A photovoltaic strip assembly is disclosed comprising a polyimide substrate, a thin film voltaic strip, and a transversely grooved, protection covering of a chlorofloural polymer. The grooves are provided to increase the flexibility of the strip, and may be V-shaped, flat bottomed with splayed sides, or rounded to provide dome shapes between them. Similar grooves may be provided in the exposed surface of the substrate to further increase the flexibility of the strip. The grooves of the substrate may be aligned with ridges between the grooves of the protective covering, to receive these ridges when the strip is wound around a rechargeable battery or energy cell. In a different embodiment the grooves are between rows of hump-shaped protuberances. The protuberances of adjacent rows may be staggered.