Optimum operation strategy and economic analysis of a photovoltaic-diesel-battery-mains hybrid uninterruptible power supply

This paper presents the optimum operation strategy and economic analysis of a photovoltaic-diesel-battery-mains hybrid uninterruptible power supply (U PS). The system involves a photovoltaic, battery and bi-directional inverte r that is connected in parallel to the grid. A diesel generator is required when the grid is not available for a longer time. The optimum operation st rategy of the system is proposed for the diesel-connected mode (when the gr id fails for several hours), while the economic analysis is evaluated for t he grid-connected mode. The optimum strategy determines the 'set point' val ue for starting and stopping the diesel generator, resulting in a lower sys tem operation cost within its lifetime. The optimum value is obtained by co mparing the cost of the diesel fuel consumption and the battery wear. The e conomic analysis includes the system operation as UPS and demand side manag ement. The system will reduce the power flow from the mains by increasing t he power from the inverter to the load when the tariff is high. However, wh en the grid tariff is low, the power from the mains is used to charge the b attery and to meet the load simultaneously. (C) 2000 Elsevier Science Ltd. All rights reserved.