How I-V Curves Vary with Irradiance and Temperature

The shape and position of a photovoltaic module’s I-V curve are strongly influenced by environmental conditions, particularly irradiance and temperature. These two factors affect different parts of the curve and influence the power output of the module in distinct ways.

Irradiance primarily affects the current produced by the module. As irradiance increases, a greater number of photons are available to generate charge carriers, and the short-circuit current \(I_{\mathsf{sc}}\) increases almost proportionally. Consequently, the entire I-V curve shifts upward. The open-circuit voltage \(V_{\mathsf{oc}}\) also increases slightly with higher irradiance, but this change is much smaller than that of the current. Since power is the product of voltage and current (\(P = I \times V\)), higher irradiance directly increases the module’s maximum available power.

Temperature primarily affects the module’s voltage. As cell temperature rises, the semiconductor material becomes less effective at maintaining voltage, resulting in a decrease in open-circuit voltage \(V_{\mathsf{oc}}\). This decrease shifts the I-V curve to the left. Short-circuit current \(I_{\mathsf{sc}}\) increases only very slightly with temperature, and this effect is generally small. Since the decrease in voltage occurs more rapidly than the increase in current, higher temperatures result in a significant drop in maximum power. This is why photovoltaic modules produce less power in hot weather than in cool, sunny conditions.

In actual operation, irradiance, temperature, and the solar spectrum vary simultaneously. A bright, cool day generates high currents and high voltages, leading to good performance. A hot day with high irradiance produces high currents but lower voltages. Cloudy conditions or low irradiance shift the curve downward, resulting in lower power at all operating points. Understanding how these dependencies modify the I-V curve is essential for predicting photovoltaic performance under real-world conditions and optimizing system design.