There is global interest in design and development of stratospheric airships1 (also referred to as HAAs, ie, High Altitude Airships), which can serve as a long endurance platform for deployment of equipment for several commercial and strategic applications eg, next generation wireless broadband telecommunications, 2 digital broadcasting, 3 coastal surveillance, 4 remote sensing and GPS augmented navigation systems. 5 These airships are designed to be able to maintain a quasi-stationary position at altitudes of around 20 km, where ambient winds are of low magnitude. Such airships function as low-altitude satellites, but offer much shorter transmission distances and ranges with high resolution, and lesser signal propagation errors. They are much more economical compared to satellites, as they can be relocated or brought down and refurbished with latest equipment.

The power requirements for an airship are two-fold, to meet the needs of the on-board mounted equipment, as well as the propulsive power needed to either maintain its station in the presence of ambient winds, or to travel at a required speed when it is to be relocated. Since such airships are to be deployed for long durations (several weeks or months), the only practical mechanism to address their power needs is a Solar Regenerative Fuel Cell (SRFC) system. In such a system, adequate amount of solar arrays are mounted at the top of envelope of the airship. During day time, the solar arrays generate enough power to meet the needs, and any excess power is used to charge the onboard batteries, which meet the power requirements at night time, or during lean periods. The working principle of a typical SRFC is depicted in Figure 1.