To realize an efficient energy supply system for an isolated microgrid, a joint design framework that considered the capacity sizing alongside operational planning is essential. In this work, an integrated planning model was developed to investigate the techno-economic performances of a high renewable energy-based standalone microgrid. The approach combines capacity sizing and operation scheduling, considering demand-side management strategies for different system design scenarios. The evaluated scenarios involved the combination of wind turbine, photovoltaic system, diesel generator, with either battery energy storage or pumped thermal energy storage. A demand response program based on instantaneous renewable energy availability is proposed with dynamic pricing economic model for improving the overall system flexibility. Mixed-integer linear programming algorithm on MATLAB® is deployed as the optimization solver. The minimization of the sum of system costs which includes equivalent annual costs of the investments, running costs and costs based on demand-side management strategies is the objective function. The combination of photovoltaic, wind turbine and pumped thermal energy storage is found to be the most techno-economically efficient system configuration for the considered microgrid. More so, the proposed demand response strategy minimizes the mismatch between the generation and the load demand profile effectively, thereby increasing the system flexibility.