A PLC CONTROLLER ALGORITHM FOR OPTIMUM OPERATION OF PHOTOVOLTAIC-BATTERY SYSTEM Ahmad Al-Kandari* Mahmoud Gilany* A. Shaltout** * College of Technological Studies, Kuwait * *Cairo University Abstract: This paper presents a smart controller for optimal operation of solar systems. The controller is based on better utilization of the storage battery. In most of the commercial solar systems, the battery is charged during the daytime to be used at night or when the photovoltaic power is not available. In this project, a PLC unit continuously monitors the system status. According to the system conditions, the battery can be used to support the PV array at the period of high demand. The battery output is continuously regulated to ensure that the PV array is operated at the peak power point to extract the maximum available power. It also used to support the load during peak period in order to reduce the maximum rated capacity for the PV and consequently reduces the total cost. In all modes of operation, the controller protects the battery from being over charged or deep discharged. It also keeps the battery current within the optimum limits. 1. Introduction Renewable energy sources (RES), such as solar and wind energy, provide an alternative source of energy. Since they are abundant, free, inexhaustible, and environmentally friendly, they have recently gained much attention by the research community all over the world. Recently, conversion of solar energy directly into electricity for domestic applications using arrays of photovoltaic (PV) cells is gaining increase attention [1- 3]. However, it is commonly known that the main factor which limits the wide spread use of solar systems is their high initial cost. This high expenditure, in many cases, favors the use of conventional energy since it provides less cost/kWh. Many techniques have been developed to force the PV array to operate around the maximum power point. Reference [4] uses neural network to estimate maximum power point. Some systems use an on-line maximum power point tracking algorithm [5,6]. These algorithms are based on controlling the system to ensure the maximum utilization of the installed capacity. 1-4244-0557-2/06/$20.00 ©2006 IEEE This paper is intended to propose algorithms that can be used to reduce the cost of the solar systems to compete with the conventional systems. In the following sections the proposed control system circuitry and strategies are presented. II. Methodology Reduce the cost/kWh can be achieved by several ways: - Reducing the initial cost, by reducing the peak load demand in order to use smaller size for the PV array. This can be achieved as follows: a- Reducing the load, by using high efficiency and energy saving equipments. b- Using the storage battery to support the PV array during the peak periods to clip the maximum power demand and shift it to the lower demand period. c- Operating the system to track the maximum power line to utilize the maximum available power. - Battery reservation: as the battery is an expensive element in the system, extending the life of the battery and to reducing the frequency of battery replacement will improve the overall cost per kwh. Most of the available systems are using the battery in a passive manner, which is to charge the battery during the day and use its stored energy to supply the load when the PV array is off. In this paper, the battery plays an active role to fulfill the three above-mentioned techniques. It supports the PV array when the load demand is high, and it stores power when there is an excess energy. In both cases, it modifies the power flow to operate the PV array at the maximum power line. This system is perfect where the solar radiation is usually high, which is the case of the Middle East countries. In such cases, the battery can be fully charged in shorter period as a result of the higher radiation. III. System Layout Figure 1 shows the layout of the proposed scheme. It comprises a PV array supplying a DC load. The system 112