Photovoltaic self-consumption heating system: analytical model, experimental results and autonomy prospects

Mención Internacional en el título de doctorIn the European Union, buildings are responsible for 40% of energy consumption and 36% of CO₂ emissions, which contribute significantly to anthropogenic climate change. Since heating represents the major portion of energy consumption in buildings in Spain, renewable heating systems emerge as an alternative to mitigate this problem. This thesis proposes a heating system in which the PV production is self-consumed by a heat pump. For this purpose, a photovoltaic off-grid system that feeds an air-water heat pump to heat a small building through radiant loor has been designed and built. The building, despite the aim of being independent, incudes connection to the grid, so the heat pump supply can be switched between the photovoltaic microgrid and the conventional grid. The photovoltaic array, with a total area of 15.7m² and useful area of 14m², is composed by 12 modules, nominal power of 180W each. Heat pump's nominal heating power is 6kW, which is in fine with building's maximum thermal load. To size properly this type of photovoltaic system, it is necessary to go beyond peak sun hours term commonly used by installers and to simulate realistically photovoltaic production over time. The method known as five-parameter model, details the working curve of a module for a given cell temperature. In this thesis, production has been addressed from a physical point of view, emphasizing the influence of solar cells' temperature on their efficiency. A heat transfer model has been developed, which allows to determine accurately cell temperature under changing meteorological conditions, and then to calculate the photovoltaic production in each moment, basing on technical specifications commonly provided by the modules' manufacturers. This dissertation includes the experimental validation of both cell temperature and photovoltaic production models. The efficiency of the used modules, according to their total area, is 13.73% at 25°C, 12.08% at 50°C and 10.76% at 70°C. The proposed method is easily adaptable to any type of photovoltaic module, once its material composition is known, and its output can be simulated for any tilt angle and location, for where meteorological data are available. Depending on obtained working temperatures, the use of hybrid photovoltaic/thermal modules can be considered. The photovoltaic production model was simulated for the heating period from 4/12/2012 to 30/04/2013, predicting an achievable production of 1265.8kWh and an average cell temperature of 21.3°C, which reaches an average daily maximum value of 47.5°C. The intercepted solar energy during that period was 8869.4kWh, so the efficiency of the array according to its useful area would be 14.3%, instead of the nominal value of 15.4%. The photovoltaic heating system was experimentally tested during the same heating period. The array produced 820.8kWh of electricity. The seasonal photovoltaic efficiency was 9.26%. The achieved production was significantly lower than the achievable one, according to the simulation. The heat pump was fed with 723.9kWh of electricity, 501.4kWh of which carne from photovoltaic source: useful efficiency of the system 5.7%. Several factors caused that efficiency, such as electrical losses in diverse conversions, control system's limitations, storage system's capacity and fit of the production to the demand. The ammount of heat supplied to the radiant floor was 2321.9kWh. The seasonal COP was 3.2 and system's global efficiency was 18.2%. The system was isolated from the grid at 69.3%. Greenhouse gases emissions saved were 170.5kgco₂ comparing to feeding the theat pump with conventional electricity (for an emission factor of 0,34kgco₂ /kWh); 835.9 kgco₂ comparing to supplying the same heat ammount through a gas-oil C boiler; 573.6 kgco₂ comparing to a natural gas boiler. On the other hand, refrigerant leaks were equivalent to 132.1 kgco₂.Actualmente, en la Unión Europea los edificios demandan un 40% del consumo total de energía y son responsables del 36% de emisiones de gases de efecto invernadero, contribuyendo significativamente al calentamiento global antrópogénico. Dado que la calefacción supone la principal porción del consumo energético en los edificios en España, los sistemas de calefacción renovable surgen como una alternativa para mitigar dicha problemática. Esta tesis plantea un sistema de calefacción fotovoltaica en el que la producción eléctrica es auto-consumida por una bomba de calor. Para ello se ha diseñado y construido un sistema fotovoltaico sin inyección a red para alimentar una bomba de calor aire-agua que calienta un pequeño edificio mediante suelo radiante. El edificio, tendente a la autonomía, incluye conexión a red, por lo que el suministro a la bomba de calor puede permutarse entre la micro-red fotovoltaica y la red convencional. El campo fotovoltaico, con un área total de 15,7m² y útil de 14m² , está compuesto de 12 paneles, de 180W de potencia nominal cada uno. La potencia térmica nominal de la bomba de calor es de 6kW, al igual que la carga térmica máxima del edificio. Para dimensionar adecuadamente un sistema fotovoltaico de estas características es necesario simular realísticamente la producción fotovoltaica a lo largo del tiempo. En esta tesis, se ha abordado la producción desde un punto de vista físico, haciendo hincapié en 'la influencia de la temperatura de las celdas solares en su eficiencia. Se ha desarrollado un modelo de transferencia de calor que permite determinar con exactitud la temperatura de celda para condiciones meteorológicas cambiantes y, a partir de ahí, la producción fotovoltaica en cada momento, basándose en especificaciones comunmente suministradas por los fabricantes de módulos. La validación experimental del modelo, tanto para la predicción de la temperatura de celda como para la producción fotovoltaica, es incluida en la presente tesis. La eficiencia de los módulos utilizados, respecto a su área total, es de 13.73% a 25°C, 12.08% a 50°C y 10.76% a 70°C. El método planteado es fácilmente adaptable a cualquier tipo de módulo fotovoltaico a partir de los materiales que lo componen, y su producción simulable para cualquier ángulo de inclinación y localización, para la que se disponga de datos meteorológicos. Dependiendo de las temperaturas de trabajo obtenidas, la utilización de paneles híbridos fotovoltaicos/térmicos puede ser planteada. En concreto, el modelo de producción fotovoltaico fue simulado para el periodo de calefacción entre el 4/12/2012 y el 30/04/2013, prediciendo una producción fotovoltaica alcanzable de 1.265,8kWh y una temperatura media de trabajo de celda de 21,3°C, que alcanza una máxima diaria media de 47,5°C. La energía solar interceptada durante ese periodo fue de 8.869,4kWh, por lo que la eficiencia del campo considerando su área útil sería del 14,3%, frente al 15,4% nominal. El sistema de calefacción fotovoltaica fue estudiado experimentalmente durante el mismo periodo de calefacción. El campo produjo 820,8kWh de electricidad, por lo que la eficiencia fotovoltaica estacional fue del 9,26%. La producción obtenida fue inferior a la potencialmente alcanzable, de acuerdo con la simulación. La bomba de calor fue alimentada con 723,9kWh de electricidad, de los cuales 501,4kWh provenían de la fuente fotovoltaica: eficiencia útil del sistema del 5,7%. Multiples factores provocaron dicha eficiencia, tales como las pérdidas eléctricas en las diferentes conversiones, limitaciones del sistema de control, capacidad del sistema de almacenamiento y ajuste de la producción a la demanda. El calor suministrado al suelo radiante fue 2.321,9kWh. El COP estacional de la bomba de 11 calor fue de 3,2 y el rendimiento global del sistema del 18,2%. El sistema operó autónomo de la red a un 69,3%. Las emisiones de gases de efecto invernadero ahorradas fueron de 170,5kgco₂ respecto a alimentar la bomba de calor con electricidad convencional (para un factor de emisión de 0,34kgco₂ /kWh); de 835,9kgco₂ respecto a suministrar el mismo calor a partir de gas-oil C; de 573,6 kgco₂ respecto al uso de gas natural. Por otra parte, las fugas de refrigerante equivalieron a 132,1 kgco₂.Los resultados científicos que se presentan son fruto de la financiación por parte del Ministerio de Ciencia e Innovación del proyecto Diseño, construcción y evaluación experimental de un sistema de refrigeración solar y trigeneración de alta eficiencia para edificios e invernaderos (ENE2010-20650-C02-01) y de la ayuda FPI (BES-2011-050706). El Ministerio de Economía y Competitividad financió la Estancia Breve (EEBB-I-13-06021) en la Universidad de Wisconsin-Madison.Programa Oficial de Doctorado en Ingeniería Mecánica y de Organización IndustrialPresidente: Francisco Javier Rey Martínez.- Secretario: María Carmen Venegas Bernal.- Vocal: Rafael Antonio Salgado Mangua

Heat pump for radiant cooled and heated floor driven by a microphotovoltaic system

This paper reports a solar trigeneration system installed at the Solar Energy Experimental Plant owned by the Spanish National Research Council (CSIC), located in Arganda del Rey, 20km east from Madrid.The authors want to express their gratitude to the Ministerio de Economía y Competitividad of Spain for funding the research project ENE2010-20650-CO2-01

Energy and economic analysis of domestic heating costs based on distributed energy resources: A case study in Spain

Energy electrification is part of the European strategy for the decarbonization of the building sector and energy transition in cities. The present paper compares the heating costs of covering the heating demand by different systems: (i) domestic gas boiler and an air-to-air heat-pump, (ii) without and (iii) with local PV backup; in order to analyze the effects of the electric price volatility along with the weather condition dependency of the renewable systems. The study presents a heat pump model and a PV generation model to estimate the hourly performance of both systems. These models are then applied in an average dwelling in Bilbao, Spain, in November 2020, and November 2021. Results show that in November 2020 the combined use of a heat pump with PV generation to cover the heat demand was 66% cheaper than covering the same demand with a natural gas boiler. By contrast, the combined use of the PV and heat pump resulted in a 15% higher energy bill compared to the natural gas in 2021 due to the increase of the electricity prices (3 times higher), the lower temperatures (25%) and less solar radiation (70%)

Energy, Environmental and Economic Analysis of Air-to-Air Heat Pumps as an Alternative to Heating Electrification in Europe

Heat pumps (HP) are an efficient alternative to non-electric heating systems (NEHS), being a cost-effective mean to support European building sector decarbonization. The paper studies HP and NEHS performance in residential buildings, under different climate conditions and energy tariffs, in six different European countries. Furthermore, a primary energy and environmental analysis is performed to evaluate if the use of HPs is more convenient than NEHS, based on different factors of the electric mix in each country. A specific HP model is developed considering the main physical phenomena occurring along its cycle. Open data from building, climatic and economic sources are used to feed the analysis. Ad hoc primary energy factors and greenhouse gas (GHG) emission coefficients are calculated for the selected countries. The costs and the environmental impact for both heating systems are then compared. The outcomes of the study suggest that, in highly fossil fuels dependent electricity mixes, the use of NEHS represents a more efficient decarbonization approach than HP, in spite of its higher efficiency. Additionally, the actual high price of the electric kWh hampers the use of HP in certain cases.European Commission's H202

HOLISDER Project: Introducing Residential and Tertiary Energy Consumers as Active Players in Energy Markets

Although it has been demonstrated that demand-side flexibility is possible, business application of residential and small tertiary demand response programs has been slow to develop. This paper presents a holistic demand response optimization framework that enables significant energy costs reduction for consumers. Moreover, buildings are introduced as main contributors to balance energy networks. The solution basis consists of a modular interoperability and data management framework that enables open standards-based communication along the demand response value chain. The solution is being validated in four large-scale pilot sites, which have diverse building types, energy systems and energy carriers. Furthermore, they offer diverse climatic conditions, and demographic and cultural characteristics to establish representative results.Research leading to these results has been supported by HOLISDER project. This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 768614. The APC was funded by HOLISDER project

ENER-BI: Integrating Energy and Spatial Data for Cities’ Decarbonisation Planning

Given the current climate emergency, our planet is suffering. Mitigation measures must be urgently deployed in urban environments, which are responsible for more than 70% of global CO2 emissions. In this sense, a deeper integration between energy and urban planning disciplines is a key factor for effective decarbonisation in urban environments. This is addressed in the Cities4ZERO decarbonisation methodology. This method specifically points out the need for technology-based solutions able to support that integration among both disciplines at a local level, enriching decision-making in urban decarbonisation policy-making, diagnosis, planning, and follow-up tasks, incorporating the spatial dimension to the whole process (GIS-based), as well as the possibilities of the digital era. Accordingly, this paper explores the demands of both integrated urban energy planning and European/Basque energy directives, to set the main requisites and functionalities that Decision Support Systems (DSSs) must fulfil to effectively support city managers and the urban decarbonisation process.This research was funded by European Commission, grant number 691883

Engaging domestic users on demand response for heating cost reduction with a recommendation tool: Case study in Belgrade

[EN] The European Union has established a legislative framework that aims to enable consumers and businesses to take information-based decisions to save energy and money. Additionally, the increase of Distributed Energy Resources (both on generation and consumption) requires additional efforts to maintain the reliability and stability of the electric grid and the need of flexibility from residential buildings. The present study introduces a domestic decision support tool for reducing heating costs. This app provides detailed recommendations to end-users based on the day-ahead hourly weather forecast, electric and district heating tariffs predictions, heating demand, and heating systems dynamic performance. The tool was tested in 6 dwellings of a neighborhood of Belgrade during the last months of 2021 heating season (March-May). Energetic results suggest that 40% of participants followed the given recommendations and changed their heating pattern. Additionally, survey results show that end-users found the lack of information and knowledge as the main barrier to actively participate in the energy market, also preferring to have automatic control in their heating system. Authors conclude that recommendation tools are key elements in user-engagement, but they should be supported by additional information and training.Research leading to these results has been supported by HOLISDER project, Spain. This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 768614. This paper reflects only the authors’ views and the Commission is not responsible for any use that may be made of the information contained therein

ENER-BI: Integrating Energy and Spatial Data for Cities’ Decarbonisation Planning

Given the current climate emergency, our planet is suffering. Mitigation measures must be urgently deployed in urban environments, which are responsible for more than 70% of global CO2 emissions. In this sense, a deeper integration between energy and urban planning disciplines is a key factor for effective decarbonisation in urban environments. This is addressed in the Cities4ZERO decarbonisation methodology. This method specifically points out the need for technology-based solutions able to support that integration among both disciplines at a local level, enriching decision-making in urban decarbonisation policy-making, diagnosis, planning, and follow-up tasks, incorporating the spatial dimension to the whole process (GIS-based), as well as the possibilities of the digital era. Accordingly, this paper explores the demands of both integrated urban energy planning and European/Basque energy directives, to set the main requisites and functionalities that Decision Support Systems (DSSs) must fulfil to effectively support city managers and the urban decarbonisation process.This research was funded by European Commission, grant number 691883

Deepint.net: A rapid deployment platform for smart territories

This paper presents an efficient cyberphysical platform for the smart management of smart territories. It is efficient because it facilitates the implementation of data acquisition and data management methods, as well as data representation and dashboard configuration. The platform allows for the use of any type of data source, ranging from the measurements of a multi-functional IoT sensing devices to relational and non-relational databases. It is also smart because it incorporates a complete artificial intelligence suit for data analysis; it includes techniques for data classification, clustering, forecasting, optimization, visualization, etc. It is also compatible with the edge computing concept, allowing for the distribution of intelligence and the use of intelligent sensors. The concept of smart cities is evolving and adapting to new applications; the trend to create intelligent neighbourhoods, districts or territories is becoming increasingly popular, as opposed to the previous approach of managing an entire megacity. In this paper, the platform is presented, and its architecture and functionalities are described. Moreover, its operation has been validated in a case study where the bike renting service of Paris—Vélib’ Métropole has been managed. This platform could enable smart territories to develop adapted knowledge management systems, adapt them to new requirements and to use multiple types of data, and execute efficient computational and artificial intelligence algorithms. The platform optimizes the decisions taken by human experts through explainable artificial intelligence models that obtain data from IoT sensors, databases, the Internet, etc. The global intelligence of the platform could potentially coordinate its decision-making processes with intelligent nodes installed in the edge, which would use the most advanced data processing techniques.This work has been partially supported by the European Regional Development Fund (ERDF) through the Interreg Spain-Portugal V-A Program (POCTEP) under grant 0677_DISRUPTIVE_2_E, the project My-TRAC: My TRAvel Companion (H2020-S2RJU-2017), the project LAPASSION, CITIES (CYTED 518RT0558) and the company DCSC. Pablo Chamoso’s research work has been funded through the Santander Iberoamerican Research Grants, call 2020/2021, under the direction of Paulo Novais

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality