Thermal performance evaluation and efficiency mapping of SUNTAP PVC solar collectors under southern African solar irradiance

This study presents a comprehensive thermal performance evaluation of an innovative SUNTAP solar collector fabricated from polyvinyl chloride (PVC) with an internal aluminium lining. Testing was conducted under authentic Southern African solar irradiance conditions over 30 consecutive days during June (Southern Hemisphere winter), capturing irradiance values spanning 155–955 W/m². High-precision Pt500 RTD sensors monitored inlet and outlet fluid temperatures at 30-minute intervals between 09:00 and 16:00 daily, yielding 450 validated measurement data points. The collector (gross absorber area: 1.26 m²; tilt: 20°; north-facing) achieved a mean monthly thermal efficiency of 38.0 ± 1.7%, with peak daily efficiency of 42.1% under optimal clear-sky conditions and a minimum of 31.4% during overcast periods. Maximum fluid temperature rise was 26°C, and total useful energy delivery over the evaluation period was 47.65 kWh from 125.4 kWh incident radiation. Pearson correlation analysis yielded R² = 0.89 (p < 0.001) between outlet temperature and incident solar radiation, confirming strong thermal coupling. No statistically significant performance degradation was detected over the 30 days (linear regression slope: −0.008% day⁻¹; p = 0.68). These findings validate the SUNTAP collector as a cost-effective solar thermal solution for domestic water heating in developing economies and identify glazing, back-insulation, and selective surface coatings as primary optimization pathways.