A thermochemical heat storage system using Ca(OH)2/CaO
in a fluidized bed reactor (FBR) is integrated with a biomass power
plant of a steam Rankine cycle (SRC) as one of the Carnot battery
systems that are expected to provide renewable electricity highly
flexibly. This study utilizes the proposed fluidized bed model under
the nonsteady state operation to evaluate the energy efficiency and
cost by varying the fluidized bed configuration and the power generation
capacities. In addition, the performances of the SRC and those of
the organic Rankine cycle (ORC) were compared, and the fuel cost reduction
by the biomass savings was considered. The levelized cost of storage
(LCOS) of the SRC in the base case (6.25 MWe, bed volume
= 100 m3, bed height/diameter ratio = 4, FBR inlet gas
velocity = 0.087 m/s) was 0.804 and 0.197 USD/kWhe when
the charging electricity cost was 0.100 and 0 USD/kWhe,
respectively. The charging electricity cost has a dominant effect
on the LCOS. The stored energy efficiency and the round-trip efficiency
were 58.2 and 13.7% (without biomass saving), respectively, and the
net power generation was 1247.3 MWhe/year. The effect of
fluidized bed volume, bed height/diameter ratio, and power generation
capacity of the SRC has a slight influence on the energy efficiency
and LCOS. However, the gas velocity in the FBR has a substantial influence
on the net energy generation and LCOS. In the case that power generation
capacity is 3 MWe and the charging electricity cost is 0 USD/kWhe, the LCOS is 0.204 USD/kWhe (SRC) and 0.520 USD/kWhe (ORC), respectively, indicating that SRC has a cost advantage
for a 3 MWe-class power plant. This is because SRC has
higher power generation efficiencies (24.3%) than that of the ORC
(11.4%), generating more electricity from the stored heat. The effect
of biomass saving on LCOS was 0.026–0.053 USD/kWhe (SRC) and 0.096 USD/kWhe (ORC). Increase of power generation
efficiency and/or effective utilization of exhaust heat from the turbine
is important to increase energy efficiency and decrease LCOS.