NOVELTY - The solar cell unit comprises a rigid and a non-planar substrate, a first photovoltaic cell comprising a first back-electrode disposed on a first portion of the substrate and a second photovoltaic cell comprising a second back-electrode disposed on the substrate, a first and a second semiconductor junction layer disposed on the first and the second back-electrode respectively, a first and a second transparent conductive layer disposed on the first and the second semiconductor junction layer. The substrate has a first end and a second end.    USE - The solar cell unit is useful in a solar cell assembly (claimed) for converting solar energy into electrical energy.    ADVANTAGE - The solar cell unit has excellent UV shielding properties and good water proofing characteristics, and is cost effective.    DETAILED DESCRIPTION - The solar cell unit comprises a rigid and a non-planar substrate, a first photovoltaic cell comprising a first back-electrode disposed on a first portion of the substrate and a second photovoltaic cell comprising a second back-electrode disposed on the substrate, a first and a second semiconductor junction layer disposed on the first and the second back-electrode respectively, a first and a second transparent conductive layer disposed on the first and the second semiconductor junction layer. The substrate has a first end and a second end. The transparent conductive layer of the first photovoltaic cell is in serial electrical communication with the back-electrode of the second photovoltaic cell. The first photovoltaic cell is adjacent to the second photovoltaic cell. The first transparent conductive layer is in serial electrical communication with the second back-electrode. The first transparent conductive layer is electrically isolated from the second transparent conductive layer. The first back-electrode is electrically isolated from the second back-electrode. The substrate has a Young's modulus of greater than or equal to 70 GPa. The substrate is made of a linear material. A portion of the substrate is a rigid solid rod and is characterized by a circular cross-section, an ovoid cross-section, a triangular cross-section, a pentangular cross-section, a hexagonal cross-section, a cross-section having at least one arcuate portion, or a cross-section having at least one curved portion. A first and a second portion of the substrate are characterized by a first and a second cross-sectional shape. Ninety percent of the length of the substrate is characterized by the first cross-sectional shape. The first cross-sectional shape is planar and the second cross-sectional shape has an arcuate side. A cross-section of the substrate is circumferential and has an outer diameter of 14-17 mm and is characterized by an inner radius defining a hollowed interior of the substrate, and an outer radius defining a perimeter of the substrate. The thickness of the substrate is 1-2 mm. The solar cell unit has a length of 5-10000 mm. The photovoltaic cells comprises a first terminal photovoltaic cell at the first end of the substrate, a second terminal photovoltaic cell at the second end of the substrate, and an intermediate photovoltaic cell between the first terminal photovoltaic cell and the second photovoltaic cell. The transparent conductive layer of each intermediate photovoltaic cell is in serial electrical communication with the back-electrode of an adjacent photovoltaic cell. The photovoltaic cells comprise one hundred or more photovoltaic cells. A transparent tubular casing is disposed onto the transparent conductive layer of all or a portion of the photovoltaic cells. The substrate is configured so that a fluid is passed through the substrate. The semiconductor junction of a photovoltaic cell comprises a homojunction, a heterojunction, a heteroface junction, a buried homojunction, a p-i-n junction, or a tandem junction. The semiconductor junction comprises an absorber layer and a junction partner layer in which the junction partner layer is deposed on the absorber layer. The photovoltaic cell comprises an intrinsic layer disposed on the semiconductor junction of the photovoltaic cell. The transparent conductive layer is disposed on the intrinsic layer. A filler layer is disposed onto the transparent conductive layer of all or a portion of the photovoltaic cells. The filler layer has a viscosity of less than 1x 10-6 cP, and a thermal coefficient of expansion of greater than 500x 10-/ degrees C. The filler layer is formed from silicon oil mixed with a dielectric gel, and from a polydimethylsiloxane polymer liquid (30-90 wt.%), a first silicone elastomer (2-20 wt.%) and a second silicone elastomer (2-20 wt.%). The polydimethylsiloxane polymer liquid has silicone compound of formula ((CH3)3SiO(SiO(CH3)2)nSi(CH3)3), where n is integers chosen such that the polymer liquid has an average bulk viscosity that falls in the range of 50-100000 centistokes. A water resistant layer is disposed onto the transparent conductive layer of all or a portion of the photovoltaic cells. The casing is disposed on the water resistant layer. A fluorescent material is coated on the water resistant layer. An antireflective coating is disposed on the transparent tubular casing. The antireflective coating is disposed onto the transparent conductive layer of all or a portion of the photovoltaic cells. INDEPENDENT CLAIMS are included for:    (1) a solar cell assembly; and    (2) a method.    DESCRIPTION OF DRAWING(S) - The drawing shows the three-dimensional tubular profile of the solar cell unit.    Substrate (102)    Back electrode (104)    Absorber (106)    Window layer. (108)