In Canada, many remote communities rely on diesel power for the majority of their energy needs, which can cause negative ecological and health impacts while limiting economic development. Bifacial photovoltaics present an alternative to diesel power. With high average latitudes, these communities show potential for large bifacial gains due to high albedo caused by snow and a high fraction of diffuse light; however, high-latitude conditions deviate from standard test conditions, with low average temperatures, light incident from many directions, and high average air masses, resulting in increased energy yield prediction uncertainty. This thesis describes the performance of bifacial silicon heterojunction cells and modules under high-latitude operating conditions, including high angles of incidence and high air masses. Optical losses in the cell and module are described, and module characteristics are incorporated in DUET, the SUNLAB's energy yield prediction software, as an incidence angle modifier and air mass modifier. The percentage change in energy yield when considering air mass is shown to increase with increasing latitude: for a single-axis-tracked installation, the annual difference in energy yield is 0.5% in a low-latitude location (33°N), and more than 2.5% in a high-latitude location (69°N). Air mass correction is demonstrated to improve energy yield prediction accuracy compared to the absence of spectral correction. This work improves energy yield prediction accuracy for high-latitude locations, facilitating adoption of solar energy in diesel-dependent remote communities in Canada and abroad.

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%.

In this work we proposed and demonstrated a novel and very cost effective method to fabricate bifacial solar cells with conventional structure. Bifacial cells collect sunlight from both faces, and hence have an obvious advantage over monofacial cells by occupying the same physical area and converting solar energy to electricity more efficiently. Despite this fact, bifacial cells are not that popular simply because of the costs associated with them. These costs are related to both manufacturing of the actual cells and integration of modules/solar panels. The cost of manufacturing is higher than regular commodity cells because the number of processing steps for fabrication is higher than their monofacial counterparts. The main reasons for that is a necessity of some kind of lithography step and/or alignment to make the grid pattern on both sides separately. Also metallization has to be done on both sides separately, one at a time. The method proposed in this work gets rid of both of those limitations by use of a lithography/alignment-less method for patterning contact holes, and a low temperature metallization scheme used for both the front and rear surfaces to grow metal simultaneously. This technique is simple and cost effective enough to be potentially incorporated in a batch process in industry, thereby reducing the cost of manufacturing. In this thesis we have presented preliminary results from the cells (bifacial and monofacial) fabricated using the above technique with proposals for further improvements. The measurement data underscores the clear advantage in using bifacial cells over monofacial cells fabricated using this method, in terms of efficiency. This also demonstrates that this proposed method is a viable way to manufacture bifacial cells with lower cost and relative ease. We also fabricated and measured monofacial solar cells in order to study the beneficial effects of including buried contacts as a possible part of device structure. The study shows significant improvement in efficiency due to incorporation of deep trenches for metal contacts in device design. / text

No description available.

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.

Bifacial solar modules can absorb and convert solar irradiance to current on both their front side and back side. Several elements affects the bifacial yield, especially the ground albedo around the system or the installation configuration. In this document, investigations carried out at EDF R&D facilities regarding the use of bifacial modules in large scale PV farm are presented. Tests on the outdoor facilities were conducted to validate and improve a bifacial stand model developed under a Dymola/Modelica environement. Furthermore, a global optimization method was implemented to determine the optimal configuration of a large bifacial plant with modules facing south. Investigations showed the importance of a new albedo model to accurately evaluate the irradiance received on the rear side. The new model shows a relative error on the rear irradiance under 5% when compared with experimental data. Techno-economical optimization of a bifacial plant was conducted at different locations and for different ground albedo. The results shows that the gain on the specific production can vary between 7.2 and 14.2% for a bifacial plant when compared with a monofacial plant. Bifacial plants are expected to become more profitable than monofacial plants in some of the cases tested when their module cost will reach 68 c€/Wp.

This thesis is based on a project "Bifacial Photovoltaic Energy Production Analysis" to build a detailed simulation model system accurately simulate bifacial panel performance under real field radiation conditions and deployment configuration, and to predict its corresponding energy yield. To the author’s up-to-date knowledge, the model system is unpreceded among same type simulation software in complexity, details in consideration, ranges of deployment and parameters. The model system can also be used as a platform for more components and variables to be added on, such as adding on more rows of panel arrays to simulate bifacial solar farm scenario; and adding spectral information for more accurate analysis. The system components’ sub-models were carefully chosen based on a broad literature review in related aspects; especially in sky diffuse radiance, ground reflection, and bifacial solar cells. Built in MATLAB© based on mathematical expressions from above said models, the system consists of 5 bifacial panels and their racking as shading objects and the central panel performance is under investigation and has taken consideration of all possible panel azimuth and elevation combinations. Model simplification and resolution are carefully considered so to achieve a good balance in complexity, computation load and output accuracy. Output reliability is confirmed with other people’s work. Furthermore, the model has been fully checked and peer tested. Outputs under different parameter settings are analysed and discussed. Conclusions and recommended future work are provided at the end of the thesis.

The master thesis has evaluated the specific combination of bifacial solar cells and extensive green roofs. This was done in terms of energy production per year, profitability as well as discussions around ecosystem services. Three cases have been simulated with different temperature profiles for both bifacial, vertical bifacial and monofacial. The reason for three cases was due to the uncertainty in temperature decreasing properties of vegetation i Sweden. One case was simulated for a normal black bitumen roof for the three types of solar PV. The result with the best energy production was found in the configuration with azimuth -10o, inclination 40o and height above roof at 40 cm. This was the case with the largest simulated temperature decrease. Albedo was set to 0.2 and this resulted in a bifacial gain of 9-10% for the three cases with green roofs installed. Albedo was found to be a larger factor in the energy production outcome than the temperature decrease from the vegetation. The solar cells contributes to shading the green roof partially which increases the local biodiversity as well as expands the lifetime of the vegetation. The combination was deemed profitable since the middle case had an annuity of 1841 SEK/year, but the case with the bitumen roof was found to be even more profitable with an annuity of 4160 SEK/year. This indicates that the extra cost of installing a green roof does not pay itself back with a higher energy production. / Det här examensarbetet har undersökt kombinationen bifacialsolceller med extensivt grönt tak med avseende på optimal utformning av en sådan anläggning på ett tak samt systemproduktion och lönsamhet hos anläggningen. Då det inte finns något klart modelleringsverktyg för hur stor temperatursänkning det gröna taket kan åstadkomma så har tre olika fall med olika temperaturprofil simulerats. Resultaten visade på att ju högre temperatursänkning det gröna taket kan bidra med desto lägre höjd bör bifacialsolcellerna installeras på. Den bästa systemproduktionen fås vid vinkeln 40o samt azimuth -10o för alla tre fall. Detta gav för medelfallet en bifacial gain på 9,6% vid jämförelse mot vanliga enkelsidiga solceller. Resultatet för vertikalt installerade bifacialsolceller gav minst 12% lägre systemproduktion än de med vinkel 40o men med hög osäkerhet kring tillförlitligheten i resultatet. Vertikal bifacial kan vara intressant då det ligger ett värde i att producera elektricitet efter ett normalt hushålls elkonsumtionskurva, men är mindre intressant för kontorsbyggnader där elkonsumtionen är relativt konstant under dagen. Lönsamhetskalkylen visade att kombinationen bifacialsolceller med grönt tak var lönsam, men inte lika lönsam som att installera på svart tak. För medelfallet gav bifacialsolceller på grönt tak en annuitet på 1841 kr/år medan annuiteten för bifacialsolceller på svart tak var hela 4160 kr/år. Ur ett rent ekonomiskt perspektiv är kombinationen alltså inte den mest lönsamma. Från känslighetsanalyserna konstaterades att albedo är den aspekt som har störst påverkan på systemproduktionen och denna är relativt låg för det gröna taket. Ett högre albedo hade därför varit att föredra till bifacialsolceller, vilket kan erhållas genom att exempelvis varva grönt tak med vita stenar. Vidare är kombinationen en platseffektiv lösning för tak som oftast är en outnyttjad ytresurs, där de olika installationerna bidrar med olika positiva nyttor var för sig. Bifacialsolcellerna bidrar till en ökad självförsörjningsgrad samt hjälper till att driva på den tekniska innovationen framåt. Gröna tak bidrar med många ekosystemtjänster såsom bullerreducering, dagvattenfördröjning, rening av luftpartiklar, lokal temperatursänkning. Kombinationen bidrar till en ökad biologisk mångfald och en lägre växtperiod för det gröna taket mot om den hade varit fristående.

abstract: Demand for green energy alternatives to provide stable and reliable energy solutions has increased over the years which has led to the rapid expansion of global markets in renewable energy sources such as solar photovoltaic (PV) technology. Newest amongst these technologies is the Bifacial PV modules, which harvests incident radiation from both sides of the module. The overall power generation can be significantly increased by using these bifacial modules. The purpose of this research is to investigate and maximize the effect of back reflectors, designed to increase the efficiency of the module by utilizing the intercell light passing through the module to increase the incident irradiance, on the energy output using different profiles placed at varied distances from the plane of the array (POA). The optimum reflector profile and displacement of the reflector from the module are determined experimentally. Theoretically, a 60-cell bifacial module can produce 26% additional energy in comparison to a 48-cell bifacial module due to the 12 excess cells found in the 60-cell module. It was determined that bifacial modules have the capacity to produce additional energy when optimized back reflectors are utilized. The inverted U reflector produced higher energy gain when placed at farther distances from the module, indicating direct dependent proportionality between the placement distance of the reflector from the module and the output energy gain. It performed the best out of all current construction geometries with reflective coatings, generating more than half of the additional energy produced by a densely-spaced 60-cell benchmark module compared to a sparsely-spaced 48-cell reference module.ii A gain of 11 and 14% was recorded on cloudy and sunny days respectively for the inverted U reflector. This implies a reduction in the additional cells of the 60-cell module by 50% can produce the same amount of energy of the 60-cell module by a 48-cell module with an inverted U reflector. The use of the back reflectors does not only affect the additional energy gain but structural and land costs. Row to row spacing for bifacial systems(arrays) is reduced nearly by half as the ground height clearance is largely minimized, thus almost 50% of height constraints for mounting bifacial modules, using back reflectors resulting in reduced structural costs for mounting of bifacial modules / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019