ESS are in use for numerous applications but is so happens often that one ESS cannot suce all
the needs of a particular user. So, it becomes necessary to incorporate more than one ESS to cater
to all requirements. Such a system, which uses two or more ESS combined together, is known as a
hybrid ESS (HESS). ESSs can work in either of two modes—high-power mode or sprinter mode and
high-energy mode or marathon mode . High-power ESSs respond fast and include flywheel
ES, SMES, SCES, BESS, etc., whereas high-energy ESSs respond slowly and include PHS, CAES, fuel
cells, BESS, etc. Batteries such as Li-ion batteries are suitable for both high-power and high-energy
applications. Generally, HESSs are designed such that both modes are available for a single
application.