Energy Storage for 1500 V Photovoltaic Systems: A Comparative Reliability Analysis of DC- and AC-Coupling

There is an increasing demand in integrating energy storage with photovoltaic (PV) systems to provide more smoothed power and enhance the grid-friendliness of solar PV systems. To integrate battery energy storage systems (BESS) to an utility-scale 1500 V PV system, one of the key design considerations is the basic architecture selection between DC- and AC-coupling. Hence, it is necessary to assess the reliability of the power conversion units, which are not only the key system components, but also represent the most reliability-critical parts, in order to ensure an efficient and reliable 1500 V PV-battery system. Thus, this paper investigates the BESS solutions of DC- and AC-coupled configurations for 1500 V PV systems with a comparative reliability analysis. The reliability analysis is carried out through a case study on a 160 kW/1500 V PV-system integrated DC- or AC-coupled BESS for PV power smoothing and ramp-rate regulation. In the analysis, all of the DC-DC and DC-AC power interfacing converters are taken into consideration along with component-, converter-, and system-level reliability evaluation. The results reveal that the reliability of the 1500 V PV inverter can be enhanced with the DC-coupled BESS, while seen from the system-level reliability (i.e., a PV-battery system), both of the DC- and AC-coupled BESSs will affect the overall system reliability, especially for the DC-coupled case. The findings can be added into the design phase of 1500 V PV systems in a way to further lower the cost of energy.