Pumps as turbines for efficient energy recovery in water supply networks

The present work aims to enhance the energy efficiency of water supply networks by investigating technical and economical feasibility of energy recovery plants at low installed capacities. A cost effective stainless steel machine is investigated in pump and turbine operation and established conversion methods are used for predicting the best efficiency point of the turbine. The obtained results show a reasonable agreement of the BEP, but experimental investigations are still indispensable for a determination of complete Q-H-characteristics. The hydraulic machine is implemented in field at the transfer shaft of a high-level tank and valuable data concerning investment costs and water hammer have been collected. A proposed cost classification scheme will facilitate the acquisition of investment costs for further applications. The economic profitability of the hydropower plant is evaluated by the net present value method and the obtained results give incentives to exploit unused energy recovery potential within water supply systems

The European project 20Plµs : 20 percent efficiency on less than 100µm thick industrially feasible crystalline-Si solar cells

The European project 20plμs is developing Si wafer solar cells with efficiencies above 20% on wafers less than 100 μm thick. Three principal solar cell process routes are investigated. The three approaches are distinguished by the doping type and maximum process temperature: p-type monocrystalline Cz-Si and multicrystalline Si solar cells subjected to high temperature processes are called pht, and n-type Cz-Si cells fabricated with low and high temperature processes are called nlt and nht, respectively. Already at the project’s midterm, a particular pht solar cell process was transferred to pilot line production. Key issues such as wafering, surface passivation, light trapping, metallisation and life cycle analysis were tackled to determine which process should be transferred. To date, by integrating the processes investigated within the project into full solar cells, efficiencies up to 18.7% (pht), 19.0% (nht) and 20.8% (nlt, 4 cm2) have been achieved on 100 μm thick large area Si wafers

Exploring flow-biofilm-sediment interactions: Assessment of current status and future challenges

Biofilm activities and their interactions with physical, chemical and biological processes are of great importance for a variety of ecosystem functions, impacting hydrogeomorphology, water quality and aquatic ecosystem health. Effective management of water bodies requires advancing our understanding of how flow influences biofilm-bound sediment and ecosystem processes and vice-versa. However, research on this triangle of flow-biofilm-sediment is still at its infancy. In this Review, we summarize the current state of the art and methodological approaches in the flow-biofilm-sediment research with an emphasis on biostabilization and fine sediment dynamics mainly in the benthic zone of lotic and lentic environments. Example studies of this three-way interaction across a range of spatial scales from cell (nm - mu m) to patch scale (mm - dm) are highlighted in view of the urgent need for interdisciplinary approaches. As a contribution to the review, we combine a literature survey with results of a pilot experiment that was conducted in the framework of a joint workshop to explore the feasibility of asking interdisciplinary questions. Further, within this workshop various observation and measuring approaches were tested and the quality of the achieved results was evaluated individually and in combination. Accordingly, the paper concludes by highlighting the following research challenges to be considered within the forthcoming years in the triangle of flow-biofilm-sediment: i) Establish a collaborative work among hydraulic and sedimentation engineers as well as ecologists to study mutual goals with appropriate methods. Perform realistic experimental studies to test hypotheses on flow-biofilm-sediment interactions as well as structural and mechanical characteristics of the bed. ii) Consider spatially varying characteristics of flow at the sediment-water interface. Utilize combinations of microsensors and non-intrusive optical methods, such as particle image velocimetry and laser scanner to elucidate the mechanism behind biofilm growth as well as mass and momentum flux exchanges between biofilm and water. Use molecular approaches (DNA, pigments, staining, microscopy) for sophisticated community analyses. Link varying flow regimes to microbial communities (and processes) and fine sediment properties to explore the role of key microbial players and functions in enhancing sediment stability (biostabilization). iii) Link laboratory-scale observations to larger scales relevant for management of water bodies. Conduct field experiments to better understand the complex effects of variable flow and sediment regimes on biostabilization. Employ scalable and informative observation techniques (e.g., hyperspectral imaging, particle tracking) that can support predictions on the functional aspects, such as metabolic activity, bed stability, nutrient fluxes under variable regimes of flow-biofilm-sediment. (C) 2020 Elsevier Ltd. All rights reserved

Low-head pumped hydro storage: A review on civil structure designs, legal and environmental aspects to make its realization feasible in seawater

The energy transition requires large-scale storage to provide long-term supply and short-term grid stability. Though pumped hydro storage is widely used for this purpose, regions without natural topography do not have the potential for traditional high-head pumped hydro storage. To address this, multiple projects for low-head and seawater pumped hydro storage have been proposed, though few have been implemented. Here, we review the state of the art of the components of low-head seawater pumped hydro storage projects, for construction in shallow seas or integrated into coastal defenses. We reference all civil infrastructure components, in addition to legal, environmental/biological, and financial constraints, drawing knowledge from proposed, planned, and constructed tidal power and seawater pumped hydro storage projects worldwide. Combining this knowledge, we make a preliminary evaluation of the feasibility for low-head seawater pumped hydro storage in the North Sea. We find that an elevated storage basin is more economical than an excavated one in shallow bathymetry (10 m deep or less), while the reverse is true in deeper water. Corrosion and fouling prevention are already well developed due to implementation of these measures at tidal power plants. Dam construction is feasible if measures are taken to address piping, macro-instability (primarily from rapid drawdown), and bursting of the clay layer. Within the context of Europe, legal and environmental regulations may be the most formidable hurdles to such projects

Nanocrystal formation in silicon oxy-nitride films for photovoltaic applications: Optical and electrical properties

Thin films of nanocrystalline SiOxNy are studied in view of their application in silicon heterojunction (SHJ) solar cells. In particular, the formation of the nanocrystals and their effects on the electrical and optical properties of the films are investigated. The role of the oxygen content on the properties of the layers is clarified as well. The obtained layers show very high conductivity (44 S/cm), low activation energy (1.85 meV) and high Tauc gap (2.5 eV), promising features for their application in photovoltaics