NOVELTY - Solar cell unit (300) comprises: a solar cell (402) comprising a rigid substrate that is either tubular or a solid rod, a back-electrode circumferentially disposed on the substrate, a semiconductor junction layer circumferentially disposed on the back-electrode and a transparent conductive layer circumferentially disposed on the semiconductor junction; a filler layer circumferentially disposed on the transparent conductive layer; and a transparent tubular casing (310) circumferentially disposed on the filler layer to circumferentially seal the solar cell.    USE - The solar cell unit is useful in solar cell assemblies for converting solar energy into electrical energy.    ADVANTAGE - The solar cell unit provides: the outer transparent tubular casing layer having excellent UV shielding properties whereas the inner transparent tubular casing layer has good water proofing characteristics; multiple transparent tubular casing layers which reduce costs and/or improve the overall properties of transparent tubular casing; transparent tubular casing layer having excellent optical properties (e.g. index of refraction); and silicone adhesives having high degree of flexibility and very high temperature resistance. The solar cell unit is stable upon exposure to UV radiation.    DETAILED DESCRIPTION - Solar cell unit (300) comprises: a solar cell (402) comprising a rigid substrate that is either tubular or a solid rod, a back-electrode circumferentially disposed on the substrate, a semiconductor junction layer circumferentially disposed on the back-electrode and a transparent conductive layer circumferentially disposed on the semiconductor junction; a filler layer circumferentially disposed on the transparent conductive layer, where the filler layer has a first refractive index; and a transparent tubular casing (310) circumferentially disposed on the filler layer to circumferentially seal the solar cell, where the tubular casing has a second refractive index that is smaller or equal in value to the first refractive index.    DESCRIPTION OF DRAWING(S) - The figure shows the photovoltaic element with tubular casing.    Solar cell units (300)    Transparent tubular casing (310)    Elongated cylindrical solar cell (402)    Electrode strips (420)