Energetica India Magazine: september 2020

SOLAR POWER In larger collectors, an increasing number of photovoltaic cells is installed at a larger height. The irradiance-reflecting ground width is also larger, meaning the percentage of rear irradiance capture is eventually the same, regardless of solar tracker size. 27 energetica INDIA- September_2020 Figure 1. Normalized height concept Figure 2. Equivalent trackers of normalized height value However, due to aspects not relating to bifaciality, such as ad- equate solar installation height, the 2P array available in the marketplace is located at a lower normalized height step com- pared to the 1P array. That means the obliquity of solar rays impacting on the 2P col- lector increases, and it implies a less intense reflected irradi - ance captured by the cells. That is known as normalized solar tracker height . In the solar industry the concept ‘aspect ratio’ is also used, a parameter that comes from the aerospace engineering. Figure 3. Different geometrical condition on solar trackers The more or less efficiency on this geometrical tracker condi - tion is directly linked to the view factor (VF) of it. Apart from the VF itself, there are two basic parameters that imply a later adjustment in the captured irradiance: • Mismatch . The reflected rays impact on the photovoltaic cells at different angles, resulting in captured irradiance dif- ferences. This difference or mismatch translates into reduced power generation by the panel as a whole. For common solar tracker geometry and albedo values, the mismatch ranges be- tween 1% and 3%. • Shading factor . The shades produced by the own structure of the solar tracker also imply a reduction in power generation. In this regard, the torque tube and the purlins are the interme- diate elements responsible for most of the backside shading. In the existing marketplace, and considering the most com- mon solar tracker configurations, 1P and 2P, we are referring respectively to torque tube of square elements with a width of 100 mm or 150 mm installed, at a mere 200 mm from the cap- turing surface, which is the photovoltaic panel row. Regardless of the projected tracker, shading affects mostly the central photovoltaic cells, which sit closer to the torque tube. For common tracker geometry and albedo values, the shading factor ranges between 3% and 6%. Not only the torque tube but the purlin itself is also located along the trajectory of the ground-reflected rays coming diag - onally towards the PV panel. The larger the purlin is, the more interference will produce. In this sense, a typical 1P purlin of 440mm produces lower affection in terms of shadowing than the common 2P purlin of 2350mm. This length requirement or restriction comes directly from the fixing options of the mod - ules, where fixing in both halves of each module is needed.