Comparative study of the performance of solar photovoltaic module technologies installed in Kumasi, Ghana, in Sub-Saharan Africa

Abstract

The purpose of this study was to compare the performance of heterojunction (HIT), polycrystalline (poly-Si) and thin film (a-Si) solar photovoltaic (PV) modules installed in Kumasi in Sub-Saharan Africa. Sixteen modules (6 HIT, 5 poly-Si and 5 a-Si) were visually inspected followed by electrical performance tests using I-V curve tracer after 12 years of field exposure. Hotspot tests were performed using infrared (IR) thermography after the I-V tracing. The visual inspection tests did not show any significant defects in the case of the poly-Si and HIT modules. One (1) a-Si module, however showed evidence of hotspot. The average power degradation rates for the poly-Si modules were 1.75%/yr, 1.25%/yr, 1.75%/yr, 1.6%/yr and 1.7%/yr (representing percentage drops of 21%, 15%, 21%, 19.23% and 20.23%), respectively. These values are more than the acceptable limit of 1.0%/yr for a 25-year warranty statement issued by most manufacturers. Two a-Si modules also recorded degradation rates of 1.03%/yr and 1.2%/yr (representing percentage drops of 12.3% and 14.4%) which are above the acceptable limit. The I-V data of the a-Si module which recorded a high degradation rate of 1.2%/yr and a drop of 14.4% is confirmed by the high temperature difference of 27.7°C and the hue white colour shown in the IR image. The 6 HIT modules, on the other hand, recorded very low average power degradation rates of 0.18%/yr, 0.16%/yr, 0.53%/yr, -0.2%, -0.05% and -0.03%, which are within the acceptable limit (representing power drops of 1.98%, 1.9%, 6.3%, -2.6%, -0.53, -0.27%, respectively). These results are consistent with the low temperature difference that were recorded in the hotspot tests. Three out of the five poly-Si modules recorded power performance factors (PPFs) above the acceptable limit of 80% for a 25-year warranty statement. All the HIT and a-Si modules however, recorded PPFs above the acceptable limit. The results indicate that the HIT modules performed far better in this particular environment and are recommended for consideration in any procurement decision.