Solar expert Marc Schifferle of ten Haaft explained that a module's peak wattage (Wp) is a laboratory rating that real-world conditions rarely match. Reaching 200 W requires perpendicular sunlight, irradiance of 1,000 W/m² and cell temperature no higher than 25 °C. Heating to 65 °C cuts output by about 14%, while partial shading can reduce it by 30–80%. Allowing for controller efficiency of 90–98% and Central European conditions, a panel delivers roughly 80% of its rating, with about 76% reaching the battery. In a hot-weather test a 210 Wp module produced 164 W.
