End-Of-Use Fly Ash as an Effective Reinforcing Filler in Green Polymer Composites

The aim of this study is to use fly ash powder in an environmentally friendly matrix, in a novel way, addressing environmental and disposal problems. Fly ash/epoxy composites were prepared and studied varying the filler content. An investigation of structural and morphological characteristics was conducted using of X-ray diffraction patterns and scanning electron microscopy images, which revealed the successful fabrication of composites. Thermomechanical properties were studied via dynamic mechanical analysis and static mechanical tests. The composites exhibited an improved mechanical response. Broadband dielectric spectroscopy was used to investigate the dielectric response of the composite systems over the frequency range from 10−1 to 107 Hz and the temperature range from 30 to 160 °C. The analysis revealed the presence of three relaxation processes in the spectra of the tested systems. Interfacial polarization, the glass-to-rubber transition of the polymer matrix, and the rearrangement of polar side groups along the polymer chain are the processes that occur under a descending relaxation time. It was found that dielectric permittivity increases with filler content. Finally, the influence of filler content and the applied voltage under dc conditions was analyzed to determine the ability of the composites to store and retrieve electric energy. Fly ash improved the efficiency of the storing/retrieving energy of the composites

Thermosiphonic Hybrid PV/T Solar Systems

Thermosiphon solar water heaters and Photovoltaic (PV) devices are well known solar systems that provide heat and electricity, respectively. In this work, these two systems are combined into a hybrid hotovoltaic/Thermal (PV/T) solar system which can simultaneously provide electricity and heat, thus achieving a higher conversion rate of the absorbed solar radiation than standard PV modules. When properly designed, PV/T systems can extract heat from PV modules which can be used to heat water or air. By doing so the operating temperature of PV modules is reduced, which is beneficial, as it keeps their electrical efficiency at a sufficient level. In this paper, the design considerations and experimental results of a thermosiphonic hybrid PV/T solar system are presented. The electrical and thermal energy output for a pc-Si PV/T module type under the climatic conditions of Patras are presented

Performance of solar systems employing collectors with colored absorber

Flat plate solar collectors are of black appearance because of the color of the absorber, which is employed to maximize the absorption of solar spectrum. Generally, to avoid the monotony of the black color we can use collectors with absorbers of blue, red–brown, green or other color. These collectors are of lower thermal efficiency than that of the usual black type collectors, because of the lower collector absorptance, but they are of more interest to architects for applications on traditional or modern buildings. In this paper, applications of solar collectors with colored absorbers in a large hot water system suitable for multi-flat residential or office buildings, a house heating system, and an industrial process heat system are presented. The collectors are analyzed with respect to their performance and practical applications, aiming to give guidelines for their wider use on buildings. These systems are simulated on an annual basis at three different locations at different latitudes, Nicosia, Cyprus (35°), Athens, Greece (38°) and Madison, Wisconsin (43°). All simulations are carried out with TRNSYS. The results show that although the colored collectors present lower efficiency than the typical black type collectors, the difference in energy output depends on the absorber darkness. For a medium value of the coefficient of absorptance (α = 0.85), the colored collectors give satisfactory results regarding the drop of the amount of collected energy for the three locations (about 7–18%), compared to collectors with black absorbers (α = 0.95). This implies the use of proportionate larger collector aperture area to have the same energy output as that of typical black colored collectors. Additionally, the economic figures obtained for the systems investigated are very promising

Performance of a Solar Water and Space Heating System Employing Collector with Colour Absorber

To avoid the monotony of the black colored flat plate solar collectors we can use absorbers of blue, red-brown, green or other color. Because of the lower collector absorptance these collectors have lower thermal efficiency than that of the usual black type collectors, they are however of more interest to architects for applications on traditional or modern buildings. In this paper a solar hot water and space heating application with colored-absorber collectors of high (usual type) and low (selective) emissivity is presented and analyzed with respect to their performance. The house considered is 150 m2 insulated construction with a UA value of 1200 kJ/hr°C, kept at 21°C. The solar system consists of solar collectors with total aperture area of 50 m2 and a 3000 lt storage tank. The solar system provides part of the heating load and satisfies also the hot water needs of a 4-persons family. The system is simulated with TRNSYS on an annual basis at three different locations, Nicosia, Cyprus; Athens, Greece and Madison, Wisconsin. The first two locations represent locations with hot summer and mild winters, whereas the latter represents a location with mild summer and severe winter and was considered for comparison purposes. The results show that the energy output depends on the absorber darkness. For a medium value of the coefficient of absorptance, the colored collectors give satisfactory results with respect to the drop of the amount of collected energy, compared to collectors with black absorbers. This implies the use of slightly larger collector aperture area to have the same energy output as that of typical black colored collectors, which is acceptable comparing the aesthetic improvement of the solar system

Modeling and Simulation of Solar Systems Employing Collectors with Colored Absorber

To avoid the monotony of the black colored flat plate solar collectors we can use absorbers of blue, red-brown, green or other color. Because of the lower collector absorptance these collectors have lower thermal efficiency than that of the usual black type collectors, they are however of more interest to architects for applications on traditional or modern buildings. In this paper applications of solar collectors with colored absorbers are presented and analyzed with respect to their performance, aiming to give guidelines for their wider use on buildings. These systems are simulated with TRNSYS on an annual basis at two different locations, Nicosia, Cyprus and Athens, Greece. The results show that the energy output depends on the absorber darkness. For a medium value of the coefficient of absorptance, the colored collectors give satisfactory results with respect to the drop of the amount of collected energy, compared to collectors with black absorbers. This implies the use of slightly larger collector aperture area to have the same energy output as that of typical black colored collectors

ICS solar water heater study using artificial neural networks

In this paper we present a study in which a suitable Artificial Neural Network (ANN) and TRNSYS are combined in order to predict the performance of an Integrated Collector Storage (ICS) prototype. We use the experimental data that have been collected from outdoor tests of an ICS solar water heater with cylindrical water storage tank inside a CPC reflector trough, to train the ANN. The ANN is then used though the Excel interface (Type 62) in TRNSYS to model the annual performance of the system by running the model with the values of a typical meteorological year for Athens, Greece. In this way the specific capabilities of both approaches are combined, i.e., use of the radiation processing and modelling power of TRNSYS together with the “black box” modelling approach of ANNs. We present the details of the calculation steps of both methods that aim to the accurate prediction of the system performance and we show that this new method can be used effectively for such prediction

Modelling of an ICS solar water heater using artificial neural networks and TRNSYS

A study, in which a suitable artificial neural network (ANN) and TRNSYS are combined in order to predict the performance of an Integrated Collector Storage (ICS) prototype, is presented. Experimental data that have been collected from outdoor tests of an ICS solar water heater with cylindrical water storage tank inside a CPC reflector trough were used to train the ANN. The ANN is then used through the Excel interface (Type 62) in TRNSYS to model the annual performance of the system by running the model with the values of a typical meteorological year for Athens, Greece. In this way the specific capabilities of both approaches are combined, i.e., use of the radiation processing and modelling power of TRNSYS together with the “black box” modelling approach of ANNs. The details of the calculation steps of both methods that aim to perform an accurate prediction of the system performance are presented and it is shown that this new method can be used effectively for such predictions

Evaluating the Environmental Performance of Solar Energy Systems Through a Combined Life Cycle Assessment and Cost Analysis

The paper presents a holistic evaluation of the energy and environmental profile of two renewable energy technologies: Photovoltaics (thin-film and crystalline) and solar thermal collectors (flat plate and vacuum tube). The selected renewable systems exhibit size scalability (i.e., photovoltaics can vary from small to large scale applications) and can easily fit to residential applications (i.e., solar thermal systems). Various technical variations were considered for each of the studied technologies. The environmental implications were assessed through detailed life cycle assessment (LCA), implemented from raw material extraction through manufacture, use, and end of life of the selected energy systems. The methodological order followed comprises two steps: i. LCA and uncertainty analysis (conducted via SimaPro), and ii. techno-economic assessment (conducted via RETScreen). All studied technologies exhibit environmental impacts during their production phase and through their operation they manage to mitigate significant amounts of emitted greenhouse gases due to the avoided use of fossil fuels. The life cycle carbon footprint was calculated for the studied solar systems and was compared to other energy production technologies (either renewables or fossil-fuel based) and the results fall within the range defined by the global literature. The study showed that the implementation of photovoltaics and solar thermal projects in areas with high average insolation (i.e., Crete, Southern Greece) can be financially viable even in the case of low feed-in-tariffs. The results of the combined evaluation provide insight on choosing the most appropriate technologies from multiple perspectives, including financial and environmental

Characteristics of the urban heat island effect in the coastal Mediterranean city of Kalamata, Greece

The urban heat island effect for the coastal Mediterranean city of Kalamata is studied, for June to September during two consecutive years, 2019–2020. Temperature data were gathered by fixed temperature stations, placed in representative locations, covering all the major areas (urban, suburban, and rural). Results showed that the urban area is warmer than suburban and rural ones. The maximum heat island intensity was also estimated, usually achieved during nighttime and early in the morning. As there are no such data for Kalamata, this work helps to identify issues of energy consumption and human comfort. Especially for small Mediterranean cities, the work could be useful for a researcher to clarify the UHI Intensity. Detailed data are presented in the work, both for the clarification of UHI and its intensity and for the characteristics of each area, which could be useful for the development of UHI mitigation strategies, in small coastal cities