We study periodic steady states of a lattice system under external cyclic energy supply using simulation. We consider different protocols for cyclic energy supply and examine the energy storage. Under the same energy flux, we found that the stored energy depends on the details of the supply, period and amplitude of the supply. Further, we introduce an adiabatic wall as internal constrain into the lattice and examine the stored energy with respect to different positions of the internal constrain. We found that the stored energy for constrained systems are larger than their unconstrained counterpart. We also observe that the system stores more energy through large and rare energy delivery, comparing to small and frequent delivery. * Equilibrium states of the many body systems are well established. They are described by thermodynamics with its foundation justified by statistical mechanics. The central result of statistical mechanics, i.e., the equilibrium probability distribution of a system in a heat bath as given by the Boltzmann distribution, is considered to be the textbooks knowledge.Such a general framework for non-equilibrium steady states does not exist yet.Nonetheless, different approaches that address specific non-equilibrium situations have been developed. For non-equilibrium systems that fall under linear response regime, i.e., equilibrium systems under small perturbations, phenomenological arguments led to the formulation of the fluctuation-dissipation theorem (FDT) [1][2][3]. These systems can also be described by linear irreversible thermodynamics, which provides an expression for the entropy production in the form of affinities and fluxes [4,5]. Further developments concern the extension of FDT to non-equilibrium steady states (NESS). Various forms of FDTs were proposed, which link the response to a small perturbation from the NESS to the correlation functions in the NESS [3,6,7]. For systems in which fluctuations are eminent, results now known as the fluctuation theorems (FT) were proved, which are valid also for deep NESSs.These theorems establish restrictions on the probability distribution of quantities defined on trajectories [8,9]. Different FTs have been proved for a variety of systems such as chaotic [10] or stochastic systems [11], and for various processes such as diffusion [12] or relaxation [13]. The FTs for the probability distribution of work, were proved by Jarzynski and Crook [14,15]. By generalizing the concept of thermodynamic quantities on the trajectory level, these relations can be unified under the framework of stochastic thermodynamics [8]. They are particularly relevant for small systems such as molecular motors or nano-devicies [16,17], chemical reaction systems [18] and systems with strong fluctuations [19]. The central results of contemporary non-equilibrium thermodynamics are critically reviewed in Ref. [20].Here, we address the problem of energy storage in NESSs. It is interesting and relevant for potential applications, e.g., in energy harvesting [21], to know how the av...