3 thermocouples are evenly distributed
along the vertical centre-line of the inlet. The mean temperature
from the three measurements was taken as the inlet temperature.
The same method is used to determine the outlet temperature. To
measure the temperatures of absorber surface, 12 thermocouples
are fixed onto the surface evenly. The external surface temperature
of glazing is measured with 3 thermocouples. The thermocouples
are inserted inside the reflective aluminium shields to reduce as far
as possible the measurement error.