The subject matter is consistent with the goals of Oman Vision 2040, which seeks to diminish reliance on non-renewable resources and promote the use of clean resources such as renewable energy to lower production costs and consequently boost the competitiveness of economic sectors. Energy Storage System (ESS) solutions will play a dominate role in achieving this aim. Storing energy is very beneficial specially with the availability of the renewable energies like solar energy. The solar energy during the day can be stored during the low demand and utilized during the high demand. Moreover, in spot markets, the excess energy in the grid will not be wasted. As it is expected that the renewable energy sector in the world will achieve rapid growth and the current trend towards implementing economic reforms so the regional energy storage system market will be booming. Energy storage will help to reduce the cost of the electricity compared with the conventional energy system within the upcoming years and will make some stability improvement for the electrical network systems as well. This thesis has focused on the technical and economic feasibility of the application of Pumped Hydro Storage (PHS) in Oman’s main interconnected system (MIS). The study has been carried out to achieve suitable selection of the PHS and location. The sizing and the preliminary design of PHS has been determined. Finally, a simplified economic study has been carried out for the proposed design. The detailed examination of Oman's MIS revealed the emergence of a pronounced duck curve effect, resulting from the mismatch between peak renewable generation during midday and peak electricity demand in the early evening. This effect, along with the intermittent nature of solar energy, highlighted the need for energy storage solutions to maintain grid stability and optimize the utilization of renewable resources. Through a comprehensive site identification and evaluation process, the study identified several potential locations for PHS development in Oman, with Wadi Dhyqa 1 (A1) emerging as the most suitable site based on the multi-criteria decision-making analysis. The preliminary design of the PHS system, considering factors such as configuration, turbine selection, and storage system components, further demonstrated the technical feasibility of implementing PHS in Oman. The techno-economic analysis, which compared the levelized cost of energy (LCOE) of PHS with that of open-cycle gas turbine (OCGT) and combined cycle gas turbine (CCGT) power plants, revealed that PHS is a more cost-effective option, particularly when the OCGT and CCGT plants operate at lower capacity factors or when fuel prices are high. This finding underscores the economic viability of PHS as a long-term solution for managing the variability of renewable energy sources in Oman's MIS.