Simplified life-cycle analysis of PV systems in buildings: present situation and future trends

The integration of photovoltaic (PV) systems in buildings shows several advantages compared to conventional PV power plants. The main objectives of the present study are the quantitative evaluation of the benefits of building-integrated PV systems over their entire life-cycle and the identification of best solutions to maximize their energy efficiency and CO₂ mitigation potential. In order to achieve these objectives, a simplified life-cycle analysis (LCA) has been carried out. Firstly, a number of existing applications have been studied. Secondly, a parametric analysis of possible improvements in the balance-of-system (BOS) has been developed. Finally, the two steps have been combined with the analysis of crystalline silicon technologies. Results are reported in terms of several indicators: energy pay-back time, CO₂ yield and specific CO₂ emissions. The indicators show that the integration of PV systems in buildings clearly increases the environmental benefits of present PV technology. These benefits will further increase with future PV technologies. Future optimized PV roof-integrated systems are expected to have an energy pay-back time of around 1·5 years (1 year with heat recovery) and to save during their lifetime more than 20 times the amount of CO₂ emitted during their manufacturing (34 times with heat recovery). © 1998 John Wiley & Sons, Ltd.     

PV power systems and the environment: results of an expert workshop

Photovoltaic (PV) power systems can lead to significant reduction of emissions to the environment. Contrary to conventional fossil fuel-based electricity production, the environmental aspects of PV power systems are mostly related to indirect processes such as cell and module manufacturing and ‘end of life’ waste management. Careful assessment of such environmental aspects throughout all life-cycle stages is required to reveal the contribution that PV power systems can make to environmental sustainability within the energy sector. An expert workshop was held in Utrecht, The Netherlands, on 25–27 June 1997 that addressed issues and approaches regarding the environmental aspects of PV power systems, including energy payback times, CO₂ mitigation potential, environmental life-cycle assessment and health and safety assessment and control. Various issues of environmental importance were identified during the workshop and recommendations were made for further work to ensure that PV power systems will indeed fulfil the promise of environmental sustainability. © 1998 John Wiley & Sons, Ltd.     

Does information and communication technology and financial development lead to environmental sustainability in India? An empirical insight

This paper examines the relationship between CO₂ emissions, electricity consumption, financial development, Economic growth, Informational Communication Technology (ICT) from 1990 to 2018 in India. We have applied the structural break co-integration approach like Gregory Hansen approach to check long-term relations between the variables. ARDL bounds testing approach is used to know the long run and short-run elasticity. We find that electricity consumption is positively contributing CO₂ emissions or reducing environmental sustainability in India. However, ICT has negative and significantly improving environmental sustainability or reducing emissions when measured in both ICT internet connection (ICT_INT) and ICT mobile Phones (ICT_MOB). Similarly, financial development and CO₂ emissions are negatively related. The result indicates the existence of Environmental Kuznets Curve in India's case. Overall, environmental sustainability achieved in ICT and financial development sectors. Therefore govt. needs to focus more on the stringent policy in electricity production by investing more in the renewable energy sector to curb environmental degradation.     

Critical Aspects and Recent Advances in Structural Engineering of Photocatalysts for Sunlight‐Driven Photocatalytic Reduction of CO2 into Fuels

The catalytic conversion of CO₂ into valuable fuels is a compelling solution for tackling the global warming and fuel crisis. Light absorption and charge separation, as well as adsorption/activation of CO₂ on the photocatalyst surface, are essential steps for this process. This article reviews the CO₂ photoreduction mechanisms and critical aspects that greatly affect the photoreduction efficiency. Additionally, different materials for CO₂ photoreduction are provided, including d⁰ and d¹⁰ metal oxides/mixed oxides, sulfides, polymeric materials, and metal phosphides with visible response, metal‐organic frameworks, and layer double hydroxides. Furthermore, various structural engineering strategies and corresponding state‐of‐the‐art photocatalytic systems are reviewed and discussed, such as bandgap engineering, geometrical nanostructure engineering, and heterostructure engineering. Each strategy has advantages and disadvantages, requiring further adjustment to further improve the photocatalytic performance of the photocatalyst. Based on this review, it is greatly expected that efficiently artificial systems and the breakthrough technologies for CO₂ reduction will be successfully developed in the future to solve the energy shortage as well as the environmental problem.     

From CO2 to Electricity: Photosynthesis-Based Functionally Cooperating Mini-Generator

Recently, the global warming and climate changes have aroused focus of attentions. Hence, there is an increased demand to capture, utilize, and sequestrate the greenhouse gas, i.e., carbon dioxide (CO₂), for promising applications. Functionally cooperating mini-generators are a kind of self-propelled smart devices that can harvest environmental energy and convert it to electricity through Faraday's law. But traditional mini-generators are based on an energy-consuming process appealing for energy consumption from high-grade state to low-grade one. Herein, a mini-generator based on photosynthesis with CO₂ as the fuel is designed. The generator can convert the internal energy of O₂ bubbles produced by photosynthesis to electricity. This is an energy conversion from the lowest energy state to the applicable energy. Based on the high-efficiency photosynthesis of hydrophyte, spontaneously water-dissolved CO₂ can afford to induce regularly cycled surfacing-diving motion, and the induced electrical output can simultaneously actuate multiple electronic components. Owing to the weather sensitivity of the photosynthesis, the system can be used to monitor weather through reading the changes of output electrical signals. By integrating the artificial smart device with natural plants, this research will promote the applications of miniaturized devices toward green development.     

Micro- and Nano-Technology: A Critical Design Key in Advanced Thermoelectric Cooling Systems

Advanced thermoelectric (TE) cooling technologies are now receiving more research attention, to provide cooling in advanced vehicles and residential systems to assist in increasing overall system energy efficiency and reduce the impact of greenhouse gases from leakage by current R-134a systems. This work explores the systems-related impacts, barriers, and challenges of using micro-technology solutions integrated with advances in nano-scale thermoelectric materials in advanced TE cooling systems. Integrated system-level analyses that simultaneously account for thermal energy transport into and dissipation out of the TE device, environmental effects, temperature- dependent TE and thermo-physical properties, thermal losses, and thermal and electrical contact resistances are presented, to establish accurate optimum system designs using both p-type nanocrystalline-powder-based (NPB) Bi _x Sb_2−x Te₃/n-type Bi₂Te₃-Bi₂Se₃ TE systems and conventional p-type Bi₂Te₃-Sb₂Te₃/n-type Bi₂Te₃-Bi₂Se₃ TE systems. This work established the design trends and identified optimum design regimes and metrics for these types of systems that will minimize system mass, volume, and cost to maximize their commercialization potential in vehicular and residential applications. The relationships between important design metrics, such as coefficient of performance, specific cooling capacity, and cooling heat flux requirements, upper limits, and critical differences in these metrics in p-type NPB Bi _x Sb_2−x Te₃/ n-type Bi₂Te₃-Bi₂Se₃ TE systems and p-type Bi₂Te₃-Sb₂Te₃/n-type Bi₂Te₃-Bi₂Se₃ TE systems, are explored and quantified. Finally, the work discusses the critical role that micro-technologies and nano-technologies can play in enabling miniature TE cooling systems in advanced vehicle and residential applications and gives some key relevant examples. Pacific Northwest National Laboratory—operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC05-76RLO1830.     

Energy pay-back time and life-cycle CO2 emission of residential PV power system with silicon PV module

The concerns about environmental impacts of photovoltaic (PV) power systems are growing with the increasing expectation of PV technologies. In this paper, three kinds of silicon-based PV modules, namely single-crystalline silicon (c-Si), polycrystalline silicon (poly-Si) and amorphous silicon (a-Si) PV modules, are evaluated from the viewpoint of their life-cycle. For the c-Si PV module it was assumed that off-grade silicon from semiconductor industries is used with existing production technologies. On the other hand, new technologies and the growth of production scale were presumed with respect to the poly-Si and a-Si PV modules. Our results show that c-Si PV modules have a shorter energy pay-back time than their expected lifetime and lower CO₂ emission than the average CO₂ emission calculated from the recent energy mix in Japan, even with present technologies. Furthermore the poly-Si and the a-Si PV modules with the near-future technologies give much reduction in energy pay-back times and CO₂ emissions compared with the present c-Si PV modules. The reduction of glass use and the frameless design of the PV module may be effective means to decrease them more, although the lifetime of the PV module must be taken into account. © 1998 John Wiley & Sons, Ltd.     

Effect of geometric dimensions on thermoelectric and mechanical performance for Mg2Si-based thermoelectric unicouple

The generating efficiency of thermoelectric generation (TEG) depends not only on the thermoelectric (TE) performance of TE device, but also on its mechanical performance. And choosing suitable TE materials and geometric dimension can improve the working performance of TE device. Mg₂Si is one of the most promising TE materials in the medium temperature range, and Mg₂Si-based TE devices have broad application prospects. In this paper, a three-dimensional finite model of the Mg₂Si-based TE unicouple used for recovering vehicle exhaust waste heat is constructed for the performance analysis. The TE performance and mechanical performance of the Mg₂Si-based TE unicouple under the influence of different geometric dimensions are investigated, respectively. The curves of the output power, the power conversion efficiency and the thermal stress distribution varying with different geometric dimensions are discussed in detail. The calculated result would be helpful for further understanding of the TE and mechanical properties of the Mg₂Si-based TE unicouple, and it can also provide guidance for further strength check and optimum geometric design of TE unicouples in general.     

CO2 Conversion Toward Real-World Applications: Electrocatalysis versus CO2 Batteries

Electrochemical carbon dioxide (CO₂) conversion technologies have become new favorites for addressing environmental and energy issues, especially with direct electrocatalytic reduction of CO₂ (ECO₂RR) and alkali metal-CO₂ (M–CO₂) batteries as representatives. They are poised to create new economic drivers while also paving the way for a cleaner and more sustainable future for humanity. Although still far from practical application, ECO₂RR has been intensively investigated over the last few years, with some achievements. In stark contrast, M–CO₂ batteries, especially aqueous and hybrid M–CO₂ batteries, offer the potential to combine energy storage and ECO₂RR into an integrated system, but their research is still in the early stages. This article gives an insightful review, comparison, and analysis of recent advances in ECO₂RR and M–CO₂ batteries, illustrating their similarities and differences, aiming to advance their development and innovation. Considering the crucial role of well-designed functional materials in facilitating ECO₂RR and M–CO₂ batteries, special attention is paid to the development of rational design strategies for functional materials and components, such as electrodes/catalysts, electrolytes, and membranes/separators, at the industrial level and their impact on CO₂ conversion. Moreover, future perspectives and research suggestions for ECO₂RR and M–CO₂ batteries are presented to facilitate practical applications.     

大功率CO2激光器输出光束远场光强分布测量

本文描述了用二维扫描法测量大功率TE CW CO2激光器输出光束远场光强分布的实验方法.并对测量系统的可靠性、实用性进行了分析,给出了对2kW TE CW CO2激光器的实际测量结果.     

Titanium Disilicide as High-Temperature Contact Material for Thermoelectric Generators

Thermoelectric devices can be used to capture electric power from waste heat in a variety of applications. The theoretical efficiency rises with the temperature difference across the thermoelectric generator (TEG). Therefore, we have investigated contact materials to maximize the thermal stability of a TEG. A promising candidate is titanium disilicide (TiSi₂), which has been well known as a contact material in silicon technology for some time, having low resistivity and thermal stability up to 1150 K. A demonstrator using highly doped silicon as the thermoelectric material has been integrated. A p- and an n-type wafer were oxidized and bonded. After cutting the wafer into pieces, a 200-nm-thick titanium layer was sputtered onto the edges. After a 750°C rapid thermal annealing step, the TEG legs were connected by a highly conductive TiSi₂ layer. A TEG with 12 thermal couples was integrated, and its joint resistance was found to be 4.2 Ω. Hence, we have successfully demonstrated a functional high-temperature contact for TEGs up to at least 900 K. Nevertheless, the actual thermal stability will be even higher. The process could be transfered to other substrates by using amorphous silicon deposited by plasma-enhanced chemical vapor deposition.     

Perovskite Oxides for Cathodic Electrocatalysis of Energy-Related Gases: From O2 to CO2 and N2

The oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO₂RR), and nitrogen reduction reaction (NRR) are important cathodic reactions for renewable fuel production and energy conversion technologies. However, the sluggish kinetics of these reactions hinders the practical applications of the relevant technologies. Perovskite oxides, a promising family of catalysts with great flexibility in composition and structure engineering, exhibit versatility in electrocatalysis of these reactions. In this review, beginning with a brief introduction on the fundamentals of ORR, CO₂RR, and NRR, the mechanistic understanding of the electrocatalysis by perovskite oxides is discussed based on both molecular orbital and band theories. The recent advances of perovskite oxide-based electrocatalysts for ORR, CO₂RR, and NRR are then highlighted. Strategies for developing perovskite oxide-based ORR catalysts are emphasized with representative examples, intending to draw on the experience of developing ORR catalysts to both CO₂RR and NRR catalysts. Finally, perspectives on the perovskite oxide-based electrocatalysis are discussed by paying particular attention to the practical applications and future development of perovskite oxide-based catalysts.     

Long-Lived Liquid Marbles for Green Applications

Liquid marbles allow for quantities of various liquids to be encapsulated by hydrophobic particles, thus ensuring isolation from the external environment. The unique properties provided by this soft solid has allowed for use in a wide array of different applications. Liquid marbles do however have certain drawbacks, with lifetime and robustness often being limited. Within this review, particle characteristics that impact liquid marble stability are critically discussed, in addition to other factors, such as internal and external environments, that can be engineered to achieve a robust long-lived liquid marble. New emerging applications, which will benefit from this improvement, are explored such as unconventional computing, cell mimicry, and soft lithography. Incorporation of liquid marbles and liquid crystal technologies shows promise in utilizing structural color for optical display applications, and within green and environmental applications, liquid marble technology is increasingly adapted for use in energy conversion, heavy metal recovery, CO₂ capture, and oil removal.     

Stress Analysis and Output Power Measurement of an n-Mg2Si Thermoelectric Power Generator with an Unconventional Structure

We examine the mechanical stability of an unconventional Mg₂Si thermoelectric generator (TEG) structure. In this structure, the angle θ between the thermoelectric (TE) chips and the heat sink is less than 90°. We examined the tolerance to an external force of various Mg₂Si TEG structures using a finite-element method (FEM) with the ANSYS code. The output power of the TEGs was also measured. First, for the FEM analysis, the mechanical properties of sintered Mg₂Si TE chips, such as the bending strength and Young’s modulus, were measured. Then, two-dimensional (2D) TEG models with various values of θ (90°, 75°, 60°, 45°, 30°, 15°, and 0°) were constructed in ANSYS. The x and y axes were defined as being in the horizontal and vertical directions of the substrate, respectively. In the analysis, the maximum tensile stress in the chip when a constant load was applied to the TEG model in the x direction was determined. Based on the analytical results, an appropriate structure was selected and a module fabricated. For the TEG fabrication, eight TE chips, each with dimensions of 3 mm × 3 mm × 10 mm and consisting of Sb-doped n-Mg₂Si prepared by a plasma-activated sintering process, were assembled such that two chips were connected in parallel, and four pairs of these were connected in series on a footprint of 46 mm × 12 mm. The measured power generation characteristics and temperature distribution with temperature differences between 873 K and 373 K are discussed.     

Examination of a Thermally Viable Structure for an Unconventional Uni-Leg Mg2Si Thermoelectric Power Generator

We have fabricated an unconventional uni-leg structure thermoelectric generator (TEG) element using quad thermoelectric (TE) chips of Sb-doped n-Mg₂Si, which were prepared by a plasma-activated sintering process. The power curve characteristics, the effect of aging up to 500?h, and the thermal gradients at several points on the module were investigated. The observed maximum output power with the heat source at 975?K and the heat sink at 345?K was 341?mW, from which the ??T for the TE chip was calculated to be about 333?K. In aging testing in air ambient, a remarkable feature of the results was that there was no notable change from the initial resistance of the TEG module for as long as 500?h. The thermal distribution for the fabricated uni-leg TEG element was analyzed by finite-element modeling using ANSYS software. To tune the calculation parameters of ANSYS, such as the thermal conductance properties of the corresponding coupled materials in the module, precise measurements of the temperature at various probe points on the module were made. Then, meticulous verification between the measured temperature values and the results calculated by ANSYS was carried out to optimize the parameters.     

Metal–CO2 Batteries at the Crossroad to Practical Energy Storage and CO2 Recycle

Metal–CO₂ batteries show great promise in meeting the growing energy, chemical, and environmental demands of daily life and industry, because of their advantages of high flexibility and efficiency in both energy storage and CO₂ recycle applications. It has been a trend that Li/Na‐CO₂ and Zn/Al‐CO₂ systems show different developments to achieve practical energy storage (e.g., high electricity supply) and CO₂ recycling (e.g., flexible chemical production), respectively, which is often neglected. This inhibits the application of metal–CO₂ batteries in maximizing energy supply and value‐added CO₂ conversion. This progress report presents a critically selected overview of the individual developments of metal–CO₂ batteries with emphasis on diverse fundamental origins, performance advantages, and the future of these two systems. Furthermore, the reaction pathways, particularly for catalytic materials, for the Li/Na‐CO₂ and Zn/Al‐CO₂ systems are discussed. Finally, the challenges of these two systems along with a hybrid Li/Na‐CO₂ battery design that may simultaneously provide high operating voltages and flexible chemicals are outlined.     

A Materials Perspective on Direct Recycling of Lithium-Ion Batteries: Principles,Challenges and Opportunities

As the dominant means of energy storage technology today, the widespread deployment of lithium-ion batteries (LIBs) would inevitably generate countless spent batteries at their end of life. From the perspectives of environmental protection and resource sustainability, recycling is a necessary strategy to manage end-of-life LIBs. Compared with traditional hydrometallurgical and pyrometallurgical recycling methods, the emerging direct recycling technology, rejuvenating spent electrode materials via a non-destructive way, has attracted rising attention due to its energy efficient processes along with increased economic return and reduced CO₂ footprint. This review investigates the state-of-the-art direct recycling technologies based on effective relithiation through solid-state, aqueous, eutectic solution and ionic liquid mediums and thoroughly discusses the underlying regeneration mechanism of each method regarding different battery chemistries. It is concluded that direct regeneration can be a more energy-efficient, cost-effective, and sustainable way to recycle spent LIBs compared with traditional approaches. Additionally, it is also identified that the direct recycling technology is still in its infancy with several fundamental and technological hurdles such as efficient separation, binder removal and electrolyte recovery. In addressing these remaining challenges, this review proposes an outlook on potential technical avenues to accelerate the development of direct recycling toward industrial applications.     

Recent Progress in Electrocatalytic Methanation of CO2 at Ambient Conditions

Electrochemical CO₂ reduction under ambient conditions is a promising pathway for conversion of CO₂ into value-added products. In recent years, great achievements have been obtained in the understanding the mechanism and development of efficient and selective catalysts for electrochemical CO₂ reduction. However, the electrochemical CO₂ reduction is still far from practical applications. Based on the gap between current research and practical applications, the state-of-the-art of the theoretical and experiment investigations on different electrocatalysts for the electrocatalysis of CO₂ to CH₄ is systematically and constructively reviewed. First of all, strategies for enhancing the catalytic activity and selectivity of electrochemical reduction of CO₂ to CH₄ are also examined in this review. The modulated strategies mainly involve the following aspects: i) tuning the applied potentials, ii) morphology engineering, iii) crystallographic facets engineering, iv) defect engineering, v) alloying. Furthermore, the influence of the electrolyte on the activity and selectivity for electrocatalysis of CO₂ to CH₄ is also reviewed. This review will build a systematic understanding in the electrochemical CO₂ reduction to CH₄ and may help to provide new insight for designing and optimizing the catalysts and/or electrolyte.     

Validating Steady-State and Transient Modeling Tools for High-Power-Density Thermoelectric Generators

Steady-state and transient models have been created in a MATLAB/Simulink environment for high-power-density thermoelectric generators (TEG). These numerical models, comprising simultaneously solved, nonlinear, energy balance equations, simulate novel TEG architectures, such as a cylindrical TEG with gas/liquid heat exchangers. Model validation studies, including component-level testing of thermoelectric (TE) subassemblies, interface thermal resistance tests, and full-scale TEG tests, were performed under different operating conditions and designs. Targeted finite-element analysis studies were also conducted. A full-scale cylindrical-shaped TE generator was built using high-power-density, segmented TE elements and tested on a test-bench with hot air and cold water with maximum power output of 608?W. Measured performance data from these tests were used in model validation. Process outlet temperatures, pressure drops, hot and cold shunt temperatures along the length of the TEG, TEG voltage, and TEG current are some of the performance variables included in the model validation. The validated model is now being used with more confidence to optimize new TEG designs for different applications.     

Skutterudites: Thermoelectric Materials for Automotive Applications?

The power output of a thermoelectric generator (TEG) was investigated under engine partial-load operation based on measured exhaust gas temperatures and mass flow rates. Materials with properties required for highend temperature TE couples (>500°C) were evaluated. Various possible material combinations for p- and n-legs of these couples as well as the conflicting targets of high efficiency and low cost as required for automotive mass production are discussed. New skutterudite materials for both p- and n-legs as identified during a joint research project are presented, which can help to overcome this conflict. Efficiencies >10% were achieved with these new materials, which have potentially twofold lower production costs than telluride-based materials due to the price of their elements. Some potential for improvement in efficiency and costs has been identified by developing highly integrated TEG units, specifically designed for automotive applications. These initial results of the material development and the evaluation of different integration concepts will be applied in a subsequent step for the fabrication of a pilot number of TEG modules/units.