**6. Chemical energy storage**

Hydrogen or any other synthetic gas is used as electrolyte and synthetized into methane gas with carbon di oxide, this technology is known as secondary energy carrier. This storage system is cleaner and can be storage system of above 100GWh energy, but their efficiency is low about 40%–50%, security is low and also cost is high. Many countries are using hydrogen storage system, in which fuel cell is basic manner to utilize hydrogen. Currently the main aim for its application is to improve its cost, efficiency and lifespan, leading to a prospect of better renewable energy utilization and large-scale hydrogen as the fundamental energy system.

#### **6.1 Battery energy storage**

High temperature batteries and liquid electrolyte flow batteries are two general types of batteries used in energy management system. In year 2009 sodium sulphur batteries were consider as most mature high temperature batteries; liquid electrolyte flow battery has this advantage that their energy and power component can be sized independently [8].
