The renewable energy resources (RERs) have been globally accepted for power generation due to the high prices of fossil fuels, environmentally friendly, low operation and maintenance (O&M) costs, no carbon emission and escalation in power demand due to rapid growth in population and industrialization. A microgrid (MG) power system that consists of the diesel generator, wind turbine generator (WTG), photovoltaic (PV) and electric storage system (ESS) is utilized in this study with the aim of improving the reliability and minimizing the cost of energy (COE) and annualized cost of the system (ACS). This objective is achieved by using the expected energy not served (EENS), loss of load expectation (LOLE), cost of load loss, loss of load probability (LOLP), net present cost (NPC), annualised fuel cost (AFC), annualised emission cost (AEC), annualised maintenance cost (AMC), annualised capital cost (ACC) and annualized replacement cost (ARC) of the system. These operating parameters are used in this work to investigate the effects of RERs in a power system. To achieve the main objective of this paper, the basic probability concept is utilized to find the reliability indices of the proposed power system as well as the development of a software in the MATLAB programming environment by using fmincon optimization tool to investigate the economic impact of RERs in a micro grid power system. The results obtained from the research work show that RERs can be used to improve the reliability and reduce the COE and ACS of a power system.