• Energy Research
• 2021-2025close

To address the climate change, the development of electrification is being rapidly conducted worldwide, especially in automobile industry. Regarding mobile machinery, many companies also have been forced to develop electrification technologies with a focus on electric mini excavators. Nevertheless, concerning middle class or larger sizes of excavators, it is not regarded that electrification technologies are the best solution, demanding huge battery capacity. Hence, it is expected that machines powered by internal combustion engines (ICE) will continue to be indispensable. To make hydraulic excavator more efficient, numerous studies to reduce throttling losses being major losses in hydraulic systems have been conducted. However, less throttling losses are likely to lead to inefficient operation considering the ICE efficiency map.In order to solve this issue, a hydraulic system called STEAM being one of the constant pressure systems has been proposed to improve overall system efficiency. Important features of this system are that the ICE can be operated at the most efficient point, and recoverable energy is allowed to be recuperated by accumulators. However, it might be difficult to be accepted by the industry due to using a multitude of valves. Alternatively, a three pump open center system allows engineers to design simple layout of the machines and enables machines to provide fluid efficiently by three pumps with less throttling losses. It seems that there is a new possibility by merging both architectures. Therefore, the purpose of this study is set to design a new hybrid architecture which combines an open center system with STEAM.In this thesis, basic principles and a design guideline to develop a hydraulic circuit of the new hydraulic architecture are discussed. To confirm the improvement of the system efficiency, simulations and experiments with the test rig are carried out and achievements are discussed. Dissertation, RWTH Aachen University, 2023; Düren : Shaker Verlag, Reihe Fluidtechnik. D 115, 1 Online-Ressource : Illustrationen (2024). doi:10.18154/RWTH-2024-04089 = Dissertation, RWTH Aachen University, 2023 Published by Shaker Verlag, Düren

Geostructures experience repetitive load cycles, which gradually affect their long-term performance. This thesis explores the long-term response of soils subjected to mechanical load-unload, heat-cool, freeze-thaw, and atmospheric pressure oscillations. The research methodology involves new instrumented cells (oedometer, temperature-controlled triaxial chamber, and pressure-controlled drying chamber), various geophysical monitoring methods (X-ray micro-CT, NMR, S-wave, and EM-waves), and simulations using discrete element modeling. Results show that soils subjected to repetitive mechanical or environmental loading experience shear and volumetric strain accumulation and changes in saturation (during barometric pressure cycles). In all cases, soils evolve towards an asymptotic terminal void ratio; the change in void ratio is pronounced when the soil exhibits grain-displacive ice formation during freeze-thaw cycles. The initial stress obliquity defines the shear strain response, which may be either shakedown -at low stress obliquity-, or ceaseless shear strain accumulation in ratcheting mode when the maximum stress obliquity approaches failure conditions. Finally, we provide simple engineering guidelines to estimate the long-term behavior of soils subjected to repetitive mechanical or environmental loading.

A minimal energy demand should be required in buildings both to optimize the performance of the building façade and to control solar gains. According to the existing studies and national standards, the climate zone classification is usually based on both the degree-days methodology and outdated climate data, thus managing HVAC systems inappropriately or leading to users’ thermal discomfort in indoor spaces. To evaluate the current limitations and to characterize solar gains in the Spanish building stock, an innovative approach is presented. For this purpose, seven clustering algorithms were implemented by distinguishing between winter and summer seasons during the calculation procedures. Solar irradiation from 8,948 locations in Spain were used. Likewise, the control of solar gains was analysed with the regulatory approach of Spain and with those developed through the study. The results of this research revealed that climate zones set by the Spanish Technical Building Code could imply to use values of monthly accumulated solar irradiation with discrepancies between 43.17 and 84.41 kWh/m2, compared to the real values. Hence, an accurate method focused on k-means clustering should be adopted. Furthermore, the results can be used for a more accurate analysis of solar control and improve the energy efficiency of buildings. Spanish Ministry of Science and Innovation Project PID2021-122437OA-I00 “Positive Energy Buildings Potential for Climate Change Adaptation and Energy Poverty Mitigation (+ENERPOT)” Thematic Network 723RT0151 “Red Iberoamericana de Eficiencia y Salubridad en Edificios” (IBERESE) financed by the call for Thematic Networks of the CYTED Program for 2022

In this paper, a physics-based model for dust accumulation on the front and rear surfaces of a bifacial module is presented. The accumulation on both the surfaces is assessed considering deposition, rebound and resuspension phenomena. The lift-off phenomenon of dust particle from ground is included additionally for the rear surface. This composite model is utilized to estimate soiling on both sides, which is extended to analytically assess the energy loss of the bifacial module. Experimentation has been carried out in four phases on a 10 kWp rooftop solar PV power plant. In the first phase, result shows soiling is less on glass than on the transparent back sheet-based rear surface. In the second phase, it is observed that surface density of dust on back surface for 34 days is 0.08 g/m2, for 79 days 0.6 g/m2 and for 126 days 1.8 g/m2 which are deviated from model based calculated ones by 10%, 33.33% and 4.4% respectively. The surface density of dust accumulated on the glass-based rear surface is about (1/6)th of the front glass surface, which is validated by the model also. The measured transmittance reduction is 3.2% for the back glass substrate and 29.6% for the front glass without manual cleaning for the test period. The model leads to the interesting result that the average energy generation loss for the bifacial plant is 1.4%/day compared to 1.7%/day for the monofacial plant since the generation enhancement from the rear surface more than compensates for the soiling loss from the back surface.

Thermoelectric devices may have an essential role in the development of fuel-saving, environmentallyfriendly, and cost-effective energy sources for power generation based on the direct conversion of heat into electrical energy. A wide usage of thermoelectric energy systems already exhibits high reliability and long operation time in the space industry and gas pipe systems. The development and application of solar thermoelectric generators (TEGs) arelimited mainly by relatively low thermoelectric conversion efficiency. Forthe first time, we propose to use the direct energy conversion of solar energy by TEGs based on the high-performance multilayer thermoelectric modules with electric efficiency of ~15%. Solar energy was absorbed and converted to thermal energy, which is accumulated by a phase-change material (aluminum alloys at solidification temperature ~900 K). The heat flow from the accumulator through the thermoelectric convertor (generator) allows electrical power to be obtained and the exhaust energy to be used for household purposes (heating and hot water supply) or for the operation of a plant for thermal desalination of water.

A novel experimental method for power efficiency loss is presented in this paper. It is used to quantitatively determine the impact of dust deposition on the PV power generation panel. To determine the selection range of unknown parameters in the experiment process, a photovoltaic panel with five collected dust samples (Toner (C), Soil, Cement (CaO, SiO4), Gypsum (Ca2SO4.2H2O), and Sand (AL2O3, SiO4)) is designed. According to experimental results, the extinction coefficient for the five pollutants are recorded. Eventually, the impact of dusts on the results is proofed by repeating in two continuous days of same conditions. The results show that the proposed process has a high effect on the reduction of output power (62% to 96%), decrease of irradiance (34% to 93%) and increase of output power due to increase of tilt angle as a doubling of power except toner. The experimental and calculated results are in agreement. The results show that non-uniform distribution of dust deposit pollutants on the photovoltaic panel significantly reduces the power output.Received: 09 January 2023 Accepted: 06 February 2023Published: 16 February 2023

The daily non-uniform power demand is a serious problem in power industry. In addition, recent decades show a trend for the transition to renewable power sources, but their power output depends upon weather and daily conditions. These factors determine the urgency of energy accumulation technology research and development. The presence of a wide variety of energy storage mechanisms leads to the need for their classification and comparison as well as a consideration of possible options for their application in modern power units. This paper presents a comparative analysis of energy storage methods for energy systems and complexes. Recommendations are made on the choice of storage technologies for the modern energy industry. The change in the cost of supplied energy at power plants by integrating various energy storage systems is estimated and the technologies for their implementation are considered. It is revealed that in the large-scale power production industry, the most productive accumulation methods for energy systems and complexes are the following: pumped hydroelectric energy storage systems, thermal and thermochemical accumulations, and hydrogen systems. These methods have the best technical and economic characteristics. The resulting recommendations allow for the assessment of the economic and energy effect achieved by integration of storage systems at the stage of designing new power units.

The University of Algarve, in consortium with “Cristal Construções – Materiais e Obras de Construção Civil”, “Itelmatis Control Systems” and “Itecons – Instituto de Investigação e Desenvolvimento Tecnológico para a Construção, Energia, Ambiente e Sustentabilidade”, is developing a new concept of outdoor heated sustainable swimming pool, having a higher energy efficiency and lower environmental footprint. The main objective is to minimise energy and water consumptions, while assuring a comfortable temperature for the user, extending the utilization of the pool in the Algarve region, from the summer months, to at least 8 months of the year. In order to do it, different systems will be tested, including solar thermal and photovoltaic panels, inverted underfloor heating, heat accumulator exchanger with phase change materials and energy dissipating pipes. An innovative thermal insulation system will be included in the interior of the pool tank, together with a new system for the covering of the water plane. All these systems will be monitored and controlled by an industrial automation system that will communicate, via a programmable logic controller, using industry standard communication protocols, with a SMART platform, that will be in charge of the global operation's optimisation. This platform will support an intelligent and predictive control and monitoring module, that controls the automation system to maximize the energy usage of the renewable sources, while assuring the user preferences. One of the main outputs of this project is the construction of a smaller scale prototype of a swimming pool, with the characteristics mentioned above, in order to test and validate the proposed developments.

A minimal energy demand should be required in buildings both to optimize the performance of the building façade and to control solar gains. According to the existing studies and national standards, the climate zone classification is usually based on both the degree-days methodology and outdated climate data, thus managing HVAC systems inappropriately or leading to users’ thermal discomfort in indoor spaces. To evaluate the current limitations and to characterize solar gains in the Spanish building stock, an innovative approach is presented. For this purpose, seven clustering algorithms were implemented by distinguishing between winter and summer seasons during the calculation procedures. Solar irradiation from 8,948 locations in Spain were used. Likewise, the control of solar gains was analysed with the regulatory approach of Spain and with those developed through the study. The results of this research revealed that climate zones set by the Spanish Technical Building Code could imply to use values of monthly accumulated solar irradiation with discrepancies between 43.17 and 84.41 kWh/m2, compared to the real values. Hence, an accurate method focused on k-means clustering should be adopted. Furthermore, the results can be used for a more accurate analysis of solar control and improve the energy efficiency of buildings. Spanish Ministry of Science and Innovation Project PID2021-122437OA-I00 “Positive Energy Buildings Potential for Climate Change Adaptation and Energy Poverty Mitigation (+ENERPOT)” Thematic Network 723RT0151 “Red Iberoamericana de Eficiencia y Salubridad en Edificios” (IBERESE) financed by the call for Thematic Networks of the CYTED Program for 2022