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Prediction of energy production is crucial for the design and installation of PV plants. In this study, five free and commercial software tools to predict photovoltaic energy production are evaluated: RETScreen, Solar Advisor Model (SAM), PVGIS, PVSyst, and PV*SOL. The evaluation involves a comparison of monthly and annually predicted data on energy supplied to the national grid with real field data collected from three real PV plants. All the systems, located in Castile and Leon (Spain), have three different tilting systems: fixed mounting, horizontal-axis tracking, and dual-axis tracking. The last 12 years of operating data, from 2008 to 2020, are used in the evaluation. Although the commercial software tools were easier to use and their installations could be described in detail, their results were not appreciably superior. In annual global terms, the results hid poor estimations throughout the year, where overestimations were compensated by underestimated results. This fact was reflected in the monthly results: the software yielded overestimates during the colder months, while the models showed better estimates during the warmer months. In most studies, the deviation was below 10% when the annual results were analyzed. The accuracy of the software was also reduced when the complexity of the dual-axis solar tracking systems replaced the fixed installation., This research was funded by Spanish Ministry of Science and Innovation, grant number RTI2018-098900-B-I00 and the Regional Government of Castilla y León under the “Support Program for Recognized Research Groups of Public Universities of Castilla y León” (ORDEN EDU/667/2019) and “Health and Safety Program” (INVESTUN/19/BU/0004).

There are several compilations of sky classifications that refer to Meteorological Indices (MIs) (variables usually recorded at meteorological ground stations), due to the scarcity of sky scanner devices that can supply the experimental data needed to apply the CIE standard sky classification. The use of one rather than another MI is never justified, because there is no standardized criterion for their selection. In this study, forty-three MIs, traditionally used to define different sky conditions, are reviewed. Feature Selection (FS) is a key step in the design of a sky-classification algorithm using MIs as an alternative to data from sky scanners. Four procedural methods for FS -Pearson, Permutation Importance, Recursive Feature Elimination, and Boruta- are applied to an extensive data set of MIs that includes CIE standard sky classification data, which was used as a reference. The use of FS procedures significatively reduced the original set of MIs, permitting the construction of different classification trees with high performance for the sky classification. In the case of the Pearson FS method, the classification tree only used two MIs. The advantage of the Pearson FS method is that it functions independently from the machine-learning algorithm used latter for the sky classification.

Daylight availability knowledge is the first step for an energetic and visually efficient building and city design. It can be estimated with the Vertical Sky Component (VSC), which is defined as the ratio of the vertical diffuse illuminance over the unobstructed horizontal diffuse illuminance, simultaneously measured at the same point. These illuminance magnitudes are obtained from luxmeter measurements but these data are scarce. Alternatively, VSC can be obtained from prior knowledge of the sky illuminance distribution, which can be measured with a sky scanner device or by reference to the CIE (Commission Internationale de L&rsquo, &Eacute, clairage) Standard classification for homogeneous skies. Both approaches are compared in this study. The coherence of the results obtained for the four cardinal orientations are analyzed by applying classical statistical parameters and luxmeter measurements as references for the results. The measurement campaign was completed between September 2016 and January 2019 in Burgos (Spain), as representative case study and specific contribution of this work. It was observed that the VSC values were higher than 100 in many cases: 21.94% for the south- and 33.6% for the east-facing vertical surfaces. The study highlights the good daylighting conditions in Burgos, mainly due to the predominance of clear skies over much of the year. This fact implies high daylight availability that, with efficient city planning and building design, could potentially lead reduction energy consumption of buildings, improvements in visual comfort, and the well-being of occupants.

Spain is a country with a high dependence on fossil fuels. For this reason, in 2007, it implemented a bonus system that aimed to encourage the production of renewable energies, particularly photovoltaic solar energy. These production bonuses, guaranteed by the Spanish government, led to an exponential increase in the number of companies in the market and, consequently, the MWh produced. However, in 2012, given the excessive budgetary burden involved in maintaining this “feed-in tariff” system and after several years of institutional instability, the aforementioned system of incentives for phoyovoltaic (PV) energy was eliminated. This paper has tried to analyze the consequences of this institutional change, a clear example of the “hold up” problem. For this purpose, a sample of 5354 companies, which was divided, geographically, into Spanish regions and, temporarily, into three different periods, has been taken, considering diverse economic and financial variables. The results show a notable weakening of the sector that, due to the effects of the regulatory change, has lost attractiveness and profitability for investors and is consequently suffering from stagnation, which has led to the disappearance of many companies in the sector., Raquel Fernández González gratefully acknowledge the financial support provided by the Xunta de Galicia under Grants ED431C2018/48 and ED431E2018/07 and the Ministry of Economy and Competitiveness under Grant RTI2018-099225-B-100. This research was funded by Regional Government of Castilla y León under the “Support Program for Recognized Research Groups of Public Universities of Castilla y León” (ORDEN EDU/667/2019) and the Spanish Ministry of Science, Innovation & Universities under the I + D + i state program “Challenges Research Projects” (Ref. RTI2018-098900-B-I00).

Spain is among the European countries with the greatest photovoltaic potential. During the first decade of the 2000s, Spain was a European leader in installed photovoltaic power and job creation in the renewable energy sector, strongly influenced by a very favorable regulatory framework and public subsidies at a time of economic growth. That situation would be completely reversed with the regulatory changes introduced in 2012 to combat the tari deficit and the instability in the electricity supply system, problems accentuated by the economic crisis. The main objective of this study is to present an exhaustive review of the legislative changes that have a ected photovoltaic energy in Spain. Using real data on electricity production and the remuneration of a typical photovoltaic plant, we show that there was a very significant fall in the economic returns that investors had come to expect, within a system that prioritized, first and foremost, the initial investment rather than the levels of electricity production. The changes to the legislative framework a ecting a typical 100 kWp photovoltaic (PV) facility that entered into service before 2007 provoked a significant decrease of 8.7% in expected revenues, calculated from real data of production and income. These economic losses can be even higher, with a drop in revenue of almost 25% if the entire period of the installation’s useful life is analyzed. Public support for renewable energy is important for its introduction into the electricity market, but so is regulatory stability that o ers investment security and predictability for maintaining investment and development in the renewable energy sector, Regional Government of Castilla y León under the “Support Program for Recognized Research Groups of Public Universities of Castilla y León” (ORDEN EDU/667/2019) and the Spanish Ministry of Science, Innovation, and Universities under the I + D + i state program “Challenges Research Projects” (Ref. RTI2018-098900-B-I00)

The determination of optimal illumination conditions in buildings is of great interest both for reducing energy consumption and for exploiting solar resources with greater efficiency and sustainability. The most commonplace method of estimating daylight is the luminous efficacy approach, using the more widely measured solar irradiance. In this present study, a new model of diffuse luminous efficacy over a horizontal surface is proposed. A comparative study of twenty-two classic models is presented, to obtain diffuse illuminance, using both, the original mathematical models and the adapted models with local coefficients, in order to determine the most suitable models for Burgos, a city located in north-western Spain. With this purpose in mind, twelve models are selected for all sky conditions, five models for modelling clear sky, two for partly cloudy sky, and three for overcast sky. These twenty-two models are then compared with the new model both for all sky conditions and for particular sky conditions (clear, partly cloudy, and overcast). The behaviour of the new model showed greater accuracy than most of the classic models under analysis. Hence, the advantage of the diffuse luminous efficacy model that can be applied both to all sky and to particular sky conditions., Spanish Government (Ministerio de Economía y Competitividad) (ENE2014-54601-R). David González Peña would also like to thank the Junta de Castilla-León for economic support (PIRTU Program, ORDEN EDU/310/2015).

Sky classification is a complex problem, due in part to such abstract conceptual definitions as clear, intermediate, and overcast, as well as other intermediate ranges. The CIE (Commission Internationale de L’Éclairage) Standard classification offers a solution to this problem, although its application requires data on the luminance distribution of the whole sky that are less commonly available. A benchmarking and classification system of ten meteorological indices is introduced in this study to classify the sky types from overcast to clear. The indices can be calculated from measurements of global, diffuse, and direct irradiance that are widely available from meteorological ground stations. The classification system uses confusion matrices, a machine-learning tool that generates a visual display of the results of supervised-learning algorithms. The CIE Standard skies classification, applied to half hourly sky-scanner measurements in Burgos (Spain), over the period June 2016 - May 2017, is used in this study as a baseline reference for a comparative review of the results from the meteorological indices and their results. They are classified by four performance ratings: Accuracy, Jaccard, Cohen, and Matthews, which feature both classification similarity and the randomness of any agreement. All meteorological indices yielded a high average degree of accuracy - close to 80% - in a detailed review of their classification. Neverthless, the results suggested that Perez’s Clearness Index based on global, diffuse and direct radiation measurements offered the most precise classification of the skies, followed closely by the Klucher Clearness Index and the Perraudeau Nebulosity Index., Regional Government of Castilla y León under the “Support Program for Recognized Research Groups of Public Universities of Castilla y León” (ORDEN EDU/667/2019) and the Spanish Ministry of Science, Innovation & Universities under the I + D + i state programme “Challenges Research Projects” (Ref. RTI2018-098900-B-I00)

Composite materials have great potential for growth due to their excellent properties and their multiple applications. The study of the thermal properties of the new composites resulting from the combination of epoxy resin and phase change materials (PCM), as well as thickening agents and thermally conductive compounds, was the objective of this work. For this purpose, different samples were manufactured by combining epoxy resins, organic PCMs (paraffins), and aluminum particles. Several properties were analyzed: thermal behavior (by differential scanning calorimetry technique), hardness, etc. To carry out this analysis, parameters of PCM quantity and metallic particles in the composition were varied. The results showed that the epoxy resin acted as a matrix containing the rest of the components and encapsulating the PCM. The organic PCM showed reversibility when subjected to multiple cycles. The enthalpy of the organic PCM&ndash, resin compound varied linearly according to the PCM content in the sample. For the content of this material in the samples to reach up to 40%, the use of thickening agents was necessary. The use of metallic particles improved the conductivity of the composites even while maintaining a low percentage by weight of metallic particles. Thermal simulations of the composite in bottom-coating a photovoltaic panel estimated a reduction of several degrees Celsius, showing the potential use of the PCM&ndash, epoxy resin for improving the energy production of such panels.

Daily data of Global, Diffuse and Beam Horizontal Insolation and Global Vertical (North, South, East and West orientations) insolation recorded in Burgos, Spain, are presented in this paper. Ten-minute irradiance data sets are collected over forty-five months in the experimental campaign to produce estimates of daily insolation levels. This data was derived in association with the article titled: “The PV Potential of Vertical Façades: a classic approach using experimental data from Burgos, Spain” (Díez-Mediavilla et al., in press) [1]. This dataset can be used to develop and test new solar radiation and daylight models and estimate the thermal load and lighting needs in buildings for the improvement of energy efficiency.

Solar energy potential analysis on oriented and tilted surfaces, such as building façades, is of capital importance to estimate the energy production potential in integrated systems, such as BIPVs. The spatial distribution of solar diffuse energy outstands as one of the most critical factors in order to improve performance simulations. Nevertheless, most wide spread models have been only evaluated on equator facing tilted surfaces and with daily mean or hourly mean time ranges. Thus, in this paper, 30 transposition solar diffuse irradiance models, from the semiphysical classical ones to the newest non-parametric models, are reviewed, classified according to their characteristics and evaluated against empirical 10-min averaged diffuse irradiance values gathered from high precision pyranometers placed on vertical positions facing the four cardinal directions. Models’ performance is evaluated by several statistical estimators and a benchmark has been carried out by a non-parametrical aggregating procedure. Results show that the most accurate models appear to be the non-parametric ones. From these, The Multi-Layer Perceptron obtains the best results. From the parametric models, the one whose estimations are closest to the measures is the Perez et al. with local optimized coefficients. Perez et al. model with the original coefficients, Skartveit and Olseth and Igawa et al. models also show a good performance.

Among the various methods of measuring diffuse solar irradiance, shadowing devices are ones of the most commonly used in solar research all over the world. These instruments work with a basic pyranometer, properly calibrated for the measurement of solar irradiance, with a shadowing element, which can be a disk or a band (Drummond’s shadow-band), that prevents the direct incidence of solar beam irradiance on the sensor. This method is capable of precise measurements, but sensor outputs have to be corrected, so as to quantify the amount of diffuse irradiance that the band blocks from reaching the sensor. Several authors have advanced different expressions for this correction factor, most of which only apply to horizontal and equator-oriented tilting pyranometers. In this work, we present a general approach to calculate the geometrical correction factor for a tilted sensor, oriented towards all possible azimuth and zenith angles, which permits the measurement of solar diffuse irradiance on any tilted and oriented surfaces. Furthermore, five total correction models are adapted for measurement in any given direction and evaluated on vertical walls pointing the four cardinal directions. Our results show that geometrical correction improves the Mean Bias Difference (MBD), the Root Mean Squared Difference (RMSD) and the l0:99 statistics by 60%, 62% and 56%, respectively, in contrast with the raw data. The LeBaron et al. model gives the most accurate figure for total correction according to MBD, RMSD and l0:99 statistics, with promising average performances of 97%, 91%, and 96%, respectively, Spanish Government (grant ENE2011-27511)

Potential photovoltaic (PV) production from vertical façades facing the four cardinal points of the compass are calculated from daily average vertical global insolation readings measured in Burgos, Spain. Ten-minute data sets are collected over forty-five months, from January 2014 to September 2017, in the experimental campaign to produce estimates of daily average insolation levels, from which the PV potential of the vertical surfaces was calculated. Given the scarcity of data on Global Vertical Insolation (GVI), the main sky-related variables were processed in four classic decomposition models (Isotropic, Circumsolar, Klucher, and Hay) to predict the insolation values. Both the experimentally measured GVI values and those calculated with the models were then compared using the statistical indicators RMSE and MBE. The results highlighted the economic viability of Building Integrated PhotoVoltaic (BIPV) facilities, even on the north-facing façades, in comparison with the horizontal facility at the same location., Regional Government of Castile and Leon (Junta de Castilla-León) (Ref. BU034U16) through the European Regional Development Fund, and from the Spanish Ministry of Economy, Industry and Competitiveness, under the I + D + i State Programme Challenges for Society (Ref. ENE-2014-54601-R

Daylighting is recognized as an important and useful strategy in the design of energy efficient buildings. Daylight is still the best source of light for good colour rendering and visual comfort. In this study, a new model of global luminous efficacy over a horizontal surface is proposed. A comparative study of eighteen classic models is presented, to obtain global horizontal illuminance, using both, the original formulation and new formulae with local adaptations, in order to determine the most suitable models for the conditions in Burgos (Spain). With this aim in mind, the selected models consisted of six models developed for all sky conditions, five models for clear sky conditions, three for partly cloudy sky and four for modelling overcast sky conditions. These eighteen models were also compared with the proposed model using experimental global illuminance measurements for different sky conditions. It was shown that the proposed model behaved in a better way than most of the classic models selected from the literature; both for all sky conditions and for particular sky conditions (clear, partly cloudy and overcast). The proposed model was therefore generally applicable, with no need to employ a different model for each particular sky condition., Spanish Government (Ministerio de Economía y Competitividad) (ENE2014-54601-R)

A new design for the use of photovoltaic and thermal (PV/T) technology with thermal storage is reported in this work. In the new design, a phase change material (PCM) tank is added to the backside of the photovoltaic panel. The advantages of this design are the storage of thermal energy and the efficiency improvement of the photovoltaic (PV) panel as a result of the temperature control of the PV cell during the phase change process. In addition, a perimeter with a black surface surrounds the PV panel to increase the absorption of thermal energy. The thermal energy is then transferred to the backside of the PCM tank by heat pipes. One prototype with lauric acid as PCM was tested under two different operating configurations and resulted in an overall daily efficiency of 50% coulding be improve by controlling the PCM temperature during the day., Regional Government of Castilla y León, Spain (Ref. BU034U16) and the Spanish Ministry of Science, Innovation & Universities under the I+D+i state program “Challenges Research Projects” (Ref. RTI2018-098900-B-I00)

Outdoor daylight conditions in Burgos, Spain, are studied throughout a full year. The CIE standard sky type is selected in accordance with the lowest RMSD (Root Mean Square Deviation) following the comparison of both the theoretical and the experimental luminance distributions in the sky hemisphere. The original criterion to determine the type of sky, the SSLD (the Standard Sky Luminance Distribution), is difficult to apply in certain places and at times when the solar elevation is higher than 35°. In consequence, two alternative procedures are used and compared in this study: the Tregenza method and the Normalization Rate (NR) introduced by Littlefair. The selection was taken from luminance distribution data of 145 patches of the sky hemisphere recorded between June 2016 and May 2017. The most frequent sky type observed in Burgos was V.5. (cloudless polluted with a broad solar corona), with a frequency of occurrence close to 20%. Notwithstanding that observation, the group of clear skies exhibited a higher frequency (in almost 50% of the cases under study, using both methods). The skies above Burgos were of an overcast sky type in less than 25% of cases, a situation with a higher likelihood in winter and in autumn, while in spring and summer the skies tended to be clear and cloud free. Both of the methodologies showed similar results in percentage terms and in confusion matrixes with almost insignificant differences when compared on a monthly, a seasonal, and an annual basis. Nevertheless, some mismatches were located in the highest solar elevation values., Regional Government of Castilla y León (Ref. BU034U16), under European Regional Development Fund, and the Spanish Ministry of Economy, Industry and Competitiveness, under the I+D+i State Programme Challenges for the Society (Ref. ENE-2014-54601-R)

An exhaustive evaluation of the performance of decomposition models to estimate direct and diffuse components from the global horizontal solar irradiance has been carried out in this work. The main objective of this work has been to compare the model performance for two different time bases, hourly and monthly average hourly bases. An extensive database of horizontal solar irradiance from nine locations in Spain was used for the study. The data span through January 1980 to December 2012 of hourly solar irradiance for the nine locations and thus indicate a cumulative year sum of 132 years. This study first investigated the decomposition of the hourly horizontal irradiance into hourly direct and diffuse components using six decomposition models widely referenced in the bibliography. In the hourly decomposition investigation, it was observed that there are no significant differences between the six models for each specific location. Nevertheless, the performance of each of the models was strongly dependent on cloudiness conditions and the solar altitude at the location which is associated with the climatic condition of each site. Further investigations using the six decomposition models were conducted to estimate monthly average hourly values of direct and diffuse components of the solar irradiance with proper assessment of the different models' performance at various locations. Based on the results of the investigations which present no significant differences in the performance of the different models, an extremely simple algorithm was developed to estimate monthly average hourly values of direct and diffuse solar irradiance, which reduces the statistical errors in all locations investigated., Spanish Government (ENE2014-54601R) and the 506 Regional Government of Castile and Leon (BU358A12-2)

This paper presents a methodology to design and to predict the behaviour of electronic circuits, which combines artificial neural networks and design of experiments. This methodology can be used to model output variables in electronic circuits either with similar features to the circuit configuration that is analysed in this study or with more complex configurations in order to improve the process of electronic circuit design.

Two complete years of operation of two grid-tied PV facilities is presented. Energetic and economic performance of both installations has been compared. Located in the same place, the installation of these facilities followed the same construction criteria – PV panels, panel support system and wiring – and the facilities are exposed to the same atmospheric temperature and solar radiation. They differ with regard to their inverter topology used: one facility uses a central inverter and the other a string inverter configuration. The performance of the facilities has been determined using a procedure based on a small number of easily obtained parameters and the knowledge of the analyzed system and its operation mode. Electrical losses have been calculated for both systems and a complete comparison between them has been carried out. The results have shown better performance for distributed system in economic and energetic terms., Spanish Government (Grant ENE2011-27511) and the Department of Culture and Education of the Regional Government of Castilla y León, Spain (Grant BU358A12-2).

Renewable energies, including photovoltaic energy, are attracting widespread international attention, in reaction to worsening environmental problems and the diminishing long-term sustainability of fossil fuel energies. In this work, the potential benefits of installing photovoltaic panels on several buildings at the Spanish Naval Military School (Escuela Naval Militar, ENM) of Mar ın are considered. The two salient advantages are significant economic savings from the production and the sale of electricity to the Spanish Electricity Network and achieving selfsufficiency in electricity requirements. Consequently, the main objective of this work is to estimate the energy potential of photovoltaic installations on the roofs of the ENM buildings. This is the first time that a project of this nature and size is presented to the Spanish Navy. To that end, a three-dimensional geographic analysis of the buildings is performed using three freeware software: Trimble SketchUp, Skelion, and Photovoltaic Geographical Information System. An economic study is also conducted to determine the feasibility of the installations, by estimating the Net Present Value of the photovoltaic installation and the Internal Rate of Return associated with the project. Subsequently, a sensitivity analysis that considers the most important parameters for the calculation of the amortization period is reported. The results show that the installation could fulfill the ENM electrical demands and could, in addition, generate significant economic benefits. The conclusions end with a recommendation to consider the merits of the proposed solution., Regional Government of Castilla y Le on (Ref. BU034U16), under European Regional Development Fund, and the Spanish Ministry of Economy, Industry and Competitiveness under the IþD þ i state programme Challenges for the Society (Ref. ENE-2014-54601-R). One of the authors, David Gonz alez Pe~na, thanks Junta de Castilla-Le on for economic support (PIRTU Program, ORDEN EDU/301/2015)

pp. 292-302 Current PV cells technology takes advantage mainly from beam radiation. In this context the sun-trackers are such devices for efficiency improvement. On the other hand, projected shadows between devices make mandatory to increase the distances between mounting systems. Thus, the land’s capacity for mounting PV panels can be dramatically decreased. This fact conducts us to wonder where the optimum efficient point is. First, in this paper different types of sun-tracking systems are classified according to the movement they perform (cinematic classification). Further, three real PV installations-fixed, horizontal-axis tracking and dual-axis mount tracking—located in the same geographical area in Spain (they are approximately under the same weather conditions) are analyzed. These installations have been studied in order to establish which one is the most efficient and affordable—Specific Energy Production (SEP) and Performance Ratio (PR) analysis. PVGIS solar radiation estimate tool has been used for comparing the theoretical radiation potential on each plant. The land requirements have been considered in the analysis of the Ground Cover Ratio (GCR) and the Surface Performance Ratio (SPR). Moreover, comparing three main financial indicators let us carry out a financial study: Payback Time (PBT), Net Present Value (NPV) and Internal Rate of Return (IRR). In the case study, final annual energetic results demonstrate that the dual-axis plant shows a relevant SEP advantage, but if we take into account the land occupied for this sort of devices we find much more profitable the horizontal-axis sun-tracking system, with a SPR value 4.24% higher than the fixed system we have studied. Its PBT is also a 22% lower than the dual-axis tracking installation SI

A new procedure is presented to analyse the performance of grid-tied PV facilities. It needs limited amounts of data that are easily sourced and is based on knowledge of the analysed system and its mode of operation. The procedure is applied, in a case study, to compare real PV production at two 100 kWp grid-connected PV installations. Located in the same geographical region, the installation of these two facilities followed the same construction criteria – PV panels, panel support system and wiring – and the facilities were exposed to the same atmospheric temperature and solar radiation. They differ with regard to their inverter technology: one facility uses an inverter with an integrated transformer system and the other uses a transformerless inverter. The results show that the transformerless inverter system performed better than the isolated system by a factor of 1.2%, which, in economic terms, represents more than 2000 €/year, Spanish Government (Grant ENE2011-27511) and the Department of Culture and Education of the Regional Government of Castilla y León, Spain (Grant BU358A12-2).

A detailed description is made of a software application that is designed to optimize a sun-tracker mechanism. It takes the main characteristics of any given installation site into account: geographical coordinates, inclination and orientation of the assembly platform. The desired result is a low-cost mechanism, which will have minimum-length construction elements, which will maximize coverage, and which will furthermore have the most energy efficient configuration. A multi-objective optimization technique (MOEAs) and numerical methods have successfully been applied to achieve these design objectives. In addition, the most computationally efficient kinematic model for the mechanism is analysed. Keywords Sun tracker, optimized design, parallel kinematics, Newton-Raphson, genetic algorithms, NSGA-II. 1. Introduction The regulatory framework for photovoltaic energy production in Spain (R.D. 1578/2008 of 26 th September [1] and R.D.L. 14/2010 of 23

A device is proposed for the measurement of diffuse solar irradiance on tilted surfaces pointing-to as well as fixed on the equatorial direction. Most commercial devices are not designed for this purpose. Here, we present a specific design for a system based on a single multi-lobe shadow-ring that allows us to measure diffuse irradiance with several tilted pyranometers – from 60 to 90 degrees from the horizontal plane – and on different azimuth angles. This first prototype allows us to measure in the four cardinal directions. The ring is designed to minimize the covered celestial dome observed by each sensor. Moreover, the complete device needs a very small installation area and its simplicity means it is inexpensive and easy to operate. The measurements have subsequently to be corrected with a geometrical correction factor that takes into account the portion of the sky vault blocked by the shadow-ring. These measurements are essential for estimating solar potential on tilted surfaces – such as building façades – and for improving current anisotropic solar models, among many other applications., Spanish Government (grant ENE2011-27511)

This paper presents the performance of 10 arithmetic models used to estimate diffuse solar irradiance on inclined surfaces in a comparative study with actual data readings made available on an hourly and a daily basis. The data readings have been taken from a south facing surface inclined at 42° in an area at some distance from the provincial capital in the Spanish province of Valladolid. In order to confirm the results, three statistical parameters have been used in the study; root mean square error (RMSE), mean bias error (MBE) and Stone’s t-statistic. The results obtained favour the Muneer model, followed by the Reindl model, for hourly as well as for daily values. The Temps–Coulson model gives rise to great discrepancies with respect to the values measured. The results for the Perez model are not good due to the use of parameters that are not specifically calculated for the area in this study, which underlines the need to take an area’s features into account so that predictions for diffuse irradiance measured on inclined surfaces may be as accurate as possible.

Direct solar irradiance has to be determined for the design of many energy applications such as photovoltaic systems and concentration systems, and the generation of solar potential maps for energy use. Knowledge of the accurate values of radiation components in a local area will allow optimal sizing of solar energy conversion systems. The estimated values of direct solar irradiance from models are still necessary at those sites where no measurements are available. In this work, different models used for the estimation of the direct component of solar irradiance are analyzed. First, an evaluation of the performance of eight existing original models was performed from which three were selected. Second, the selected models were calibrated to adapt them to our studied geographical area, which is the important aspect of this work, and an assessment of performance improvements for locally adapted models is reported. Experimental data consisted of hourly horizontal global, direct, and diffuse solar irradiance values, provided by the National Meteorological Agency in Spain (AEMET) for Madrid. Long-term data series, corresponding to a total period of time of 32 years (1980–2011), have been used in this study. Only clear sky models were treated at present. The three selected models were adapted to the specific location of Madrid, and root mean square error (RMSE) and mean-biased error were determined. By comparing the performance in the direct horizontal irradiance estimation from existing original and the corresponding locally adapted models, it is found that the values of RMSE decreased from 9.9% to 5.7% for the Louche model, from 7.8% to 7.4% for the Robledo-Soler model, and finally from 8.8% to 6.7% for the European Solar Radiation Atlas model. Thus, significant improvements can be reached when parametric models are locally adapted. In our case, it is up to approximately 4% for the Louche model. It is expected that calibrated algorithms presented in this work will be applicable to regions of similar climatic characteristics., Spanish Government (grant ENE2011-27511) and the Department of Culture and Education of the Regional Government of Castilla y León, Spain (grant BU358A12-2)

In our published paper, Gueymard’s model showed a performance that was significantly worse than the results obtained by other authors like Utrillas et al. [3] or Kambezidis et al. [4]. As a consequence, Dr. Gueymard has called our attention to the existence of an erratum [2] to his original paper [1], where the correct values of some of his model coefficients are given. Unfortunately, we had not taken into account these correct coefficient values in our publication. Therefore, the comments it contains about the results of Gueymard’s model are obviously not valid. As a consequence, we have repeated the performance evaluation of Gueymard’s model using the correct coefficients. The new results effectively show noticeable differences, as described further below.

A study is conducted of real PV production from two 100 kWp grid-connected installations located in the same area, both of which experience the same fluctuations in temperature and radiation. Data sets on production were collected over an entire year and both installations were compared under various levels of radiation. The installations were assembled with mono-Si panels, mounted on the same support system, and the power supply was equal for the inverter and the measurement system; the same parameters were also employed for the wiring, and electrical losses were calculated in both cases. The results, in economic terms, highlight the importance of properly selecting the system components and the design parameters for maximum profitability.

A small hydropower plant in Spain is studied from an energetic and economic perspective. The viability of the facility is examined using the freeware software RETScreen. Calculated and standard operational data are compared, thereby demonstrating the feasibility of the project from all points of view. The study highlights the growing interest in renewable energies., research project BU019A08 supported by the Department of Culture and Education of the Regional Government of Castilla y León, Spain

The implementation process of a photovoltaic system and its connection to the national grid in Spain is examined from an economic, an administrative and a legal standpoint. In the first place, this case study describes the solar farm, and it goes on to examine the economic aspects of electricity production, its associated costs, and relevant grants and financial subsidies. Finally, problems related to the administration of the project and the issuing of permits by local and regional authorities are discussed., project BU019A08 supported by the Department of Culture and Education of the Regional Government of Castilla y León, Spain

Publisher Summary This chapter shows a comparative assessment of tilted diffuse solar irradiation models using hourly horizontal diffuse solar irradiation measurements. Detailed measurements on inclined and horizontal surfaces are carried out at the C.I.B.A. Laboratory of Valladolid (Spain) and are unique in the Castile and Leon region. Ten sky diffuse models are used to estimate diffuse irradiation on tilted surfaces. Root mean square and mean bias errors are used to determine the performance of each tilted diffuse model and a comparison among the results has been made. From the results it can be seen that Reindl and Perez's models are better than the others and they are both recommended for predicting diffuse solar irradiation on tilted surfaces. The RMSE and MBE values of the models were calculated and compared for four clearness index values.