“The main characteristic of bifacial modules is their ability to absorb sunlight from their rear face.” This is what Vítor Pedreira, photovoltaic project manager at Amara-e, said.
During participation in the webinar “Getting to know bifacial modules: practical applications“, carried out by Canal Solar, the expert commented on the particularities of this double-sided technology and highlighted its advantages compared to conventional panels, which capture electricity exclusively from the front.
“The big difference to a traditional solar panel is that its back layer is not made up of a white backsheet. Instead, a transparent backsheet or another layer of glass (double glass) is used, allowing diffuse light reflected from the ground or other nearby objects to be absorbed by the photovoltaic cell,” explained Pedreira.
Furthermore, according to the expert, when sizing a bifacial plant there are still some variables that need to be observed very carefully, whereas in the case of a conventional plant the same level of detail is not necessary.
“These are parameters that will influence, mainly, the capture of light from the rear face. Therefore, they are more important in sizing the module with double-sided technology – and they can influence positively or negatively, depending on the variables we adopt”, he pointed out.
Sizing Parameters
The first parameter, perhaps the most important, for the executive, is Albedo – which is an index that demonstrates how reflective a terrain is. “Lighter soils tend to reflect a greater amount of the light that falls on them, thus increasing the portion of light that reaches the back of a bifacial panel,” he explained.
“The higher the Albedo, the higher the generation. Therefore, it is essential to understand the type of land that will be installed at the plant, and whether it would be worth it, in terms of energy gains, to install crushed stone or a lighter surface to increase electricity generation”, he added.
In installations with bifacial modules, height is also crucial when it comes to irradiance on the back of the photovoltaic panel. According to Amara-e's project manager, choosing the right height can make a big difference in double-sided generation, because a shaded cell or set of shaded cells affects a large part of the panel.
“We do not recommend bifacial installations on roofs, as, logically, the module will be very close to the surface that will reflect the light. And then, we won’t have this greater height to be able to increase the solar radiation that falls on its back face”, he reported.
“The ideal is to maintain at least a height of 60 cm. If it is smaller, it would be interesting to simulate the PVSyst to also see what result we can achieve with a lower height, in addition to trying to seek heights close to 1 m, which will then have ideal scenarios for greater generation”, highlighted the specialist.
Read more: Bifacial modules dominate the photovoltaic sector in 2020 in Brazil
The last parameter for bifacial sizing is the distance between the rows, called Pitch. However, how can it influence the generation of the back side of the modules?
For Vítor Pedreira, this variable is widely considered in soil plants with conventional panels, but it should be even more important when analyzing panels with double-sided technology, as in addition to the direct shadow caused, the diffused light that will be reflected on the back.
“This value is used to determine the GCR (Ground Coverage Ratio), which represents the division of the module area by the total area of the plant. In other words, by increasing the distance between them, we consequently increase the total area required to install the system. With this, we have a larger space where solar rays fall on the ground and reflect on the bifacial modules, producing more energy”, he reported.
Even so, according to him, this variable raises several doubts for customers, as many are used to the distance of 7 meters from pillar to pillar. “When they go to a plant with bifacial technology, we recommend that, in order to have a gain of more or less 1 or 2% in generation, increase this distance to up to 12 meters, for example”.
So, according to Pedreira, this is a parameter that is always requested not to be discarded from the beginning, as they may indeed be viable and compensate for the additional expense of land and, possibly, other items.
