In a modified configuration, the above hybrid hydraulic-electric
generator concept can also facilitate the use of an energy storage
system in the tower volume as shown in Fig. 1c. During storage
times (when wind power generation is too high), wind energy is
transferred to shaft work by hydraulic pump and motor. Part of the
work is used to generate electricity to satisfy the user’s demand
while the surplus work is stored in the open accumulator (inside
the tower) through air compression. During regeneration times
(when wind power generation is too low), compressed air is
allowed to exit the open accumulator and expand near isothermally
to provide power through an air motor that drives
the generator to produce electricity. In general, the energy storage
and regeneration depend on profile of user’s demand and real-time
electricity price. Wind energy is stored when it goes higher than
the demand, and the stored energy is regenerated and sold at high
electricity price when electricity demand is increasing. Storage in
the tower becomes more practical as the turbine size increases.