Tons Of CO2 Emissions Research Articles

Long-term performance of roof-top GCPV systems in central Viet Nam

In pursuit of the objective of achieving "net zero emissions," many countries worldwide, including Viet Nam, have prioritized the utilization of photovoltaic technology for energy conversion. Specifically, the implementation of roof-top grid-connected photovoltaic systems (GCPV) has emerged as a highly efficient solution in urban areas. These systems offer several advantages, such as minimizing land usage, lowering monthly electricity expenses, preventing building heat, generating income for households, and reducing transmission and distribution costs. This article focuses on a comprehensive long-term analysis conducted on 51 roof-top GCPV systems in the tropical monsoon climate of Hue City, Viet Nam, during the period from 2019 to 2023. The analysis findings reveal that roof-top GCPV systems with a capacity of 3-6 kW are well-suited for households in the central region of Viet Nam, characterized by a tropical monsoon climate. These systems exhibit an average sizing ratio of 1.03. The annual average daily final yield peaked at 3.28 kWh/kWp/day in 2021 and reached its lowest point at 2.97 kWh/kWp/day in 2022. Notably, the typical slope of the yield gradually increases with the installed capacity and the studied year. Furthermore, the monthly average daily final yield demonstrates a seasonal pattern, with higher yields observed from March to August and lower yields from September to January, aligning with the climate of the study area. As the years progress, the capacity factor and performance ratio of roof-top GCPV systems display a declining trend. Throughout the entire study period, these systems successfully mitigated 664 metric tons of CO2 emissions. The evaluation of long-term yield data offers valuable insights for photovoltaic installers, operators, and system owners, aiding in system maintenance and optimizing load utilization across different time periods. Long-term performance can be used by energy managers and owners of roof-top GCPV systems to identify supply shortfalls and initiate countermeasures.

TOWARDS A SUSTAINABLE FUTURE IN ALUMINIUM PRODUCTION: ENVIRONMENTAL AND ECONOMIC BENEFITS OF REVOLUTIONARY INERT ANODE TECHNOLOGY

The aluminium industry currently produces significant greenhouse gas emissions and relies on energy-intensive production technology, substantially burdening the environment. The primary goal of aluminium production is to achieve expertise in carbon-free technologies and alternative energy sources. Global business companies and scientific foundations are crucial in driving progress towards sustainability objectives. Reducing the average 16 tonnes of CO2 emissions and 14,000 kWh of electricity required for every tonne of primary aluminium production presents a significant challenge. Traditional aluminium production can incur environmental costs of up to $1,000 per tonne. Addressing this issue is unfeasible without revolutionary scientific and technological innovations. The development of inert anode technology is considered one of the greatest innovations of the 21st century, potentially transforming the aluminium industry fundamentally. Due to the threat of global climate change, green strategies have become a top priority on the world’s political and economic agendas, with many areas setting net zero CO2 targets for 2050. This scientific study highlights the importance of integrating inert anode technology into the green platform of the aluminium industry as a crucial step towards achieving long-term sustainability.

Environmentally sustainable gastroenterology practice: Review of current state and future goals.

The health-care sector contributes 4.6% of global greenhouse gas emissions, with gastroenterology playing a significant role due to the widespread use of gastrointestinal (GI) endoscopy. In this review, we aim to understand the carbon footprint in gastroenterology practice associated with GI endoscopy, conferences and recruitment, identify barriers to change, and recommend mitigating strategies. A comprehensive search of PubMed, Embase, and the Cochrane Library was conducted to explore the carbon footprint in gastroenterology practice, focusing on endoscopy, inpatient and outpatient settings, and recruitment practices. Recommendations for mitigating the carbon footprint were derived. This narrative review analyzed 34 articles on the carbon footprint in gastroenterology practice. Carbon footprint of endoscopy in the United States is approximately 85,768 metric tons of CO2 emission annually, equivalent to 9 million gallons of gasoline consumed, or 94 million pounds of coal burned. Each endoscopy generates 2.1 kg of disposable waste (46 L volume), of which 64% of waste goes to the landfill, 28% represents biohazard waste, and 9% is recycled. The per-case manufacturing carbon footprint for single-use devices and reusable devices is 1.37 kg CO2 and 0.0017 kg CO2, respectively. Inpatient and outpatient services contributed through unnecessary procedures, prolonged hospital stays, and excessive use of single-use items. Fellowship recruitment and gastrointestinal conferences added to the footprint, mainly due to air travel and hotel stays. Gastrointestinal endoscopy and practice contribute to the carbon footprint through the use of disposables such as single-use endoscopes and waste generation. To achieve environmental sustainability, measures such as promoting reusable endoscopy equipment over single-use endoscopes, calculating institutional carbon footprints, establishing benchmarking standards, and embracing virtual platforms suchas telemedicine and research meetings should be implemented.

Green hydrogen for energy storage and natural gas system decarbonization: An Italian case study

The increase of the electricity production from non-programmable and intermittent Renewable Energy Sources (RESs) generates criticalities in the balance between the energy supply and demand, requiring significant energy storage capabilities for the next future. The exploitation of the available NG Transmission Network (NGTN) by implementing the Power to Gas (PtG) technology is particularly promising since it allows a massive energy storage capability and the decarbonization of the NGTN by green hydrogen injection into the grid with growing percentages up to 100%. The objective of this work is to analyse the actual feasibility of distributed green hydrogen generation and its injection into the national NGTN. A mathematical model has been developed to assess the dynamic operation of a PtH2 integrated system to produce green hydrogen using photovoltaic-powered electrolysers and to inject it into the NGTN upstream of a Regulating and Measuring Station (RMS) located in central Italy. Three different surface sizes are considered for the installation of PV panels (100 m2, 300 m2 and 500 m2) and the optimal hydrogen accumulation size has been calculated in order to ensure the uniformity of the supplied mixture throughout the year. Obtained results show that employing the optimal accumulation size, hydrogen percentage in the NG-H2 mixture ranges between 0% and 0.90% by volume. In the best-case scenario (i.e., when considering a surface area of 500 m2), the cost of hydrogen production is 5.10 EUR/kg H2 and the PtH2 plant allows to save 32.348 tonnes of CO2 emissions every year.

Analysis of the Actual Usage and Emission Reduction Potential of Electric Heavy-Duty Trucks: A Case Study of a Steel Plant

In order to understand the driving characteristics of electric heavy-duty trucks in practical application scenarios and promote their usage to replace diesel trucks, this study analyzed the actual usage of electric and diesel heavy-duty trucks in a steel factory based on vehicle-monitoring data and remote online monitoring data and estimated the emission reduction potential of the application of electric trucks by using a mileage-based method and the greenhouse gas emission model. The results showed that the electric heavy-duty trucks in the steel factory mostly operated for over 14 h, with a vehicle kilometers traveled (VKT) of 50–300 km each day, which could meet most of the demands of the transportation of the steel industry. The average daily energy consumption for most trucks falls within the range of 210–230 kWh/100 km, with higher consumption in winter than in summer, which can save approximately 18–26% in operating costs compared with diesel trucks. It is estimated that the usage of these electric heavy-duty trucks can achieve an annual reduction of 115.8 tons of NOx emissions, 0.7 tons of PM emissions, and 18,000 tons of CO2 emissions. To further promote the application of electric heavy-duty trucks in China, several policy suggestions, such as introducing priority road-right policies, promoting vehicle and battery leasing markets, and exempting zero-emission vehicles during heavy pollution days, were proposed.

Steel slag wastes to fight the climate change

Steel slags are solid by-products generated from the steel-manufacturing industries. They are considered valuable wastes for capturing of carbon dioxide (CO2) directly from the air and industrial sources and storing it permanently in the form of mineral carbonation. In this study, two historic steel slags are presented as sustainable materials for mineral carbonation. The effects of contacting time between CO2 and slags as well as temperature were investigated as two important parameters during mineral carbonation. The amount of carbonation, chemical and physical properties of carbonated samples have been characterised using Calcimeter, Fourier-transform infrared spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM). The results showed that depending on the source and composition of the steel slags, the maximum CO2 sequestration after 4 days at 60 °C is reached as high as 300 kg per tonne for samples. The FT-IR results showed the symmetric stretching of O-C-O bonds at 1400-1500 cm-1, gradually increased with increasing temperature and contacting time, indicating the significant capture of CO2 due to the carbonation process. SEM images confirmed that for both samples after the mineralisation, several carbonate layers were created in the structure of steel slags. The results indicated that CO2 sequestration in steel slag is positively correlated with contacting time and temperature, hence the current study provides the optimal conditions to accelerate the process of carbonation for industrial application. It is estimated that these steel slags alone could carbonate about 150-200 million tonnes of CO2 emissions which is equivalent to one third of annual UK greenhouse gas emissions.

Methane Pyrolysis in a Liquid Metal Bubble Column Reactor for CO2-Free Production of Hydrogen

In light of the growing interest in hydrogen as an energy carrier and reducing agent, various industries, including the iron and steel sector, are considering the increased adoption of hydrogen. To meet the rising demand in energy-intensive industries, the production of hydrogen must be significantly expanded and further developed. However, current hydrogen production heavily relies on fossil-fuel-based methods, resulting in a considerable environmental burden, with approximately 10 tons of CO2 emissions per ton of hydrogen. To address this challenge, methane pyrolysis offers a promising approach for producing clean hydrogen with reduced CO2 emissions. This process involves converting methane (CH4) into hydrogen and solid carbon, significantly lowering the carbon footprint. This work aims to enhance and broaden the understanding of methane pyrolysis in a liquid metal bubble column reactor (LMBCR) by utilizing an expanded and improved experimental setup based on the reactor concept previously proposed by authors from Montanuniversitaet in 2022 and 2023. The focus is on investigating the process parameters’ temperature and methane input rate with regard to their impact on methane conversion. The liquid metal temperature exhibits a strong influence, increasing methane conversion from 35% at 1150 °C to 74% at 1250 °C. In contrast, the effect of the methane flow rate remains relatively small in the investigated range. Moreover, an investigation is conducted to assess the impact of carbon layers covering the surface of the liquid metal column. Additionally, a comparative analysis between the LMBCR and a blank tube reactor (BTR) is presented.

Concentrated solar power integration with refinery process heaters

Crude oil heating is considered an energy-intensive process in the oil industry that requires a huge amount of heat to process the crude oil. There is scarcity of a thorough research that deals with the techno-economic viability of introducing renewable energy solutions to the refinery industry including its environmental benefits. Therefore, a renewable energy solution i.e. a parabolic trough system is reviewed and examined to support minimizing the burning of natural gas in crude heaters and relying on thermal heat from sun radiation to increase crude oil temperature prior to going into the fractionation column. The system is designed to support refinery operation during day time whereas system design and analysis were done from thermal and financial points of view. Furthermore, benefits such as natural gas savings, reduction in CO2 emissions, and total payback period are presented in the paper to reflect the feasibility of constructing such a solution. Moreover, a MATLAB simulation was carried out to define the design points for the solar field and related heat exchanger components. This is to assure that the system can operate during winter and summer seasons given that the direct normal irradiance (DNI) is typically variant throughout the year. It has been concluded that integrating a parabolic trough collector into the operation of an oil refinery, i.e. crude oil heater, can potentially result in natural gas savings of 555,515 MMBtu and can prevent 30,020 tons of CO2 emissions annually. Moreover, the system is anticipated to result in cost savings of approximately 1.65 M $ per year.

Capacity-Operation Collaborative Optimization for Wind-Solar-Hydrogen Multi-Energy Supply System

In pursuit of widespread adoption of renewable energy and the realization of decarbonization objectives, this study investigates an innovative system known as a wind-solar-hydrogen multi-energy supply (WSH-MES) system. This system seamlessly integrates a wind farm, photovoltaic power station, solar thermal power station, and hydrogen energy network at the power grid level. Central to the study is the introduction of a bi-level collaborative optimization model—an innovative algorithmic framework specifically tailored for complex multi-energy systems. This model co-optimizes both the capacity planning of essential system components and their annual load distribution, adeptly navigating the complexities of optimizing capacity and annual load distribution under uncertain energy sources and load conditions. A layered methodology synergistically combines linear programming with an advanced version of non-dominated sorting genetic algorithm-II. When applied to a real-world case study in Zhangbei, China, this approach identifies an optimal system capacity, leading to annual green power generation of 201.56 GW and a substantial reduction of over 173,703 tons of CO2 emissions. An economic analysis further reveals that each 1% reduction in CO2 emissions corresponds to a modest 1.7% increase in the system’s levelized cost of energy. Moreover, a comprehensive exploration of the impacts of various capacity parameters on the WSH-MES system’s performance is conducted. These insights offer invaluable guidance for the large-scale advancement of efficient renewable energy utilization and the attainment of decarbonization targets.

The Dirty Secret of SSDs: Embodied Carbon

Scalable Solid-State Drives (SSDs) have ushered in a transformative era in data storage and accessibility, spanning both data centers and portable devices. However, the strides made in scaling this technology can bear significant environmental consequences. On a global scale, a notable portion of semiconductor manufacturing relies on electricity derived from coal and natural gas sources. A striking example of this is the manufacturing process for a single Gigabyte of Flash memory, which emits approximately 0.16 Kg of CO 2 - a considerable fraction of the total carbon emissions attributed to the system. Remarkably, the manufacturing of storage devices alone contributed to an estimated 20 million metric tonnes of CO 2 emissions in the year 2021. In light of these environmental concerns, this paper delves into an analysis of the sustainability trade-offs inherent in Solid-State Drives (SSDs) when compared to traditional Hard Disk Drives (HDDs). Moreover, this study proposes methodologies to gauge the embodied carbon costs associated with storage systems effectively. The research encompasses four key strategies to enhance the sustainability of storage systems. Firstly, the paper offers insightful guidance for selecting the most suitable storage medium, be it SSDs or HDDs, considering the broader ecological impact. Secondly, the paper advocates for implementing techniques that extend the lifespan of SSDs, thereby mitigating premature replacements and their attendant environmental toll. Thirdly, the paper emphasizes the need for efficient recycling and reuse of high-density multi-level cell-based SSDs, underscoring the significance of minimizing electronic waste. Lastly, for handheld devices, the paper underscores the potential of harnessing the elasticity offered by cloud storage solutions as a means to curtail the ecological repercussions of localized data storage. In summation, this study critically addresses the embodied carbon issues associated with SSDs, comparing them with HDDs, and proposes a comprehensive framework of strategies to enhance the sustainability of storage systems.

Experimental research and energy saving analysis of an integrated data center cooling and waste heat recovery system

To better make use of the waste heat in distributed data centers, a new design of integrated waste heat recovery system that can meet different needs including heating for users and data center cooling is introduced. The system can switch among different operation modes including waste heat recovery mode, natural cooling mode, composite cooling mode and refrigeration mode based on the ambient temperature. The integrated waste heat recovery system is experimented in the enthalpy-difference laboratory, and the experimental results show well consistency compared with the modeling results. The operation strategies to switch among different modes are determined based on the experimental and modeling results. The paper introduced PUE (Power Usage Effectiveness) and ERE (Energy Reuse effectiveness) to comprehensively evaluate the cooling and energy reutilization effectiveness of the system. According to the evaluation result, the integrated waste heat recovery system has well performed energy effectiveness, environmental and economic effect. The ERE values of using the integrated waste heat recovery system in Chinese typical climate cities including Harbin, Beijing, Xi'an, Shanghai and Guangzhou are 0.87, 1.02, 1.04, 1.17 and 1.29 respectively. Using this system at 96 kW distributed data center instead of CRAC (computer room air conditioning) system can save 152.7 MWh electricity, 56.4 tons of standard coal, and 244.7 tons of CO2 emission in Beijing annually. The payback periods of this new system in different climate regions in China are all within 3 years.

Aquatic environment impacts of floating photovoltaic and implications for climate change challenges

With the aggravation of global warming and the increasing demand for energy, the development of renewable energy is imminent. Floating photovoltaic (FPV) is a new form of renewable energy generation. However, the impact of FPV on the aquatic environment is still unclear. By long-term empirical monitoring and data analysis, this paper reveals the shading effect of large-scale FPV power station on aquatic environment for the first time. The results show that: (1) Compared with the non-photovoltaic (NP) zone, FPV only significantly reduces the concentration of dissolved oxygen in the photovoltaic (P) zone. (2) The concentration of chlorophyll a, nitrate nitrogen and total phosphorus increase, while pH and ammonia nitrogen decrease. FPV only causes an effect of the same order of magnitude as the initial concentration, and has no significant adverse effects on the nutritional status of the water body at a coverage ratio less than 50%. (3) FPV has a cooling effect on the water body during the daytime and a thermal insulation effect at night, with the most pronounced impact on peak water temperature (Tw). The heating and cooling process of Tw in P zone usually lags behind the NP zone by 1–3 h. The diurnal fluctuation and vertical difference of Tw as well as the stability of water body are reduced under the shading of FPV, alleviating the influence of climate change on Tw and water body stratification. (4) If 10% of the water area larger than 1 km2 in China are used to develop FPV, more than 900 million tons of CO2 emissions can be reduced, and about 5 billion m3 water can be saved, which is significant in the context of climate change. In general, this paper provides a reference for the future aquatic environmental impact assessment of FPV and the formulation of related policies.

Digital twin-driven energy modeling of Hywind Tampen floating wind farm

This paper presents energy modeling of Hywind Tampen floating wind farm based on digital twin technology. Upon its completion, the Hywind Tampen wind farm is the largest floating wind farm in the World and the first floating wind farm to supply electricity for oil and gas fields. The wind farm is located about 140 km off the Norwegian coast with water depth between 260 and 300 m and consists of eleven wind turbines with a capacity of 8.6 MW each. Together with ten gas turbines, it will supply electricity for two oil and gas fields at the Norwegian Continental Shelf (NCS), namely the Gullfaks field with three platforms and the Snorre field with two platforms. In this paper, digital twins of the wind turbines and the oil platforms are created in Unity 3D. Energy from the wind farm is modeled from the first principle and is calculated using inputs from the historic weather data all year round. Simulation results show the wind farm can supply up to one-third of the total electricity needed by the oil and gas platforms almost constantly, which associated with reduction of 200,000 tonnes of CO2 emissions and 1000 tonnes of NOx emissions annually.

Thermodynamic and feasibility analysis of using diesel generator exhaust gases for ship main engine preheating at port periods

In this study, the feasibility and potential impact on fuel consumption of the proposed preheating system driven by diesel generator exhaust gas instead of steam to satisfy main engine pre-heating demands especially under port operation conditions have been analyzed according to the 1st and 2nd laws of thermodynamics. The proposed novel term named performance criteria (PC) and exergy efficiency (ε) values of the main engine preheating and cooling water systems of the Ro-Ro ship selected for the case study under the existing voyage and port operating conditions have been determined by written Matlab-2021a codes merging CoolProp-6.4.2 database with Python. It was determined that even at the lowest operating load of the diesel generator (25%), the exhaust heat energy would be sufficient to preheat the main engine with also reducing the fuel consumption. As a result, during the 12-hour port period, 22% of the boiler fuel consumption and 8% of the ship's fuel consumption can be saved. Accordingly, if a shipping company uses Mine Gas Oil as fuel, it will be able to achieve fuel savings of approximately US$ 32.000 on annual basis. Considering the fuel saving values, it has been determined that 1.016 tons of CO2 emissions for per port operation and 106 tons of annual CO2 emissions can be reduced. It was determined that, the PC and Ɛ values of the system decrease as the ambient temperature increases. In this context, there is a 7% decrease in the PC and a 5% decrease in the Ɛ for existing system and 8% decrease in the PC and a 2.5% decrease in the Ɛ for proposed system. It was also determined that the proposed new system is both physically and economically feasible and that the investment cost, which was determined to be in the range of US$ 30.000-US$ 35.000, can pay for itself after 1 year.

Analysis of the Energy Performance of a Retrofitted Low-Rise Residential Building after an Energy Audit

The main reason for this research is to support the Korean government building retrofitting program initiated to evaluate energy usage trends, propose energy-saving technologies, and focus on reducing the energy demand in residential buildings through energy efficiency improvement. This is achieved by assessing the energy saved after introducing a simple retrofitting measure to an existing residential building. The energy savings in the building were realized after collecting relevant data from the house occupants, analyzing electricity bills, and introducing energy conservation measures (ECMS), leading to an improvement in the energy performance of the building. The building envelope saved 2098 kWh and 6307 kWh of energy via the heating and cooling equipment with an initial incremental cost of USD 500, fuel cost savings of USD 306, and a simple payback of 1.6 years. The analysis takes the occupants 2.6 years to recoup the initial cost of USD 2400 invested with an electricity savings of 2144 kWh. Also, 3.3 tons of CO2 emissions per year were reduced, equivalent to 3.3 people reducing energy use by 20%. Finally, the actual and simulated data are almost the same for the consumption period, with only a slight difference in October and December, given 0.92 as the Pearson Correlation coefficients.

Feasible study on the sustainable and clean application of steel slag for abrasive waterjet machining

The rapid development of the global steel industry has led to a surge in steel slag. The resource utilization of steel slag has become a hot research topic in the solid waste industry. In this study, a new method of resource utilization of steel slag by replacing garnet with it for abrasive waterjet (AWJ) processing was presented for the first time. Typical brittle material marble and plastic material 6061 aluminum alloy were used as workpieces to evaluate the process performance of the method. The results show that the density, hardness, and surface shape of the steel slag meet the requirement of an ideal abrasive. Steel slag demonstrates comparable performance to the widely utilized garnet abrasive in terms of kerf width and roughness. Particularly, the cutting efficiency of steel slag per unit cost is more than 250% of garnet. Considering the price disparity between the two abrasives, the approach has the potential to reduce operational costs by 45% for AWJ factories, resulting in annual savings of approximately ¥60 million for the AWJ industry in China. Simultaneously, it holds the potential to save 1.549 × 105 GJ of energy and reduce 1.159 × 104 tons of CO2 emissions in the world annually.

Leveraging demand-capacity balancing to reduce air traffic emissions and improve overall network performance

Improvements in European air traffic management (ATM) constitute one of the key levers to reduce aviation emissions in the future to reach ambitious goals. In this paper, we evaluate the benefits of improved network-centric ATM with coordinated optimisation of capacity, delays, re-routings and emissions vs the present fragmented ATM which has generated high delays and extensive re-routing due to sub-optimal capacity provision. In addition, we analyse the impact on flight efficiency of a novel trajectory-independent airport-pair charging scheme, which makes shortest routes the cheapest for Airspace Users (AUs), which is not always the case with the current charging scheme in Europe. We test and evaluate proposed changes in ATM using a case study based on real data covering 3,000–4,000 flights in large parts of Western European airspace. We find that network-centric ATM can reduce variable costs borne by AUs by 21% and in particular re-routing cost (and associated emissions) by almost 64%. Furthermore, airport-pair charging can save almost 11% of costs for AUs and up to 320,000 tons of CO2 emissions — if accompanied by adequate capacity changes that reflect the shift in demand towards shorter trajectories. We conclude that various stakeholder initiatives to reduce the fragmentation in European ATM and to move towards a more network-centric approach have merits and should be pursued by the policy makers.

Electrosynthesis of ethylene glycol from C1 feedstocks in a flow electrolyzer

Ethylene glycol is a widely utilized commodity chemical, the production of which accounts for over 46 million tons of CO2 emission annually. Here we report a paired electrocatalytic approach for ethylene glycol production from methanol. Carbon catalysts are effective in reducing formaldehyde into ethylene glycol with a 92% Faradaic efficiency, whereas Pt catalysts at the anode enable formaldehyde production through methanol partial oxidation with a 75% Faradaic efficiency. With a membrane-electrode assembly configuration, we show the feasibility of ethylene glycol electrosynthesis from methanol in a single electrolyzer. The electrolyzer operates a full cell voltage of 3.2 V at a current density of 100 mA cm−2, with a 60% reduction in energy consumption. Further investigations, using operando flow electrolyzer mass spectroscopy, isotopic labeling, and density functional theory (DFT) calculations, indicate that the desorption of a *CH2OH intermediate is the crucial step in determining the selectively towards ethylene glycol over methanol.

Performance analysis and optimization of a coupled open and close liquid desiccant sorption system using LiCl solution

The efficient utilization of low-grade heat for air conditioning has been a topic of world concern, especially for low-grade heat below 80℃. In this study, a novel coupled open and close liquid desiccant sorption system driven by 70 ∼ 80℃ low-grade heat is proposed. This system employs a generator to provide strong solution for both the dehumidifier and absorber, achieving the air temperature and humidity independent control to reduce driving temperature and enhance system performance. A mathematical model is developed to simulate the proposed new system, and a comparative analysis is conducted with a traditional combined absorption refrigeration with liquid desiccant dehumidification system using LiCl solution. It is found that the COP of the new system is 0.76, which is higher than 0.65 of the traditional system when the hot water temperature is 75℃, the reason is that the new system avoids the sensible heat consumption of regenerated air which accounts for 17% of the total heat consumption in the traditional system. Furthermore, it is observed that the outlet concentration difference between the absorber and dehumidifier exists in the new system. The cycle is optimized to improve the concentration difference, leading to a 5.5% increase in the COP. After that, economic performance analysis shows a payback period of 2.65 years for a 150 kW cooling capacity system, with a reduction of 86.6 tons of CO2 emissions per year due to the decrease in power consumption.

The social value of offsets.

It is unclear how much carbon should be stored in temporary and risky offsets to compensate one ton of CO2 emissions. Here we cast the social value of an offset (SVO), measured in terms of economic damages avoided, as a well-defined fraction of the social cost of carbon reflecting offset duration, and risks of non-additionality and failure. The SVO reflects the value of temporary storage, and overcomes shortcomings in the climate science and economics of previous contributions1-4. The SVO is policy relevant. An efficient net-zero policy will consist of offsets if their SVO/cost ratio exceeds the benefit/cost ratio of alternatives. The SVO yields an indicator of the equivalence of offsets to permanent carbon storage measured by the ratio of the SVO to the social cost of carbon. We provide a matrix of equivalence factors for different risks, permanence and climate scenarios. Estimation yields a rule of thumb: one offset sequestering one ton for 50 years is equivalent to between 0.33 and 0.5 tons permanently locked away. Equivalence offers a means of replacing perpetual offset contracts by simpler, easy to monitor short-term contracts, has applications to carbon life cycle analysis5 and the valuation of carbon debts6, and can be the basis of comparing offsets of different qualities in the voluntary and compliance markets.