The thermal solar collector was of a direct-flow design; which consisted of tubes with a co­axial heat transfer conduit connected to a manifold with a parallel inlet/outlet pipe configuration. Twenty evacuated tubes were installed equating to an absorber area of 2.046 m2, with vacuums in the order of 10-5 mbar. Filtered water was the heat transfer fluid used throughout this study, with no anti-freeze component being added to the system. All data was recorded using Thermomax’s in-house solar simulator as shown in Figure 1. Thirty-six Tungsten Halogen lamps (3500 K) were used to produce 18 kW of power to irradiate the collector surface. This system was capable of generating average irradiances in the range 200 to 1500 Wm-2. A correction factor for the spectral discrepancy between the solar simulator and natural sunlight was applied using the effective transmittance — absorptance product method4 and the cool sky was used to minimise the influence of
thermal irradiance on the collector. The solar simulator rig (i. e. solar cradle and cool sky) was capable of a 90° rotation between the vertical and horizontal planes. Acquisition of the data was recorded on in-house software program designed using National Instruments LabVIEW 7, where the deviation of the measured parameters was consistent with EN12975-2.