Modelling and experimental characterization of photovoltaic/thermal systems for cooling and heating of buildings in different climate conditions
- Autores: Khaled Mohamed Elsaid Elsaid Ramadan
- Directores de la Tesis: Alberto Coronas Salcedo (dir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2021
- Idioma: español
- Tribunal Calificador de la Tesis: Juan Carlos Bruno Argilaguet (presid.), Carla Isabel Montagud Montalvá (secret.), Marco Beccali (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Termodinámica de Fluidos por la Universidad de Burgos; la Universidad de Santiago de Compostela; la Universidad de Valladolid y la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The 2030 Framework for Climate and Energy established that EU countries need to increase the share of renewable energy and save energy to reduce their greenhouse gas emissions. The incorporation of photovoltaic technologies into buildings has a great potential in reducing the CO2 emissions for climate change mitigation. Buildings with limited roof area require efficient solar systems to maximize the production per available area and efficient air-conditioning system to maximize the use of on-site PV energy. District cooling and heating network is the effective solution to use and share renewable energy sources in buildings.
Most of photovoltaic installations suffer from a drop-in cell efficiency as a result of increasing the PV cell temperature, decreasing the open circuit voltage. By cooling the solar cells with a fluid stream either by natural or forced circulation can reduce this PV cell temperature. The flexibility of integrating hybrid photovoltaic/thermal systems into building for solar heating and electricity generation, makes it possible to attain higher performance with less space needed. However, photovoltaic/thermal systems are efficient only when its heat was used for a useful purpose. The useful heat stream from the PV/T is appropriate for a domestic hot water application and space air heating in winter (cold climate). Nevertheless, in summer (hot climates) the fluid stream could be wasted because of the limited application based on this temperature range.
The PV power performance can be enhanced by using different solar concentrators in order to increase the input solar radiation to the PV cells which leads to increase the current output as well as the power output. As the light intensity on the cell is increased by the concentration ratio, the useful hot stream temperature produced from cooling the PV module is increased. For building applications, LCPV/T systems would be preferable due to their potential for non-tracking, high reliability and low cost. Further, Silicon-based cells fit well into low concentration solutions.
The available literature features a broad number of studies that have explored solar PV, PV/T and LCPV/T systems, but none of them presenting a comprehensive enough assessment of i) the impact of transforming installed PV module to water-based LCPV/T ; ii) the dynamic performance of on-site energy generation from PV, PV/T and LCPV/T and iii) the dynamic matching between energy generation and production in buildings with limited available area.
A solar PV, PV/T and LCPV/T coupled with efficient space cooling and heating systems can provide buildings with electricity, heating and cooling in a very flexible way throughout the year. The energy efficiency in buildings requires cost and efficient optimal solutions to reduce the investment cost and to increase the energy production as much as possible. The leading challenges faced upon accepting the PV systems for cooling and heating approach is that the hours of the day that experience the greatest production of solar power may occur when the consumption is at its lowest rate or vice versa, as well as the required high capital investment of storage batteries and water tanks. Balancing supply and demand with a connection to the electricity grid and the district cooliThe integration of photovoltaic/thermal (PV/T) and efficient air conditioning systems into buildings allows the provision of heating, cooling and electricity with a reduction in greenhouse emissions. The integration configurations of: a) photovoltaic (PV) systems with air-cooled electric chillers and air-to-water heat pump (HP) systems; b) air-based PV/T systems with air-to-water HP systems; c) Low concentrated photovoltaic/thermal systems (LCPV/T) with compression and absorption chillers; and d) LCPV/T coupled with water-to-water HP have a great potential in boosting the share of onsite PV-electricity.
Most of PV installations suffer from a drop-in cell efficiency as a result of increasing the PV cell temperature, decreasing the open circuit voltage. By cooling the solar cells with a fluid stream either by natural or forced circulation can reduce this PV cell temperature. The useful heat stream from the PV/T is appropriate for a domestic hot water application and space air heating in winter. However, in summer, the fluid stream could be wasted because of the limited application based on this temperature range. This application could be the regeneration of dehumidification and adsorption systems. The PV power performance can be enhanced by using different solar concentrators in order to increase the input solar radiation to the PV cells which leads to increase the current output as well as the power output. As the light intensity on the cell is increased by the concentration ratio, the useful hot stream temperature produced from cooling the PV module is increased. For building applications, LCPV/T systems would be preferable due to their potential for non-tracking, high reliability and low cost. Further, Silicon-based cells fit well into low concentration solutions.
By heating up the useful fluid leaving the PV/T into the linear parabolic concentrator and insert this combination between Vtrough mirrors, this stream could be heated up to 90°C which makes it useful for operating thermally driven air conditioning. Meanwhile, the PV cell temperature is kept below 75°C. For building integration, the payback period of the concentrated PV/T could be minimized when the useful fluid stream can be used to supply absorption chillers for hot climates at 75-90 °C, adsorption chillers at 50-70 °C, desiccant systems at 50-65 °C for high humidity climates, water heaters at 40-65 °C, and evaporator-heat pump at temperature level below 30 °C. However, the geometry of the V-trough results in shading the PV module in the early morning and afternoon.
The experimental performance, dynamic modelling validation and simulation of the commercial PV and PV/T and the developed LCPV/T are carried out. The energy impact of PV, PV/T and LCPV/T incorporated with space cooling and heating systems in existing case buildings under different climate conditions are presented. The environmental impact and the cost assessment of a set of strategies for operating photovoltaic and different cooling and heating systems are investigated. Also, a design methodology of the placement of a grid-tie PV and LCPV/T systems mounted on a rooftop and integrated with the existing aircooled chiller with the possibility of attaching the sized absorption chiller to use the thermal power from the LCPV/T system for cooling has been presented. This practice is done to provide existing buildings incorporated in the electricity grid and the chilled/ hot water network in the Mediterranean climate with electricity, heating and cooling, all while aiming for maximum investment profitability and maximum energy generation.
The performance of the polycrystalline module PV, monocrystalline PV panel, air-based PV/T collector, and water-based LCPV/T has been investigated for the two different size and activity buildings; the office building of 2,672 m2 in Tarragona and the university building of 16,109 m2 in Cairo. The results of this study reflect that integrating the LCPV/T with compression and absorption chillers in Egypt climate while LCPV/T with water-to-water reversible HP systems in Spain climate into the power grid and cooling/heating district network has a great potential in boosting the recoverable thermal energy utilization. The flexibility of incorporating LCPV/T energy for the bidirectional low temperature network in urban districts reduces thermal losses and provides producer and consumer (prosumer) buildings. In comparison to the typical configuration of PV integrated compression chiller, the proposed configuration of LCPV/T coupled with the compression and absorption chillers reduces the payback period by 10-40% in the case building in Cairo. Substituting the connection to the campus water network with the use of reversible HP reduces the operating cost for cooling and heating in the case building in Spain by 15-30%.
The payback of the PV system coupled with air cooled compressor chiller/air-to-water HP to meet the building cooling is about 9 years (without importing to the grid) and 7 years (with importing to the grid). The payback of the air-based PV/T assists the air-towater HP to meet the building heating demand is about 8 years (without importing to the grid) and 7 years (with importing to the grid). The payback of the LCPV/T system assisted the single stage heat recovery absorption chiller and powered the water-towater HP simultaneously to meet the building cooling demand in hot climate is about 7 years (without importing to the grid), 5 years (with importing to the grid) and less than 4 years (with importing to the grid and the chilled water network) and less than 3 years (with importing to the grid and the bidirectional cooling and heating network).
