage, flicker, frequency and distortion.
a. Voltage: The voltage operating window should be selected in a manner that minimises
nuisance tripping. Based on International Electro technical Commission (IEC) Standard
61727:2004, the operating range can be 85 to 110% of the nominal voltage. Thus, for India,
the operating range based on a voltage of 230 V would be 195.5 to 253 V.
b. Flicker: As per IEC 61727, operation of the PV system should not cause voltage flicker in
excess of the limits stated in the relevant sections of IEC 61000-3-3 for systems less than 16
A or IEC 61000-3-5 for systems with current of 16 A and above.
c. Frequency: When the utility grid frequency deviates outside specified conditions, the PV
system should cease to energise the utility line. IEC 61727 specifies the frequency limits to
be ±1 Hz, which is when the system should stop energising the utility line within 0.2 s.
d. Distortion: 1 The current experience of several European utility-scale producers shows that
harmonics are not currently a concern at the LT distribution level, and that penetration from
33 to 50% of distribution transformer/line capacity is considered safe. 2 European
distribution grids are much more robust than their Indian counterparts; hence, studies will
be required to establish standard practices in the Indian case.
e. Direct current (DC) injection: According to IEC 61727, the PV system should not inject DC
power greater than 1% of the rated inverter output current into the utility distribution grid
under any operating condition.
f. Power factor: The PV system should operate at a lagging power factor greater than 0.9 when
output is greater than 50% of rated inverter output power.
2. Safety and protection issues: The following protection issues need to be kept in mind while
designing PV systems:
a. Islanding protection: In the event of loss of grid supply, utilities require that the PV system
should stop feeding power to the grid. This can be achieved either by an in-built protection
in the inverter/Power Control Unit (PCU), or, if this is not supplied or is insufficient to satisfy
the utility, it can be provided by external relays.
b. Grounding.
c. Lightning surge protection.
d. Ground earth/fault detection: When the size of the PV array becomes large enough to cause
Appendix 2 CSTEP | Page 107