Elsevier

Renewable Energy

Volume 81, September 2015, Pages 293-307
Renewable Energy

New integrated simulation tool for the optimum design of bifacial solar panel with reflectors on a specific site

https://doi.org/10.1016/j.renene.2015.03.047Get rights and content

Highlights

  • A new simulation tool was developed to predict the yearly yield of a bi-facial solar panel with a reflector accurately.

  • The new simulation tool, consists of several open-source software packages, was used to analyse the solar cells performance.

  • The bifacial solar panel that was optimized using the simulation tool shows 26% higher yearly yield in the simulation result.

  • A bifacial solar panel prototype with the optimized design was built and tested.

Abstract

The use of a commonly available planar reflector such as a plane mirror can boost the energy output of a bifacial solar panel effectively without increasing much in the overall cost. However, the actual energy yield from the solar panel in this case is dependent on the light reflected from the reflector and surrounding objects to the rear surfaces of the solar cells. The design of the bifacial solar panel with the reflector has to be optimized in order to achieve the maximum yield on a specific site setup. Therefore, a new simulation tool consisting of several open-source software packages with the bifacial solar cell model is developed to predict the yearly yield of the bifacial solar panel with the reflector accurately. The simulation tool includes the effects of the temperature changes in solar cells and the variation in solar irradiance incident on both front and rear sides at different time in a day, the manufacturing mismatch of the solar cells, and also the reflected light from the nearby objects. The simulation tool is verified experimentally and used to determine the optimum design of a site-specified bifacial solar panel that can achieve the maximum increase of 26% in yearly yield.

Introduction

A bifacial solar panel can utilize both surfaces to convert sunlight into electrical energy. A simple planar reflector such as mirror had been used to boost its output by reflecting sunlight to its rear surface [1], [2], [3]. A simulation method for the bifacial solar cells with such a reflector had been reported. The optical simulation of bifacial solar cells had been done using a three dimensional Monte Carlo ray tracer with the photo-generated current output simulated by a commercial TCAD software [1]. This approach calculates the surface reflections of the solar cells accurately and predicts the photo-generated current for different types of reflectors. However, it does not take into account of the effect of installation location and environment on the performance of the bifacial solar cells. Besides, performance drop due to manufacturing mismatch and variation in reflected sunlight intensity on the solar cells from time to time is not included in the simulation too.

Performance of the bifacial solar panel with a reflector is heavily dependent on the amount of reflected light from the nearby objects on the site and the design of solar panel, or more specifically, the spacing of solar cells in the panel and the distance from the reflector. This is because the amount of sunlight reflected from the reflector to the rear surface of the panel is dependent on the sunlight direction and intensity, which is varying from time to time and dependent on the installation location. The rear surface of the bifacial solar cell can be shaded by the same solar cell or the solar cells nearby and the effect of shading is dependent on the design of solar panel. Moreover, large objects in the installation environment, such as the buildings nearby may reflect sunlight to the solar panel at a certain period of time but block the sunlight from reaching the panel at another period of time. Therefore, an accurate simulation model for the bifacial solar panel that takes into account of all the above-mentioned factors is required to simulate the output of the solar panel and predict its yearly yield accurately, so that the solar panel design can be optimized based on its yearly yield.

The solution of optimum spacing in the solar panel and distance from the reflector on a specific location that output the highest yearly yield cannot be found easily using indoor experimental approach, such as the method used in Ref. [4], since the different atmospheric attenuation and solar incident angle on different days cannot be reproduced easily using solar simulator. Outdoor experimental approach, on the other hand, can provide more reasonable answer but it requires a very long measurement period with numerous different solar panel setups with different spacing and distances being measured at the same time. Comparing outdoor measurement results at different times is not appropriate because the results are affected by different solar incident angles on different days. However, simulation results from a more accurate simulation model can be used as the initial value for in the outdoor experiments in order to reduce the number of solar panel setups.

A new and accurate simulation tool is therefore developed using open-source software packages, namely SMARTS [5], [6], Radiance [7] and PC1D programs [8], [9]. The SMARTS program is to simulate the solar irradiance on a specifically geographical location taking into account the local climate. The function of Radiance program is to simulate the reflected light from the surrounding subjects that will be received by the front and rear surfaces of the bifacial solar cells at a specific solar panel design. The PC1D programme is used to simulate the yield based on the light irradiance received by both sides of all the bifacial solar cells. Additional scripts are developed to be the interface with each program in order to facilitate the flow of input and output data between the programs as well as calculate the yield of the simulated solar panel. These three software packages are integrated to become a useful simulation tool that is able to simulate the performance of the bifacial solar panel at a particular installation location taking into account the factors mentioned above. A heat transfer model for the bifacial solar cells is developed and integrated with the software packages such that the simulation tool can determine the performance of the solar cells taking into account of the solar cell temperature.

By combining the capabilities of several software packages, it is possible to assess the solar panel outdoor performance in more details with high accuracy. Due to the complexity and a vast amount of uncertainties in the physical phenomena that happens in the real world at outdoor, exact quantitative results that can match with the outdoor measurement ones precisely is still unlikely to get from the simulation tool. However, the results can be much more useful than any rough estimate for the performance assessment of the solar panel design that heavily depends on the outdoor environment and the actual sunlight. In addition, the intermediate outputs generated from the open-source software packages can be used to analyse the performance of the solar cells in more details. Also, this simulation tool can be constantly upgraded and improved if the capabilities of these open-source packages are improved or enhanced by the developers.

This paper begins with a detailed description of the simulation program. Output from the simulation program is then verified by comparing its result to the measured current–voltage characteristic curve of a bifacial solar panel. Finally, the bifacial solar panel design is optimized based on its yearly yield that is calculated using the simulation tool.

Section snippets

Methodology

A simulation tool for a bifacial solar panel with a reflector was developed. Several experiments were conducted to obtain unknown parameters of the bifacial solar cell and verify the output from each model. The overall accuracy of the simulation model was then evaluated by comparing the simulation results with the measured current–voltage characteristic curve of the bifacial solar panel placed under the sun. Then, the yearly yield was estimated using the simulation tool. Lastly, optimization of

Conclusion

A simulation tool is developed to predict the yearly yield of a bifacial solar panel with a reflector and to analyse the solar cells performance in details. It consists of 3 parts: the SMARTS program that simulates solar irradiance, the Radiance program that models light irradiance received by every bifacial solar cell, and PC1D program that calculates the current–voltage characteristic curve of each solar cell. The simulation result from each part is verified by comparing the simulated result

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    Hence, accurate modeling of rear illumination is necessary to make informed decisions when developing large-scale solar systems. Several studies have investigated a variety of optical effects in bifacial systems through modeling (Yusufoglu et al., 2014; Reise and Schmid, 2015; Pelaezet al., 2019a, 2019b, 2019c; Egido and Lorenzo, 1986; Pérez Oria and Sala, 1988; Lo et al., 2015; Lindsay et al., 2015; Shoukry et al., 2016; Chiodetti et al., 2016; Hansen et al., 2017; Janssen et al., 2017; Vogt et al., 2018; McIntosh et al., 2019; Horvath et al., 2019; Jäger et al., 2020). The two common methods for modeling the rear illumination of PV modules are view-factor (Yusufoglu et al., 2014; Egido and Lorenzo, 1986; Pérez Oria and Sala, 1988; Lindsay et al., 2015; Shoukry et al., 2016; Chiodetti et al., 2016; Hansen et al., 2017; Janssen et al., 2017; Jäger et al., 2020) and ray tracing (Reise and Schmid, 2015; Pelaez et al., 2019a, 2019b, 2019c; Lo et al., 2015; Vogt et al., 2018; McIntosh et al., 2019; Horvath et al., 2019).

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