Rounded IV curve knee

A normal IV curve is smooth and continuous. It has a horizontal leg that slopes down slightly, a downward leg that is close to vertical, and a bend called the knee between them. This signature is a knee that bends more gradually and looks rounder than expected for the module. Judge the knee shape against the cell technology. Crystalline silicon cells normally have sharp knees, while thin film modules normally have rounder, gradual knees. A rounder knee can be a sign that the module is aging. Before you blame aging, check the slopes of the horizontal and vertical legs. If those slopes have changed, the knee can look rounder even though it has not changed itself. Before reading anything into a deviation, rule out measurement errors, instrument set-up problems and wrongly entered module or string data. Shading and soiling also change the curve shape. You get the curve with a portable IV curve tracer on a module or string, under a known irradiance. The shape of the curve helps identify the failure and work out how much power is lost.

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• sentence 2: support check: partial - D.5 names a 'rounder knee' variation, but the passages don't define it as 'more gradual than expected for the module' (the gradual/round wording appears only for thin film as normal). -->