Solar Photovoltaic modules use light energy (photons) from the Sun to generate electricity through the photovoltaic effect, but not using the heat which the Sun generates. The solar Module electrical connections are made in series to achieve a desired output voltage or in parallel to provide a desired current capability (amperes), depending upon the application of choice.
Module performance is generally rated under standard test conditions (STC): irradiance of 1,000 W/m2, solar spectrum of AM 1.5 and module temperature at 25°C. Electrical characteristics include nominal power (PMAX, measured in W), open circuit voltage (VOC), short circuit current (ISC, measured in amperes), maximum power voltage (VMPP), maximum power current (IMPP), peak power, (watt-peak, Wp), and module efficiency (%). The actual performance parameters of the module changes as lighting, temperature and load conditions change.
Impact of temperature on PV module performance
Temperature is the key factor that impacts the output power of solar panels and it needs to be within the specified limits. Behavior of different solar panels changes with its operating ambient temperature resulting in decrease of the output power with every increase in temperature.
Sun’s radiation consists of two components – heat and light. An increase in temperature does not change solar energy reaching the panels, however, it reduces the amount that can be converted into electricity from the solar panel.
Energy that the solar panels produce is a function of power, further power is the product of current and voltage (P= I x V). So, while an increase in temperature slightly increases the current in solar cells, the voltage is decreased by a greater amount which results in reduced power output, and resulting in solar module parameters going away from the desired system specifications.
The Temperature Coefficient
Every PV modules has its different unique temperature coefficient value (Pmax) in the data sheet provided by the manufacturer. This is in the form of negative percentage and it reveals the temperature effect on the PV module.
Solar Panels are rated at 25oC and therefore the temperature coefficient percentage depicts the change in efficiency with each degree up and down in temperature. For instance, if the temperature coefficient of a panel is -0.40%, then for every 1oC rise, the panel’s maximum power will reduce by 0.40%.So, on a hot day, when panel temperatures may reach 45oC, a panel with a temperature coefficient of -0.40% would result in a maximum power output reduction of 8%.
Similarly the temperature coefficients of voltage are also represented in negative, indicating the drop in voltage of the solar modules at elevated temperatures. Considering the voltage temperature coefficient value of -0.3% for each and every degree raise in temperature, for a module installed in field with operating at a temperature of 45oC, the voltage of the module will drop by 6% from the rated value measured at STC conditions on the nameplate.
So, it becomes imperative for solar system installers and owners of the solar system to consider these things while installation and owning a solar system for various applications.