Energy storage plays a crucial role in ensuring reliable power supply in a renewable microgrid. The supply and demand variability is found in different time scales (i.e., instantaneous, diurnal, and seasonal). The nominal discharge duration of multiple storage options can be matched effectively for variability in all relevant time scales. An optimum mix of storage options is important to design a cost-effective system. This paper proposes a generic sizing methodology using pinch analysis and design space for hybrid energy storage in a PV-based isolated power system. Pinch analysis utilises a time series simulation of the system where generation should always exceed the load. The methodology defines the design space as feasible combinations of short, medium, and long-term storage size and PV array rating for the given loads. These design space curves are approximated by quadratic equations and the correlations are used as constraints to determine the optimal mix of supply and storage that minimise the life cycle cost. Four different practical cases in Indian context -a remote village, telecom tower, welding shop, and a standby system for a lift load -are analysed to illustrate the sizing method. As an example, the optimal size for a PV based microgrid supplying a remote telecom tower with an average load of 72 kWh/day is 40 kW(p) of PV, 5 m(3) of hydrogen storage and 58 kWh of battery. The proposed methodology extends the design space approach to obtain an optimal minimum cost solution.