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84 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
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Darker shadow
Power

(a) Voltage

Shadowed area increasing
Power

(b) Voltage

FIGURE 4.14 Effect of a partial shadow on the P–V curve of a PV array affecting 25% of its surface as
changing from no shadow to 90% reduction of irradiance (a) and effect of a 50% intensity shadow as the shad-
owed area is increasing from nonshadowed to fully shadowed condition (b).

While the majority of the systems typically still use the traditional hill-climbing MPPT method
for tracking, the focus has shifted toward the interaction of the parallel-operating trackers in a large
PV system. Furthermore, with the appearance of new grid requirements, for example, power ramp
limitation (PRL) and frequency-sensitive operation, the MPPT operation is no longer the standard
operating mode of PV plants.

4.4.8 Grid Integration Functions for PV Systems

Recently, with the increasing penetration of PV into the grid, as well as the increasing number of large
PV plants connected to the MV network, grid integration and grid support requirements for large
PV plants have been released or are under development. The European Network of Transmission
Systems Operators for Electricity released grid codes where large-scale PV power plants (LPVPP)
are required to have fault ride through, voltage support, and frequency-sensitive mode (FSM) capa-
bilities [64]. Furthermore, LPVPPs have to adhere to the MV grid codes in providing reactive cur-
rent injection during grid faults and maintaining connection during grid faults all the way down to
0 V grid voltage. While, in most cases, these requirements are for all generators, in a few countries
(e.g., Germany, Spain), grid codes that are specific to plants without a synchronous generator have
been published. An overview of grid codes for PV plants is provided in [65].
While many of the grid requirements PV plants must fulfill are not necessarily only PV specific,
a few but general application for distributed generation functionalities/features that are typical to PV
plants are discussed in the succeeding part.