Linear Operation of Photovoltaic Array With Directly Connected Lithium-Ion Batteries

This paper proposes linear operation of a photovoltaic array which is directly connected to lithium-ion batteries. The array voltage is fixed at the total battery voltage. When the amount of insolation is given, the array power decreases as the cell temperature rises. The maximum power point (MPP) voltage at the highest temperature of a year is selected as the array voltage. This voltage determines the optimal number of the batteries. The array power is guaranteed to be equal to the MPP power or greater through the year. Some simulation and experiment were executed to verify the effectiveness of the method. The utilization efficiency reaches 96.5%. The loss of power proved to be small compared with the maximum power point tracking, which can be economically recovered by using PV modules of larger capacity. A simple switch can substitute for a dc-dc converter.