NOVELTY - A solar panel backside film comprises: either polyethylene terephthalate (PET) film having a net peak area as measured by differential scanning calorimetry of -15-5 J/g measured from the endpoint of its glass transition point up to 230 degrees C, and an additive to opacity the polyethylene terephthalate film; and polymeric layer adhered to the polyethylene terephthalate film to create a solar panel backside film; or polyethylene terephthalate film having an intrinsic viscosity of greater than or equal to 0.60 and at least one other polymeric layer adhered to the polyethylene teraphthalate to create a solar film.    USE - In solar panel (claimed); in solar panel constructions.    ADVANTAGE - The solar panel backside film has a reflectivity of greater than or equal to 50 (preferably greater than or equal to 70) % at a point in the visible range of light; enhances the durability, longevity and performance of photovoltaic modules placed in a solar panel; has a shrinkage of less than 1% measured at 150 degrees C when held for 15 minutes in accordance with ASTM 2305-02; exhibits an elongation to break of at least 10% after 2000 hours of exposure to 85 degrees C and 85% relative humidity; exhibits after exposure to 2000 hours at 85 degrees C and 85% relative humidity an adhesion failure mechanism between the polyethylene terephthalate film and polymeric layer that is not cohesive within the polyethylene terephthalate film; improves PET films to construct opaque, reflective, low shrink solar backside films that maintain their physical and mechanical integrity and do not crack or exfoliate during extended exposure to environmental conditions such as heat and moisture; addresses the deficiencies of conventional films used in solar panel constructions. When the solar film when applied to a solar panel and exposed to 2000 hours of 85 degrees C and 85% relative humidity, then the polyethylene terephthalate film does not exhibit visible racks or exfoliation.    DETAILED DESCRIPTION - A solar panel backside film comprises: either polyethylene terephthalate (PET) film having a net peak area as measured by differential scanning calorimetry of -15-5 J/g measured from the endpoint of its glass transition point up to 230 degrees C, and an additive to opacity the polyethylene terephthalate film; and polymeric layer adhered to the polyethylene terephthalate film to create a solar panel backside film (where the solar panel backside film has a reflectivity of greater than or equal to 50% at a point in the visible range of light, and the solar panel backside film, when applied to a solar panel and exposed to 2000 hours at 85 degrees C and 85% relative humidity, then the polyethylene terephthalate film does not result in exfoliation or visible cracks in the polyethylene terephthalate film); or polyethylene terephthalate film having an intrinsic viscosity of greater than or equal to 0.60 and at least one other polymeric layer adhered to the polyethylene teraphthalate to create a solar film (where the solar film when applied to a solar panel and exposed to 2000 hours of 85 degrees C and 85% relative humidity, then the polyethylene terephthalate film does not exhibit visible racks or exfoliation). INDEPENDENT CLAIMS are included for the following:    (1) a solar panel comprising: glass; several solar cells encapsulated in a polymer and adhered to the glass; and the solar panel backside film adhered to the polymer on a surface opposite the glass; and    (2) preparation of the solar panel backside film involving: providing a polyethylene terephthalate film having a net peak area as measured by differential scanning calorimetry of -15-5 J/g measured from the endpoint of its glass transition point up to 230 degrees C, and an additive to opacity the polyethylene terephthalate film; and applying a polymeric layer to the polyethylene terephthalate film to create a solar panel backside film (where the solar panel backside film has a reflectivity of greater than or equal to 50% at a point in the visible range of light, and the solar panel backside film, when applied to a solar panel and exposed to 2000 hours at 85 degrees C and 85% relative humidity, does not result in exfoliation or visible cracks in the polyethylene terephthalate film).