This paper investigates vehicle-to-home (V2H) operation that provides backup power under outage of the external electric grid. First, we introduce a novel optimization model that aims at maximizing backup duration. Motivated by the optimization problem, a new algorithm for V2H system is proposed. Subsequently, we extend the model to vehicles-to-homes (Vs2Hs) composed of multiple homes, electric vehicles, and photovoltaic generation. An algorithm for Vs2Hs considering scheduling of its energy resources is suggested. Numerical simulations show that the proposed algorithms provide sufficient backup duration while maintaining relative simplicity. The effectiveness of Vs2Hs is also investigated using simulations.