Operating Characteristics of an EDLC-Battery Hybrid Stand-Alone Photovoltaic Power System

Yousuke NOZAKI  Kazuya AKIYAMA  Toshiaki YACHI  Hiroshi KAWAGUCHI  Kosuke KUROKAWA  

IEICE TRANSACTIONS on Communications   Vol.E84-B   No.7   pp.1907-1914
Publication Date: 2001/07/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Energy in Electronics Communications
photovoltaic power system,  electric double-layer capacitor,  lead acid batteries,  DC-DC converter,  

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Stand-alone photovoltaic (PV) power systems are potential power sources for telecommunications equipment especially equipment installed outdoors. To be practical, they must have a high conversion efficiency and a long lifetime. We have proposed a stand-alone photovoltaic power system that uses electric double-layer capacitors (EDLCs) and lead acid batteries as power storage devices. This system smooths out the fluctuations in power generated by the PV array by using the EDLC's charge-and-discharge power; this reduces the number of battery charge-and-discharge cycles. We simulated the system's operating characteristics and evaluated the photovoltaic array mismatching loss, system conversion loss, battery contribution factor, averaged battery state-of-charging, and maximum depth-of-discharging. The results show that the system is effective at reducing the mismatching loss and battery contribution factor, so the system efficiency is expected to be improved by using high conversion efficiency DC-DC converters. Moreover the system can maintain the averaged battery state-of-charging during operation. This indicates that smaller batteries can be used. The maximum depth-of-discharging can be kept lower than in the conventional system. Consequently, the proposed system should have a longer battery lifetime.