Review of the legislative framework for the remuneration of photovoltaic production in Spain: a case study

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 sectorRegional 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

Real energy payback time and carbon footprint of a GCPVS

Grid connected PV systems, or GCPVS, produce clean and renewable energy through the photovoltaic e ect in the operation stage of the power plant. However, this is the penultimate stage of the facilities before its dismantlement. Before starting generating electricity with zero CO2 emissions, a negative energy balance exists mainly because of the embodied energy costs of the PV components manufacturing, transport and late dismantlement. First, a review of existing studies about energy life cycle assessment (LCA) and Carbon Footprint of PV systems has been carried out in this paper. Then, a new method to evaluate the Real Energy Payback Time (REPBT), which includes power looses due to PV panels degradation is proposed and di erences with traditional Energy Payback Time are analysed. Finally, a typical PV grid connected plant (100 kW nominal power) located in Northern Spain is studied in these sustainability terms. This facility has been firstly completely modelled, including PV modules, inverters, structures and wiring. It has been also considerated the energy involved in the replacement of those components with shorter lifespan. The PV panels degradation has been analysed through the comparison of normalised flash test reports on a significant sample of the installed modules before and 5 years after installation. Results show that real PV degradation a ect significantly to the Energy Payback Time of the installation increasing slightly a 4:2% more the EPBT value for the case study. However, along a lifespan of 30 years, the GCPVS under analysis will return only 5:6 times the inverted energy on components manufacturing, transport and installation, rather than the expected 9:1 times with the classical estimation

Photosynthetic active radiation, solar irradiance and the CIE standard sky classification

Plant growth is directly related to levels of photosynthetic photon flux density, Qp. The improvement of plant-growth models therefore requires accurate estimations of the Qp parameter that is often indirectly calculated on the basis of its relationship with solar irradiation, RS, due to the scarcity of ground measurements of photosynthetic photon flux density. In this experimental campaign in Burgos, Spain, between April 2019 and January 2020, an average value of the Qp/Rs ratio is determined on the basis of measurements at ten-minute intervals. The most influential factor in the Qp/Rs ratio, over and above any daily or seasonal pattern, is the existence of overcast sky conditions. The CIE standard sky classification can be used to establish an unequivocal characterization of the cloudiness conditions of homogeneous skies. In this study, the relation between the CIE standard sky type and Qp/Rs is investigated. Its conclusions were that the Qp/Rs values, the average of which was 1.93 0.15 mol J�����1, presented statistically significant di erences for each CIE standard sky type. The overcast sky types presented the highest values of the ratio, while the clear sky categories presented the lowest and most dispersed values. During the experimental campaign, only two exceptions were noted for covered and partial covered sky-type categories, respectively, sky types 5 and 9. Their values were closer to those of categories classified as clear sky according to the CIE standard. Both categories presented high uniformity in terms of illumination.Spanish Ministry of Science and Innovation, grant number RTI2018-098900-B-I00 and Consejería de Educación, Junta de Castilla y León, grant number BU021G1

Experimental analysis of a novel PV/T panel with PCM and heat pipes

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

New device for the simultaneous measurement of diffuse solar irradiance on several azimuth and tilting angles

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

Implementation of PV plants in Spain: a case study

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, Spai

Regression and ANN models for electronic circuit design

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

Benchmarking of meteorological indices for sky cloudiness classification

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

Extension of PAR Models under Local All-Sky Conditions to Different Climatic Zones

Four models for predicting Photosynthetically Active Radiation (PAR) were obtained through MultiLinear Regression (MLR) and an Artificial Neural Network (ANN) based on 10 meteorological indices previously selected from a feature selection algorithm. One model was developed for all sky conditions and the other three for clear, partial, and overcast skies, using a sky classification based on the clearness index (kt). The experimental data were recorded in Burgos (Spain) at ten-minute intervals over 23 months between 2019 and 2021. Fits above 0.97 and Root Mean Square Error (RMSE) values below 7.5% were observed. The models developed for clear and overcast sky conditions yielded better results. Application of the models to the seven experimental ground stations that constitute the Surface Radiation Budget Network (SURFRAD) located in different Köppen climatic zones of the USA yielded fitted values higher than 0.98 and RMSE values less than 11% in all cases regardless of the sky type.This research was funded by the Spanish Ministry of Science and Innovation, grant number RTI2018-098900-B-I00, and Consejería de Empleo e Industria, Junta de Castilla y León, grant number INVESTUN/19/BU-0004

Compounds with epoxy resins and phase change materials for storage in solar applications

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–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–epoxy resin for improving the energy production of such panels.Departmen of Culture and Education of the Regional Government of Castilla y León, Spain (ORDEN EDU/667/2019 de 5 de Julio