An atomistic effective Hamiltonian technique is used to investigate the finite-temperature energy storage properties of a ferroelectric nanocomposite consisting of an array of ${\mathrm{BaTiO}}_{3}$ nanowires embedded in a ${\mathrm{SrTiO}}_{3}$ matrix, for electric field applied along the long axis of the nanowires. We find that the energy density versus temperature curve adopts a nonlinear, mostly temperature-independent response when the system exhibits phases possessing an out-of-plane polarization and vortices, while the energy density more linearly increases with temperature when the nanocomposite either only possesses vortices (and thus no spontaneous polarization) or is in a paraelectric and paratoroidic phase for its equilibrium state. Ultrahigh-energy density up to $\ensuremath{\simeq}141 \mathrm{J}/{\mathrm{cm}}^{3}$ and an ideal 100% efficiency are also predicted in this nanocomposite. A phenomenological model, involving a coupling between polarization and toroidal moment, is further proposed to interpret these energy density results.