Extensive studies have already been performed in the past to integrate more than one ‘green’ energy source, e.g., solar, wind and hydrogen, for power generation. For actual operation in a realistic environment, such a hybrid process must be fully functional despite random fluctuations in energy supplies and power demands. A common option for accommodating the uncertain disturbances and their cumulative effects is to introduce battery into a properly structured system. However, by using an ad hoc approach, these schemes may be either overdesigned or inoperable. A generic mathematical programming model is thus adopted in the present study to compute a so-called temporal flexibility index for use as a performance measure. In order to demonstrate the usefulness of this assessment criterion, a large collection of photovoltaic–fuel cell (PVFC) systems can be configured for a specific application and then compared accordingly so as to identify the best combination of energy supply ratio and battery capacity. A MATLAB/Simulink simulation program has also been developed in this work to validate these design decisions.