Energy storage technologies (EST) will have an important position in combination of renewable energy sources (RES) in modern electrical power systems and smart grid. EST can provide more balancing and flexibility to the power system, providing incorporation of intermittent RES to the smart grid. Energy storage technologies have a critical function to provide ancillary services in the generation mode for smart grid. This paper gives a short overview of the current energy storage technologies and their applications available and the opportunities and challenges the power systems faces for successful integration of RES to smart grid. This paper also discusses different types of EST experimentally tested in smart grid environment such as electrochemical batteries and ultra-capacitor energy storage systems. This paper is concluded by giving some important experimental results, recommendations and suggestions to whom, which are studying on different energy storage applications including battery and ultra-capacitors in the smart grid.