The high penetration of renewable energy resources presents many challenges to the grid, such as frequency and voltage instability and system dispatching. Therefore, it is necessary that the volatile and randomized power challenges of these resources be solved in such a way that the stability of the power system is not compromised and that these resources can participate in the dispatching program and also the electricity market. One of the solutions to offset the power fluctuations and prediction errors is the use of energy storage systems (ESSs) along with these resources. In this regard, due to the wide variety of technologies of ESSs, determining the appropriate type of ESSs based on technical and economic issues is of great importance. Also, due to the high cost of the storage system, the capacity required for these systems should be optimized to meet both technical and economic needs. Finally, different technologies must be considered in order to compensate for various types of fluctuations and forecast errors. Also, due to economic issues, it may not be necessary to compensate for any fluctuations or errors so that the optimum capacity of ESS can be determined on the basis of the minimum final cost. This chapter categorizes different kinds of fluctuations and uncertainties of renewable energy resources in different timescales with different intensities. Also, different ESS technologies and their characteristics which are important in the selection of them are surveyed. Each of these technologies could be used for different applications in power systems. Finally, according to the type of fluctuations and uncertainties, the appropriate options of ESSs are selected based on the techno-economic aspects.
