| Περίληψη: | Buildings consume around 37% of the final energy in Greece, emit greenhouse gases and favour the development of the urban heat island phenomenon. Consequently, this significantly motivates the development and implementation of new strategies for energy efficient building design. In the frame of zero-energy buildings, the integration of renewable energy sources along with energy saving strategies must be the target. The abundance of sunlight and need for alternative cooling technologies in Greece create opportunities for BIPV applications. Among different cooling technologies being under intensive research and development, are the addition of semi-transparent photovoltaic on window systems.
PV glazing is an innovative technology which can reduce energy consumption of the buildings providing energy efficiency through electricity generation, heat gain reduction and daylighting. With fabrication costs comparative with conventional double-glazed systems, it is highly expected that STPVs have a strong potential to dominate the fenestration market in the near future. After major advances in the PV industry, there are many semitransparent PV technologies which can be used to utilize multi-functional photovoltaic (PV) glazing with several properties and structures. However, applicability of a particular technology requires its extensive environmental and energy characterization in building integration.
In addition, an appropriate methodology is proposed for the assessment of the overall energy performance and optimal integration of different PV glazing technologies according to the characteristics and the use of the building itself. To this end, STPV window prototypes in small and full scale were developed from the addition of unique c-Si solar cells with holes and thin film a-Si PV module and suitable experimental testing procedure was used to determine their thermal and daylighting performance. Small samples were initially characterized by ultraviolet–visible–near infrared (UV/VIS/NIR) spectrophotometry and solar simulator irradiation in a benchtop wind tunnel of controllable environmental conditions. Afterwards, their overall energy performance was demonstrated through long-term monitoring of real integrated Si-based PV systems indicating a suitable experimental test procedure to characterize and compare such systems with conventional windows. Additionally, the impact of various window design parameters (optical, thermal) and PV technology on the temperature profile, solar energy yield and daylighting performance of the STPV windows were assessed. Results indicated that PV windows can effectively reduce heat gains during summer with slight increase on heating loads during winter compared to conventional systems. Integration of STPV windows also leads to reduced indoor illuminance and therefore further optimization is needed through dynamic computer modelling.
An accurate numerical model could balance interaction between thermal, daylighting and the power output and optimize integration of STPV windows maximizing energy efficiency and indoor comfort. To this end, Optics/WINDOW software was used for the development of the window systems with the desired properties and calculation of their U-value and solar heat gain coefficient. Afterwards an energy model in TRNsys, able to combine the energy generation and thermal behavior of the STPV systems, was developed and used to simulate the conditions to the interior of the test rooms. More specifically, heat transfer by mean of conduction convection and radiation, was taken into consideration from the heat transfer model to analyze the effect of the PV windows and the five parameter model was used for the electrical modelling and the estimation of their annual energy yield. Finally, annual illuminance profiles based on the local climate data were used from Daysim/Radiance software for the calculation of the appropriate daylighting and glare indices. Validation of the model results was performed through the comparison between simulation and the relevant experimental data for the same time periods and varying weather conditions. In all cases a very good fit was obtained, with relevant errors lower than ±5% indicating its accuracy.
Afterwards, validated model was used for the estimation of the annual energy demand of the reference building using typical meteorological year of Agrinio city in Greece. Comparison with the results from the conventional systems revealed the energy saving potential of the STPVs. Sensitivity analysis identified the optimal design parameters for the proposed systems based on the requirements for minimum energy use and maximum comfort in buildings. Best performance was achieved for South-West orientation and full replacement by c-Si solar cells. However, taking into consideration the selection criteria between PV glazing technologies, building typology and climate conditions of Greece, combined integration of the examined PV technologies is proposed leading to 44% energy efficiency and comfortable indoor environment. In addition, major contribution arising from this thesis is that proposed methodology is able to analyse the influence of each PV technology on built environment, while providing optimized integration. It can also be extended to other emerging technologies, building typologies or occupancy schedules and climate conditions.
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