Page 81 - A Comprehensive Guide to Solar Energy Systems

76 A COmPrEHENSIVE GUIDE TO SOlAr ENErGy SySTEmS

FIGURE 4.25 Renewable penetration versus annual power outages [46].

With the decline in hard costs, module level power electronics (mlPE), including
microinverters and power optimizers, have seen a rise in popularity. recent data has
found that the price premium PV systems with mlPEs over conventional string systems
was negligible, and even less due to soft cost efficiencies realized in their use (i.e., ease of
installation) [2].
A Schneider Electric White Paper on “How New microgrid Technologies Enable Opti-
mal Cooperation Among Distributed Energy resources” identified several limitations and
potential solutions to increased penetration of rE [48]. Primary requirements include pro-
tection system design and power quality control.
Protection System Design: mixing inverter-based renewable generation with traditional
rotating generators presents several problems. During a fault, or short circuit, condition,
PV inverter current is limited to roughly 120% of inverter-rated current, to protect the in-
verter itself. Compared to rotating machines, the magnitude of inverter short circuit cur-
rent permitted is low and would cause frequent system interruptions [48].
Power Quality Control: most inverters today harmonize frequency and voltage with
other generators. Unlike traditional alternators, inverters are not “grid-forming” in that
they cannot rely on themselves to form grid voltage and do not have the “natural inertial
link between rotational speed and grid frequency” [48].
An Emerging Solution—Robust Inverter-Based Control Loop Design: New inverter-
based generators (IBGs) “embed advanced voltage and frequency control loops” that en-
able them to be grid-forming, and incorporate power storage that smoothes the variability
of renewables by decoupling instantaneous generation from demand [48].