The periods when the resistance was turned can be clearly
identified when inlet temperatures suddenly increase. The air at the collector output reached temperatures
between 45 °C and 80 °C. When the resistance is turned on, the difference (To-Ti) decreases, due to the
increase of the collector thermal losses. A mean difference (To-Ti) of 50ºC was measured at the solar noon
when the solar irradiance is maximum for air entering the collector at outdoor temperature. This
difference is around 40ºC when the air is heated by the electrical resistance