Use conditions and efficiency measurements of DC power optimizers for photovoltaic systems

Abstract

No consensus standard exists for estimating annual conversion efficiency of DC-DC converters or power optimizers in photovoltaic (PV) applications. The performance benefits of PV power electronics including per-panel DC-DC converters depend in large part on the operating conditions of the PV system, along with the performance characteristics of the power optimizer itself. This work presents a case study of three system configurations that take advantage of the capabilities of DC power optimizers. Measured conversion efficiencies of DC-DC converters are applied to these scenarios to determine the annual weighted operating efficiency. A simplified general method of reporting weighted efficiency is given, based on the California Energy Commission's CEC efficiency rating and several input / output voltage ratios. Efficiency measurements of commercial power optimizer products are presented using the new performance metric, along with a description of the limitations of the approach.

Analysis of the influence of DC optimizers on photovoltaic production

“…These effects lead to the weakest PV cells determining the output power of the whole string of modules. Therefore, additional potential benefits of distributed power electronics include increased design flexibility by allowing mismatched or longer strings of PV panels, improved monitoring, and increased system availability [20].…”

Modeling Microinverters and DC Power Optimizers in PVWatts

“…At present the CEC database does not include information on weighted DC power optimizer efficiency; however, this information may be provided by the manufacturer. If it is not, a value of 99% is recommended for newer devices [4,7], and a lower efficiency of 97.5% [10] is recommended for older technologies.…”

“…Consumers are realizing their potential to increase design flexibility, monitor system performance, and improve energy capture. It is becoming increasingly important to accurately model PV systems employing these devices, with numerous commercial [2][3][4][5] and independent research [8][9][10][11] publications providing modeling strategies and guidelines. This document summarizes existing published documents to provide uniform, impartial recommendations for how the performance of distributed power electronics can be reflected in NREL's PVWatts calculator (http://pvwatts.nrel.gov/).…”

Performance Assessment of Mismatch Mitigation Methodologies Using Field Data in Solar Photovoltaic Systems

“…In addition to bypass diodes methodology, distributed maximum power point tracker (dMPPT) methods have been used to eliminate the electrical characteristic mismatch problems in the solar PV systems [29][30][31][32]. The commonly used dMPPT methodologies are DC optimizers [33][34][35] and DPP converters [24,[36][37][38][39][40]. The general schematic of DC optimizer and DPP converters are shown in Figure 4b,c.…”