Sizing Curve for Design of Isolated Power Systems

Isolated power systems meet the electricity demand by generating power close to its point of utilisation. It is viewed as an option to electrify communities located in remote areas where extending the grid could be uneconomic. The principal 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 mainly two categories, analytical methods and simulation based schemes for system sizing. 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 a normalised generator rating vs. storage capacity coordinates for these options.