Bifacial Photovoltaic Modules Research Articles

Stochastic approach for maximum power point determination for bifacial PV modules by implementing two different cell models

Purpose This paper presents the determination of the maximum power point of a bifacial photovoltaic (PV) system using two different cell models. The optimal power point is determined by using genetic algorithm (GA), as an optimisation tool. The purpose of this paper is to find which of the two analysed models gives better results in the determination of the maximum power point of a bifacial PV system for different solar irradiations. The quality of the results gained from both models is analysed based on the value of the objective function. Design/methodology/approach In this research work, the maximum power point of bifacial PV modules is determined by using two different PV cell models, such as the simplified and two-diode models of PV cells. Based on the input electrical data for the analysed bifacial PV module as well as the mathematical model of the two PV cell presentations, the values for the current and the voltage at the maximum power point for a given solar irradiation and working temperature are determined by the algorithm for each solution in the population and generation. Findings From the presented results and the performed analysis, it can be concluded that GA is quite appropriate for this purpose and gives adequate results for both models and for all working conditions. The two-diode model was found to be more suitable compared with the simplified model due to its complexity. Therefore, although the power difference for each of the scenarios for the two compared models does not differ significantly among the two models, it is in favour of the two-diode model. Which implicates that the for fast and simple calculation the simplified model can also do the job. Practical implications This approach can be very successfully applied in the design process of a PV plant to forecast the output characteristics of the PV system if there is enough information about the weather conditions for a given location. This procedure can be very helpful in the process of selection of right PV module and inverter for a given location. Originality/value An optimisation technique using GA as an optimisation tool has been developed and successfully applied in the determination of the maximum power point for a bifacial PV module using to different models of solar cell. The results are compared with the analytically determined values as well as with the values given from the producer and they show good agreement.

3D View Factor Power Output Modelling of Bifacial Fixed, Single, and Dual-Axis Agrivoltaic Systems

This study investigates the performance of agrivoltaic systems employing bifacial photovoltaic modules. A comparison between yield in Sweden and Italy was carried out. Three agrivoltaic system designs were evaluated: vertical fixed, single-axis tracker, and dual-axis tracker. The results showed that the specific production varied between 1090 to 1440 kWh/kWp/yr in Sweden and 1584 to 2112 kWh/kWp/yr in Italy, where the lowest production was obtained with the vertical fixed agrivoltaic system while the highest production was obtained with the dual-axis tracking agrivoltaic system. The vertical fixed design had a higher electricity production during low solar elevation angles, while the single-axis and dual-axis tracking designs had significantly higher power production during mid-day. The electricity production gain using a dual-axis tracker design was mostly during mid-day, but the increase compared to the single-axis tracker was only 1-2%. The study concludes that low-height, fixed agrivoltaic systems without tracking are well-suited for high-latitude countries like Sweden, while elevated systems with tracker solutions are more suitable for locations like Italy. The findings suggest that the performance of agrivoltaic systems with bifacial photovoltaic modules is highly dependent on geographical location and the specific characteristics of the crops grown beneath them.

Modelling of bifacial photovoltaic farms to evaluate the profitability of East/West vertical configuration

East/West (E/W) vertical bifacial photovoltaic (PV) modules can achieve higher profits than the conventional North/South (N/S) tilted configuration depending on the design choices and external conditions. In this study a model based on 2D view factor concept is developed to estimate the power generated by a large-scale bifacial PV farm, considering the non-uniformity of the incident irradiance and the spectral impact. A validation using measured data is performed, focusing on the non-uniformity of the rear irradiance. This model is used to compare the profitability between E/W vertical and N/S tilted PV farm configurations, considering higher prices during noon with respect to morning/evening periods. The results identify the ratio between these two price values as the key variable that influences the comparison between the PV farm configurations. Specifically, a sufficiently high price ratio ensures the higher profitability of E/W vertical modules, however, the exact value is dependent on the location and the design variables. In general, higher row-to-row distance and lower diffuse fraction enhance the profitability of the E/W vertical over the N/S tilted configuration. On the other hand, elevation of the modules, curtailment strategies and hybrid solutions have a minor influence.

Spectro-angular analysis of roadside-integrated bifacial solar power systems with reflecting sound barriers

Bifacial photovoltaic modules along highways provide energy supply and act as sound barriers simultaneously. This study examines the impact on energy production when incorporating sound barriers with varying light reflection properties into this integrated solar infrastructure along roadways. Specifically, we use advanced computational simulations to analyze the effects of integrating black, ideal specular, and ideal diffuse (Lambertian) reflectors into an existing highway solar power plant located in the Netherlands. Our analysis combines realistic spectro-angular irradiance data as input with our in-house reverse ray tracing software. Our calculations show that for an east-west facing system, an ideal diffuse reflector increases the annual yield by 70%, while a specular reflector decreases the yield due to shading. Most notably, the diffuse reflector doubles the energy yield during winter months, thereby offering a pathway to decrease the seasonal energy demand and supply gap.

Quantifying spectral albedo effects on bifacial photovoltaic module measurements and system model predictions

AbstractWe provide a comprehensive analysis of the effect of spectral albedo on photovoltaic (PV) module measurements and system model predictions. We demonstrate how to account for albedo in indoor bifacial device measurements by adjusting the applied irradiance using the scaled rear irradiance method, exemplified on fabricated silicon heterojunction (SHJ) modules. System model performance is studied using a detailed 3D finite‐element model, DUET, for fixed‐tilt and horizontal single‐axis tracked (SAT) arrays between 15 and 75°N. Spectral effects cause variations in measured SHJ module short‐circuit current up to 2% and efficiency variation up to 0.3% abs. We further demonstrate that rear‐side spectral mismatch factors (SMMs) resulting from including or omitting spectral albedo in PV system modeling vary between ±13%, while total (front+rear) SMMs vary up to 3%, depending on the deployment configuration and latitude. SAT array SMMs are weakly correlated with latitude, while fixed‐tilt array SMMs increase with latitude, driven by an increasing proportion of ground‐reflected light on the front‐side of modules. Ground‐reflections can constitute between 2% and 32% of total incident module irradiance, with notably high (>10%) contributions for fixed‐tilt arrays at high latitude. Effects of spectral albedo are most significant for: (1) fixed‐tilt deployments at high latitudes, (2) wide bandgap technologies such as perovskite and cadmium telluride cells, (3) albedos which vary steeply over the technology's absorption range, and (4) high albedo ground covers. Overall, we demonstrate that omitting spectral albedo effects can result in PV measurement and system‐level modeling uncertainties on the order of several percent in these cases.

Performance of stand-alone bifacial photovoltaic module using non-biodegradable waste as reflectors for tropical climatic region of southern India: An experimental approach

Bifacial photovoltaic modules (Bi-FM) generate more power compared to mono-facial modules (Mo-FM) even in diffused light conditions. Deployment of reflectors in Bi-FM increases the cost of implementation. The unique feature of this proposed work is that it utilizes waste material as reflectors. The cost of the reflective material is 10% of the total module cost, and the proposed work is economically viable due to waste reusability. In this work, three different non-biodegradable materials (polyvinyl chloride flex, thermocol, and aluminium foil) are reused as reflectors to improve their generation using Bi-FM. A detailed study is made using the waste materials as reflectors and the performance ratio is computed for different irradiation conditions observed across a day. The average performance ratio of thermocol and polyvinyl chloride flex is 20% and 8% respectively, higher than that of aluminium foil. Using a reflector made of PVC flex has a 3.59-year lifespan as compared to Bi-FM by employing a reflector made of aluminium foil. The deployment of non-biodegradable materials reduces the cost requirements. The proposed setup also increases the reusability of non-biodegradable waste materials as reflectors and improves the power generation of Bi-FM.

Design Optimization of Large-scale Bifacial Photovoltaic Module Frame Based on FEM and RSM

Design Optimization of Large-scale Bifacial Photovoltaic Module Frame Based on FEM and RSM

Design and Analysis of a Hybrid Stand-Alone Microgrid

This research article presents a comprehensive investigation into the design, optimization, and performance analysis of a hybrid stand-alone microgrid for an industrial facility in Iraq at coordinates 36.51 and 43.99. The system consists of photovoltaic (PV) modules, inverters, a battery energy storage system (BESS), a generator, and AC loads. Leveraging the capabilities of PVsyst version 7.3.1, HOMER Pro version 3.14.2 and SAM version 2022.11.21 software tools, this study assesses the feasibility and functionality of the hybrid stand-alone microgrid. In this study, PVsyst software is used for detailed designing and analysis of a PV plant, and the PVsyst design file is then used in HOMER Pro software to optimize and design the proposed hybrid stand-alone microgrid, and for detailed performance analysis SAM software is employed. This paper also investigates the impact of ground clearance and ground albedo on the annual generation of bifacial PV modules at various tilt angles. Key findings include a promising normalized production rate of 4.53 kWh/kWp/day with a performance ratio of 0.815 and annual energy production estimates of 84.31 MWh (P50), 79.57 MWh (P90), and 78.24 MWh (P95) for monofacial PV modules, highlighting the system’s potential for renewable energy generation. Notably, this research demonstrates the hybrid stand-alone microgrid’s capacity to significantly reduce CO2 emissions, saving approximately 1811.6 tons over a 30-year period, thus contributing to sustainability and environmental conservation goals. Additionally, this study reveals operational challenges during the winter months, necessitating generator support to meet load demands. The successful installation and experimental validation of the hybrid stand-alone microgrid underscore its practical viability and its role in advancing clean energy solutions. This research provides valuable insights into hybrid stand-alone microgrid design, emphasizing its importance in ensuring reliable power supply and environmental stewardship.

A horizontal single-axis tracking bracket with an adjustable tilt angle and its adaptive real-time tracking system for bifacial PV modules

An efficient photovoltaic (PV) tracking system enables solar cells to produce more energy. However, commonly-used PV tracking systems experience the following limitations: (ⅰ) they are mainly applied to single-sided PV panels; (ⅱ) they employ conventional astronomical algorithms that cannot adjust the tracking path in real time according to variable weather. In this study, a model of horizontal single-axis tracking bracket with an adjustable tilt angle (HSATBATA) is developed, and the irradiance model of moving bifacial PV modules is designed, which considers the mounting height, spacing and ground shading of PV panels. Furthermore, an adaptive real-time tracking (ARTT) algorithm is put forward to obtain the optimal tracking path for PV cells, which considers the energy consumption of tracking motors, the front and back irradiance of solar cells, cell temperature and ambient wind speed. The test results indicate that the presented ARTT algorithm enhances the energy of PV modules by 32.7 % and 7.5 %, respectively, compared to the fixed bracket and the conventional tracking algorithm. Additionally, the number of motor starts of the PV tracking system is reduced by 71.7 % compared with that of the conventional algorithm, which greatly contributes to extending the service life of PV tracking brackets and lowering the cost of electricity. Present study will help to improve the theoretical research system of PV tracking bracket construction, irradiance modeling of moving bifacial modules, and intelligent tracking algorithms.

Agrivoltaic systems potentials in Sweden: A geospatial-assisted multi-criteria analysis

Agrivoltaic systems represent an intelligent solution combining electricity production from solar photovoltaic technology with agricultural production to avoid land use conflicts. Geographic Information System technologies can support the implementation and spread of agrivoltaic systems by identifying the most suitable areas using useful spatially explicit information concerning techno-agro-socio-economic criteria.In this study, we have developed a procedure to identify and classify suitable areas for agrivoltaic systems in Sweden. An Ordinal Priority Approach based multi-criteria decision-making algorithm is established to calculate the weights of the selected evaluation criteria through expert interviews. The land use data refers to the Corine Land Cover 2018 product.The results show that about 8.6% of the Swedish territory, approximately 38,485 km2, is suitable for installing agrivoltaic systems. Among this area, about 0.2% is classified as “excellent”, about 15% as “very good”, about 72% as “good”, about 13% as “moderate”, and about 0.1% as “poor”. Most “excellent”-classified areas are in Kalmar, Skåne, and Gotland. In contrast, most “very good” sites are in Skåne, Kalmar, and Östergötland.By deploying vertically mounted agrivoltaic systems with bifacial photovoltaic modules, the total potential installed capacity for “excellent” areas is about 2.5 GWp, while for areas classified “excellent” and “very good” is about 221 GWp. The total “excellent” areas can potentially supply about 2.4 TWh of electricity against the electricity consumption in 2021 of about 143 TWh. On the other hand, the land classified as “excellent” and “very good” could potentially provide about 207 TWh. The County of Västra Götaland shows the greatest potentials in terms of total potential electricity supply from agrivoltaic systems with about 227 TWh, followed by Skåne with a total potential of 206 TWh.

Optimal Photovoltaic Array Layout of Agrivoltaic Systems Based on Vertical Bifacial Photovoltaic Modules

An agrivoltaic (APV) plant is a complex system, where photovoltaic (PV) energy generation is concomitant with agricultural production. These activities can be antagonistic as the presence of PV installation might reduce the favorable conditions for agriculture and vice versa. In this context, vertical bifacial PV (AbPV) farms represent a fascinating perspective to optimize the land's dual‐use request. This means finding geometrical configurations for the AbPV plant to produce the same energy as ground‐mounted PV farms, not hinder agricultural activities, and limit the photosynthetically active radiation deficit. This study evaluates the performances of a vertical bifacial APV plant, located in Sicily, as a function of the PV modules’ plan allocation. The analyses developed through two software tools, SAM and PVsyst, compare the relative capabilities of monofacial and vertical bifacial farms in terms of acceptable PAR debit, and energy yield as a function of the array density. The land equivalent ratios of vertical AbPVs from a maximum value of 1.93 (p/h = 2.5) and a minimum of 1.56 (p/h = 5.0) for crops which have low sensitive response to the drop of solar radiation, while from 1.71 and 1.42 for crops which have higher sensitive response to the drop of solar radiation.

Evaluation of the bifaciality coefficient of bifacial photovoltaic modules under real operating conditions

Among the parameters that define a bifacial photovoltaic module, the bifaciality coefficients indicate the rear and front side ratio of the most representative IV curve points of a photovoltaic panel, that is, Isc, Voc and Pm. However, these parameters are defined under the ideal Standard Test Conditions (STC). Therefore, to provide a realistic insight regarding the performance of bifacial modules, it is necessary to evaluate these coefficients under real operating conditions. For such purpose, an outdoor campaign was performed to experimentally measure the maximum power bifaciality coefficient of two modified bifacial modules that resemble a rear and a front monofacial panel respectively. As a first result, if the measurements are translated to STC, using a linear approximation, the bifaciality matches the value indicated by the manufacturer. Additionally, the operating bifaciality coefficient shows a linear decrease trend, proportional to the irradiance level decrease. This result implies that on cloudy days, the average bifaciality factor is below the corresponding one from sunny days. Finally, for irradiances below 200 W/m2, there is a non-linear increase in the bifaciality, with greater values than the corresponding to the ideal STC conditions, which presumably are caused by the non-linearity performance of photovoltaic modules at low irradiances.

Cool roofs boost the energy production of photovoltaics: Investigating the impact of roof albedo on the energy performance of monofacial and bifacial photovoltaic modules

Photovoltaics (PVs) provide clean and affordable energy contributing to the decarbonisation of the energy sector. High surface temperature of the PV modules reduces their efficiency and the corresponding energy production and increases the sensible heat released to the atmosphere contributing to urban overheating. For roof mounted PVs, increase of the roof albedo helps to decrease the surrounding ambient temperature, raises the efficiency of the PVs and increases the reflected solar radiation received by the modules. Numerous studies have assessed the impact of increased roof albedo on the energy yield of the monofacial and bifacial PVs for given installation characteristics and specific climatic conditions. There is a serious need to collect, analyse, compare, and parameterize the existing information in order to provide more global and holistic knowledge to the PVs industry. We have analysed 13 and 57 case studies reporting the impact of modified roof albedo on the energy yield of monofacial and bifacial PV modules, respectively. It is concluded that, on average, increasing the roof albedo by 0.1 contributes to enhance the energy production of monofacial and bifacial PV modules by 0.7% and 4.55% respectively while delivering important co-benefits to urban heat mitigation. Parametric relations between the potential increase of the roof albedo and the increase of the annual energy yield are proposed for both monofacial and bifacial PV modules. The impact of the geographic and installation parameters on the energy production of the modules is analysed and discussed. The results of such a study could help to identify the optimal roof albedo for maximizing energy performance and reducing energy costs.

Investigation of the Use of Evolutionary Algorithms for Modeling and Simulation of Bifacial Photovoltaic Modules

The purpose of this study is to employ and improve evolutionary algorithms, namely the genetic algorithm (GA) and the differential evolution algorithm (DE), to extract the parameters of the equivalent circuit model (ECM) of a bifacial photovoltaic module using the representative model of a diode with five parameters (1D5P). The objective is to simulate the characteristics of the I–V curves for various irradiation and temperature scenarios. A distinctive feature of this study is the exclusive use of the information in the technical sheet of the bifacial module to conduct the entire extraction and simulation process, eliminating the need to resort to external sources of data or experimental data. To validate the methods, a comparison was made between the simulation results and the data provided by the bifacial module manufacturer, contemplating different scenarios of irradiation and temperature. The DE was the most accurate algorithm for the 1D5P model, which presented a maximum average error of 1.57%. In comparison, the GA presented a maximum average error of 1.98% in the most distant scenario of STC conditions. Despite the errors inherent to the simulations, none of the algorithms presented relative errors greater than 8%, which represents a satisfactory modeling for the different operational conditions of the bifacial photovoltaic modules.

Extensive Energy, Exergy, Economic, Exergoeconomic, Enviroeconomic, and Energy Payback Time Analysis and Investigation on Bifacial Solar Photovoltaic Module with Nonbiodegradable Waste as Reflectors

The ability of bifacial photovoltaic (PV) to absorb solar radiation on either side increases the energy output. Reflectors increase the albedo and help to increase the performance. Reflectors face discoloration and degradation with time and they increase the overall implementation cost of bifacial PV systems. However, the cost of reflectors can be reduced by using nonbiodegradable waste as reflectors. They also increase the reusability of nonbiodegradable waste materials and reduce their impact on the environment and the cost of reflectors. To make a comprehensive analysis, an investigative approach of energy, exergy, economic, exergoeconomic, enviroeconomic, and energy payback time (6E) analysis is conducted for the bifacial PV module with nonbiodegradable waste, such as polyvinyl chloride (PVC) flex, polystyrene foam, and aluminum foil as reflectors in this study. The 6E analysis includes the analysis of energy, exergy, economic, exergoeconomic, enviroeconomic, and energy payback time factors. The analysis results indicate that the PVC flex as a reflector enhances the bifacial PV performance better compared to polystyrene foam and aluminum foil. The average power, average energy efficiency, and average exergy efficiency of bifacial PV with PVC flex reflector observed during the study are 224 W, 27%, and 31%, respectively. The use of nonbiodegradable waste also has a positive impact on the environment and economy.

Comparing methods for the long-term performance assessment of bifacial photovoltaic modules in Nordic conditions

The main objective of this study is to discover which performance loss rate (PLR) calculation methods provide the most reliable results for vertical bifacial photovoltaics (VBPV) in Nordic conditions. For this purpose, over 1600 filter-metric-aggregation-model combinations for PLR calculation are compared. Accurate determination of PLR is crucial for estimating the economic profitability of a PV system, but standardized methodology is lacking as is the understanding on how the common PLR calculation frameworks perform for both VBPV technology and Nordic climatic region. Here, four-year, minute-resolution datasets from adjacent VBPV modules and a weather station in Turku, Finland (60°N) are used. After removing crude outliers, a benchmark PLR of −1.46±0.03 %/year was obtained by averaging the remaining over 1200 filter-metric-aggregation-model combinations. The year-on-year method with a daily/weekly aggregated temperature- and irradiance-corrected performance model was found robust and reliable to Nordic high seasonality. In contrast, several commonly used methods, such as the PVUSA model, produced unrealistic results. Unexpectedly, temperature correction increased the seasonal pattern of the performance ratio, and PLR varied with irradiance conditions and between the front and rear sides of the module. This work expands the best practices of PLR calculation to complement the development of global PLR calculation standards.

Analysis of the Output Characteristics of a Vertical Photovoltaic System Based on Operational Data: A Case Study in Republic of Korea

The proliferation of renewable energy sources to achieve carbon neutrality has rapidly increased the adoption of photovoltaic (PV) systems. Consequently, specialized solar PV systems have emerged for various installation purposes. This study focuses on grid connecting vertically installed bifacial PV modules facing east and west by establishing a test bed within Republic of Korea. Based on weather and generation data collected in Republic of Korea, located in the middle of latitude 34.98° N, from January to July 2023, we analyzed and compared the generation patterns, peak generation, peak hours, and total generation of conventional and vertical PV systems. Moreover, PVsyst was used to model the solar PV generation and analyze the consistency and viability of vertical PV generation by comparing actual operational data with simulation results. The vertical PV system demonstrated a peak power generation of 89.1% compared with the conventional PV system with bifacial modules. Based on operational data from January to July, the power generation output of the vertical PV system decreased to 65.7% compared with that of the conventional system with bifacial modules. This corresponded to 78.8% to 80.2% based on the PVsyst simulation results. In particular, the investigations related to the peak generation levels and occurrence times of vertical PV systems provide insights into the practicality of vertical solar PV systems and their potential for improving the PV hosting capacity.

Development and challenges of bifacial photovoltaic technology and application in buildings: A review

Bifacial photovoltaic (bPV) modules can both obtain the front and rear light to get higher power output, which has attracted extensive attention and is expected to substitute for mono-facial photovoltaic technology (mPV). The bPV technology has always been developing with new technologies and applications constantly emerging. However, there is little review on bPV technology applied in buildings. The current reviews mainly focus on the principle and performance research of bPV technology. This work focuses on reviewing the application status of bPV technology in buildings, which aims to contribute to the large-scale application of bPV technology in buildings and reduce building energy problems. The latest innovative development of bPV technology and the key issues in the application of bPV technology in buildings were summarized and analyzed. For the further development of bPV technology, research on battery materials and structures is beneficial for improving the utilization rate of light at different wavelengths. For the building application of bPV technology, the issue of uneven irradiation of the rear side is a key factor hindering the large-scale application of bPV in buildings, and the use of back reflectors can effectively alleviate this problem.

A Building-Integrated Bifacial and Transparent PV Generator Operated by an “Under-Glass” Single Axis Solar Tracker

Nearly Zero Energy Buildings (NZEBs) play a key role in the world energy transition. This is motivating the scientific community to develop innovative electrical and thermal systems characterized by very high efficiency to specifically address the energy needs of modern buildings. Naturally, the integration of the latest generation photovoltaic (PV) systems into buildings helps to satisfy this need, and, with this objective in mind, an innovative and highly efficient building-integrated photovoltaic (BIPV) system is presented and discussed in this paper. The proposed PV system is purpose-built to be fully integrated into a variety of buildings (preferably into their rooftops) and assumes the form of a PV skylight. It is based on a certain number of innovative rotating bifacial PV modules, which are specifically made to be installed “under-glass” within a custom-made transparent casing. Thanks to their properties, the PV modules can be rotated using a very low-power, reliable, and efficient mono-axial solar tracking system, fully protected against adverse atmospheric agents. Once the proposed PV skylight is fully integrated into a building, it generates electricity and, additionally, helps to improve both the energy performance and the aesthetic appearance of the building. The electricity generation and illuminance performances of the proposed PV skylight are experimentally tested using a low-power homemade prototype driven by different solar tracking logics and under different operating conditions; the most relevant results are summarized and extensively discussed. The main outcome of the experimental study is that the most effective performance of the PV skylight is obtained by installing, in its available surface, the maximum possible number of rotating bifacial PV modules, side by side and with no empty spaces between them.

Energy performance of an innovative bifacial photovoltaic sunshade (BiPVS) under hot summer and warm winter climate

The bi-facial photovoltaic sunshade (BiPVS) is an innovative solution that utilizes vertically mounted bi-facial photovoltaic modules to provide shading. The BiPVS is capable of converting incident solar radiation into electricity on both the front and rear sides of the module, resulting in higher electrical efficiency compared to traditional mono-facial PV sunshades. The BiPVS has great potential as a sustainable solution for building shading and energy generation, which allows for improved indoor light/thermal environment and building energy efficiency. In this study, the bi-facial photovoltaic sunshade (BiPVS) was implemented in an office under typical hot summer and warm winter climate of Shenzhen, China. The energy performance of the BiPVS was analyzed using Energyplus. The comprehensive building energy saving was evaluated by comparing the energy consumption of the office with and without the BiPVS. Results showed that the total annual photovoltaic power generation was 133.19 kWh, while the comprehensive building energy savings were 159.65 kWh. Additionally, carbon dioxide emissions were reduced by 83.29 kgCO2 per year. The proposed method can help optimize the design parameters of BiPVS according to specific climate conditions, building types, and orientation, and contribute to the development of high-efficiency BIPV technology and support efforts towards carbon neutrality.