Numerical modeling of all-day albedo variation for bifacial PV systems on rooftops and annual yield prediction in Beijing

Bifacial PV modules capture solar radiation from both sides,enhancing power generation by utilizing reflected sunlight.However,there are difficulties in obtaining ground albedo data due to its dynamic variations.To address this issue,this study established an experimental testing system on a rooftop and developed a model to analyze dynamic albedo variations,utilizing specific data from the environment.The results showed that the all-day dynamic variations in ground albedo ranged from 0.15 to 0.22 with an average of 0.16.Furthermore,this study evaluates the annual performance of a bifacial PV system in Beijing by considering the experimental conditions,utilizing bifacial modules with a front-side efficiency of 21.23%and a bifaciality factor of 0.8,and analyzing the dynamic all-day albedo data obtained from the numerical module.The results indicate that the annual radiation on the rear side of bifacial PV modules is 278.90 kWh/m^(2),which accounts for only 15.50%of the front-side radiation.However,when using the commonly default albedo value of 0.2,the rear-side radiation is 333.01 kWh/m^(2),resulting in an overestimation of 19.40%.Under dynamic albedo conditions,the bifacial system is predicted to generate an annual power output of 412.55 kWh/m^(2),representing a significant increase of approximately 12.37%compared to an idealized monofacial PV system with equivalent front-side efficiency.Over a 25-year lifespan,the bifacial PV system is estimated to reduce carbon emissions by 8393.91 kgCO_(2)/m^(2),providing an additional reduction of 924.31 kgCO_(2)/m^(2)compared to the idealized monofacial PV system.These findings offer valuable insights to promote the application of bifacial PV modules.

Influence and characteristic of shading on photovoltaic performance of bifacial modules and method for estimating bifacial gain

Bifacial PV modules have unique advantages in low-carbon building applications such as BIPV systems but often suffer from the shading problem resulting from higher surrounding objects or building facades.Point-blank quantitative studies of PV performance of bifacial modules operating in actual environments as affected by shading on PV cells are lacking due to the difficulties of analysis caused by the existing multiple variable factors.By constructing an experimental comparison system on a flat roof of a building,we experimentally tested and analyzed the comparative variation characteristics of PV performance of bifacial and mono-facial modules under different shading area fractions.The results show that from the viewpoint of photoelectric efficiency,the PV performance of both bifacial and mono-facial PV modules clearly varied with the shading fraction of PV cell in some linear rules,though it is difficult to find regularity from the perspective of output power which was also affected by dynamic solar radiation intensity.An abnormal phenomenon emerged that the photoelectric efficiencies of the bifacial modules with small shading fraction were higher compared to the case without shading.Based on the findings of the experimental results,a regression approximation method based on shading test results(RAST Method)is further proposed to analyze and calculate the bifacial gain of bifacial modules.In the case of the existing roof installation,the mean bifacial gains of the two bifacial modules with different inclination angles were 8.86%and 11.30%,respectively.