We demonstrate a practical and robust encapsulation for environment-stable solar window modules based on multi-crystalline silicon solar cells with ultra-violet-curable optically clear resin (OCR) films. Compared to encapsulation with polyvinyl butyral (PVB) films, OCR films significantly improved the operational stability in solar window modules following a harsh damp heat test, at 85 degrees C of temperature and 85% of relative humidity for 1 k h. Such advance can be realized by suppressed chemical reactions with water molecules in OCR films. We further investigate the optical characteristics of PVB and OCR encapsulation films using ultraviolet/vis. spectrophotometer and Fourier-transform infrared spectroscopy measurements to support the claim. We believe that this is the first module-level demonstration (400 mm k 400 mm) of solar windows encapsulated with OCR films fabricated below 60 degrees C by using UV curing technology, which exhibit a power conversion efficiency of similar to 10%, even after undergoing the damp heat tests.