A method, apparatus, and system for charging an electrical storage system in a vehicle. The vehicle comprises a support frame, a propulsion, an electric storage system, an extendable structure, and a power management unit. The propulsion system, the electrical storage system, and the power management unit are physically coupled to the support frame. The electrical storage system supplies the electrical energy to the propulsion system. The group of thermoelectric modules physically is physically coupled to the extendable structure and generates a current in response to a heat being transferred through the group of modules. The power management unit is electrically coupled to the electrical storage system and the group of thermal thermoelectric modules and controls storing the electrical energy in the electrical storage system using the current from the group of thermoelectric modules and supplying the electrical energy to the propulsion system.