Key Parameters Contributing Gain in Bifacial PV Systems

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Bifacial PV modules are the upcoming product & future of solar Industry. They offer several advantages over traditional solar PV Modules. Power can be produced from front and back side of a bifacial module thus increasing total energy generation within same area. Since both sides of these modules are UV resistant, they are more durable and have reduced potential-induced degradation (PID) concerns especially when the module is frameless, however it increases the chances of breakage.

The yield gain over conventional monofacial modules is mainly determined by the conversion efficiency for solar irradiance incident on the rear side of a bifacial PV module, and the amount and quality of solar irradiance incident on the rear side. Bifacial modules allow a unique vertical mounting configuration. Various studies indicate that vertically installed bifacial PV modules in higher latitude locations produce energy which is comparable to monofacial modules installed at conventional latitude tilt, and significantly higher than that of vertically mounted monofacial modules.

Below are the major key parameters that contribute to the gain in bifacial PV system:

Albedo is the measure of solar irradiance incident on the rear side. It is defined as the ratio of irradiance reflected to the irradiance received by a surface. Albedo depends on soil surface colour & texture. This require proper soil condition study for its optical properties for uniform gain throughout the year. Hence soil preparation activity is very important for getting maximum gain from bifacial modules. The whiter & smoother is the surface the better is the albedo resulting in higher bifacial gain. It can also vary with seasons like for winter with white snow it is about 90%, for spring with green grass it is around 25%, summer with dry grass accounts to 33% and fall with humid soil gives nearly 15% of gain, hence making snow the best and volcanic rock the worst case for albedo.

Height is another key factor taken into consideration while designing the bifacial modules. Bifacial performance is increased by increasing the height of the installation thereby reducing the shadow intensity projection. According to our study, at the height 0.5m, 0.8m and 1.2m gain obtained is approximately -3%, 5% and 8% respectively, but this gain is limited to certain height. Increasing the height beyond certain height the saturation will set in the gain.

Pitch also plays a vital role in contributing the energy gain. Greater is the pitch, more is the reflected area resulting lower Ground Coverage Ratio (GCR) thus giving higher bifacial energy gain. However, increasing the pitch is not a feasible option as it comes along with issues of land constraints and increasing the total cost of the project. The cost of bifacial modules is about 8% higher over conventional monofacial modules with an advantage of 5-10% gain.

According to bifacial module market share forecast, its deployment is about to be 3% by end of 2018 and the market aims to rise sharply, reaching 40% by 2025. We at Mahindra will be deploying 10-20MW of Bifacial modules by first quarter of 2019 and shall be sharing more insights on Bifacial modules post installation in our upcoming article release.

Credits: Mahindra Susten

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