Article

Optimal solar tracking strategy to increase irradiance in the plane of array under cloudy conditions: A study across Europe

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Abstract

In this study, we have performed an analysis of potential irradiation increase across Europe, derived from moving photovoltaic (PV) modules to a horizontal position during cloudy and overcast situations. The motivation of research is that PV technology has expanded outside countries endowed with high solar irradiation and it is nowadays present in high-latitude regions and areas with frequent cloud cover. Unlike concentrating solar technologies, PV panels can make use of both beam and diffuse irradiance. During cloudy or overcast situations, most of solar irradiance comes from the diffuse component, which approaches an isotropic behavior under those circumstances. Then, a PV panel facing the zenith would receive more irradiation than a PV panel following the Sun's path. In our approach, we have used data from several Baseline Surface Radiation Network stations. Results showed a yearly potential irradiation increase of 3.01% with respect to a reference single-axis tracking system (SATS) in the northern-most station. Values for other stations were correlated to climate. Thus, the sunniest station would increase its annual irradiation by 0.16% compared to a reference SATS. Daily irradiation increases of up to 19.91% were registered. Two predictive models were created to develop a SATS, which could determine in advance the optimum position of PV panels. Model 1, which was based on the persistence of irradiance, was designed to work real time in order to increase production. Yearly gains of up to 2.51% of irradiation were registered. However, Model 2 was developed to update production forecasts in the intra-day electricity markets so that PV plant owners can maximize their revenues. It is based on irradiance predictions from a numerical weather prediction service and underperformed current SATS.

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... The effect of indirect light on βopt has been explored for fixed systems [7]- [10], SATs [11]- [13] and dual-axis trackers (DATs) [13]- [17]). The increase in the annual yield arising from accounting for indirect light when optimizing an SAT's tracking angle has been calculated by Antonanzas et al. to be 0-2.5% depending on location for monofacial modules [11], by Pelaez et al. to be 0.5-1.0% in Albuquerque and 0.8-1.3% in Seattle for bifacial modules [12], and by Rodriguez-Gallegos et al. to be 0.2-1.8% for monofacial and 0.5-3.3% for bifacial modules (although the bifacial gain is likely an overestimate as the study assumes a bifaciality of 100% and no ground shading from neighboring modules) [13]; higher latitudes and higher albedos gave higher gains [12], [13]. ...
... The effect of indirect light on βopt has been explored for fixed systems [7]- [10], SATs [11]- [13] and dual-axis trackers (DATs) [13]- [17]). The increase in the annual yield arising from accounting for indirect light when optimizing an SAT's tracking angle has been calculated by Antonanzas et al. to be 0-2.5% depending on location for monofacial modules [11], by Pelaez et al. to be 0.5-1.0% in Albuquerque and 0.8-1.3% in Seattle for bifacial modules [12], and by Rodriguez-Gallegos et al. to be 0.2-1.8% for monofacial and 0.5-3.3% for bifacial modules (although the bifacial gain is likely an overestimate as the study assumes a bifaciality of 100% and no ground shading from neighboring modules) [13]; higher latitudes and higher albedos gave higher gains [12], [13]. These studies omit a few of the subtler effects we discuss later To date, most published algorithms for determining βopt of practical trackers under direct and diffuse light are relatively simple [11], [14], [16]. ...
... The increase in the annual yield arising from accounting for indirect light when optimizing an SAT's tracking angle has been calculated by Antonanzas et al. to be 0-2.5% depending on location for monofacial modules [11], by Pelaez et al. to be 0.5-1.0% in Albuquerque and 0.8-1.3% in Seattle for bifacial modules [12], and by Rodriguez-Gallegos et al. to be 0.2-1.8% for monofacial and 0.5-3.3% for bifacial modules (although the bifacial gain is likely an overestimate as the study assumes a bifaciality of 100% and no ground shading from neighboring modules) [13]; higher latitudes and higher albedos gave higher gains [12], [13]. These studies omit a few of the subtler effects we discuss later To date, most published algorithms for determining βopt of practical trackers under direct and diffuse light are relatively simple [11], [14], [16]. They utilize photosensors to measure the clear-sky index, and when that index exceeds some threshold, β switches from βd to zero. ...
Article
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The optimal tilt βopt of the modules in a single-axis tracker is often determined by assuming all sunlight is direct and ground reflectance is zero. Prior works, however, have demonstrated that βopt is smaller when diffuse light is significant. In this article, we determine how βopt decreases as the conditions change from clear sky to overcast, accounting for many complicated effects like row-to-row shading of diffuse light, ground reflection, structural shading, cell-to-cell mismatch, and angular and spectral dependencies. We find that when compared to monofacial systems, bifacial systems tend to have a higher βopt when it is cloudier and a lower βopt when it is sunnier. We also quantify the increase in annual yield that arises when accounting for indirect light at three example sites with different climates, finding it to be ∼30% lower for a bifacial system than a monofacial system; the gain was 0.8%– 1.5% for bifacial systems and 1.1%–2.1% for monofacial systems, where the highest gain was attained in the cloudiest climate
... The amount of solar radiation received on a PV module depends on latitude, day of the year, slope or tilt angle, surface azimuth angle, time of the day, and the angle of incident radiation [7,8]. The factors that can be controlled to maximize the amount of radiation flux received upon the PV module are surface azimuth angle and tilt angle by installing a PV module properly [9]. ...
... More generally, the assessment of the effect of the PV module azimuth angle on the amount of produced energy is shown in Figure 13. The final observed dependence can be described by the regression Equation (9). It represents the polynomial function of the second degree with the coefficient of determination R 2 = 0.998. ...
... It represents the polynomial function of the second degree with the coefficient of determination R 2 = 0.998. 0.1943 2.1746 8568.8 (9) where is the energy produced by the PV system per month (kWh) and is the azimuth angle (°). Figure 13. Relation between the PV system energy production and the azimuth angle. ...
Article
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Energy balance of the photovoltaic system is influenced by many factors. In this article the effect of tilt and azimuth angle changes of the photovoltaic system energy production is analyzed. These parameters have significant impact on the amount of solar radiation which hits on the photovoltaic panel surface and therefore also on the energy absorbed by the module surface. The main aim of research was identification of the optimal position of photovoltaic system installation in the southern Slovakia regions. The experimental apparatus had two setups consisting of polycrystalline photovoltaic modules. The first setup was used for identification of the tilt angle changes in the range (0–90°). The second one was focused on the detection of the azimuth angle effect to the energy production. The measurement results were statistically processed and mathematically analyzed. Obtained dependencies are presented as two-dimensional and three-dimensional graphical relations. Regression equations characterize time relations between the tilt or azimuth angle and the energy produced by the photovoltaic system in Southern Slovakia. Obtained simplified mathematical model was verified by analytical model. Presented models can be used for the dimensioning and optimization of the photovoltaic system energy production.
... In this way, the production of each installation, which is considered proportional to annual solar radiation, is calculated under the hypothesis that each installation will follow an optimal tracking strategy adapted to its own geometry. Therefore, this study aims to advance the characterization of the electrical behavior of shaded solar trackers, which is an issue where the scientific community has made a considerable effort, simulating tracking strategies for an improvement in photovoltaic production [12,14,42]. ...
... Substituting the vector expressions (10)- (12) in Equation (7), we obtain Equation (13), in which the dependence of I on → n is made explicit, ...
Article
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Solar tracking is an efficient strategy to increase the radiative capture of photovoltaic collectors. Within the multiple efforts made in recent decades to improve the production of these facilities, various works have studied solutions to optimize the number of rotation axes (single or dual rotation axes), the degree of collector coverage, the distances between trackers, the geometric arrangement of trackers or the minimization of shading between collectors. However, although in this type of installation it is common to find collectors with geometric shapes other than rectangles, no studies on the influence of the shape of the collectors on the radiative incidence are found in the literature. In this connection, the present work systematically addresses the study of incident solar radiation in photovoltaic installations with dual-axis trackers with collectors of different geometric shapes. By means of the exhaustive study, the conclusion is drawn that, for dual-axis photovoltaic installations with an optimal tracking strategy, the main variables that influence the annual radiative incidence are the spacing between collectors, the coverage ratio (GCR), and the collector surface, while the type of arrangement of collectors and the shape of these do not show predictive values.
... Moreover, even after acquiring the tilt angle of the PV panel (the tilt angle perpendicular to the sun) that allows the greatest amount of sunlight, it may not be the best option for the electricity generated from SPB when the shading effect of SPB is considered. Therefore, to maximize the electricity generated from SPB, it is important to propose an optional solar tracking method for SPB that can maximize the amount of sunlight and minimize the shading effect [11] . Moreover, as the electricity generation of the smart SPB differs by climate factor, the climate factors should be considered as key factors affecting the technical performance of SPB. ...
... Especially, Korea Meteorological Administration in South Korea expresses the weather conditions by dividing the sky conditions into the following four categories based on the amount of clouds: (i) clear: 0-30% clouds; (ii) partly cloudy: 30-60%; (iii) very cloudy: 60-90%; and (iv) mostly cloudy: 90-100% [37] . As the technical performance of the PV panel depends on the amount of sunlight (solar radiation) reaching the PV system, various climate factors affecting the amount of sunlight reaching the PV panel are very important from the perspective of the technical performance of the smart SPB [11,12,[36][37][38] . Accordingly, the various climate factors can be divided into two categories according to their impact on the technical performance of the smart SPB (positive or negative impact): (i) climate factors positively affecting the technical performance of the smart SPB; and (ii) climate factors negatively affecting the technical performance of the smart SPB. ...
Article
To reduce greenhouse gas emissions, many countries have decided to build nearly-zero-energy buildings (nZEBs) with renewable energy sources. Among the various products that can be applied to buildings to produce clean energy, the demand for the solar photovoltaic blinds (SPB), an emerging technology for building integrated photovoltaic (BIPV) system applications that can simultaneously block the incoming sunlight and generate electricity, is increasing. Thus, to maximize the technical performance of SPB (the solar radiation reaching the PV panel), it is important to develop a method that can accurately track the sun's position considering the various climate factors. Therefore, this study aims to conduct a technical performance analysis of SPB based on the solar tracking method considering the climate factors. Towards this end, this study conducted an experiment in South Korea using the prototype model of smart SPB. The results demonstrate that the technical performance of smart SPB can be improved up to 24.8% by using the optimal solar tracking method considering the climate factors. This study can help in further developing a hybrid solar tracking method for maximizing the technical performance of smart SPB considering the climate factors.
... This method varies the optimum angle of greatest solar incidence to prevent the back panels from being shaded (Figure 1). Although the result of using backtracking is a lower angle of incidence of solar collection, it is more favourable than the projection of shadows among adjacent solar panels [26]. ...
... For these reasons, there is a niche in scientific work focused on the development of options utilising backtracking and on the optimisation of solutions responding to the challenges posed by solar panels which are not exclusively focused on classical tracking [9,26,28,29]. ...
Article
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This paper investigates how to optimally orient the photovoltaic solar trackers of an axis parallel to the terrain, applying the sky model of Hay–Davies. This problem has been widely studied. However, the number of studies that consider the orientation (inclination and azimuth of the terrain) is very limited. This paper provides an examination of incident solar irradiance that can be extended to terrain with variable orientation and in consideration of different azimuths of the axis of rotation. Furthermore, a case study of the south of Spain is provided, considering different inclination and orientation terrain values. The results obtained in this study indicate, as a novelty, that for lands that are not south facing, the rotation axis azimuth of solar trackers should be different from zero and adjusted to the same direction as the land azimuth in order to maximize energy production. Annual energy production is sensitive to changes in the rotation axis azimuths of solar trackers (an influence of around 3% of annual energy production).
... Many models have been developed for latitude-tilted applications [16]. While latitude-tilted solar panels possess the ability to capture more direct solar irradiation, horizontal solar panels have been found to perform better under diffuse irradiation conditions [17][18][19][20]. ...
... Cloud Ceiling: the presence of clouds above a panel will scatter solar irradiance and decrease the amount of irradiation a panel receives; the cloud ceiling is measured at the altitude where at least 5/8ths of the sky above the weather station is covered by clouds [17][18][19][20][21][22][23][24][25]; • Latitude: the latitude of each location will dictate the sun deflection angle; this will affect the amount of sunlight the panel receives [12,[21][22][23]25,26]; • Month: when the sun rises and sets and how high it will appear in the sky at any location on the earth is determined (in part) by the time of year at that location [13,21]; • Hour: the time of day determines how high the sun is in the sky-or whether or not it is present at all. Hour controls for the sun's position in relation to the time of day [21]; • Humidity: water affects incoming sunlight through refraction, diffraction, and reflection. ...
Article
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Solar energy is a key renewable energy source; however, its intermittent nature and potential for use in distributed systems make power prediction an important aspect of grid integration. This research analyzed a variety of machine learning techniques to predict power output for horizontal solar panels using 14 months of data collected from 12 northern-hemisphere locations. We performed our data collection and analysis in the absence of irradiation data—an approach not commonly found in prior literature. Using latitude, month, hour, ambient temperature, pressure, humidity, wind speed, and cloud ceiling as independent variables, a distributed random forest regression algorithm modeled the combined dataset with an R2 value of 0.94. As a comparative measure, other machine learning algorithms resulted in R2 values of 0.50–0.94. Additionally, the data from each location was modeled separately with R2 values ranging from 0.91 to 0.97, indicating a range of consistency across all sites. Using an input variable permutation approach with the random forest algorithm, we found that the three most important variables for power prediction were ambient temperature, humidity, and cloud ceiling. The analysis showed that machine learning potentially allowed for accurate power prediction while avoiding the challenges associated with modeled irradiation data.
... Experimental results showed that energy generated in cloudy weather using proposed method increased by 18% [19]. In this method, as a disadvantage, the rays reflected from the ground are not collected by the PV panel [20]. ...
... Some researches in the literature support the findings of the current study. Electric yield may be increased up to 25-45% compared to fixed structures with an optimum tilt angle using the dual axis STS [20,28]. Using latitude, longitude, and altitude information of the location where the STS was located and date and time information as input, the position of the sun was determined by mathematical equations. ...
... (31) and (32) are obtained Fig. 12. Radiation decay rate r on collectors estimated according to: (a) Liu-Jordan model [46], (b) Hay -Davies model [47] and (c) Perez model [48]. Table 3 shows the six possible estimates of when combining the results of the yields given by equations (28)e (30). resulting from the different alternatives considered and previously described. ...
Article
World population growth is leading to an increased demand for energy and food. This is creating a conflict over land use as terrain for large renewable energy facilities is not available for agricultural. As a solution, agrivoltaics combines the use of the land for agricultural and photovoltaic exploitation. In this work, the conversion of photovoltaic installations with N–S horizontal trackers into agrivoltaic installations by cultivating tree crops in hedgerows between the rows of collectors is analysed. Specifically, the shading of the crop on the photovoltaic panels is studied. It has been proved that there is an area between the collectors in which the crop would not shade the photovoltaic panels. Likewise, a new tracking/backtracking strategy is proposed to avoid shading in cases where the crop exceeds this region of no influence. Finally, it has been found that the Land Equivalent Ratio for an agrivoltaic plant in Córdoba (Spain) with N–S horizontal trackers and olive groves in hedges up to 3.0 m high and 1.5 m wide can increase between 28.9% and 47.2%. Thus, these PV installations are potentially adaptable to agrivoltaic installations making renewable energy facilities compatible with a more efficient and sustainable agricultural model.
... Most recently, in 2018, Antonanzas et al. [27] proposed two predictive models to develop a single-axis tracking system which could determine the optimum position of PV panels. The study has been validated on some European Baseline Surface Radiation Network (BSRN) stations for the year 2015. ...
Article
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This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Abstract The performance of a photovoltaic (PV) installation is affected by its tilt and azimuth angles, because these parameters change the amount of solar energy absorbed by the surface of the PV modules. Therefore, this paper demonstrates the impact of the azimuth angle on the energy production of PV installations. Two different PV sites were studied, where the first comprises PV systems installed at-13°,-4°, +12° and +21° azimuth angles in different geographical locations, whereas the second PV site included adjacent PV systems installed at-87°,-32°, +2° and +17° azimuth angles. All the investigated PV sites were located in Huddersfield, UK. In summary, the results indicate that PV systems installed between-4° and +2° presented the maximum energy production over the last 4 years, while the worst energy generation were observed for the PV system installed at an azimuth angle of-87°. Finally, the probability projections for all observed azimuth angles datasets have been assessed. Since PV systems are affected by various environmental conditions such as fluctuations in the wind, humidity, solar irradiance and ambient temperature, ultimately, these factors would affect the annual energy generation of the PV installations. For that reason, we have analysed the disparities and the probability of the annual energy production for multiple PV systems installed at different azimuth angles ranging from-90° to +90° degrees, and affected by different environmental conditions. These analyses are based on the cumulative density function modelling technique as well as the normal distribution function.
... Second, to maximize the amount of sunlight entering the smart SPB and to minimize the shading effect, the tracker type of the smart SPB was determined. Generally, the tracker type of the PV system can be mainly categorized into the following: (i) fixedrack tracker; (ii) single-axis tracker; and (iii) double-axis tracker [27][28][29] . • Fixed-rack tracker : As the fixed-rack tracker is fixed at a certain angle, it cannot track the daily motion of the sun. ...
Article
In urban areas with dense buildings, it is expected that the building-integrated photovoltaic (BIPV) system, will become widespread. Especially, the solar photovoltaic blinds (SPB), which can block the sunlight coming into the room and produce electricity, is emerging as a new technology trend. To facilitate the installation of the SPB, this study analyzed the techno-economic performance of the smart SPB considering the PV panel type and solar tracking method used. Towards this end, this study conducted experiments using the developed smart SPB, as well as a comparative analysis in terms of the techno-economic aspects based on the experiment results. The analysis results of this study were as follows: at the same cost, (i) the monocrystalline silicon (mono-Si) PV panel generated 350.5% more electricity than the amorphous silicon (a-Si) PV panel; and (ii) the direct solar tracking system generated 12.9% more electricity than the indirect solar tracking method. Accordingly, the mono-Si PV panel and the direct solar tracking method were selected for the optimal smart SPB. The installation of the smart SPB with the proposed optimal design on the south-facing window of buildings can be helpful for raising the electricity self-sufficiency rate of buildings by up to 20.3%.
... Humidity affects both the efficiency of the panel and the amount of irradiance the panel receives. This is because the water vapor in the air affects the amount of diffuse irradiance that reaches the panel and humidity can also have a soiling effect on the panel if water vapor seeps into the glass casing [24][25][26]. The Köppen-Geiger climate classifications were treated as categorical variables while temperature, cloud ceiling, and humidity were treated as continuous variables. ...
... For example, it is more advantageous to set a PV panel horizontal than to follow the sun's path on cloudy or overcast days where most of the incident radiation arrives isotropically from the entire sky [32,33]. Antonanzas [34] constructed a real-time tracking algorithm to maximize energy production under varying weather conditions and a 3.01% radiation increase is found. Moreover, Fern?ndez [35] presented a new series of mathematical expressions for various single-axis tracking systems. ...
Article
Existing structural designs of various single-axis tracking systems have potentially limited energy production. This paper presents the design and performance analysis of a single-axis tracking system with a novel tracking structure. Tracking mathematic expressions based on the sun-earth geometric relationships and a predicted solar radiation model are presented. The ratio of annual solar radiation incident upon the proposed tracked panel relative to that upon a dual-axis tracked panel is 96.40%. The simulation results show that it has significant advantages over the existing single-axis tracking structures at almost all latitudes. The proposed tracking structure is a competitive choice and will provide a new perspective on enhancing solar energy yield.
... Works have been done to enhance the tracking performance under particular scenarios, such as cloudy weather [9], [10] and high latitude locations [11]. On the contrary, this work aims to analyze the different conditions worldwide. ...
Article
This article models the performance of photovoltaic tracking algorithms worldwide, based on the overall insolation collection, by comparing two tracking algorithms, namely tracking the sun (TS) and tracking the best orientation (TBO). In general, the latter is expected to receive higher irradiance with the drawback of requiring a higher installation and maintenance cost (due to the extra sensors). The aim of this research is then to quantify how big the difference is on irradiance collection from these two trackers worldwide by analyzing the data from 61 ground weather stations. In addition, three different tracking mounting structures are considered in this work: first, horizontal single axis tracker (HSAT); second, tilted single axis tracker (TSAT); and third, dual axis tracker (2T). Furthermore, the irradiance collection from front and rear sides are estimated for installations of monofacial and bifacial modules. The simulations reveal that, although the TBO results are higher than the TS ones, there is not a big difference on their insolation collection for latitude locations below 60° (<1.8%). Nevertheless, for higher latitude locations, TBO tracking systems can achieve a considerably higher performance reaching values of up to 3.3%, 7.1%, and 2.9% for HSAT, TSAT, and 2T systems, respectively. It was also observed that for bifacial and 2T systems in particular, high albedo values would produce a considerable enhancement on the TBO performance with respect to TS.
... Most recently, in 2018, the authors in [27] proposed two predictive models to develop a single-axis tracking systems which could determine the optimum position of PV panels. The study has been validated on some European Baseline Surface Radiation Network (BSRN) stations for the year 2015. ...
Article
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... Jacobson M Z et al. [26] calculated the optimal inclination angles of solar panels in different regions, and compared them and concluded that horizontal single-axis tracking is recommended for all regions except high latitude regions. Antonanzas J et al. [27] studied the best tracking strategy under cloudy conditions. ...
Article
The study focuses on the performance comparison of solar single-axis tracking low-concentration photovoltaic/thermal (LCPV/T) system with different axes. The axes of the single-axis tracking LCPV/T systems are arranged along the east-west (EW) axis, north-south (NS) axis, and south-east 18° (SE-18°) axis, respectively. The thermal performance of the single-axis tracking system with different axes is discussed through simulated and experimental methods. Simulation study shows that the EW tracking system receives the highest amount of radiation and produced highest electrical energy throughout the year. The experimental research demonstrates that low-concentrating technology significantly improves the performance of the system. Chiefly, the overall thermal efficiency maintains between 50%-70%, and the maximum thermal efficiency achieved in the experiment reaches 68%. The average overall efficiency and exergy efficiency of the NS axis, EW axis and SE-18° axis are 59% and 20%, 64% and 23%, 59% and 20%, respectively. Both the energy and exergy performance of the EW axis is better than the other two axes. The placement of the axis has a significant impact on the thermal and electrical performance of the LCPV/T system. Consequently, the combination of low-concentrating and single-axis tracking technologies has an excellent prospect in practical application.
... However, in cloudy weather conditions, due to the lack of direct incident light, the effect of concentration of sunlight in trackers [18][19][20] using lenses is sharply reduced. Since most solar trackers work automatically [21][22], one of the optimal solutions for determining solar coordinates under such conditions was given in the work of J. Antonanzas [23] and others. There are also other problems that can occur, especially when using large-volume solar trackers [24 -25]. ...
Article
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In this article, daily power values are presented and average performance indicators are analyzed, obtained from a sample of solar panels made of polycrystalline silicon mounted on fixed bases and solar trackers relative to the direction of sunlight. Experiments have shown that the average efficiency of solar panels mounted on a solar tracker is almost 3 times higher than that of fixed panels.
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High-efficiency solar energy is an emerging technology which can reduce greenhouse gas emissions. A four-terminal (4T) partial concentrator photovoltaic (CPV⁺) is a promising hybrid concept to maximize the electricity yield by integrating existing photovoltaic technologies. This paper describes the mathematical modeling of a 4T CPV⁺ module for sun-tracking control optimization. The CPV⁺ module consists of low-cost auxiliary solar cells placed around the concentrator multijunction solar cells. We derived a mathematical model to predict the generated power of the 4T CPV⁺ module that incorporates inclination angle of array, location, date/time, lens optical efficiency, and solar irradiance data. The simulation revealed that the 4T CPV⁺ module with mono-facial auxiliary solar cells should always face toward the sun, similar to the conventional CPV modules, regardless of irradiance conditions. The short-term outdoor experiment using a prototype module validated the mathematical model and stayed within the margin error for generated power-per-unit module area (∼14 W/m²). The derived model will be fundamental for enhanced modeling and design optimization of the 4T CPV⁺ module.
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As the importance of sustainable energy has been rapidly growing, a concentrative photovoltaic (CPV) solar system is drawing much attention. In order for a system to operate efficiently, a deliberate solar tracking system must be equipped because an optimal tilt of solar panel is changed as the Sun orbits its trajectory. However, many existing tracking methods did not clearly consider the effect of various weather conditions, even though the performance of tracking method is subject to them. In this paper, we propose a CPV solar system that chooses the most proper solar tracking method among the group of heterogeneous tracking algorithms, based on an inference on the current weather conditions with Bayesian network (BN). We use 13 features derived from image processing and implement four tracking algorithms which have relative performance depending on nine different weather conditions. We constructed the working CPV system and collected the 1630 image data every three minutes for five hours over a period of 16 days. The proposed BN shows 93.9% accuracy for inferencing weather conditions, and the proposed system shows 16.58% higher power productivity, compared to a pinhole system and other existing methods.
Chapter
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This work proposes and evaluates methods for extending the forecasting horizon of all-sky imager (ASI)-based solar radiation nowcasts and estimating the uncertainty of these predictions. In addition, we evaluated procedures for improving the temporal resolution and latency of satellite-imagery-derived solar nowcasts. Based on these contributions, we assessed the reliability of ASIs and satellite-derived solar radiation nowcasts, with 1-min time-resolution and up-to-90-min ahead. The study was conducted in a location in Southern Spain using a set of cloudy days, specifically selected as representative of the most challenging conditions regarding solar radiation nowcasting. The results reveal that the use of ASI-based models provide low benefits compared to the use of satellite-based models for point solar radiation nowcasting. Given the frequency of occurrence of the different sky types in the study area, the results suggest that the use of a simple smart persistence algorithm, in combination with a low-resolution satellite nowcasting model could be an adequate choice, avoiding the challenges associated with the use of ASIs.
Chapter
Today, solar energy has an important place among the renewable energy sources in the world due to its high energy potential. Therefore the share of solar energy is gradually increasing in electricity generation. It is difficult to get maximum efficiency from the solar photovoltaic (PV) panels installed permanently because they can’t benefit from solar energy continuously. Therefore one of the most effective ways to prevent loss of energy efficiency is the solar tracking systems that provide up to 40% efficiency. In this study, it is aimed to increase the efficiency of solar PV plants by following the sun throughout the day and to maximize the power produced by solar PV panels by exposing it to more light. Therefore a single-axis passive-controlled solar tracker system design is recommended for 42,000 kWp solar PV power plants in the Çukurova region. The efficiency effect of the proposed tracker system for high-power solar PV plants is examined. By comparing the performance analysis of the proposed solar PV system having a solar tracker system with a fixed angle solar PV system, the effectiveness of the proposed system is revealed for high-power solar PV plants.
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A novel off-grid small power generation system using locally available sources is proposed in this paper for the areas, where the open-wells or the permanent sources of water are available. Although, the system can be installed anywhere, but its installation in remote and rural areas, where there is no access of electricity, can be an interesting application. The proposed system comprises of a solar photovoltaic (SPV) system, solar water pump, pico-hydro turbine-generator and pumped-hydro energy storage system. Its operation is quite different from all other existing SPV power generating systems. In this paper, an innovative power generation technique is developed, due to which the output power of the proposed system is absolutely unaffected by the changes that occur in solar irradiation. The proposed system does not require the use of batteries, inverter, transformer, and charging or controlling circuits at all. The attractive features of the system are simplicity, reliability and ability to generate continuous power at constant voltage irrespective of variations or absence of solar irradiation. The mathematical model of the proposed system has been developed in the paper. The simulation is carried out using real solar irradiation for performance evaluation of the proposed model.
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Photovoltaics is experiencing significant growth because it is a renewable energy resource capable of contributing positively to the global energy system. However, the high variability in solar resources and the inter-collectors shadows negatively influence the energy conversion of a photovoltaic plant, making it necessary to develop technologies that minimize these negative aspects. Considering these issues, this paper analyses the influence of the design variables of a PV plant with two-axis tracking (collector size and distance between collectors) on its energy conversion. For that purpose, the tracking/backtracking strategy considered has two important advantages: it allows eliminating the inter-collector shading and optimizes the collection of global solar irradiance during both tracking and backtracking, by considering not only the optimization of direct component of solar irradiance but also the diffuse and reflected components. Based on this analysis, specific design recommendations are proposed for two-axis tracking PV plants located in Cordoba (Spain). It has been proved that differences in orientation between the collectors running according to this tracking/backtracking strategy and those with pure astronomical tracking increases when the clearness index decreases. Similarly, the results show that the period of time requiring backtracking during sunrise and sunset is longer when GCR decreases. In any case, it has been shown that photovoltaic plants in Cordoba with this new tracking strategy could provide annually, at least, 2% more energy than plants using some existing tracking strategies, even those defined as ideal. Hence, this tracking/backtracking strategy might significantly contribute to the development of photovoltaic plants with two-axis trackers.
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The integrity of the Baseline Surface Radiation Network (BSRN) radiation monthly averages are assessed by investigating the impact on monthly means due to the frequency of data gaps caused by missing or discarded high time resolution data. The monthly statistics, especially means, are considered to be important and useful values for climate research, model performance evaluations and for assessing the quality of satellite (time- and space-averaged) data products. The study investigates the spread in different algorithms that have been applied for the computation of monthly means from 1-min values. The paper reveals that the computation of monthly means from 1-min observations distinctly depends on the method utilized to account for the missing data. The intra-method difference generally increases with an increasing fraction of missing data. We found that a substantial fraction of the radiation fluxes observed at BSRN sites is either missing or flagged as questionable. The percentage of missing data is 4.4%, 13.0%, and 6.5% for global radiation, direct shortwave radiation, and downwelling longwave radiation, respectively. Most flagged data in the shortwave are due to nighttime instrumental noise and can reasonably be set to zero after correcting for thermal offsets in the daytime data. The study demonstrates that the handling of flagged data clearly impacts on monthly mean estimates obtained with different methods. We showed that the spread of monthly shortwave fluxes is generally clearly higher than for downwelling longwave radiation. Overall, BSRN observations provide sufficient accuracy and completeness for reliable estimates of monthly mean values. However, the value of future data could be further increased by reducing the frequency of data gaps and the number of outliers. It is shown that two independent methods for accounting for the diurnal and seasonal variations in the missing data permit consistent monthly means to within less than one Wm<sup>−2</sup> in most cases. The authors suggest using a standardized method for the computation of monthly means which addresses diurnal variations in the missing data in order to avoid a mismatch of future published monthly mean radiation fluxes from BSRN.
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Several studies show that from about 20% to 50% more solar energy can be recovered by using photovoltaic systems that track the sun rather than systems set at a fixed angle. For overcast or cloudy days, recent studies propose the use of a set position in which each photovoltaic panel faces toward the zenith (horizontal position). Compared to a panel that follows the sun’s path, this approach claims that a horizontal panel increases the amount of solar radiation captured and subsequently the quantity of electricity produced. The present work assesses a solar tracking photovoltaic panel hourly and seasonally in high latitudes. A theoretical method based on an isotropic sky model was formulated, implemented, and used in a case study analysis of a grid-connected photovoltaic system in Montreal, Canada. The results obtained, based on the definition of a critical hourly global solar radiation, were validated numerically and experimentally. The study confirmed that a zenith-set sun tracking strategy for overcast or mostly cloudy days in summer is not advantageous.
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Optimum tilt and azimuth angles for solar panels were calculated for a grid of 0.1° by 0.1° National Solar Radiation Database (NSRDB-SUNY) cells covering the continental United States. Optimum tilt and azimuth angles varied by up to 10° from the rule of thumb of latitude tilt and due south azimuth, especially in coastal areas, Florida, Texas, New Mexico, and Colorado. The yearly global irradiation incident on a panel at this optimum orientation was compared to the solar radiation received by a flat horizontal panel and a 2-axis tracking panel. Compared to global horizontal irradiation, irradiation at optimum fixed tilt increased with increasing latitude and by 10%–25% per year. Irradiation incident on a 2-axis tracking panel in one year was 25%–45% higher than irradiation received by a panel at optimum fixed orientation. The highest increases in tracking irradiation were seen in the southwestern states, where irradiation was already large, leading to annual irradiation of over 3.4MWhm−2.
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The solaR package allows for reproducible research both for photovoltaics (PV) systems performance and solar radiation. It includes a set of classes, methods and functions to calculate the sun geometry and the solar radiation incident on a photovoltaic generator and to simulate the performance of several applications of the photovoltaic energy. This package performs the whole calculation procedure from both daily and intradaily global horizontal irradiation to the final productivity of grid-connected PV systems and water pumping PV systems. It is designed using a set of S4 classes whose core is a group of slots with multivariate time series. The classes share a variety of methods to access the information and several visualization methods. In addition, the package provides a tool for the visual statistical analysis of the performance of a large PV plant composed of several systems. Although solaR is primarily designed for time series associated to a location defined by its latitude/longitude values and the temperature and irradiation conditions, it can be easily combined with spatial packages for space-time analysis.
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Photovoltaic (PV) modules in real operation present angular losses in reference to their behaviour in standard test conditions, due to the angle of incidence of the incident radiation and the surface soil. Although these losses are not always negligible, they are commonly not taken into account when correcting the electrical characteristics of the PV module or estimating the energy production of PV systems. The main reason of this approximation is the lack of easy-to-use mathematical expressions for the angular losses calculation. This paper analyses these losses on PV modules and presents an analytical model based on theoretical and experimental results. The proposed model fits monocrystalline as well as polycrystalline and amorphous silicon PV modules, and contemplates the existence of superficial dust. With it angular losses integrated over time periods of interest can be easily calculated. Monthly and annual losses have been calculated for 10 different European sites, having diverse climates and latitudes (ranging from 32° to 52°), and considering different module tilt angles.
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The electrical yield of large-scale photovoltaic power plants can be greatly improved by employing solar trackers. While fixed-tilt superstructures are stationary and immobile, trackers move the PV-module plane in order to optimize its alignment to the sun. This paper introduces control algorithms for single-axis trackers (SAT), including a discussion for optimal alignment and backtracking. The results are used to simulate and compare the electrical yield of fixed-tilt and SAT systems. The proposed algorithms have been field tested, and are in operation in solar parks worldwide.
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This study is concerned with the evaluation of the isotropic and four anisotropic solar radiation models for inclined surfaces. The evaluation procedure was split in two stages— abbreviated and detailed analysis. Physical reasoning was used in the abbreviated analysis to demonstrate the shortcomings of the older models, while detailed evaluation was carried out for the newer models, using at least one-year's measured hourly data from each of five European sites. Plots displaying the hourly estimated radiation against measured values have been prepared along with computation of the mean bias error and the root mean square error for each slope/ azimuth. The isotropic model has been found to perform very poorly and in view of its impact on the thermal energy and daylight related calculations it is not recommended for further use. In this work further refinements have been suggested for the treatment of the background sky-diffuse radiance. The newer models including the presently proposed one have shown good agreement with the measurements.
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For some locations both global and diffuse solar radiation are measured. However, for many locations, only global radiation is measured, or inferred from satellite data. For modelling solar energy applications, the amount of radiation on a tilted surface is needed. Since only the direct component on a tilted surface can be calculated from direct on some other plane using trigonometry, we need to have diffuse radiation on the horizontal plane available. There are regression relationships for estimating the diffuse on a tilted surface from diffuse on the horizontal. Models for estimating the diffuse on the horizontal from horizontal global that have been developed in Europe or North America have proved to be inadequate for Australia [13]. Boland et al. [2] developed a validated model for Australian conditions. Boland et al. [3] detailed our recent advances in developing the theoretical framework for the use of the logistic function instead of piecewise linear or simple nonlinear functions and was the first step in identifying the means for developing a generic model for estimating diffuse from global and other predictors. We have developed a multiple predictor model, which is much simpler than previous models, and uses hourly clearness index, daily clearness index, solar altitude, apparent solar time and a measure of persistence of global radiation level as predictors. This model performs marginally better than currently used models for locations in the Northern Hemisphere and substantially better for Southern Hemisphere locations. We suggest it can be used as a universal model.
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This report analyzes an extensive set of measurements of the solar irradiance made using four identical solar arrays and associated solar sensors (collectively referred to as solar collectors) with different tilt angles relative to the earth’s surface, and thus the position of the sun, in order to determine an optimal tracking algorithm for capturing solar radiation. The study included a variety of ambient conditions including different seasons and both cloudy and cloud-free conditions. One set of solar collectors was always approximately pointed directly toward the sun (DTS) for a period around solar noon. These solar collectors thus captured the direct beam component of the solar radiation that predominates on sunny days. We found that on sunny days, solar collectors with a DTS configuration captured more solar energy in accordance with the well-known cosine dependence for the response of a flat-surfaced solar collector to the angle of incidence with direct beam radiation. In particular, a DTS orientation was found to capture up to twice as much solar energy as a horizontal (H) orientation in which the array is tilted toward the zenith. Another set of solar collectors always had an H orientation, and this best captured the diffuse component of the solar radiation that predominates on cloudy days. The dependence of the H/DTS ratio on the solar-collector tilt angle was in approximate agreement with the Isotropic Diffuse Model derived for heavily overcast conditions. During cloudy periods, we found that an H configuration increased the solar energy capture by nearly 40% compared to a DTS configuration during the same period, and we estimate the solar energy increase of an H configuration over a system that tracks the obscured solar disk could reach 50% over a whole heavily-overcast day. On an annual basis the increase is predicted to be much less, typically only about 1%, because the contribution of cloudy days to the total annual solar energy captured by a photovoltaic system is small. These results are consistent with the solar tracking algorithm optimized for cloudy conditions that we proposed in an earlier report and that was based on a much smaller data set. Improving the harvesting of solar energy on cloudy days deserves wider attention due to increasing efforts to utilize renewable solar energy. In particular, increasing the output of distributed solar power systems on cloudy days is important to developing solar-powered home fueling and charging systems for hydrogen-powered fuel-cell electric and battery-powered vehicles, respectively, because it reduces the system size and cost for solar power systems that are designed to have sufficient energy output on the worst (cloudy) days.
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An enhanced parameterization of insolation conditions based only on the knowledge of global irradiance is presented. Two limitations associated with the current approach using the clearness index are pointed out: its dependence on solar elevation and its inability to differentiate between different conditions that produce the same global irradiance. Suggestions are provided which could overcome part of these limitations. Arguments are substantiated with solid experimental evidence. It is further shown that noticeable gains in accuracy for the decomposition of global into direct and diffuse irradiance are possible if one makes optimum use of the information available within a global irradiance time series.
Article
This work describes measurements of the solar irradiance made during cloudy periods in order to improve the amount of solar energy captured during such periods. It is well-known that 2-axis tracking, in which solar modules are pointed at the sun, improves the overall capture of solar energy by a given area of modules by 30–50% versus modules with a fixed tilt. On sunny days the direct sunshine accounts for up to 90% of the total solar energy, with the other 10% from diffuse (scattered) solar energy. However, during overcast conditions nearly all of the solar irradiance is diffuse radiation that is isotropically-distributed over the whole sky. An analysis of our data shows that during overcast conditions, tilting a solar module or sensor away from the zenith reduces the irradiance relative to a horizontal configuration, in which the sensor or module is pointed toward the zenith (horizontal module tilt), and thus receives the highest amount of this isotropically-distributed sky radiation. This observation led to an improved tracking algorithm in which a solar array would track the sun during cloud-free periods using 2-axis tracking, when the solar disk is visible, but go to a horizontal configuration when the sky becomes overcast. During cloudy periods we show that a horizontal module orientation increases the solar energy capture by nearly 50% compared to 2-axis solar tracking during the same period. Improving the harvesting of solar energy on cloudy days is important to using solar energy on a daily basis for fueling fuel-cell electric vehicles or charging extended-range electric vehicles because it improves the energy capture on the days with the lowest hydrogen generation, which in turn reduces the system size and cost.
Conference Paper
A strategy for tracking photovoltaic (PV) arrays is examined. The tracking strategy employs a microprocessor-based controller which commands the PV array to move (referred to as backtrack) such that no interarray beam shading occurs. This strategy will permit higher ground cover ratios (closer interarray spacing), which reduces area-related costs such as land purchase and site preparation. Results indicate that backtracking actually increases the solar energy collection as compared to conventional single-axis tracking with shading losses. Further, since direct shading is eliminated, backtracking allows the use of series-configured panels, which offers benefits of flexibility, optimum fault tolerance, and cost savings associated with bypass and blocking diodes
Performance comparison of different models for the estimation of global irradiance on inclined surfaces
  • A M Gracia
  • T Huld
Gracia, A.M., Huld, T., 2013. Performance comparison of different models for the estimation of global irradiance on inclined surfaces. JRC Technical Reports.
Measured and modelled improvement in solar energy yield from flat plate photovoltaic systems utilizing different tracking systems and under a range of environmental conditions
  • M Koussa
  • A Cheknane
  • S Hadji
  • M Haddadi
  • S Noureddine
Koussa, M., Cheknane, A., Hadji, S., Haddadi, M., Noureddine, S., 2001. Measured and modelled improvement in solar energy yield from flat plate photovoltaic systems utilizing different tracking systems and under a range of environmental conditions. Appl. Energy 88, 1756-1771.
BSRN Global Network recommended QC tests
  • C N Long
  • E G Dutton
Long, C.N., Dutton, E.G., 2002. BSRN Global Network recommended QC tests, V2.0. BSRN Technical Report. <http://ezksun3.ethz.ch/bsrn/admin/dokus/qualitycheck.pdf>.