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[EN] Cities are expected to be protagonists of the energy transition and, among other challenges, the decarbonation of the residential consumption could greatly benefit from photovoltaic generation in the built environment. To assess its potential, the present study analyses the possibility to cover the electric demand of the city of Valencia with rooftop-installed PV panels. Specific types of buildings has been selected to study the potential of each one of them with respect to their demand and with a specific production/consumption model. The total potential energy production for the city of Valencia is estimated to be enough to satisfy the demand of domestic electricity. The economic investment scenario has been analysed (best- and worst-case scenarios), and the corresponding environmental benefits have been studied. The results of the present article are encouraging in the context of a global energy transition, necessary in the present times to keep human consumption within the planetary limits., This study has been supported by Climate-KIC¿s Pathfinder Programme (Task ID TC2018A_2.1.5-PRO_P066¿1B) and by the Cátedra de Transición Energética Urbana (Las Naves-UPV)

[EN] The alarming increase in the average temperature of the planet due to the massive emission of greenhouse gases has stimulated the introduction of electric vehicles (EV), given transport sector is responsible for more than 25% of the total global CO2 emissions. EV penetration will substantially increase electricity demand and, therefore, an optimization of the EV recharging scenario is needed to make full use of the existing electricity generation system without upgrading requirements. In this paper, a methodology based on the use of the temporal valleys in the daily electricity demand is developed for EVrecharge, avoiding the peak demand hours to minimize the impact on the grid. The methodology assumes three different strategies for the recharge activities: home, public buildings, and electrical stations. It has been applied to the case of Spain in the year 2030, assuming three different scenarios for the growth of the total fleet: low, medium, and high. For each of them, three different levels for the EV penetration by the year 2030 are considered: 25%, 50%, and 75%, respectively. Only light electric vehicles (LEV), cars and motorcycles, are taken into account given the fact that batteries are not yet able to provide the full autonomy desired by heavy vehicles. Moreover, heavy vehicles have different travel uses that should be separately considered. Results for the fraction of the total recharge to be made in each of the different recharge modes are deduced with indication of the time intervals to be used in each of them. For the higher penetration scenario, 75% of the total park, an almost flat electricity demand curve is obtained. Studies are made for working days and for non-working days., One of the authors was supported by the Generalitat Valenciana under the grant ACIF/2018/106.

[EN] Syngas produced from small-scale biomass gasification plants (tens of kW) can generate power from biomass resources. However, due to the syngas gensets demand is marginal, compared to gasoline gensets, it is not easy to find a genset specially designed to run on syngas. In this paper, an experimental study of a genset running on two kinds of fuel has been carried out. The genset used is a 10 kW ICE initially designed to run on gasoline, in parallel, simulations based on CHEMKIN-PRO software were made. The study focuses on the comparison of the ICE operation independently working on gasoline and syngas. Modifications were required in the genset to adapt the intake system to run on syngas. The syngas is obtained from a gasifier. According to the test, it is possible to convert a gasoline engine to a 100% syngas engine through straightforward modifications in the inlet manifold but reducing the efficiency and power. The electrical power running the genset on gasoline was 6.7 kW, whereas, with syngas, it is 4.8 kW (31.4% of reduction). The efficiency running the ICE on gasoline was 13.7% at its rated power, whereas for the genset fuelled on syngas, it was 10.5% (23.4% reduction)., This work was completed in the framework of the activities of the Renewable Area research group of the Instituto Universitario de Investigacion en Ingeniería Energética (IUIIE) of Universitat Politecnica de Valencia and by the project "Microred Inteligente Híbrida de Energías Renovables para solucionar el Trilema AguaAlimentacion-Energía en una comunidad rural de Honduras (Task ID 2020_ACDE_000306)

[EN] Off grid electrification is key to achieving universal electricity access. Despite the potential of biomass gasifiers as a clean technology to ensure reliable systems, they are not as well looked upon as their advantages suggest. In particular, the software HOMER, which researchers and technicians use the most to simulate and design Microgrids, does not include biomass gasification among its simulation technologies. Although some authors did simulate biomass gasifiers in HOMER, the necessary parameters and procedures to calculate and include them in the tool remain unclear, non-replicable, and leave open research questions as regards modelling. Using the inbuilt Biogas power plant modules in HOMER, this paper presents a set of steps to include the technical and economic parameters to simulate fuelling an electric generator through the syngas produced in a downdraft biomass gasification plant. Two case studies of isolated rural communities in Honduras and Zambia show the viability of the procedure. These case studies also confirm the technical and economic viability of islanded biomass-photovoltaic hybrid renewable energy microgrids. In both cases, the energy demand supplied and distributed by the microgrid had a Levelized Cost of Energy lower than the alternative of extending the electric grid to the communities., We do appreciate the work of MSc Josefine Axelsson, who conducted part of the study of Mumbeji, Zambia. This is an extended and updated version of a paper originally presented at the 15th Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES 2020) held in Cologne, Germany over the period 1st to September 5, 2020 (denoted then as paper SDEWES2019.0458 - Modelling a gasifier with HOMER for the simulation of off-grid hybrid renewable energy microgrids). This work was supported in part by the Spanish public administration under the grant FPU2016/00962, by the regional public administration of Valencia under the grant ACIF/2018/106, by the Food and Agricuture Organisation under the Letter of Agreement (PO number: 332412). And finally, by the Catedra de Transicion Energetica Urbana (Las Naves-UPV).

[EN] The methods currently used for designing a fluidized bed reactor in gasification plants do not meet an integrated methodology that optimizes all the different parameters for its sizing and operational regime. In the case of small-scale (several tens of kWs biomass gasifiers), this design is especially complex, and, for this reason, they have usually been built in a very heuristic trial and error way. In this paper, an integrated methodology tailoring all the different parameters for the design and sizing of a small-scale fluidized bed gasification plants is presented. Using this methodology, a 40 kWth biomass gasification reactor was designed, including the air distribution system. Based on this design, with several simplified assumptions, a reactor was built and commissioned. Results from the experimental tests using this gasifier are also presented in this paper. As a result, it can be said the prototype works properly, and it produces syngas able to produce thermal energy or even electricity., This work was supported in part by the European Commission through GROW GREEN project (Agreement number: 730283-GROW GREEN-H2020-SCC-2016-2017/H2020-SCC-NBS2stage-2016. http://growgreenproject.eu/).

[EN] Control and data acquisition systems are required in researching facilities to analyze the behaviour of any process. In this paper, the results of the design and implementation of an automation and control system applied to a microgrid based on renewables energy are shown. The microgrid is located in the Laboratory for Distributed energy resources – LabDER at the Institute for Energy Engineering at UPV. The brain of the system is a PLC, programmed to carry out several tasks to guarantee the correct operation of the system. The measuring devices used are power meters, anemometer, temperature sensors and a solar cell to measure irradiance. The communication protocol used is Modbus TCP IP, Modbus RS-485 and Xanbus. All the information is centralized using a SCADA as an HMI. As a result, a robust control, and data acquisition system, able to manage a microgrid for researching purpose was obtained., The authors gratefully acknowledge to the Universitat Politècnica de València and the Instituto Universitario de Ingeniería Energética for their support to accomplish this work.

Applications of renewable electricity in cities are mostly limited to photovoltaics, and they need other renewable sources, batteries, and the grid to guarantee reliability. This paper proposes a hybrid system, combining biomass and photovoltaics, to supply electricity to educational buildings. This system is reliable and provides at least 50% of electricity based on renewable sources. Buildings with small (&lt, 500 kW) installed power based on renewables, mainly biomass, are usually expensive. Besides, in urban areas, photovoltaic capacity is limited due to roof availability. This paper analyzes different configurations, meeting these constraints to obtain an economically feasible solution based on photovoltaic-biomass modelling of small size hybrid systems. The technology used for biomass energy valorization is a fluidized bed gasification power plant, which has been modelled with real data obtained from experimental tests and previous research projects. Thereby, real costs and electric efficiency are included in the model. The techno-economic feasibility analysis using HOMER software with metered real load curves from an educational building has been modelled. The results of the model show that hybrid renewable systems are very feasible in the scenario of 50% of electricity contribution, however, higher contribution (&gt, 70%) implies high electricity costs.

European universities are in the process of experimenting with teaching by applying the new learning model according to the Bologna plan, based on specific and transversal competences. Due to the old teaching model, which is still rooted in the current learning system, professors have difficulties in assessing transversal competences. In this paper, the results of applying a methodology to assess the transversal competences: analysis and problem solving, and planning and time management is presented. Although the methodology is designed to evaluate transversal competences, it could also be used to evaluate traditional specific competences, in which the acquired technical knowledge is assessed. The methodology consists of explaining to the student how a practical problem is solved, applied to a case that an engineer can find in professional life. Subsequently, the student must solve another problem of the same type raised by the professor. The student will be given a limited time to solve the problem. The methodology is applied in two different sessions. The students have previously been informed about the performance of the test. Unlike the traditional method, the student must prepare the class before the lecture. Therefore, when the professor explains the theoretical part and how to solve the problem, it can also resolve doubts raised by the student during the preparation of the session. Additionally, the students who take less time to solve the test will have a higher score in the assessment of planning and time management. The results obtained are analysed and improvements are proposed to facilitate the acquisition of skills.

[EN] Thermal comfort indices are normally used for assessing and controlling heat stress conditions in both: insides and outsides environment. In this paper, the results of the design and test of an Arduino-base prototype for estimating heat stress index is presented. This prototype allows the accurate detection of wind speed, air temperature, relative humidity, precipitation, atmospheric pressure, irradiation and globe temperature. By means of these parameters, it is possible to obtain indices such as mean radiant temperature (MRT) and wet bulb globe temperature (WBGT). As a result, the indices are estimated, storage in a database and analyzed. These values will be used in the future to measure the mitigation of heat stress in urban environments, by means of the construction of green facades and green roof or tree planting., This work was supported by European Commission through GROW GREEN project (Agreement number: 730283-GROW GREEN-H2020-SCC-2016-2017/H2020-SCC-NBS-2stage-2016. http://growgreenproject.eu/). This work was supported in part by the regional public administration of Valencia under the grant ACIF/2018/106.

[EN] Heat stress can affect negatively human performance, behavior and even health, therefore, mean radiant temperature (MRT) and wet-bulb globe temperature (WBGT) measurement and monitoring should be obtained for any environment in which people are constantly exposed. The aim of this work is to compare the globe thermometer temperature (tg), used for calculating both MTR and WBGT, using a smaller globe compared to a standardized diameter. For such purpose, a prototype has been designed. The device consists of an Arduino MEGA board, three temperature sensors, two black globes (Copper globe, matt black painted) and an anemometer. As an effort to use a device with a globe easier to handle in a real measuring device, a 9 cm diameter globe has been used which has a smaller diameter than a standardized one (15 cm); the third temperature sensor is used to measure the air temperature. MRT monitoring tests were carried out using the proposed prototype, collected data were compared between the smaller and the standardized diameter globes measurements according to UNE EN ISO 7723 and NTP 322 recommendations. Results of this work show that it is possible to use a smaller diameter globe in a heat stress monitor, with an acceptable margin of error compared to a standardized size globe., This work was supported by the European Commission through GROW GREEN project (Agreement number: 730283 — GROW GREEN — H2020-SCC-2016-2017/H2020-SCCNBS-2stage-2016. http://growgreenproject.eu/)

[EN] In this paper, it is presented preliminary results of a methodology for thermal comfort monitoring and evaluation in urban areas based on local metering of ambient conditions and Rayman model application. In the framework of GROWGREEN European project it was installed six monitoring stations for data acquisition of air temperature, relative humidity, wind speed, solar radiation and black globe temperature. Data of first 5 months of monitoring and modelling of one location with Rayman model to calculate PET (physiological equivalent temperature) is presented. Based on PET it was calculated the percentage of hours with thermal comfort per month, and it was made a comparison between PET and black globe temperature (GT) in order to evaluate the suitability of GT as a single, low cost and robust indicator of thermal comfort in urban areas., This work was supported by European Commission through GROW GREEN project (Agreement number: 730283 -GROW GREEN -H2020-SCC-2016-2017/H2020-SCC-NBS-2stage-2016. http://growgreenproject.eu/). This work was supported in part by the regional public administration of Valencia under the grant ACIF/2018/106.

[EN] Spanish electrical generation has traditionally included high pollutant energy resources, like fuel or carbon. However, disturbing ever-increase in the average temperature of Planet Earth has led to a search for sustainability in the energy scenario. Therefore, Spanish electrical generation mix is prone to replace contaminant energy resources by non-contaminant, such renewables. Concretely, Spain is one of the countries with more solar peak annual hours. Nevertheless, having enough space to increase solar fields has been widely question. In this paper, an unrealistic scenario where all the annual Spanish consumption would be covered by photovoltaics is deeply analysed. Considering real electrical Spanish consumption data from 2017, required total quantity of solar panels has been quantified. Additionally, the study takes the hypothesis that all the panels should be placed on Spanish desert zones for two main reasons. First, total solar peak annual hours there are higher than in other Spanish regions. Last, making there the installation would give use to previous wasted zones. Obtained results indicate that around 691 million of 330Wp solar panels would be required for this issue, taking up 492175 km2. This space means only a 0.77% of all Iberian Peninsula. These outcomes clearly show that there is suitable and enough space to increase solar fields in Iberian Peninsula., This work was supported in part by the regional public administration of Valencia under the grant ACIF/2018/106.

In this paper, a procedure for the systematic evaluation of lab practices based on the development of transversal competences is presented. This procedure includes the design and completion of specific rubrics (complemented with a personal interview at the end of the session) for each of the experiments carried out during the practice, considering both individual and group educational sides. So, aspects related to the student’s behavior when working in-group (and the specific contribution of each student to the group), but also related to the individual performance, attitude, abilities and knowledge which the student should have previously acquired during the theoretical classes are considered. A practical application of the developed method to the practices related to the course on Heat Transfer at the Polytechnic University of Valencia is presented, where some results are also summarized. In such application, the suitability of the proposed procedure is highlighted as a proper mean not just to evaluate, but also to help students developing both specific and transversal competences, which they will use during their whole career and professional life.

A Model Predictive Control (MPC) strategy based on the Evolutionary Algorithms (EA) is proposed for the optimal dispatch of renewable generation units and demand response in a grid-tied hybrid system. The generating system is based on the experimental setup installed in a Distributed Energy Resources Laboratory (LabDER), which includes an AC micro-grid with small scale PV/Wind/Biomass systems. Energy storage is by lead-acid batteries and an H2 system (electrolyzer, H2 cylinders and Fuel Cell). The energy demand is residential in nature, consisting of a base load plus others that can be disconnected or moved to other times of the day within a demand response program. Based on the experimental data from each of the LabDER renewable generation and storage systems, a micro-grid operating model was developed in MATLAB© to simulate energy flows and their interaction with the grid. The proposed optimization algorithm seeks the minimum hourly cost of the energy consumed by the demand and the maximum use of renewable resources, using the minimum computational resources. The simulation results of the experimental micro-grid are given with seasonal data and the benefits of using the algorithm are pointed out.

[EN] Measuring Fuel Poverty is a requirement for the correct sizing and the better understanding of the problem. Valencia¿s city council (Spain) commissioned a study based on primary data, i.e. direct interviews to the inhabitants. The survey reached 595 valid answers and gave an accurate quantification of fuel poverty in the city. For a more complete approach, and to be able to benchmark the results, five fuel poverty indicators were measured, next the minimum income standard was chosen for a deeper analysis. This indicator presented a 23.1% of households in fuel poverty, clearly above the average value for the country. Based on the survey results, the effect of different relevant factors are discussed, like energy prices, energy quality of the dwellings, tenure status or energy illiteracy. Then, conclusions and specific policy implications are put forward classified into four categories: economic support, housing retrofitting, training in energy, and deployment of new energy actors and markets., This work was supported in part by the city council of Valencia under the contract: E-08001-2015-000021-00, and by the Catedra de Transicion Energetica Urbana (Las Naves-UPV).

[EN] In this research work, a 3 kW stove based on biomass gasification, together with a fuel obtained from agriculture wastes as an alternative to the commonly used charcoal, have been developed looking for sustainable cooking in poor communities. Alternative fuel (BSW) are briquettes obtained by carbonization and densification of agricultural solid wastes. Two laboratory methods, water boil test (WBT) and controlled kitchen test (CCT) were used to analyze the performance of this approach by comparing the proposed improved stove (ICS-G) with the traditional one (TCS), when using both types of fuels: charcoal and BSW. Results indicate that consumption of charcoal decreases by 61% using the improved ICS-G stove instead of the traditional TCS. Similar fuel savings are obtained when using BSW fuels. BSW fuel allows for a carbon monoxide (CO) emission reduction of 41% and 67%, and fine particles (PM) in a 84% and 93%, during the high and low power phases of the tests, respectively. Use of BSW fuel and ICS-G stove instead of the TCS stove with charcoal, provides a cooking time reduction of 18%, savings of $353.5 per year per family in the purchase of fuel, and an emission reduction of 3.2 t CO2/year.family., This research received no external funding. P.B.M. was funded by the Generalitat Valenciana under the grant ACIF/2018/106.

[EN] In this study, we focus on the case of Spanish energy policy and its implications for sustainable energy development. In recent years, Spanish legislation has changed dramatically in its approach to sustainable energy sources. This change is despite EU and international efforts to increase energy efficiency, and to accelerate the transition to renewable energy sources (RES) in order to reduce greenhouse gas emissions. Based on the socio-technical transitions literature, this paper assesses the role of the new legislation in this altered scenario, and analyzes the evolution of energy production in Spain in the EU context. The results are triangulated with two expert assessments. We find that Spanish energy policy is responding to the energy lobby's demands for protection for both their investment and their dominant position. This has resulted in a reduction in the number of investors combined with a lack of trust in both local and foreign investors in the sustainable energy sector, affecting also social innovations in energy transitions. We conclude that Spain is a particular case of concomitance between the energy sector and political power which raises concern about the viability of a higher level of energy sovereignty and the achievement of international commitments regarding climate change., We thank the editors' board and three anonymous reviewers for their very insightful advice on a previous version of the manuscript. This research was conducted as part of the GROW GREEN Project ID: 730283 Funded under: H2020-EU. We are grateful for funding from the Universitat Politecnica de Valencia to cover the costs of open access publishing, and for funding from the University of Valencia to cover the costs of English language editing.

La masiva implementación de recursos energéticos distribuidos y renovables es la tendencia actual para incrementar la eficiencia, sostenibilidad y fiabilidad del suministro energético y la independencia de fuentes externas. La biomasa es un recurso renovable, distribuido y abundante en España, aunque en la actualidad su uso con fines energéticos es muy limitado y poco competitivo frente a otras fuentes de energía renovable. La implementación masiva de aplicaciones de biomasa para generación de calor, electricidad y/o cogeneración requiere optimizar técnica, económica y ambientalmente su proceso de aprovechamiento. El objetivo principal de la tesis es definir una metodología de optimización del aprovechamiento energético de la biomasa en un ámbito geográfico determinado y aplicarla a la Comunidad Valenciana. Para ello, en primer lugar, se ha revisado el estado del arte de la biomasa como recurso energético y de metodologías anteriores que resolvían aspectos parciales del estudio de viabilidad de aprovechamiento energético de la biomasa. En segundo lugar se ha desarrollado una metodología, estructurada en distintos módulos, que evalúa los recursos de biomasa, cuantifica y optimiza las distancias y costes de transporte, los potenciales consumidores y caracteriza las tecnologías de aprovechamiento. Todos los módulos confluyen en un módulo de optimización y evaluación de escenarios que permite comparar distintas alternativas energéticas desde un punto de vista económico y ambiental. La metodología se ha aplicado a la Comunidad Valenciana y se ha estudiado la viabilidad de distintas aplicaciones bioenergéticas para cada comarca de la misma. El potencial energético de la biomasa residual, principalmente, agrícola y forestal asciende a casi un millón de toneladas y equivale a 260.000 toneladas equivalentes de petróleo. En la mayoría de los casos el contenido en ceniza es bajo y permite tanto aplicaciones de generación de electricidad ó cogeneración, como producción de pellets para calderas. En función de la tecnología, la potencia eléctrica instalable sería entre 85 y 145 MW, lo que equivale al 1 - 1,5% de la potencia eléctrica total instalada en la Comunidad Valenciana, y es 15 veces más que la potencia con biomasa que había instalada en 2011 (8,9 MW según datos de AVEN, Agencia Valenciana de la Energía}. La viabilidad económica de las planta de biomasa fue aceptable en la mayoría de los casos, con periodos de retorno del capital inferiores a los 10 años, especialmente en plantas de cogeneración y plantas de producción de pellets. Dicha viabilidad económica es debida, en gran medida, a la estructura logística con transporte subcontratado y previa compactación (que se mostró como la mejor alternativa en cualquier caso}, y al hecho de que las plantas tenían un tamaño razonable con cantidades de biomasa gestionada en el rango 10.000 - 80.000 t/año. El balance de emisiones de C02 fue favorable en todos los casos siendo, de nuevo, la producción de pellets y la cogeneración las aplicaciones con mejor balance, ya que el ahorro de emisiones fue entre 3 y 5 veces mayor que el correspondiente a plantas de generación de electricidad. La estructura logística óptima a nivel económico fue también la que proporcionó menores emisiones asociadas al transporte., Alfonso Solar, D. (2013). Metodología para la Optimización del Aprovechamiento Energético de los Recursos de Biomasa. Aplicación a la Comunidad Valenciana [Tesis doctoral no publicada]. Universitat Politècnica de València. doi:10.4995/Thesis/10251/31636., Alfresco

This research was based on three species: Citrus sinensis (orange), Olea europaea (olive), and Prunus amygdalus (almond). The biomass was determined for a complete tree without roots, but including stem, branches, and canopy or crown. The obtained results demonstrate that the stem volume is slightly higher for almond trees (0.035 m3/tree) than for olive trees (0.027 m3/tree). In comparison, the average stem volume of orange trees is lower (0.006 m3/tree). On the other hand, the total biomass volume including canopy branches is similar in all three species: 0.043 m3/tree for orange tree, 0.066 m3/tree for olive tree, and 0.040 m3/tree for almond tree. The new practical quantification model for these Mediterranean agricultural crops is based on total biomass calculations normally used in forestry stands. So, the obtained values were used to develop models for biomass of the stem, branches, and canopy, relating them with the diameter and volume stem. The regression analysis shows a significant correlation with minimized estimation errors. This allows a practical use of this model in biomass calculation in standing trees, both for total tree biomass and also for pruning material.