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Carbon materials have a lattice plane distance in the range of the kinetic diameter of small gas molecules making them interesting for gas separating membranes. Thin carbon layers (< 1 µm thickness) were prepared on the core side of ceramic support tubes. In gas permeation tests the smaller CO2-molecules permeate 50 times faster than the bigger CH4. The same behavior was found for enlarged tubular membranes of 0.5 m length. Because of the mole sieving behavior nearly constant separation performance was found in synthetic CO2/CH4-mixtures over a wide range of variation in pressure (from 0.2 MPa to 1.2 MPa) and gas composition (from 10% to 90% CO2). By only one membrane step a mixture of a typical biogas composition of 0.57 CH4 / 0.43 CO2 was separated in a highly concentrated CH4-stream of 94% at 1.2 MPa and a highly concentrated CO2-stream of 91% at 0.1 MPa. In real biogas treatments on two different biogas plants a robust membrane performance during the testing period of at least one month was observed. CH4 of 94% was produced from the biogas in only one membrane step. Water as well as H2S (up to 180 mg/m³) permeated through the membrane without any damage of the membrane. Both can be also separated from the biogas by the membrane in one single step. Carbon membranes are a robust alternative to polymeric membranes of lower chemical and pressure stability. There are clear advantages in costs, energy consumption, flexibility and convenience of biogas upgrading with carbon membranes in comparison to classical technologies like PSA and scrubbing.

The paper provides a brief overview of the aims and main results of IEA Wind Task 33. IEA Wind Task 33 was an expert working group with a focus on data collection and reliability assessment for O & M optimization of wind turbines. The working group started in 2012 and finalized the work in 2016. The complete results of IEA Wind Task 33 are described in the expert group report on recommended practices for "Wind farm data collection and reliability assessment for O & M optimization" which will be published by IEA Wind in 2017. This paper briefly presents the background of the work, the recommended process to identify necessary data, and appropriate taxonomies structuring and harmonizing the collected entries. Finally, the paper summarizes the key findings and recommendations from the IEA Wind Task 33 work.

Grouted connections are frequently used as structural detail of offshore wind turbines and platforms for the load transferring connection between piles and support structure. At latticed substructures this connection is commonly located at mudline. However, a potential influence of the surrounding water on the connection's fatigue behaviour was neglected in earlier tests and consequential design methods. Herein described experimental investigations at small and large-scale fatigue tests in submerged conditions showed a significant reduction of endurable load cycles. In addition, the water impact caused varied damage mechanism in the connection. © 2017 The Author(s).

Latent heat storage devices use the melting enthalpy of a so-called phase change material (PCM) to store thermal energy. Open porous metals, such as 3D wire structures, allow the design of systems with tailored storage capacity and power. A geometric unit cell was identified, modelled and COMSOL Multiphysics was used to investigate the transient behavior of the PCM melting front within the composite of PCM and 3D wire structure. As a result, the impact of the wire structures material as well as the influence of brazing the inner connections of the wire structure on storage kinetics were analyzed.

In this work, we highlight the benefits of alternative plating routes compared to the standard plating route primarily discussed in literature and currently introduced in pilot production [1, 2]. The common plating route starts with the laser ablation of the front side grid after rear side Al-printing and firing. Then, an HF dip removes the native oxide for the subsequent light induced nickel-, copper plating (LIP) with a silver capping as a finishing. Afterwards, an annealing step improves the adhesion of the plated grid and its contact resistance. Here, we want to show the advantage of three alternative process routes. In the first alternative route, the laser opening of the front side grid is performed before the firing step. During firing, the laser damage is partly cured and can lead to an increase in open circuit voltage (Voc) of 7 mV on state of the art industrial PERC solar cells. For the second process route, the removal of the native oxide is eliminated. To achieve this, special laser and plating conditions are needed. Finally, for the third alternative process route, the annealing of the plated stack can be combined with a stabilization process suppressing the light induced degradation (LID). The presented alternative routes give new degrees of freedom for process optimizations regarding precursor-induced features such as high laser damage on shallow emitters, parasitic plating (PP) for passivation layers with high pinhole density or LID.

Wafers for solar cell processing do not only have to fulfill high geometric requirements but also have to be as free of any contaminations as possible. Therefore the wafering process is followed by several cleaning steps whereby contaminations such as organics, metals and particles should be removed from the wafer surface. With increasing requirements the cleaning process has to be continuously improved. However, up to now there is no known method that allows a reproducible qualitative or quantitative detection of the remaining particle load at diamond wire sawn wafer surfaces. To evaluate the influence of modified cleaning methods on particular contamination a suitable detection method is absolutely indispensable. In this work two new methods are introduced making it possible to detect the remaining particle load on wafer surfaces. For the first time, quantitatively reproducible results are obtained for the particle load either as a sum parameter or as a grain size distribution. The functionality of the methods is evaluated to compare the effectiveness of different cleaning procedures on the final cleaning step in the wafering process.

Disposal of food and drink wastes, including packaging wastes, has a significant cost and environmental impact. All carbon containing wastes have an energy potential and the food industry should focus on recovering that energy to offset their reliance on fossil-fuel derived energy sources. This paper focuses on the novel use of intermediate pyrolysis for decarbonizing the food chain, through the treatment of food and packaging waste, to recover energy. The TCR is a versatile technology which overcomes many of the traditional problems associated with fast pyrolysis and can thermo-chemically convert a range of different feedstocks, including inaccessible lignin and some inorganic, recalcitrant materials. The feedstocks are converted into new fuel sources; char, bio-oil (thermally stable) and permanent gases, for further electrical and heat generation. Ultimately with the use of the TCR technology, the food production industry could look to using decentralized power generation located on-site of large food processing facilities to optimize their energy efficiencies.

Copper is a common impurity in photovoltaic silicon. While reported to precipitate instantly in n-type Si, copper causes light-induced degradation (Cu-LID) in p-type Si. Recently, partial recovery of Cu-LID was observed after only few minutes of dark annealing at 200°C. In this contribution, we investigate the effects of the dark anneal on Cu-LID-limited minority carrier lifetime both experimentally and by simulations. Surprisingly, after initial recovery, the dark anneal results in further degradation corresponding to a many-fold increase in recombination activity compared to the degraded state after illumination. This anneal-induced degradation can potentially cause additional losses in accidentally Cu-contaminated devices when exposed to elevated temperatures, for example during recovery and regeneration treatments of solar cells. Transient ion drift measurements confirmed that the anneal-induced degradation cannot be attributed to residual interstitial Cu after illumination. After hundreds of hours of annealing, the samples showed another recovery. To analyze these experimental results, a comparison to simulations is performed at the end of the paper.

Rotational screen printing (RSP) has recently attracted attention as a highly promising high-throughput alternative for the metallization of Silicon solar cells. Compared to other metallization approaches, RSP is already a well-developed printing method which has been used for various industrial applications during the last decades. The unique benefit of this technology is the ability to apply a thick film metallization combined with a high throughput. Within the present work, we will discuss the actual achievements and challenges of this approach. We show the results of Aluminium back surface solar cells with a RSP rear side metallization and a mean conversion efficiency of η = 19.4 % compared to reference solar cells with flatbed screen printed rear side metallization and a conversion efficiency of η = 19.3 %. We further investigate the properties of fine line cylinder screens used for RSP and conventional flatbed screen printing. Using RSP with a fine line cylinder screen, we printed contact fingers with a mean width down w f = 61 µm. Finally, we discuss the path to a further optimization of this highly promising approach.

The authors present a fully solderable, co-diffused and bi-facial PERT solar cell where the rear BSG/SiN stack acting both as dopant and passivation source reaching a mean efficiency of 20.4 %. The conductivity induced by the presence of the p+ layer at the rear reduces series resistance losses significantly by simultaneously enabling the use of lowly doped Si wafers that reduce B-O degradation while maintaining a high fill factor. Parallel processed, mono-facial pendants reach the same efficiency level. A higher FF for the mono-facials is compensated by a higher Voc for the bi-facial PERT devices. SEM analysis on test structures show an overall superior, local Al-Si contact in terms of voiding and BSF thickness with reducing printed finger width. At reverse bias, the “conventional process” shows a typical behaviour for such architecture of elevated current flow around the edges. For the “adapted process” up to -12 V, the authors demonstrate a virtually shunt-free device exhibiting reverse currents far below 1 A with no additional process step.

In this study, the material compatibility of refrigerants focusing on hydrofluoroolefines (HFO) with typical polymers in ORC plants and refrigeration units is analyzed with consistent testing conditions and a complete uncertainty analysis of the results. One state-of-the-art refrigerant, namely R245fa, as well as the low-GWP fluids R1233zd-E and R1234yf are taken into account. The investigated polymers are ethylene-propylene-diene rubber (EPDM), fluoric rubber (FKM) and polytetrafluoroethylene (PTFE). In the case of EPDM, two different compositions are analyzed. To complement the study the material compatibility with a polyolester (POE) lubricant is also investigated. The material compatibility is evaluated by changes in volume, weight, Shore A as well as in small load hardness. With the small load hardness measurements, the hardness directly at the samples surface can be determined and thus important information on chemical interaction is provided. This study points out the importance of material compatibility testing especially investigating the difference between hydrofluorocarbons (HFC) and HFO, because the unsaturated characteristic of the HFO may lead to considerable changes in material compatibility compared to HFC refrigerants.

We introduce a new plated metallization process for Silicon Heterojunction (SHJ) solar cells by selective plating of copper onto a positively masking seed layer. This process tackles the issues of high silver consumption and low grid conductivity of screen printed contacts on SHJ solar cells. Compared to other metallization approaches of plating into a negative mask, our process does not require expensive process steps or consumables to plate and then remove the mask. The process involves the deposition of a full area PVD layer of a valve metal like Al or Ti onto the ITO surface of a SHJ solar cell. The valve metal layer is self-passivating in nature and provides the ideal mix of conductivity for plating current distribution and selectivity for copper plating. As the next step, the grid is locally defined by printing or laser transferring the seed layer. Now a pulsed Cu plating step is applied to plate on the seed layer selectively while the valve metal layer is partly oxidized and parasitic Cu deposition on the valve metal surface is dissolved during reverse pulses. The valve metal layer is finally etched off in a subsequent etch bath.

The scope of this paper lies on the phenomenon of free-carrier absorption (FCA) in heavily phosphorus-doped poly-Si layers, applied at solar cells featuring poly-Si/SiO x passivating contacts at the rear. Firstly, FCA is investigated on test structures featuring poly-Si contacts of different thickness and doping level. Secondly, these passivating contacts are integrated into the rear of solar cells featuring a boron-diffused emitter at the front. The infrared (IR) response of the solar cells is analyzed and FCA losses are quantified. In agreement with theory, it is shown that J sc losses due to FCA increase with poly-Si doping level and thickness. For instance, a total J sc loss of ~0.5 mA/cm² is obtained for a 145 nm thick poly-Si layer with a doping concentration of 1.9x10 20 cm -3 .

In this contribution, atmospheric pressure dry etching (ADE) texture is integrated into a passivated emitter and rear cell (PERC) process. In order to make the texture suitable for the solar cell processing, two post-etching processes (inverted pyramid, spherical cap) are implemented and compared. The passivation of the front surface could be improved substantially by the introduction of an Al 2 O 3 layer deposited via atomic layer deposition under the classical antireflection coating SiN X . The impact of the addition of the Al 2 O 3 layer on the contact resistance cannot be neglected and becomes significant for thicknesses higher than 4 nm. Multicrystalline silicon (mc-Si) PERC solar cells are fabricated and measured, leading to a maximum efficiency of about 18.6% for the acidic texture, and for both posts-processed dry chemical etching (ADE) textures. No current gain for the ADE textured wafer compared to the acidic texture could be observed on cell level due to an inhomogeneous etching. However, a gain of 0.4 mA/cm 2 for the ADE texture was calculated from local EQE measurements. ADE texture presents therefore 2 advantages: compatibility to diamond wire sawing and a potential current gain for PERC solar cell structure.

For the comparative study with focus on mechanical long-term stability, we perform a temperature cycle (TC) test-to-failure for 1250 cycles according to IEC 61215 with laminated solar cell strings. The strings were produced with Multi Busbar (MBB) solar cells interconnected by wires and with solar cells with 3 busbars (3BB) interconnected by ribbons. One module sample comprises two electrically isolated 3-cell strings, one for each technology. The 3BB string displays a power loss of more than 5 % after 850 cycles, while the MBB string only exceeds 5% loss after 1250 cycles. After TC 1250 the 3BB string shows a degradation of -8.2 % in FF and -8.0 % in power, while the MBB string shows a degradation of -6.2 % in FF and of -5.3 % in power. In the second comprehensive comparative study we use for each interconnection technology 15 cells for isothermal storage (up to 130 °C, 42.8h) and 10 modules for TC (up to 400 cycles). Each reliability analysis includes IV and EL characterization as well as adhesion force measurements and microsection analysis. After TC 400 the MBB interconnection shows less than 1 % degradation in efficiency compared to 4-5 % degradation for 3BB ribbon interconnection in a common module setup. The cells and modules show that most of the electrical contacts are still intact with respect to the EL image after 42.8 h isothermal storage and TC 400, although the average peel forces degraded from about 2 N/mm to less than 0.5 N/mm. Both studies indicate a superior mechanical long-term stability for Multi Busbar technology compared to ribbon interconnection.

This paper describes a method to overcome current limitations in BIM software to design Building Automation and Control Systems (BACS) functions of Heating Ventilation and Air Conditioning (HVAC) systems through the extension of the IFC-files with information on control functions. The method is illustrated with the description of control functions for a use case including a boiler, a thermal storage, an air handling unit and a floor heating system modelled with a widely used BIM software tool. The focus is set on the description of three simple control functions: the definition of a heating curve, the setup of time schedules for the air handling unit and the flow temperature control for the heating circuit. The proposed method is based on available software tools linked together and enables adding complementary information on controls into the IFC-file, checking it for consistency, extracting and converting the IFC content into a linked data format. The use of semantic web technology allows for interoperability with various applications like e.g. software used for the commissioning or the supervision of HVAC systems and thus can contribute to reduce current quality and performance deficits of these systems.

In order to achieve a fast and reliable qualification of promising conductive adhesives for solar cells, different accelerated ageing test sequences, accompanied with analyses on material level are conducted. Damp-heat followed by damp heat at a current range of 8 A; humidity freeze and thermal cycling. The testing procedure in the herein presented work is adapted to identify advantages and also weaknesses of the materials in combination with the entire design. The conductive adhesives replace the lead-based soldering thereby allowing a lower processing temperature. Another potential reduction of material costs is the use of double redundant fingers instead of busbars. In this way, a considerably smaller amount of silver is needed. The interconnectors are glued between theses double redundant fingers with the conductive adhesive. Another advantage of the gluing is the possibility of using groove structured interconnectors that allow an increase in power of the solar module by reflecting light back to the solar cell. As major degradation indicator the performance of the modules containing conductive adhesives, redundant fingers and groove structured interconnectors is measured before and after the exposition of the solar module to different accelerated ageing tests and compared to the reference solar module with flat interconnectors soldered on busbars. After the accelerating ageing test damp heat (DH), there was already a clear difference in viability of the conductive adhesives. For two conductive adhesives, module power losses were comparable to the reference, for a third one power losses amounted to 14 %. The loss in power is caused by an increase in serial resistance. Analyses of the adhesives indicate a relation between the degradation in damp-heat and the adsorption of humidity of the material. Different subsequent aging tests (after DH) showed the feasibility of this innovative technology, but also unveiled weaknesses compared to a traditional soldered busbar technology. Two of the three conductive adhesives have fulfilled the IEC 61215 criteria in terms of power loss after damp heat, humidity freeze and thermal cycling.

In High-Performance mc-Si [1] random grain boundaries, although being recombination active, often enhance material quality by reducing dislocations. With this work, we take a step towards statistical large-scale investigations of crystal defects via a combined analysis of different inline-measurements on as-cut wafers: photoluminescence images for the extraction of recombination-active structures and reflection and infrared transmission images for the extraction of the grain structure. The combined extraction of recombination-active structures and grain structures allows isolating dislocations from grain boundaries for all material types. To discern dislocations from other recombination-active defect structures, an image-processing-based analysis technique has been developed. By applying this separation on wafers from various bricks of our material set, typical developments of grain structure and dislocations can be identified. As a particular application, we investigate the correlation between the development of dislocations in higher parts of the brick and grain size in the lower parts. The results support theory quantitatively: Dislocation ratio in the upper brick part shows a correlation with the square root of the weighted median of the grain size in the lower brick part (R≈0.85). However, the results also show that grain size distribution, in particular grain size homogeneity, has to be considered to account for a stronger distinction between materials.

Cement production in rotary kilns requires large amounts of thermal energy, which is provided by combustion of different fuels. Substitution of fossil fuels by refuse derived fuels (RDF) can minimize production costs and reduce CO 2 emissions, but often causes displacement of the sintering zone, impacts flame stability and cement quality. The current paper briefly introduces our numerical approach which describes particle motion and combustion characteristics of typical non-spherical RDF particles. By using these models in CFD simulations, a case study is presented. Fuel properties, primary- and secondary air settings and fuel feed location for a generic rotary kiln of industrial scale are varied to show the effects of operational settings on co-firing of RDF. Shift of flame shape and location as well as particle burnout are analyzed. Based on the information generated, optimized operational settings are identified and discussed.

Low temperature district heating (LTDH) can increase the integration of renewable and waste energy sources that have lots of reliability and acceptance issues. This article aims to identify necessary measures to enable connection of the distributed heat sources into the LTDH. An energy balance model for an area was developed on annual level. The heat supply model included a central plant and distributed plants. A multiobjective, genetic optimization was used. The results showed that the investment cost, electricity price, and heat pump performance influenced higher share of the distributed energy sources into the central district heating (DH) system. Further, bigger building area showed to be more suitable to export heat to the central DH system. © 2017 The Author(s). Published by Elsevier Ltd. Under a Creative Commons license https://creativecommons.org/licenses/by-nc-nd/4.0/

One third of the world's end energy consumption is used on heating purposes in the building sector. The larger part of energy used for heating comes from high exergy sources (e.g. coal or gas). Since living spaces are usually heated up to around 20 °C, application of low exergy sources (e.g. solar thermal energy or ground heat sources) is sufficient for low temperature district heating supply. The main target of the work carried out is to demonstrate the advantages of exergy-based assessment for increased efficiency of small scale district heating supply schemes. For this reason different supply scenarios, based on fossil and renewable energy sources, are investigated. The different renewable energy supply units are regarded individually or in two- or three-way combinations. In this study renewable and fossil-based supply are compared on the one hand and on the other hand the benefits of merging several renewable energy suppliers for a small building group with a high energy standard are identified. For evaluation and identification of the best supply solution, the exergetic-based assessment method is applied. Additionally simplified aspects of operational management and estimation of investment costs are used to compare the different supply solutions. The evaluation of the scenarios clearly shows that the combination of innovative supply strategies and exergetic assessment leads to a more “holistic understanding” of the energy conversion chain and offers prospects for optimized low temperature district heating supply. Furthermore economic considerations and an analysis of emissions are to be included in the evaluation. This paper represents modeling, simulation and exergetic analysis of renewable multi-generation units to low temperature district heating supply of a building group and covers a topic from IEA DHC Annex TS1 [1].

The building sector is responsible for more than one third of the final energy consumption of societies and produces the largest amount of greenhouse gas emissions of all sectors. This is due to the utilisation of combustion processes of mainly fossil fuels to satisfy the heating demand of the building stock. Low temperature district heating (LTDH) can contribute significantly to a more efficient use of energy resources as well as better integration of renewable energy (e.g. geothermal or solar heat), and surplus heat (e.g. industrial waste heat) into the heating sector. LTDH offers prospects for both the demand side (community building structure) and the supply side (network properties or energy sources). Especially in connection with buildings that demand only low temperatures for space heating. The utilisation of lower temperatures reduces losses in pipelines and can increase the overall efficiency of the total energy chains used in district heating. To optimise the exergy efficiency of community supply systems the LowEx approach can be utilised, which entails matching the quality levels of energy supply and demand in order to optimise the utilisation of high-value resources, such as combustible fuels, and minimising energy losses and irreversible dissipation. The paper presents the international co-operative work in the framework of the International Energy Agency (IEA), the Technology Cooperation Programme on District Heating and Cooling including Combined Heat and Power (DHC|CHP) Annex TS1.

The silver grid corrosion phenomenon of c-Si solar cells, often called “snail trails” or “snail tracks”, which occurs mainly shortly after installation of PV modules in the field, was first observed approximately one decade ago in the southern part of Europe. It was recognized quickly that these discolorations on the metal grid fingers are always accompanied by cell (micro) cracks. From the herein presented investigations, it can be shown that several different chemical mechanisms and material involvements can lead to the visual phenomenon of silver grid finger discoloration. It must therefore be clarified that the term “snail track” (or “snail trails”) only describes a failure class and not a single degradation mechanism. This work focuses on a bottom up approach, which includes the chemical analyses of the affected cell parts extracted from various industrial modules which have been installed in the field. In addition to the analytical investigations after field failure, the modules are exposed to artificial stresses to investigate the development, formation or further reaction of the snail track degradation products. Since the phenomenon is always accompanied by diffusion open areas in the module (cell gaps, cell cracks), the diffusion of reactant partners from the rear side of the module, e.g. atmospheric gases or additives from the back sheet material, has been the most suspected root cause from the beginning of the observation. The role of these reaction partners is therefore highlighted within the results. Four different snail track degradation products have been identified until now: Silver carbonate, silver sulfide, silver phosphate and silver acetate. Silver sulfide snail tracks were only found after damp-heat test (only artificially induced), all other types were found from field failed PV modules and respectively partially from stress tests. The different snail track types, materials and module components considered being involved and the formation mechanisms are presented in this work.

A basic formulation of a Phase-Change-Material (PCM)-dispersion is characterized and subsequently enhanced. Enhancement takes place in two steps. First by enlarging the fraction of PCM in the PCM-dispersion and in the second step by adding a nucleating agent to the formulation. This work shows how the increasing PCM-fraction influences the viscosity, thermal-mechanical-stability and the amount of heat that can be stored in the phase change. In addition to that it is shown how these parameters and the supercooling of the PCM-dispersion can be altered by the addition of a nucleating agent.

Aluminium, thermally evaporated with physical vapor deposition (PVD), is considered a cost efficient rear metallization for crystalline silicon heterojunction or tunnel oxide passivated solar cells. Owing to the temperature-sensitivity of the solar cell structure, potential routes of low temperature interconnection methods for PV module integration are assessed. Textured wafers with a full area 2 μm PVD-Al metallization are divided into two groups: The first is capped with sputtered 100 nm Ti and 400 nm Ag for testing solderability. The second is capped with 400 nm Ag for electrically conductive adhesive (ECA) interconnection. Low temperature soldering with Sn43Bi57 and Sn41Bi57Ag2 coated ribbons and ribbon interconnection with two ECAs are evaluated in terms of peel strength, contact resistivity and accelerated aging properties. It is found that peel strength of soldered interconnections on the Al/Ti/Ag achieve between 1.5 N mm -1 to 2 N mm -1 whereas glued interconnections on Al/Ag between 0.5 N mm -1 to 1 N mm -1 . The contact resistivity is 2.6 × 10 -3 mΩ cm2 to 3.6 × 10 -1 mΩ cm2 for both interconnection technologies. Soldered samples show a stable contact resistivity when tested in 1000 h in damp heat conditions or 200 thermal cycles. The contact resistivity of glued interconnections increases to 1 mΩ cm2 to 10 mΩ cm2 along with an observed disintegration of the Al-layer and an ablation of the Ag-capping from the Al-layer.

Battery energy storage systems have a large potential for provision of grid ancilliary services. Specifically, large battery systems have been used for the provision of primary control reserve. Batteries providing this grid service must, using corrective energy measures and control algorithms, continuously keep their state of charge within limits in order to comply with European regulations. Operational degrees of freedom exist in the regulation which can be used by batteries to facilitate keeping the state of charge within desired levels. In this paper, such degrees of freedom are described, and the effect of their utilization on battery system operation analyzed.

The increasing distributed generation of renewable energies in distribution networks leads to several challenges for distribution network operators (DNOs). During high feed-in times, voltage violations can occur if the hosting capacity of the grid for distributed generation is exceeded. The paper at hand investigates the installation of grid-supporting battery storage system (BSS) in the medium voltage (MV) level to serve mainly for voltage compliance and to defer grid reinforcement. A control approach for the BSS based on two characteristic curves is suggested. The BSS is then analyzed technically and economically for scenarios of high distributed generation. The results show that the alternative of BSS has potential to defer grid reinforcement in the presented case studies. However, the power curtailment is more viable than the BSS and grid reinforcement. The economic viability of BSS can increase in the future based on the expected reduction of battery costs. Furthermore, BSS have the technical potential for providing other services, since voltage violations occur during high feed-in times.

This paper describes the Ri.Fa.Re. timber-based solution, an innovative timber-based prefabricated panel for the energy refurbishment of the existing Italian buildingś facades. Although similar technologies have already been tested in several European countries, they are not feasible to be used in the Italian context characterized by specific geometric features of the building stock and by seismic constraints which are not relevant for most of European countries. Moreover, this research does not aim only at developing a product but also at adopting a new process, based on parametric design and lean construction principles. The main outcome of this project is a concrete kit for energy refurbishment suitable for the Italian context, including: a) a technological prefabricated but customizable product and b) a more efficient process to decrease time and cost wastes during the whole process.

Passivating and carrier selective contacts formed by metal oxide induced junctions are promising candidates to improve the efficiency of silicon solar cell. Important aspects for the optimization of such induced junctions are addressed by means of numerical device simulations. Experimentally, atomic layer deposited (ALD) molybdenum oxide (MoOx) films are tested for their ability to form a hole-selective contact. To this end, the induced c-Si band bending, the external and implied Voc and the crystallinity of the films are analyzed. It is shown that the properties of the induced p/n-junction are strongly influenced by the deposition temperature and the type of buffer layer applied. While a clear correlation between the induced band bending and the external Voc is observed, the overall level remains well below that of a reference system for which thermally evaporated MoOx was used. These results indicate that for the investigated ALD films a too low work function is limiting the formation of an efficient hole contact.

The magnitude of light-induced degradation of solar cells based on Czochralski grown silicon strongly depends on material properties. We have performed experiments to describe the activation and recombination activity of boron oxygen defects in boron compensated n -type silicon. Compensated n -type material enables flexible assessment of charge carrier influences on the defect that cannot be distinguished on p -type material. The results can be generalized to p -type material and thus provide valuable insights to the defect. Our measurements demonstrate the two-level defect nature of the slow-formed boron oxygen defect component and allow the study of the dopant dependency of the defect concentrations. Our findings strongly support a revision of the existing model of the defect composition. Based on the experimental results and literature data we have created a parameterization of the lifetime limitation in silicon due to BO defects. Established findings from literature for uncompensated p -type silicon are taken into account and ensure general validity. The parameterization is useful to discuss BO defect influences and can serve to predict material properties after LID.

We present n-type epitaxially grown wafers deposited in a reactor that allows a process transfer to inline high-throughput reactors. Those wafers exhibit an effective lifetime of up to 1720 μs locally for a phosphorous concentration of 2·1015 cm-3 and a wafer thickness of about 100 μm. In these wafers the most detrimental defects are stacking faults with polycrystalline silicon inclusions. Comparing two samples with stacking faults densities differing by one order of magnitude revealed a difference in average effective minority carrier lifetime of also one order of magnitude (reduction from more than 1500 μs down to 111 μs for the defective sample). A solar cell fabricated from a 200 μm thick epitaxial wafer of low stacking fault density and a phosphorous concentration of 3·1016 cm-3 reaches an independently confirmed efficiency of 20%, an open circuit voltage of up to 658 mV, a short circuit current density of up to 39.6 mA/cm2 and a fill factor of up to 76.9%. Differences between this cell and FZ references can be attributed to a reduced bulk lifetime caused by the high doping concentration and most probably additional recombination due to polycrystalline silicon inclusions in stacking faults, although their amount is comparably low. A second solar cell made of an epitaxial wafer with a high stacking fault density exhibits an efficiency reduction of 0.5% absolute compared to the cell made of the high quality epitaxial wafer. This result underlines the importance of minimizing the stacking fault density in epitaxial wafers, in particular the density of those with polysilicon inclusions.

Fatigue of the cell interconnectors is one of the main reasons for module failure. Especially with respect to module application in extreme climates new demands on solar cell interconnectors will arise. Optimizations in the manufacturing process to generate a product demand related microstructure are a key to improve the material behavior of interconnectors with respect to extreme climate loading conditions without increasing costs. For achieving this goal several aspects were considered in this paper: Influence of the annealing process on the fatigue behavior: Due to an optimization of the annealing process an increase in ribbon fatigue strength by a factor of four could be achieved. The effect consists of two parts: Firstly, annealing influences the geometrical shape generated during the fatigue experiment. Secondly, it affects crack formation and crack growth during fatigue. Influence of temperature on fatigue behavior: an increase in temperature leads to a significant reduction in fatigue strength (from 25 to 100 °C by factor 3). This results from increased dislocation creep at higher temperatures. Microstructural comparison of fracture patterns: The loading amplitude determines the roughness of the fracture surface: Smaller amplitudes lead to a coarser surface structure. This is important to compare accelerated lifetime testing in the lab and modules failures from the field. Simulation of temperature and microstructure dependent fatigue for lifetime prediction: Exemplarily it will be depicted how optimized fatigue behavior in the lab translates into real module lifetime under extreme climate conditions. Despite the actual numbers which show the potential of the approach, but could vary from sample to sample, the focus of the paper is the method itself and its physical background.

Extraction of recombination properties like the recombination pre-factor J0 and the Shockley-Read-Hall base lifetime from photoconductance data on test structures and half-fabricates of photovoltaic cells is not always straightforward and unambiguous. In this paper the well-known “slope method” of Kane and Swanson will be compared to the method offered by the Quokka code. The Quokka code numerically solves the distribution of the excess carrier concentration over the thickness of the wafer at several injection levels. In this way artefacts due to transport limitations are avoided and the analysis does not rely on data at a single injection level. This gives more reliable results for J0 and the base lifetime. A method to the determine the base lifetime from the implied VOC at 1 Sun illumination values is also presented.

High-efficiency solar cells are closing the gap to the theoretical efficiency limit by implementing passivated carrier-selective contacts. This work presents a study on charge carrier transport through tunnel oxide passivated contacts. In particular, structural properties of thin oxide layers are investigated with regard to tunnelling processes and local pinhole conduction. Conductive AFM measurements on n-type TOPCon test structures with and without forced oxide degradation have been performed. The current maps allowed for the first time a spatial-resolved imaging and correlation of the expected oxide degradation and spot like areas with increased currents. The areas are assigned to a different local transport process due to pinhole formation. It was found that a raise of the annealing temperature from 800 °C to 950 °C led to an increase of the pinhole density by 3 due to thermal degradation. The results show a promising approach to study the impact of pinholes to the total conductivity of carrier-selective contact.

In this paper, we study the influence of modifying the geometry of nanotexture on its electrical properties. Nanotexture is formed by an industrially feasible dry-chemical etching process performed entirely in atmospheric pressure conditions. A surface modification process is developed that allows low surface recombination velocities ( S eff,min ≤ 10 cm/s) on nanotextured surfaces. By simultaneously improving the surface passivation and the emitter diffusion processes, we achieve an equivalent passivation level ( V OC,impl ≥ 670 mV) for nanotextured surfaces to that of reference textured surfaces after applying either PECVD or ALD based deposition techniques.

Modules with half-cell layout show an increased efficiency due to reduced electrical losses and increased optical gains. In this work, we demonstrate that by reducing the tab width, additional benefits can be obtained and the demands for reducing costs of material consumption and higher Cell-To-Module power (CTM) ratios can be met. First, we present simulation results on the optimal tab width under different insolation levels and calculation of the energy yield over a year. Second, an experimental setup based on mini-modules which verifies our findings is described. It can be shown that the reduction of the tab width to about 50% does not lead to any significant loss for standard cells and an increase of efficiency by 0.85% for half-cell modules compared to full-cell modules is measured. Furthermore, the loss mechanisms in locations with different insolation levels for both half-cell and full-cell modules with different size of tab widths are discussed. Finally, energy yield based on optimized tab widths for both modules at desert (Morocco) and moderate (Germany) climates is calculated. We show that half-cell modules with optimized tab width have better performance than standard modules with full-cells in both moderate and desert regions with 1.52% and 2.20% more energy yield respectively.

We present a new characterization technique based on hyperspectral imaging applied to silicon wafers. It combines the measurement of spatially and spectrally resolved reflection features and a dedicated subsequent data analysis. This method allows for a rapid localization and classification of defects and contaminations on wafers. Thus, it complements standard imaging techniques such as infra-red or luminescence imaging. In our work, we show that hyperspectral imaging is capable of separating clean and contaminated regions including a classification of the contamination type and a quantification of the coverage.

In this contribution, we provide an insight into the light-induced degradation of multicrystalline (mc-) silicon caused by copper contamination. Particularly we analyze the degradation kinetics of intentionally contaminated B- and Ga-doped mc-Si through spatially resolved photoluminescence (PL) imaging. Our results show that even small copper concentrations are capable of causing a strong LID effect in both B- and Ga-doped samples. Furthermore, the light intensity, the dopant and the grain quality were found to strongly impact the degradation kinetics, since faster LID was observed with stronger illumination intensity, B-doping and in the grains featuring low initial lifetime. Interestingly after degradation we also observe the formation of bright denuded zones near the edges of the B-doped grains, which might indicate the possible accumulation of copper impurities at the grain boundaries.

In this paper we present a new update to PC1Dmod, which extends the original PC1D program by implementing Fermi-Dirac statistics and a range of state-of-the-art models in order to improve the accuracy of c-Si device simulation. In PC1Dmod 6.2 the list of models is further expanded to include a parameterization of incomplete ionization of dopants (Altermatt et al., J. Appl. Phys.100, 113715, 2006), with parameters for phosphorus, boron, arsenic, gallium and aluminum. The results have been verified against a previous implementation of the model. We show that the inclusion of incomplete ionization is of particular importance for moderately doped surface regions with doping densities in the range ∼5 × 10 17 to ∼5×10 19 cm -3 , resulting in a deviation of up to 15% in the simulated recombination current density and sheet resistance. The effect of incomplete ionization is also shown to be more pronounced in devices made from compensated Si material. Furthermore, the default solar spectrum has also been updated in PC1Dmod 6.2, taking advantage of the increased maximum file size to include a more realistic representation. The generation profiles calculated using PC1Dmod 6.2 together with input from OPAL 2 agree well with results from Sentaurus TCAD for both planar and pyramidally textured surfaces, thus facilitating a more direct comparison between PC1Dmod 6.2 and other simulation programs utilizing standard spectra. The simulation comparison is also extended to the electrical performance of the modeled devices, showing good agreement in the calculated short-circuit current density for a range of planar and textured solar cells with varying emitter doping. Finally, several new output options, including emitter saturation current and injection-dependent lifetime curves have been added, enabling a simpler and more direct way for users to access and plot important device properties.

Passivated emitter and rear (PERC) solar cells can show void formation within their metallized local rear contact. It is known that voids can cause enhanced rear side recombination. In this work, we present a study on void related current losses and the correlation to the local Al-doped silicon layer which forms the back-surface field (BSF) at the rear contact. At first, void related current losses have been quantitatively evaluated. By further microstructural investigation at lengthwise prepared rear contacts, a method for the analysis of BSF thickness distribution was developed. It turned out that BSFs within voids can vanish on both, small and large length scales. Regions with voids can be well passivated and result therefore in negligible current losses. The presented approach allows the quantitatively assessment of PERC solar cell rear contacts in terms of total current losses and void ratio.

The investigation of trace elemental contaminations in silicon material is of major interest as it has detrimental impacts for further process steps. Thus, the detection of surface impurities in silicon samples was investigated by sequential etching steps followed by ICP-MS measurements. Due to variations of etching solutions containing HCl, HF and HNO 3 trace element contents could be assigned to different layers of silicon samples, like the outer surface, the silicon oxide and the sub-oxide layer as well as the bulk material. The method is not only suitable for silicon wafers but can also be adapted to powdery samples like etched silicon nanowires and kerf silicon. In this study, we show exemplarily the sequential etching procedure for metallurgical silicon powder samples. This method enables the layer dependent quantification of impurities in silicon samples.

This paper presents an innovative system for solar thermal process steam and chilled water production. The system consists of a 2-stage solar thermally driven steam jet ejector chiller with latent heat and cold storage driven by motive steam from evacuated tube collectors with compound-parabolic-concentrator (CPC-collectors). Within this paper the design and the functionality of the demonstration plant and essential aspects of the system control are discussed. In addition, operational experiences, the operational behaviour of the entire system as well as performance figures are presented and evaluated.

Polymeric collectors have been exposed on outdoor testing sites in three distinct climatic locations and the climatic loads and collector temperatures have been monitored by the minute. The obtained data was analyzed with focus on the frequency and extend of the thermal loads, which the different components of the collector were exposed to. As a result this data can be correlated to accelerated aging tests.

In order to decarbonise the energy system, alternative transition pathways were assessed in recent years that agree on the crucial role of the heating sector, due to its potential to increase the renewable-based share of energy demand and to improve energy efficiency. Simultaneously, the increasing share of fluctuating renewable energy sources (RES), such as wind and photovoltaic, raises the hourly volatility in the energy system and challenges energy utilities. To balance energy demand and RES in an optimal manner storage-based heating systems can be used as flexible loads. This study discusses to what extent smart residential heating systems can contribute to the integration of RES and quantifies the trade-off between electricity savings and flexibility provision, when replacing storage heaters by heat pumps. To answer these research questions a simulation-based scenario analysis is conducted until 2050 encompassing France, Germany and the United Kingdom. These countries are of specific interest due to their substantial share of electric heating as well as their exponentially rising wind and photovoltaic (PV) generation capacities. The study reveals that the long-term potential of heating technologies for the integration of RES is relatively limited in countries such as France or Germany, given the improved insulation of buildings and the seasonal offset between PV generation and heat demand. However, in the short- to medium-term, or in countries with low shares of PV generation but high shares of wind power (such as the UK), heating technologies may facilitate the integration of RES, especially in the absence of alternative flexibility options.

Decay of ancient buildings is often due to corrosion of metallic reinforcements, which are embedded in the construction in order to improve its structural behaviour or to prevent the propagation of cracks. If wet conditions occur on the surface of steel, corrosion can start. Corrosion may weaken reinforcements and produce expanding oxides that lead to the detachment of covering materials, thus being harmful for the durability of the construction and challenging for its restoration. When dealing with heritage buildings, however, the problem becomes even more complex due to the need of non-invasive and reversible techniques. Here the only possibility is often to limit the corrosion rate by controlling moisture and temperature conditions in the assembly or the indoor climate. To this end, a method has been developed which focuses on the corrosion behaviour of steel reinforcements in constructions, considering the complex transient processes of corrosion chemistry and the local hygrothermal conditions. In particular, the model is based on the correlation between the transient hygrothermal conditions (i.e. temperature, relative humidity and water content) and the corrosion rate of steel reinforcements embedded in porous building materials i.e. mortars and bricks. It allows the prediction of the temperature and humidity dependent corrosion rate of the steel over time. The model has been validated through several laboratory tests, showing a good agreement between measured and simulated results. It assesses the corrosion risk depending on parameters which are easy to monitor and allows both preventive conservation/restoration of cultural heritage buildings and safe design of new durable building components. Concerning the former point, the model permits state-of-preservation assessments when material sampling is not possible and enables to define measures to reduce/stop corrosion of steel reinforcements.

In the field of lighting and daylighting, standard monitoring procedures to assess the overall performance of retrofit projects are scarce. Nevertheless the access to monitored data is crucial to assess whether daylighting or electric lighting systems deliver the expected performance in terms of cost-effectiveness and energy efficiency. In order to bridge this gap, a monitoring protocol is under development as part of the International Energy Agency – Solar Heating and Cooling Programme (IEA-SHC) Task 50 ‘Advanced Lighting Solutions for Retrofitting Buildings’. The protocol focuses on lighting and/or daylighting (façade or roof) retrofit in the non-residential building stock. It covers four key aspects: energy efficiency, costs, quality of the lighting environment and user satisfaction. The main features of this protocol are presented in this paper, along with some lessons learned from the ongoing application on selected case studies.

Although the energy codes or construction standards were considerably improved in the last decades, there are continuous reports on mold growth problems in buildings. Numerical prediction can be useful in assessing the risk of mold growth in new constructions and retrofit applications. Two well-known models exist and are widely used: the VTT model and the biohygrothermal IBP model. While the VTT model is an experimentally validated empirical model based on visual findings of mold growth, the biohygrothermal method models the growth of a mold hyphen in mm as a function of the transient ambient conditions. Since a hyphen is not visible to the naked eye it is not evident at what length the growth will become a nuisance. The VTT model uses a very clear six-step evaluation: the so-called mold index describing the intensity of growth on the surface. By comparing the results of the biohygrothermal and the VTT model it is possible to use the clear and acknowledged rating measure of the mold index also for the IBP model. For this purpose, a conversion function has been developed allowing the transformation of the calculated hyphen growth, in mm, into the mold index with a high level of correspondence. In collaboration of VTT and IBP a new postprocessor for the VTT model was developed which can be used to assess both: Results from hygrothermal numerical simulations or measured data. A classification employing a traffic light indicator helps to interpret the mold growth risk: green means no risk, red is not acceptable, while the yellow range indicates a possible risk and requires a specific evaluation.

One reason for heat losses in buildings is inadequate insulation. Vacuum Insulation Panels (vips) is emerging as a promising solution, being more energy efficient than conventional insulation materials, thinner and lighter. A VIP is made by placing a core insulation material inside a gas-barrier envelope and evacuating the air from inside the panel. The limitations to wide-scale VIP commercialization lie in lack of low-cost and high-volume processes to turn them into products suitable for use in buildings, and their short in-service lifetimes. These drawbacks were researched in a European funded project "nanoinsulate", and this paper gives an overview of results., European Union Commission Seventh Framework Programme Project “NanoInsulate”

In 2008 the German Ministry of Economic Affairs and Energy launched an initiative for new or retrofitted energy-efficient school buildings as focus area within their research programme “EnOB” (Energy Optimised Buildings). The initiative (www.eneff-schule.de) comprises three different energy levels: • Best practice schools with energy-efficient renovations above the requirements in the energy-saving ordinance • Three-liter-house schools with energy needs for heating, hot water and auxiliary below 34 kWh/m2year • Plus energy schools that produce more energy than they use in the annual balance Currently three different plus energy school buildings have been planned, realized and monitored within the initiative, two of them being renovations (Stuttgart and Rostock), the last one being a new school building (Hohen Neuendorf). The three energy concepts include rather different technologies to generate heat and to reduce the energy consumption of ventilation and lighting systems. This is partly due to the research initiative approach of “EnEff:Schule” that asks for testing innovative technologies. There is however a general tendency to: • Low U-values of the building envelope with about 0.11–0.15 W/m2K at the walls and roof, 0.10 W/m2K for new base plates and 0.20–0.34 W/m2K for renovated ground slabs and basement ceilings and 0.80 W/m2K for windows • Large PV areas to compensate for the remaining energy use, sometimes in combination with other technologies or systems that generate electricity • Mechanical ventilation systems with high heat recovery rates but in combination with natural ventilation • User-dependent control strategies for ventilation and heating • Use of daylight at both the window/solar shading side and the electrical lighting control The paper compares the different technologies used at the building envelope, the heating, ventilation and lighting systems, the calculated and measured energy consumptions and the building costs.

It is proven that potential-induced degradation leading to shunting of crystalline silicon solar cells (PID-s) is caused by stacking fault-like planar crystal defects penetrating the p-n junction that become decorated with sodium due to high electric fields across the dielectric antireflective coating (ARC). Often it is assumed that sodium found in PID-s affected cells originates from the cover glass used for photovoltaic modules. In this contribution, we show that PID-s also occurs at bare silicon solar cells without polymer foil or glass encapsulation. Using corona discharge induced degradation, it is shown that sodium decorated, shuntingcrystal defectsare generated. This sodium likely originates from contaminations present on the solar cell surface. Therefore, it is concluded that PID-s of solar modules also mainlyarises from sodium contaminationsof the solar cell surfaceand not from the glass. Whether PID-s occurs or not depends on the electric field across the ARC, influenced by theelectrical resistance of polymer foil and glass. So called sodium-free glass results in a low electric field due to the high resistance of the glass.