Photovoltaic (PV) module efficiency deteriorates with rising operating temperature due to thermal losses in open-circuit voltage, reduced fill factor, and increased resistive effects. This study proposes a novel Evaporative Clay Pot-Grass Passive Cooling (ECGPC) technique, integrating a porous earthen clay pot with a natural grass-based moisture-retaining thermal interface mounted on the rear of a PV module. Unlike conventional evaporative or water-spray methods, ECGPC provides sustained cooling with ultra-low water consumption, eliminating the need for continuous spraying, external control, or high energy input. An experimental investigation was conducted under real indoor conditions using two identical 50 W polycrystalline PV modules-one with ECGPC and one uncooled. Module temperature, open-circuit voltage (Voc), short-circuit current (Isc), output power, and efficiency were continuously monitored. ECGPC achieved a 30-35% reduction in operating temperature, mitigating thermal losses in Voc and enhancing electrical efficiency by up to 15.29%. The cooled module consistently delivered higher output power, with minimal variations in Isc. A key novelty of ECGPC is its extremely low water requirement of similar to 0.003 L/min, enabled by the grass layer's ability to retain moisture. Operating with an 8 W DC pump, the system demonstrated a positive net energy gain, confirming practical feasibility. Due to its simplicity, scalability, minimal water usage, and negligible energy penalty, ECGPC offers a sustainable concept that requires field validation of a cooling solution for PV installations in hot and arid regions. The method's low-resource design makes it especially suitable for enhancing PV performance where conventional cooling is impractical.