Isolated power systems have emerged as a practical substitute to grid extension for electrification of remote areas. The environmental hazards associated with conventional sources of energy like diesel and coal has forced system planners to resort to renewable energy sources(RES) based technologies such as solar and wind. Increased penetration of RES can effectively cut down system operating costs but can create reliability issues owing to their unpredictable nature. The risk of lower reliability standards can significantly hamper utilization of these sources on large scale. Thus an effective backup system is needed in order to ensure reliability standards. The backup is provided either by diesel generators or energy storage systems. The intermittent nature and cost intensive structure of RES based DGs makes it essential to perform sensitivity analyses for optimal system planning. In this paper, reliability and cost based sizing of solar-wind-battery storage system has been carried out for an Isolated hybrid power system(IHPS). Sensitivity analyses are performed by studying the effect of addition/removal of RES based DGs and storage units on system reliability. Considering variable nature of solar and wind sources, modelling of solar irradiance, wind speed and generator availability has been done using appropriate probability density functions. Dual reliability indices have been used for determining system reliability. For solving optimal sizing problem, a stochastic optimization technique Particle Swarm Optimization(PSO) has been employed. A new index termed as Incremental cost of reliability has been utilized in order to assess the additional investment required to improve reliability standards. Optimal sizing study in conjunction with sensitivity analyses facilitates a deeper insight into system planning.
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