On going demands to connect massive amounts of the heterogeneous mobile devices and data traffics make the mobile operators in desperate need to find energy-efficient solutions for coverage and real-time services. Accordingly, mobile femtocells are found to be a promising solution in the coming few decades. This paper presents energy-based analysis for mobile femtocells in Ultra-Large Scale (ULS) applications such as the smart-grid. The potential reduction of the consumed energy and service interruption due to mobility and multihop communication effects are considered as well as various performance metrics such as throughput, availability, and delay. In that sense the smart-grid is modeled as a green wireless communication system for traffic offloading while considering mobility of the femtocell base-station (FBS) as well as the FBS cut-offs for energy-saving aspects. A typical scenario, called e-Mobility, is considered as a case study where a set of mobile femtocells are utilized inside a single macrocell in order to achieve optimized utilities' usage. Numerical results achieved from the proposed smart-grid model have been verified and validated via extensive simulation results while considering typical operational conditions/parameters.