Cumulative energy demand for selected renewable energy technologies

Calculation of Cumulative Energy Demand (CED) of various energy systems and the computation of their Energy Yield Ratio (EYR) suggests that one single renewable energy technology cannot be said to be the best. Due to the difference in availability of renewable energy sources, their suitability varies from place to place. Wind energy converters, solar water heating systems and photovoltaic systems have been analysed for different types of locations. Comparing the general bandwidth of performance of these technologies, however, the wind energy converters tend to be better, followed by solar water heating systems and photovoltaic systems. Since a major part of the methodology of findingCED is very close to that of life cycle assessment and also because of the dominance of environmental impacts caused by the energy demand in the entire life cycle of any product or system, it is suggested that theCED can be used as an indicator of environmental impacts, especially in the case of power producing systems. Keywords: Cumulative energy demand; life cycle assessment; energy yield ratio; photovoltaics; solar water heating; wind energy Abbreviations: CED — Cumulative Energy Demand; EYR — Energy Yield Ratio; LCA — Life Cycle Assessment; Photovoltaics — PV; WEC — Wind Energy Converters     

Solar‐to‐Hydrogen Energy Conversion Based on Water Splitting

Artificial photosynthesis provides a blueprint to harvest solar energy to sustain the future energy demands. Solar‐driven water splitting, converting solar energy into hydrogen energy, is the prototype of photosynthesis. Various systems have been designed and evaluated to understand the reaction pathways and/or to meet the requirements of potential applications. In solar‐to‐hydrogen conversion, electrocatalytic hydrogen and oxygen evolution reactions are key research areas that are meaningful both theoretically and practically. To utilize hydrogen energy, fuel cell technology has been extensively investigated because of its high efficiency in releasing chemical energy. In this review, general concepts of the photosynthesis in green plants are discussed, different strategies for the light‐driven water splitting proposed in laboratories are introduced, the progress of electrocatalytic hydrogen and oxygen evolution reactions are reviewed, and finally, the reactions in hydrogen fuel cells are briefly discussed. Overall, the mass and energy circulation in the solar‐hydrogen‐electricity circle are delineated. The authors conclude that attention from scientists and engineers of relevant research areas is still highly needed to eliminate the wide disparity between the aspirations and realities of artificial photosynthesis.     

Risk Perception and Energy Production

Mean risk magnitude judgments expressed by Belgian and French students on 107 items combining a particular energy domain (wood and biomass, coal, gas, oil, nuclear, water, wind, geothermal and solar) and a particular aspect of the energy production process (obtaining raw materials, storage of raw materials, transport of raw materials, energy production, waste products related to energy production, energy transport, waste products transport, waste products storage, utilization of energy) are reported, and analyzed. Questions were of the form: What is the level of risk (for health and the environment) associated with the item “Electrical energy production by thermodynamic conversion”? Concerning energy domains, nuclear energy received the highest ratings, almost regardless of the aspect of the energy production process considered (from the extraction of raw materials to the storage of production wastes). This was followed by oil, obtaining the next highest ratings after those for nuclear energy, then gas, considered more risky than biomass and coal. The brand image of these two latter energy sources would be almost as positive as that of water, solar, geothermal and wind energy if a solution could be found to the problem of atmospheric emission of carbon monoxide. Concerning production process aspects, waste products (as well as the transport and storage of waste) received the highest ratings. This is not unrelated to the fact that the vast majority of studies devoted to a particular area or particular aspect have concerned nuclear waste. In contrast, no very high degree of concern was found regarding the energy (electrical) transport aspect.     

An Analysis of Stocks and Flows Associated with Water Consumption in Indian Households

The focus of urban water system metabolism studies has, by and large, been restricted to what comes under the domain of the urban water utilities: water treatment and supply, and wastewater collection, treatment, and disposal. The material and energy flows both necessitated and facilitated by the supply of treated water to households—the water demand subsystem—are by no means negligible. This article studies the key flows into households associated with water consumption and the environmental impacts related to the same for India as a whole. Electricity consumption in washing machines and water heaters contributes the most to almost all the 13 environmental impact categories considered. This is easily explained by the fossil fuel heaviness of the Indian mix (>60%). Soaps contribute the most to terrestrial eco‐toxicity and malodorous air. In India, on a national scale, all the environmental impact categories deserve attention. The absolute consumption of electricity, soaps, and detergents, and the demand for home appliances will increase in the years to come.     

Photo‐Rechargeable Electric Energy Storage Systems

The global energy demand is increasing at the same time as fossil fuel resources are dwindling. Consequently, the search for alternative energy sources is a major topic worldwide. Solar energy is one of the most promising, effective and emission‐free energy sources. However, the energy has to be stored to compensate the fluctuating availability of the sun and the actual energy demand. Photo‐rechargeable electric energy storage systems may solve this problem by immediately storing the generated electricity. Different combinations of solar cells and storage devices are possible. High efficiencies can be achieved by the combination of dye‐sensitized solar cells (DSSC) and capacitors. However, other hybrid devices including DSSCs or organic photovoltaic systems and redox flow batteries, lithium ion batteries and metal air batteries are playing an increasing role in this research field. This Progress Report reviews the state of the art research of photo‐rechargeable batteries based on organic solar cells, as well as storage modules.     

Life cycle assessment of base–load heat sources for district heating system options

Purpose  

There has been an increased interest in utilizing renewable energy sources in district heating systems. District heating systems are centralized systems that provide heat for residential and commercial buildings in a community. While various renewable and conventional energy sources can be used in such systems, many stakeholders are interested in choosing the feasible option with the least environmental impacts. This paper evaluates and compares environmental burdens of alternative energy source options for the base–load of a district heating center in Vancouver, British Columbia (BC) using the life cycle assessment method. The considered energy sources include natural gas, wood pellet, sewer heat, and ground heat.     

Liquid Norbornadiene Photoswitches for Solar Energy Storage

Due to high global energy demands, there is a great need for development of technologies for exploiting and storing solar energy. Closed cycle systems for storage of solar energy have been suggested, based on absorption of photons in photoresponsive molecules, followed by on‐demand release of thermal energy. These materials are called solar thermal fuels (STFs) or molecular solar thermal (MOST) energy storage systems. To achieve high energy densities, ideal MOST systems are required either in solid or liquid forms. In the case of the latter, neat high performing liquid materials have not been demonstrated to date. Here is presented a set of neat liquid norbornadiene derivatives for MOST applications and their characterization in toluene solutions and neat samples. Their synthesis is in most cases based on solvent‐free Diels‐Alder reactions, which easily and efficiently afford a range of compounds. The shear viscosity of the obtained molecules is close to that of colza oil, and they can absorb up to 10% of the solar spectrum with a measured energy storage density of up to 577 kJ/kg corresponding to 152 kJ mol^–1 (calculated 100 kJ mol^–1). These findings pave the way towards implementation of liquid norbornadienes in closed cycle energy storage technologies.     

Mesophilic anaerobic digestion: first option for waste treatment in tropical regions

Rural India derives its energy needs for cooking and heating through the use of fuel wood and for lighting and agricultural operations through kerosene and diesel. Use of fuel wood has aggravated the problem of de-forestation, while availability of kerosene and diesel cannot be guaranteed due to corrupt practices in the public distribution systems. In contrast, urban India derives its energy needs through LPG cylinders, petrol, and electricity. However, their cost and uncertainty rendered them beyond the reach of lower income population. This scenario is more or less true with many developing countries. To meet these objectives, biogas generation from biodegradable waste using anaerobic digestion (AD) appears to be a sustainable avenue as it could be used for (a) water and space heating of farmhouses, animal shelters, (b) generating steam for food processing plants, and (c) electricity generation, in addition to reducing the pollution/hazard potential of these wastes. Many of the underdeveloped and developing countries are in the temperate zone and thus mesophilic AD could provide a desired pathway to achieve a long delayed need of energy for comfortable living, farming, and industrial operations. Efforts made in this direction are reviewed in the present article.     

Photothermal Catalytic Gel Featuring Spectral and Thermal Management for Parallel Freshwater and Hydrogen Production

Desalination processes often require large amounts of energy to create clean water, and vice versa for the generation of energy. This interdependence creates a tension between the two essential resources. Current research focuses on one or the other, which exacerbates water‐energy stress, while few tackle both issues jointly. Herein, a low‐carbon technology, H₂O–H₂ co‐generation system that enables concurrent steady freshwater and clean energy output is reported. The water‐energy coupled technology features a spectrally and thermally managed solar harvesting gel for photoredox and photoheating effects. This photothermal catalytic gel exploits interfacial solar heating for heat confinement, and localized plasmonic heating at the catalyst active sites to remarkably improve water and hydrogen production, thus maximizing energy value per area. To this end, a stand‐alone renewable solar desalination system is successfully demonstrated for parallel production of freshwater and hydrogen under natural sunlight. By doing so, the water–energy nexus is transformed into a synergistic bond that offers opportunities to better meet expected demand rather than acting in competition.     

Flexible Solar Thermal Fuel Devices: Composites of Fabric and a Photoliquefiable Azobenzene Derivative

Controllable storage and release of solar energy has always been a highlighted scientific issue for its benefit of mankind. Solar thermal fuels (STFs) supply a closed cycle and renewable energy‐storage strategy by transforming solar energy into chemical energy stored in the conformation of molecular isomers, such as cis/trans‐azobenzene, and releasing it as heat under various stimuli. Although the potential high energy density of the STFs which are based on the hybrids of azobenzene derivatives and carbon nanomaterials has been reported the solvent‐assistant charging hinders their practicability. In this study, a solid‐state STF device is designed and fabricated by compositing one photoliquefiable azobenzene (PLAZ) derivative with a flexible fabric template. The photoinduced phase transition of the PLAZ derivative enables the charging of the flexible STFs to be totally solvent‐free. Interestingly, the energy‐storage capacity (energy density ≈201 J g^?1) of flexible PLAZ STFs has been improved by the soft fabric template. The exothermic situation is monitored with one infrared camera, which shows 4 °C temperature difference between charged and discharged samples under blue light stimulus. The flexible STFs are may be used in practice as heating equipment.     

Domestic Water Use in the United States: A Life-Cycle Approach

Water and energy are two primary natural resources used by building occupants. A life-cycle assessment (LCA) is performed for water-consuming plumbing fixtures and water-consuming appliances during their operational life for four different building types. Within the cycle studied, water is extracted from the natural environment, subjected to water treatment, pumped to buildings for use, collected for wastewater treatment, and discharged back to the natural environment. Specifically, the impacts of water use, electricity and natural gas generation, energy consumption (for water and wastewater treatment, and for water heating), and the manufacture of water and wastewater treatment chemicals are evaluated both quantitatively and qualitatively on a generalized national level in the United States of America.
It is concluded that water use and consumption within buildings have a much larger impact on resource consumption than the water and wastewater treatment stages of the life cycle. To study this more specifically, the resource consumption of four different building types-an apartment building, a college dormitory, a motel, and an office building-is considered. Of these four building types, the apartment has the highest energy consumption (for water and wastewater treatment, and for water heating) per volume of water used, whereas the office building has the lowest. Similarly, the calculated LCA score for the apartment building is typically greater than those of the other three building types.     

Enhancement of Solar Water Pasteurization with Reflectors

A simple and reliable method that could be used in developing countries to pasteurize milk and water with solar energy is described. A cardboard reflector directs sunshine onto a black jar, heating water to pasteurizing temperatures in several hours. A reusable water pasteurization indicator verifies that pasteurization temperatures have been reached.     

Boosting Photoelectrochemical Water Splitting by TENG‐Charged Li‐Ion Battery

The need for cost‐effective and sustainable power supplies has spurred a growing interest in hybrid energy harvesting systems, and the most elementary energy production process relies on intermittent solar power. Here, it is shown how the ambient mechanical energy leads to water splitting in a photoelectrochemical (PEC) cell boosted by a triboelectric nanogenerator (TENG). In this strategy, a flexible TENG collects and transforms mechanical energy into electric current, which boosts the PEC water splitting via the charged Li‐ion battery. Au nanoparticles are deposited on TiO₂ nanoarrays for extending the available light spectrum to visible part by surface plasmon resonance effect, which yields a photocurrent density of 1.32 mA cm^?2 under AM 1.5 G illumination and 0.12 mA cm^?2 under visible light with a bias of 0.5 V. The TENG‐charged battery boosts the water splitting performance through coupling electrolysis and enhanced electron–hole separation efficiency. The hybrid cell exhibits an instantaneous current more than 9 mA with a working electrode area of 0.3 cm², suggesting a simple but efficient route for simultaneously converting solar radiation and mechanical energy into hydrogen.     

Climate Impacts on Extreme Energy Consumption of Different Types of Buildings

Exploring changes of building energy consumption and its relationships with climate can provide basis for energy-saving and carbon emission reduction. Heating and cooling energy consumption of different types of buildings during 1981-2010 in Tianjin city, was simulated by using TRNSYS software. Daily or hourly extreme energy consumption was determined by percentile methods, and the climate impact on extreme energy consumption was analyzed. The results showed that days of extreme heating consumption showed apparent decrease during the recent 30 years for residential and large venue buildings, whereas days of extreme cooling consumption increased in large venue building. No significant variations were found for the days of extreme energy consumption for commercial building, although a decreasing trend in extreme heating energy consumption. Daily extreme energy consumption for large venue building had no relationship with climate parameters, whereas extreme energy consumption for commercial and residential buildings was related to various climate parameters. Further multiple regression analysis suggested heating energy consumption for commercial building was affected by maximum temperature, dry bulb temperature, solar radiation and minimum temperature, which together can explain 71.5 % of the variation of the daily extreme heating energy consumption. The daily extreme cooling energy consumption for commercial building was only related to the wet bulb temperature (R²= 0.382). The daily extreme heating energy consumption for residential building was affected by 4 climate parameters, but the dry bulb temperature had the main impact. The impacts of climate on hourly extreme heating energy consumption has a 1-3 hour delay in all three types of buildings, but no delay was found in the impacts of climate on hourly extreme cooling energy consumption for the selected buildings.     

Photocatalytic Water Splitting for Solar Hydrogen Production Using the Carbonate Effect and the Z‐Scheme Reaction

The development of innovative technologies for solar energy conversion and storage is important for solving the global warming problem and for establishing a sustainable society. The photocatalytic water‐splitting reaction using semiconductor powders has been intensively studied as a promising technology for direct and simple solar energy conversion. However, the evolution of H₂ and O₂ gases in a stoichiometric ratio (H₂/O₂ = 2) is very difficult owing to various issues, such as an unfavorable backward reaction and mismatched band potentials. Two important findings have widened the variety of photocatalysts available for stoichiometric water‐splitting, viz. the carbonate anion effect and the Z‐scheme photocatalytic reaction using a redox mediator. The bicarbonate anion has been found to act as a redox catalyst via preferential peroxide formation and subsequent decomposition to O₂. As the Z‐scheme reaction using a redox mediator mitigates band potential mismatches, it is widely applicable for various visible‐light‐active photocatalysts. This review describes the development of photocatalytic water‐splitting for solar hydrogen production using the carbonate anion effect and the Z‐scheme reaction. Moreover, recent developments in photocatalysis–electrolysis hybrid systems, an advanced Z‐scheme reaction concept, are also reviewed for practical and economical hydrogen production.     

Environmental and economic impacts of solar‐powered integrated greenhouses

Greenhouse vegetable production plays a vital role in providing year‐round fresh vegetables to global markets, achieving higher yields, and using less water than open‐field systems, but at the expense of increased energy demand. This study examines the life cycle environmental and economic impacts of integrating semitransparent organic photovoltaics (OPVs) into greenhouse designs. We employ life cycle assessment to analyze six environmental impacts associated with producing greenhouse‐grown tomatoes in a Solar PoweRed INtegrated Greenhouse (SPRING) compared to conventional greenhouses with and without an adjacent solar photovoltaic array, across three distinct locations. The SPRING design produces significant reductions in environmental impacts, particularly in regions with high solar insolation and electricity‐intensive energy demands. For example, in Arizona, global warming potential values for a conventional, adjacent PV and SPRING greenhouse are found to be 3.71, 2.38, and 2.36 kg CO₂ eq/kg tomato, respectively. Compared to a conventional greenhouse, the SPRING design may increase life cycle environmental burdens in colder regions because the shading effect of OPV increases heating demands. Our analysis shows that SPRING designs must maintain crop yields at levels similar to conventional greenhouses in order to be economically competitive. Assuming consistent crop yields, uncertainty analysis shows average net present cost of production across Arizona to be $3.43, $3.38, and $3.64 per kg of tomato for the conventional, adjacent PV and SPRING system, respectively.     

Application of Plasmonics in Solar Cell Efficiency Improvement: a Brief Review on Recent Progress

We need electrical energy for our various daily life activities, and the existing fossil fuel will serve the purpose for a limited period only. Therefore, we need to look at alternate energy resources for long-term sustainable growth. Solar energy has been considered as one of the potential viable alternate sources of non-conventional energy. Solar photon harvesting is a technique where solar photon energy is being converted to electrical energy using solar cell devices. However, the solar power conversion efficiency is usually seen to be poor limiting the applications to large extent. Improving solar cell efficiency has, thus, been a great challenge to researchers who are actively working in this field. Various technological aspects are being looked at to improve efficiency, and out of them, plasmonic light trapping technique has been considered as one of the promising techniques. In the past years, considerable research efforts are being made towards the design and execution of the solar cell devices and to understand the mechanisms of performance enhancement. The present review outlines briefly the recent progress of plasmonic solar cell efficiency improvement that has happened, especially, for last 5–6 years. Plasmonic solar cells made of Si (silicon), GaAs (gallium arsenide); plasmonic dye-sensitized solar cells; plasmonic polymer (organic) solar cells and perovskite solar cells are mainly discussed along with the critical aspects that may influence the device performance.

     

Disentangling the effects of area, energy and habitat heterogeneity on boreal forest bird species richness in protected areas

Aim  One of the few general laws in ecology is that species richness is a positive function of area. However, it has been proposed that area would merely be a proxy for energy. Additionally, habitat heterogeneity has been found to be an important factor determining species richness. Yet the relative importance of those relationships is little known, and it is still unclear how they are brought about. We aimed to dissect which factors drive the species richness of boreal forest birds, and to identify the most probable mechanisms.
Location  Forested protected areas in Finland.
Methods  Using bird line census data collected in 104 protected areas, we ran simultaneous autoregressive models to explain the species richness of forest birds. We explored the value of forest area, tree volume, tree growth, mean degree days and habitat heterogeneity as explanatory variables and used the species richness within different species groups, based on the predictions of hypothesized mechanisms, as a response variable.
Results  Energy, rather than area or habitat heterogeneity, seems to be the main driver of species richness in boreal forest birds. More specifically, productive energy was a better predictor of total species richness than solar energy. Among the tested hypothetical mechanisms, the sampling hypothesis received strong support. After accounting for sampling, solar energy had an effect on species richness.
Main conclusions  As productive energy, such as tree volume, is associated with species richness, high-energy areas should be prioritized in forest conservation planning. Reductions in productive energy may first lead to the disappearance of the rarest species due to the random sampling process. Climate change may result in increased species richness due to increasing amount of productive and solar energy in forests. However, the range shifts of bird species may not be fast enough to keep up with the temperature increases.     

A system of systems approach to energy sustainability assessment: Are all renewables really green?

Renewable energies are emerging across the globe in an attempt to slow down global warming and to improve national energy security in face of the depleting fossil fuel reserves. However, the general policy of mandating the replacement of fossil fuels with the so-called “green” energies may not be as effective and environmental-friendly as previously thought, due to the secondary impacts of renewable energies on different natural resources. Thus, an integrated systems analysis framework is essential to selecting optimal energy sources that address global warming and energy security issues with minimal unintended consequences and undesired secondary impacts on valuable natural resources. This paper proposes a system of systems (SoS) framework to determine the relative aggregate footprint (RAF) of energy supply alternatives with respect to different sustainability criteria and uncertain performance values. Based on the proposed method, the RAF scores of a range of renewable and nonrenewable energy alternatives are determined using their previously reported performance values under four sustainability criteria, namely carbon footprint, water footprint, land footprint, and cost of energy production. These criteria represent environmental efficiency, water use efficiency, land use efficiency, and economic efficiency, respectively. The study results suggest that geothermal energy and biomass energy from miscanthus are the most and least resource-use efficient energy alternatives based on the performance data available in the literature. In addition, despite their lower carbon footprints, some renewable energy sources are less promising than non-renewable energy sources from a SoS perspective that considers the trade-offs between the greenhouse gas emissions of energies and their effects on water, ecosystem, and economic resources. Robustness analysis suggests that with respect to the existing performance values and uncertainties in the literature, solar thermal and hydropower have the most and least level of RAF robustness, respectively. Sensitivity analysis indicates that geothermal energy and ethanol from sugarcane, have the lowest and highest RAF sensitivity to resource availability, respectively.     

能量效率与可更新能源

一可更新能源可减少甚至消除我们对化石能和核能的依赖,其中很多虽然已为人类使用数百年,但因为石能的普遍使用,一直都为起人类的注意。人类已发明了新技术利用这些可更新能源。其利用不赖于一定的技术是既定的事实,目前有成功建立这样的能源工业还是十分昂贵的。如果人类生产经济和市场允许的话,这些新的技术经进一步改进和简化后,就可以降低成本,并且应用起来也很可靠。相对于开发应用核能,水能和化石能数以百万计的投资耗费来讲,用于可更新资源的资金可谓微乎其微。虽然传统能源和替代能源各具优点,但保护能源往往还是解决能源短缺最便宜,最容易的途径。