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Manned Mars missions (and some unmanned precursor missions) are expected to be long duration expeditions that rely on the utilization of in-situ resources to the maximum extent possible. Traditionally, nuclear energy has been suggested as the power supply of choice for such missions. However, in the event that nuclear power is unavailable, solar energy is the only alternative power source that has received significant study to date. Unfortunately, the periodic and long duration dust storms on Mars drive the need for extensive solar arrays to provide energy needs. This work considers the possibility that wind energy may provide a secondary power source in an all-solar mission. Previous studies have shown that a viable Martian wind energy system must be ultra-lightweight, deployable, and robust. In this study, the possibility of meeting these criteria with buoyant wind energy conversion structures is studied. Conceptual designs have been assessed in terms of mass, volume, and power production. Based on current estimates of solar energy production efficiency during dust storm conditions, the design constraints on a complimentary wind energy system are determined. Using system mass per kW-hour as a figure of merit, the feasible wind speeds for three Martian buoyant wind energy conversion systems (a Savonius, a Darrieus, and a spherical) were determined and compared to previous rigid designs. The large sizes required for buoyant systems resulted in large turbines producing 10 to 30 kW in 25 m/s winds. The efficient inclusion of the buoyant chambers into the structure was found to be critical, as the mass of the balloon is significant. As a result the spherical system was seen to provide the best design. Although it is aerodynamically inefficient and untested, it was found to be feasible in a 29 m/s wind based on an estimated mass of 429 kg and 19 kW estimated power