During the recent years the popularity of solar power have increased tremendously. With the increased interest in solar power comes a development of more efficient and different types of technology to harvest the sun rays. Monofacial panels have been on the market for a long time and have rather developed simulation models. The bifacial technology on the other hand have been researched for years but just recently found its way to the market. Simulation models for the bifacial panels are continuously being developed and they are a key aspect to increase the knowledge about the bifacial technology. Most of the research that has been conducted until today is mainly about the bifacial gain, not about the bifacial simulation models.The purpose of this thesis was to evaluate and validate simulation models of bifacial solar panels in PVsyst with comparisons to measured data from six different bifacial installations in Sweden. The installations had different system configurations and varied in: tilt, azimuth, pitch, elevation, number of rows and albedo. Furthermore, the installation configuration parameters were analyzed to see how they affect the bifacial system and what an optimal configuration would be for a bifacial installation in Sweden.The results show that the main difficulties for an accurate simulation model is to determine the proper input data. The irradiance and albedo proved to be the most difficult parameters to determine. The irradiance was accurate looking at yearly level but already during monthly distribution the error is taking effect. One of the reasons for the errors is the difficulties to determine the diffuse irradiance fraction of the light, especially during cloudy days. The albedo was found to have a linear dependency on the yield, which meant that it is possible that the inaccuracy of the model are solely dependent on albedo.For tilted installations without optimizers the yearly error of the simulation ranged between -5,2% to +3,9% where the lower limit value is suspected to be caused by a wrong albedo value. For a tilted installation with optimizers the error was +9,1%. This could be caused by two reasons; the optimizers are even more dependent on the irradiance or that the software exaggerates the benefits of optimizers. The simulations of vertical installations had an error between -5,4% to -3% and are more accurate than the tilted simulations.Different parameters effect on the specific yield were studied using a simplified simulation model and stepwise change of each parameter. The results were that four of the six studied parameters have no characteristic change on each other and the optimal conditions was to maximize the pitch, elevation and albedo and minimize the number of rows. The remaining two parameters tilt and azimuth showed a dependence on the other parameters, where the optimal azimuth only was affected by tilt while the optimum tilt was affected by all the other parameters. This revelation lead to the conclusion that tilt is the most suitable parameter for optimization of installations because of its dependence on ambient conditions. The optimum tilt was found for the studied cases and in five of the six cases it would have an increased specific yield if the tilt was optimized. Note that for four of those five would lead to an increase of less than 0,5% while for the fifth an increase by 14,2%.

Recently, commercial softwares for PV system simulation released bifacial extensions. While research laboratories have developed their own simulation tools, in both cases it is imperative to display their applicability, as well as continuously assess their accuracy and/or limitations in practice, i.e. for different bifacial PV systems and field conditions. This paper presents a design and energy yield simulation study of two bifacial PV systems installed and operating in Nordic climate conditions, i.e. in Vestby, Norway ( System 1) and in Halmstad, Sweden (System 2). The aim of this study is: • To validate and compare the accuracy of two bifacial PV simulation tools newly featured in the software platforms of PVsyst and Polysun respectively, against real-field energy yield data. Each investigated system is modeled and analyzed with both simulation tools, resulting in four individual case stu dies. Further details on the systems’ monitoring set-up, the data input, modeling steps, and the involved uncertainties are presented in this paper. The results of the four case studies show higher percent deviations (both monthly and hourly data) between simulated energy results and real energy results during winter periods compared to summer periods. System 1 had a lower bifacial gain (around 2%) than System 2 which ranges from 2% in summer periods to 25% during winter. The collected field data had too high of an uncertainty to determine whether the bifacial PV simulation extensions are accurate within a certain tolerance. The reason for higher simulation inaccuracy in the winter is due to: lower production, higher uncertainty in albedo, and more diffuse irradiation. It is recommended for the bifacial PV simulation extensions include options for considering a variable albedo. The bifacial gain in System 2 was higher in the winter because of the higher albedo value given whereas in System 1, the albedo value was kept constant. Further parametric studies should be conducted on the bifacial gain using vertical mounted bifacial PV modules oriented east and west for Nordic climate conditions.

Bifacial photovoltaics (PV) is a promising technology which allows solar cells to absorb light and generate power from both front and rear sides of the cells. Bifacial PV systems generate more power per area compared to their monofacial counterparts because of the additional energy generated from the backside. However, modeling the performance of bifacial PV systems is more challenging than monofacial systems and industry requires novel and accurate modeling tools to understand and estimate the benefit of this technology. In this dissertation, a rigorous model utilizing a backward raytracing software tool called RADIANCE is developed, which allows accurate irradiance modeling of the front and rear sides of the bifacial PV systems. The developed raytracing model is benchmarked relative to other major bifacial irradiance modeling tools based on view-factor model. The accuracy of the irradiance models is tested by comparing with the measured irradiance data from the sensors installed on various bifacial PV systems. Our results show that the raytracing model is more accurate in modeling backside irradiance compared to the other irradiance models. However, this higher accuracy comes at a cost of higher computational time and resources. The raytracing model is also used to understand the impact of different installation parameters such as tilt angle, height above the ground, albedo and size of the south-facing fixed-tilt bifacial PV systems. Results suggest bifacial gain has a linear relationship with albedo, and an increasing saturating relationship with module height. However, the impact of tilt angle is much more complicated and depends on other installation parameters. It is shown that larger bifacial systems may have up to 20º higher optimum tilt angle compared to small-scale systems. We also used the raytracing model to simulate and compare the performance of two common configurations for bifacial PV systems: optimally tilted facing south/north (BiS/N) and vertically installed facing east/west (BiE/W). Our results suggest that in the case of no nearby obstruction, BiS/N performs better than BiE/W for most of the studied locations. However, the results show that for high latitude locations such as Alaska, having a small nearby obstruction may result in having better yield for vertical east-facing system than south-facing tilted system. RADIANCE modeling tool is also used in combination of a custom tandem device model to simulate the performance of tandem bifacial PV systems. Modeling results suggest that while the energy gain from bifacial tandem systems is not high, range of suitable top-cell bandgaps is greatly broadened. Therefore, more options for top-cell absorber of tandem cell are introduced.

This study aims to develop a simulation and optimisation tool for bifacial photovoltaic (PV) modules based on the open-source code OptiCE and evaluate dynamic and static albedo impact on a bifacial PV system. Further, a review of the market price development of bifacial PVs' and an optimisation to maximise energy output was conducted. Two case studies with bifacial PV modules, a single-axis tracker in Denver, USA, and a vertical and a tilted system installed at a farm outside Västerås, Sweden, were analysed in this study. The results showed that an hourly dynamic albedo value could provide more accurate simulation results of the rear side irradiance for the bifacial single-axis tracker than a static albedo value. The developed model showed an R2 accuracy of 93% and 91% for the front and rear sides, respectively, when simulated with an hourly albedo value for the bifacial single-axis tracker system. The optimisation was based on weather data from 2020. The results showed that the tilted reference system could increase its energy output by 8.5% by adjusting its tilt from 30° to 54° and its azimuth angle from 0 to -39°. In contrast, the vertical system would increase its energy output by 2.1% by rotating the azimuth angle from -90° to -66°. Conclusions that could be drawn are that bifacial PV price has closed in on the high-performance monofacial PV price the last five years and may continue to decrease in the coming years. Further, it was concluded that detailed dynamic albedo values lead to more accurate simulations of the ground-reflected irradiance. The availability of measured albedo data at the location is essential when the ground-reflected irradiance stands for a significant share of the irradiance. It was determined that during 2020 the optimal configurations of a vertical and tilted bifacial PV system in Västerås would save 11 300 SEK by consuming self-produced electricity and earn 11 600 SEK from selling the surplus of electricity for the farm outside Västerås.

Solar energy market has been rapidly growing in Sweden over the past few years. Älvdalen municipality in central Sweden is investigating the possibility of installing a utility-scale solar power plant. In the present work, we investigate technical design and economic viability of a utility-scale solar power plant in Älvdalen. Several photovoltaics (PV) designs on a 6.6-hectar land are modeled and analyzed. The installation capacity depends on design parameters, such as inter-row spacing distance and orientation.PVsyst simulation tool is used to model several PV system configurations, consisting of both mono- and bifacial PV modules. An extensive sensitivity analysis is performed to get a deep understanding of different design parameters and their effects on performance and production yield of the plant.For PV systems consisting of monofacial PV panels, a set of parameters is investigated, namely, tilt angle of PV arrays, space between rows of the plant. It is observed that an optimized design requires a careful consideration of the two parameters, since they considerably affect the amount of self-shading (shading of PV rows on each other).The optimum design generates more than 5000 MWh electricity annually.Bifacial configurations are designed in two forms: tilted (south or south-east facing) and vertical (east-west oriented). Tiled bifacial systems are basically similar to the monofacial ones. A comparison between the two systems shows that the bifacial gain is between 3 % to 10 %, depending on the tilt angle, inter-row spacing, and PV array height above the ground. Electricity generation per surface area of the vertical east-west bifacial configuration is significantly lower compared to the others and therefore, it is only economically viable together with other land applications, such as agricultural usage.Economical evaluation indicates that for the optimum design the levelized cost of energy (LCOE) is 0.67 SEK/MWh and 0.72 SEK/MWh for monofacial and bifacial system, respectively. Such financial figures are subject to change, depending on the design and financial parameters.