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.     

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.     

Open public spaces and street furniture: the potential for increased use of photovoltaics in the built environment

The trend toward industrializing architectural components, the increasing complexity and multifunctional purpose of buildings and the concern for the CO₂ emissions common to our cities is pushing design research to experiment with new environmentally friendly construction technology. Current experiments in integrating photovoltaic (PV) systems in buildings and the built environment have already been proven to offer numerous advantages. This article focuses on the notable flexibility and adaptability of PV integration in urban structures due to the features of its industrial components. To illustrate this point, I should like to offer a brief overview of some selected examples of the use of PV in public open spaces to demonstrate that it is possible to achieve a positive integration with its environmental context, while enhancing the architectural quality of the PV material and respecting its technological efficiency.     

Life cycle assessment of high‐concentration photovoltaic systems

The environmental profiles of photovoltaic (PV) systems are becoming better as materials are used more efficiently in their production, and overall system performance improves. Our analysis details the material and energy inventories in the life cycle of high‐concentration PV systems, and, based on measured field‐performances, evaluates their energy payback times, life cycle greenhouse gas emissions, and usage of land and water. Although operating high‐concentration PV systems require considerable maintenance, their life cycle environmental burden is much lower than that of the flat‐plate c‐Si systems operating in the same high‐insolation regions. The estimated energy payback times of the Amonix 7700 PV system in operation at Phoenix, AZ, is only 0.9 year, and its estimated greenhouse gas emissions are 27 g CO₂‐eq./kWh over 30 years, or approximately 16 g CO₂‐eq./kWh over 50 years. Copyright © 2012 John Wiley & Sons, Ltd.     

Greenhouse gas emissions associated with photovoltaic electricity from crystalline silicon modules under various energy supply options

The direct and indirect emissions associated with photovoltaic (PV) electricity generation are evaluated, focussing on greenhouse gas (GHG) emissions related to crystalline silicon (c‐Si) solar module production. Electricity supply technologies used in the entire PV production chain are found to be most influential. Emissions associated with only the electricity‐input in the production of PV vary as much as 0–200 g CO₂‐eq per kWh electricity generated by PV. This wide range results because of specific supply technologies one may assume to provide the electricity‐input in PV production, i.e., whether coal‐, gas‐, wind‐, or PV‐power facilities in the “background” provide the electricity supply for powering the entire PV production chain. The heat input in the entire PV production chain, for which mainly the combustion of natural gas is assumed, adds another ∼16 CO₂‐eq/kWh. The GHG emissions directly attributed to c‐Si PV technology alone constitute only ∼1–2 g CO₂‐eq/kWh. The difference in scale indicates the relevance of reporting “indirect” emissions due to energy input in PV production separately from “direct” emissions particular to PV technology. In this article, we also demonstrate the utilization of “direct” and “indirect” shares of emissions for the calculation of GHG emissions in simplified world electricity‐ and PV‐market development scenarios. Results underscore very large GHG mitigation realized by solar PV toward increasingly significant PV market shares. Copyright © 2011 John Wiley & Sons, Ltd.     

A comparative study on cost and life‐cycle analysis for 100 MW very large‐scale PV (VLS‐PV) systems in deserts using m‐Si,a‐Si,CdTe, and CIS modules

This paper is a study of comparisons between five types of 100 MW Very Large‐Scale Photovoltaic Power Generation (VLS‐PV) Systems, from economic and environmental viewpoints. The authors designed VLS‐PV systems using typical PV modules of multi‐crystalline silicon (12·8% efficiency), high efficiency multi‐crystalline silicon (15·8%), amorphous silicon (6·9%), cadmium tellurium (9·0%), and copper indium selenium (11·0%), and evaluated them by Life‐Cycle Analysis (LCA). Cost, energy requirement, and CO₂ emissions were calculated. In addition, the authors evaluated generation cost, energy payback time (EPT), and CO₂ emission rates. As a result, it was found that the EPT is 1·5–2·5 years and the CO₂ emission rate is 9–16 g‐C/kWh. The generation cost was 11–12 US Cent/kWh on using 2 USD/W PV modules, and 19–20 US Cent/kWh on using 4 USD/W PV module price. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermoelectrics: Impacts on the Environment and Sustainability

Energy saving in power generation, industry, transport, and residential applications by using waste heat with thermoelectrics (TE) may be important for an environmentally sound and sustainable energy system. It is probable that operable TE generators (TEG) will be developed for numerous applications and will save energy and reduce CO₂ emissions from plants. However, the environmental profile of a technology is not sufficiently described by just the energy and CO₂ inputs and outputs of the core process. Necessary preceding and subsequent processes, other environmental impacts, and competing technologies have to be considered as well. Furthermore, sustainability covers aspects beyond environmental soundness. So far, comprehensive studies on TE and the environment/sustainability have not been available. In this paper, the following selected aspects are discussed: resource availability, specific energy consumption of TEG production, specific energy and CO₂ savings in different application fields by TE and competing technologies, and the global potential of TE.     

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.     

Application of life-cycle energy analysis to photovoltaic module design

This paper highlights results from a collaborative life-cycle design project between the University of Michigan, the US Environment Protection Agency and United Solar Systems Corporation. Energy analysis is a critical planning and design tool for photovoltaic (PV) modules. A set of model equations for evaluating the life-cycle energy performance of PV systems and other electricity-generating systems are presented. The total PV life-cycle, encompassing material production, manufacturing and assembly, use and end-of-life management, was investigated. Three metrics—energy payback time, electricity production efficiency and life-cycle conversion efficiency—were defined for PV modules with and without balance-of-system (BOS) components. These metrics were evaluated for a United Solar UPM-880 amorphous silicon PV module based on average insolation in Detroit, Boulder and Phoenix. Based on these metrics, a minimum condition for assessing the sustainability of electricity-generating systems was proposed and discussed. The life-cycle energy analysis indicated that the aluminum frame is responsible for a significant fraction of the energy invested in the UPM-880 module. © 1997 John Wiley & Sons, Ltd.     

Life cycle assessment and cost analysis of very large‐scale PV systems and suitable locations in the world

Although the Sahara region has a high potential for solar power plants, the amount of installed photovoltaic (PV) system remains relatively low. This paper aims to evaluate these potentials of PV system installation in terms of environmental and economic viewpoints with indices of cost, energy, and greenhouse gas (GHG) emission. Two 1‐GW very large‐scale PV systems are simulated at Ouarzazate in Morocco and at Carpentras in France. The evaluation was performed using life cycle assessment. The lowest energy consumption and GHG emission are obtained while assuming cadmium telluride module. The result of our simulation shows that energy payback time is 0.9 years and CO₂ emission rate is 27.4 g‐CO_2‐eq/kWh in the Ouarzazate case. In cost estimation, generation costs are 0.06 USD/kWh in Ouarzazate and 0.09 USD/kWh in Carpentras in the case of 3% interest rate and 0.5 USD/W for multicrystalline silicon PV module price. In addition, by adapting 15% internal rate of return for 20% of budget, the generation costs become 0.09 USD/kWh in Ouarzazate and 0.13 USD/kWh in Carpentras under the same condition. Furthermore, the selection for suitable locations to install solar power plants in term of GHG emission is identified using geographical information system. Very high‐potential locations (lower than 38 g‐CO_2‐eq/kWh) could be obtained in North Chili, east and west Sahara, and Mexico. Copyright © 2015 John Wiley & Sons, Ltd.     

Energy,cost and LCA results of PV and hybrid PV/T solar systems

Hybrid photovoltaic/thermal (PV/T) solar systems provide a simultaneous conversion of solar radiation into electricity and heat. In these devices, the PV modules are mounted together with heat recovery units, by which a circulating fluid allows one to cool them down during their operation. An extensive study on water‐cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. In this paper the electrical and thermal efficiencies are given and the annual energy output under the weather conditions of Patras is calculated for horizontal and tilted building roof installation. In addition, the costs of all system parts are included and the cost payback time is estimated. Finally, the methodology of life cycle assessment (LCA) has been applied to perform an energy and environmental assessment of the analysed system. The goal of this study, carried out at the University of Rome ‘La Sapienza’ by means of SimaPro 5·1 software, was to verify the benefits of heat recovery. The concepts and results of this work on energy performance, economic aspects and LCA results of modified PV and water‐cooled PV/T solar systems, give a clear idea of their application advantages. From the results, the most important conclusion is that PV/T systems are cost effective and of better environmental impact compared with standard PV modules. Copyright © 2005 John Wiley & Sons, Ltd.     

PV thermal systems: PV panels supplying renewable electricity and heat

With PV Thermal panels sunlight is converted into electricity and heat simultaneously. Per unit area the total efficiency of a PVT panel is higher than the sum of the efficiencies of separate PV panels and solar thermal collectors. During the last 20 years research into PVT techniques and concepts has been widespread, but rather scattered. This reflects the number of possible PVT concepts and the accompanying research and development problems, for which it is the general goal to optimise both electrical and thermal efficiency of a device simultaneously. The aspects that can be optimised are, amongst others, the spectral characteristics of the PV cell, its solar absorption and the internal heat transfer between cells and heat‐collecting system. Another important level of optimisation is for the PVT device geometry and the integration into a system. The electricity and heat demand and the temperature level of the heat determine the choice for a certain system set‐up. With an optimal design, PVT systems can supply buildings with 100% renewable electricity and heat in a more cost‐effective manner than separate PV and solar thermal systems and thus contribute to the long‐term international targets on implementation of renewable energy in the built environment. Copyright © 2004 John Wiley & Sons, Ltd.     

The environmental impact of lightweight HCPV modules: efficient design and effective deployment

We present a life cycle analysis of a lightweight design of high concentration photovoltaic module. The materials and processes used in construction are considered to assess the total environmental impact of the module construction in terms of the cumulative energy demand and embodied greenhouse gas emissions, which were found to be 355.3 MJ and 27.9 kgCO_2eq respectively. We consider six potential deployment locations and the system energy payback times are calculated to be 0.22–0.33 years whilst the greenhouse gas payback times are 0.29–0.88 years. The emission intensities over the lifetimes of the systems are found to be 6.5–9.8 g CO_2eq/kWh, lower than those of other HCPV, PV and CSP technologies in similar locations. Copyright © 2016 John Wiley & Sons, Ltd.     

Update of environmental indicators and energy payback time of CdTe PV systems in Europe

Thin film technologies undergo rapid developments for increasing the module efficiencies and improving production technologies or recycling processes which affect the environmental profile of PV power generation and Energy Payback Time (EPBT). Therefore, especially for the Life Cycle Assessment (LCA) of product systems with short development cycles, the environmental profiles need to be frequently updated to ensure the representativeness and validity of the environmental assessment. The update of LCA results in this paper demonstrates that considerable improvements were reached in the environmental profile of CdTe PV power and EPBT over the last four years. Depending on the location of installation in Europe, the corresponding Greenhouse Gas (GHG) emissions of PV power for ground mounted power plants are between 19 and 30 g CO₂‐equiv./kWh and between 0.7 and 1.1 years in terms of EBPT. Furthermore, for the first time, the environmental impacts due to an already applied recycling procedure of CdTe modules and it's relative contribution to the CdTe PV life cycle has been investigated. This paper presents the main approach, results and outcomes of the study. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimizing performances of photovoltaics in Reunion Island—tilt angle

As in Reunion Island, France, around 61% of electricity is produced by using coal and fuel oil with high greenhouse emissions, it is beneficial to the environment to produce electricity from solar energy. Therefore, there is a large push to generate electricity from solar energy by use of photovoltaic (PV) arrays. However, it is important to have high efficiency of electricity generation, that is, to locate PV arrays in an optimal direction. The investigated PV systems may take 1, 2, 4, and 12 tilts per year. For the PV arrays facing the north–south direction, this paper reports investigations of their optimum tilts and the maximum amounts of generated electricity. The investigated PV arrays are located in the towns of Saint‐Benoit, Les Avirons, Piton Saint‐Leu, and Petite‐France in Reunion Island. To obtain optimal tilt of the PV arrays for electricity production from solar energy, EnergyPlus software and GenOpt software are used with Hooke–Jeeves optimization routine. For the investigated PV arrays, the percentage gains in energy, exergy, avoided fossil energy, and the percentage decrease in CO₂ emission are around 5% when compared with that of the PV array that takes only one optimum tilt per year. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

Visible Light Triggered CO2 Liberation from Silver Nanocrystals Incorporated Metal–Organic Frameworks

Widespread deployment of metal–organic frameworks (MOFs) for CO₂ capture remains challenging due to the great energy‐penalty associated with their regeneration. To overcome this challenge, a new type of photodynamic carbon capture material synthesized by incorporating Ag nanocrystals with UiO‐66 (Ag/UiO‐66) framework is presented. Upon the irradiation of visible light, Ag nanocrystals within the composites serve as “nanoheaters” to convert photon energy into thermal energy locally. Driven by such light‐induced localized heat (LLH), the adsorbed CO₂ within MOFs is remotely released. The CO₂ desorption capacity of such Ag/UiO‐66 composites can be readily regulated by control over their Ag contents and the applied light intensity. Up to 90.5% of CO₂ desorption is achieved under the investigated conditions. Distinct from the traditional light‐responsive MOFs for gas trigger release, currently developed LLH‐driven CO₂ release method not only offers a promising solution to the heat‐insulating nature of MOFs, but also demonstrates a potentially low energy method to remotely regenerate MOF adsorbents given the utilization of naturally abundant visible light as efficient stimulus.     

Deciphering Electrolyte Selection for Electrochemical Reduction of Carbon Dioxide and Nitrogen to High-Value-Added Chemicals

Electrochemical reduction of CO₂ (CO₂RR) and nitrogen (NRR) constitute alternatives to fossil fuel-based technologies for the production of high-value-added chemicals. Yet their practical application is still hampered by the low energy and Faradaic efficiencies although numerous efforts have been paid to overcome the fatal shortcomings. To date, most studies have focused on designing and developing advanced electrocatalysts, while the understanding of electrolyte, which would significantly influence the reaction microenvironment, are still not enough to provide insight to construct highly active and selective electrochemical systems. Here, a comprehensive review of the different electrolytes participating in the CO₂RR and NRR is provided, including acidic, neutral, alkaline, and water-in-salt electrolyte as aqueous electrolytes, as well as organic electrolyte, ionic-liquids electrolyte, and the mixture of the two as non-aqueous electrolytes. Through the discussion of the roles of these various electrolytes, it is aimed to grasp their essential function during the electrochemical process and how these functions can be used as design parameters for improving electrocatalytic performance. Finally, priorities for future studies are suggested to support the in-depth understanding of the electrolyte effects and thus guide efficient selection for next-generation gas-involving electrochemical reactions.     

Environmental life cycle assessment of roof‐integrated flexible amorphous silicon/nanocrystalline silicon solar cell laminate

This paper presents an environmental life cycle assessment of a roof‐integrated flexible solar cell laminate with tandem solar cells composed of amorphous silicon/nanocrystalline silicon (a‐Si/nc‐Si). The a‐Si/nc‐Si cells are considered to have 10% conversion efficiency. Their expected service life is 20 years. The production scale considered is 100 MW_p per year. A comparison of the a‐Si/nc‐Si photovoltaic (PV) system with the roof‐mounted multicrystalline silicon (multi‐Si) PV system is also presented. For both PV systems, application in the Netherlands with an annual insolation of 1000 kWh/m² is considered. We found that the overall damage scores of the a‐Si/nc‐Si PV system and the multi‐Si PV system are 0.012 and 0.010 Ecopoints/kWh, respectively. For both PV systems, the impacts due to climate change, human toxicity, particulate matter formation, and fossil resources depletion together contribute to 96% of the overall damage scores. Each of both PV systems has a cumulative primary energy demand of 1.4 MJ/kWh. The cumulative primary energy demand of the a‐Si/nc‐Si PV system has an uncertainty of up to 41%. For the a‐Si/nc‐Si PV system, an energy payback time of 2.3 years is derived. The construction for roof integration, the silicon deposition, and etching are found to be the largest contributors to the primary energy demand of the a‐Si/nc‐Si PV system, whereas encapsulation and the construction for roof integration are the largest contributors to its impact on climate change. Copyright © 2012 John Wiley & Sons, Ltd.     

An anticipatory approach to quantify energetics of recycling CdTe photovoltaic systems

Rapid growth in worldwide photovoltaic (PV) systems will soon result in a massive installed base of modules, electrical systems (ES), and balance of systems (BOS) that are expected to reach their end of life after two or three decades of operation. While existing recycling technologies will likely be available for steel, copper, aluminum, and other commodity materials found in the ES and BOS, these have yet to be accounted for in studies that assess the environmental impacts of PV recycling. More problematic is the lack of research identifying strategies to improve recovery of semiconductor and other module materials and develop recycling infrastructure to minimize energy required to transport these materials. The current leader in photovoltaics recycling is First Solar, which operates facilities for processing prompt scrap, breakage, and any end‐of‐life CdTe PV modules. This paper presents a comprehensive energy assessment of recycling the entire CdTe PV system based on First Solar's processes and identifies hotspots that present opportunities to improve the energy balance of future recycling operations. The energy savings derived from recycling a CdTe PV system reduces the lifecycle energy footprint by approximately 24% of the energy required to manufacture the PV system. By contrast, recycling just the CdTe PV module without the BOS has an approximately neutral net energy impact, recovering 13.2 kg of glass, 0.007 kg of Cd, and 0.008 kg of Te per m². Hotspot analysis shows that reducing the energy required to recover unrefined semiconductor material from the module and ensuring high recovery of steel and glass from the end‐of‐life CdTe PV system will have the greatest impact on the energy benefits of recycling. Also, transportation energy depends on the energy tradeoff between (i) material recovery and recycling operations at the decentralized location, and (ii) transporting, recovering, and recycling the PV system components at a centralized location. An optimal strategy (centralized versus decentralized) is presented to minimize the net energy footprint when distance to the centralized recycling facility and the recycling energy requirements at the decentralized recycling facility are varied. Copyright © 2015 John Wiley & Sons, Ltd.