The micro-turbines can be used to supply both thermal and electrical energy demands of islanded microgrid. Depleting fossil fuels and ever-increasing environmental concerns have attracted much attention to the renewable energy resources. Meanwhile, the stochastic nature, non-compliance with the load, inability to meet the thermal load and high cost of the wind and solar resources are disadvantages for them. In this paper, proposed microgrid includes a storage energy system, heater, micro-turbines and boiler, and is designed so that not only the mentioned problems could be solved but also the optimal size of renewable and non-renewable resources in the microgrid, for supplying electrical and thermal load, is determined. The renewable resources development strategies and optimal size for other resources is determined with using sensitivity analysis for fuel prices, pollution penalties and for government assistance in financing renewable resources. Modified Particles Swarm Optimization (MPSO) Algorithm is used to obtain global optimal solution. IEEE load as well as wind speed and solar radiation data, from the Ardabil region, have been used for our case study.