NOVELTY - The solar cell unit (300) comprises a solar cell (402) comprising a rigid substrate, a back-electrode (404) circumferentially disposed on the substrate, a semiconductor junction circumferentially disposed on the back-electrode and a transparent conductive layer disposed on the semiconductor junction, a water resistant layer and a filler layer (330) circumferentially disposed on the transparent conductive layer, a transparent tubular casing (310) circumferentially disposed onto the filler layer, and an antireflective coating circumferentially disposed on the transparent tubular casing.    USE - The solar cell unit is useful in an assembly to generate electricity and potentially heat water or other fluids.    ADVANTAGE - The solar cell unit is compact and exhibits desirable support and strength thus avoiding its easy breakage under pressure during transportation or routine handling processes, and can be assembled in various sizes and shapes.    DETAILED DESCRIPTION - The solar cell unit (300) comprises a solar cell (402) comprising a rigid substrate, a back-electrode (404) circumferentially disposed on the substrate, a semiconductor junction circumferentially disposed on the back-electrode and a transparent conductive layer disposed on the semiconductor junction, a water resistant layer and a filler layer (330) circumferentially disposed on the transparent conductive layer, a transparent tubular casing (310) circumferentially disposed onto the filler layer, and an antireflective coating circumferentially disposed on the transparent tubular casing. The substrate is either tubular or a solid rod. The rigid substrate has a solid core. The semiconductor junction comprises an absorber layer and a junction partner layer in which the junction partner layer is circumferentially disposed on the absorber layer. The absorber layer is circumferentially disposed on the back-electrode. The absorber layer has a (110) crystallographic orientation a (112) crystallographic orientation, or no crystallographic orientation. The transparent tubular casing is formed directly on the filler layer by casting or UV curing. The transparent tubular casing comprises transparent tubular casing layers including a first transparent tubular casing layer and a second transparent tubular casing layer. The first transparent tubular casing layer is circumferentially disposed on the filler layer and the second transparent tubular casing layer is circumferentially disposed on the first transparent tubular casing layer. The solar cell has a length and a diameter, in which the length is much larger than the diameter and a cross-section of the solar cell has cross-sectional radial symmetry or approximate cross-sectional radial symmetry. The semiconductor junction comprises a first composition that comprises a first semiconductor element and the second layer comprises a second composition that comprises a second semiconductor element, in which the first semiconductor element is different than the second semiconductor element. The first composition in the first layer forms a junction with the second composition in the second composition in the second layer.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of an elongated solar cell in a transparent tubular casing.    Solar cell unit (300)    Transparent tubular casing (310)    Filler layer (330)    Solar cell (402)    Substrate (403)    Back-electrode. (404)