Sizing curve for design of isolated power systems

Isolated power systems meet electricity demand by generating power close to its point of utilisation. They are an option to electrify communities located in remote areas where extending the grid could be uneconomic. Diesel generators, photovoltaic panels and energy storage using battery banks have been used for meeting the electrification needs of remote areas. The design objective for such systems is the estimation of the ratings of the generators and the storage capacity requirements for meeting specified reliability and economic constraints. A review of different methods for sizing photovoltaic-battery systems indicates that they fall into mainly two categories, analytical methods and simulation-based schemes. A generalised methodology for generating a “sizing curve” relating the generator rating and storage capacity, based on a time series simulation approach, is presented in this paper. It helps in the identification of a “design space” which enables the exploration of all the feasible system configurations meeting a given demand for a site. It further serves as a tool for system optimisation. Two specific options for isolated power generation, diesel generator-battery system and photovoltaic-battery system, are illustrated for a typical Indian site. Sizing curve and design space are plotted on normalised generator rating vs. storage capacity coordinates for these options.