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This study evaluated the HVAC energy end-use performance of 39 motorized insulating interior shades installed on the 37th floor of a high-rise commercial building in Chicago, Illinois, USA operating under realistic conditions. The study lasted for 44 weeks (spanning all four seasons). Three motorized control strategies of On-schedule, Dynamic ('smart'), and Manual, as well as one typical mini-blind Baseline control strategy, were developed and implemented to assess energy performance of the interior automated shades. The three controlled motorized control strategies are compared to the Baseline strategy as a reference. The results showed that the motorized interior insulating shades reduced daily energy consumption by up to 20.5 % with the automated control strategy, which includes the Dynamic and On-schedule strategies, and up to 11.8 % without the control, which includes only the Manual control strategy. A weather normalized energy consumption analysis, which translates the actual energy consumption values to typical year energy consumption values, indicates that the automated shades are expected to save 20–35 % in energy consumption compared to the Baseline strategy. The calculated payback period for a defined "best practice" scenario is 21.9 years considering an initial electricity rate of $0.0897/kWh in 2021. Accounting for a future utility incentive program that provides a one-time rebate of $0.25/kWh savings during the installation, the simple payback period for the "best practice" scenario was estimated to be 12.3 years with the 2021 electricity rate and 4.4 years with assumptions for future electricity rates. Results suggest that the shades are a promising energy efficiency measure, especially for buildings for which building envelope retrofits or new construction are cost prohibitive or infeasible. • Evaluated performance of motorized insulating shades in under realistic conditions. • Developed and tested three motorized control sequences to adjust shade positions. • Showed the motorized shades can reduce daily energy consumption by up to 20.5 %. • Motorized insulating shades are a promising energy efficiency measure. [ABSTRACT FROM AUTHOR]

In this study, to investigate the dynamic characteristics of automotive thermoelectric generators (ATEGs), a detailed transient energy, exergy, and economics analysis is conducted for a novel ATEG with heat pipes and a traditional ATEG for the first time. Moreover, this study provides a comprehensive analysis of the discrepancies between the results derived from the steady-state model and the transient model. To achieve this objective, a transient CFD and thermal-electric hybrid numerical model is established to accurately predict the transient characteristics of the ATEG. Results indicate that the novel ATEG achieves average improvements of 60.99 % in output voltage and 32.98 % in output power over the traditional ATEG during a complete driving cycle. Additionally, the steady-state model overestimates the performance of the ATEG. The exergy efficiency is minimally impacted by the use of heat pipes and fluctuations in transient exhaust heat, consistently remaining around 19 % for both ATEGs. In a single driving cycle, the novel and traditional ATEGs generate 0.0442 kWh and 0.0307 kWh of electricity, respectively. The cost payback periods are 2.86 years for the novel ATEG and 1.83 years for the traditional ATEG, and it is found that using steady-state models for economic analysis may underestimate the cost payback period. This study successfully bridges the research gap in energy, exergy, and economic analyses under transient conditions, offering valuable insights into the dynamic properties of ATEGs. • A transient energy, exergy and economic analysis of ATEGs is performed. • Dynamic performance differences between two ATEGs under driving cycles are compared in detail. • A comparison is made between the calculations of steady-state and transient models. • The exergy efficiency is largely unaffected by the transient fluctuating heat source. • Steady-state model overestimates ATEG's performance, underestimating the cost recovery period. [ABSTRACT FROM AUTHOR]

A prototype of a multistage cooling system with a cooling capacity of 20 kW is assembled and studied. The traditional single-stage system is split into two sub-systems according to the temperature level, which reduces the temperature difference and irreversible heat transfer loss, and further improves the system's energy efficiency. The system mainly features three modes including free-air cooling, refrigeration-based cooling and waste heat recovery, which can achieve efficient cooling while capable of recovering the waste heat to the surrounding heat users. The efficiency of the proposed cooling and heat recovery system was assessed by measuring its energy reuse effectiveness (ERE). The energy savings and environmental benefits of the system were analyzed across five cities in China, each representing different climates. Results indicate that the system achieved an ERE of 0.91 in Beijing, 38.9 % lower than the national average of the city. Additionally, an economic analysis showed a payback period of less than two years for the proposed system across all climates considered, which is 30 % shorter than that of a single-stage cooling system. • A multi-stage data center cooling system with waste heat recovery is proposed. • Temperature gradation reduces heat transfer temperature difference and irreversible loss. • Heat transfer performance of a 20 kW scale system is experimented and analyzed. • Energy Reuse Effectiveness in Beijing is 0.91, and payback period is within 2 years. [ABSTRACT FROM AUTHOR]

Hydrogel-based passive cooling emerges as a promising technology due to its high efficiency and low carbon footprint. It demonstrates the significant potential in decreasing the temperature of photovoltaic (PV) panels and boosting the power generation. However, the lack of a comprehensive theoretical model to clarify the cooling mechanisms has significantly blocked the applications of hydrogel-based PV cooling. In this work, a theoretical model integrating hydrogel structural characteristics with environmental impacts is presented, guiding the hydrogel design and assessing their global potential in PV applications. The results indicate that hydrogel PV cooling presents the encouraging prospects in low and mid-latitudes with a payback period of <5 years, but it exhibits the limited benefits in high-latitudes. Specifically, in low-latitudes such as Singapore, the application of hydrogel cooling leads to an annual average temperature drop of 10.2 °C, enhancing power generation by 6.28%. However, due to the low temperatures and limited solar radiation intensity in high-latitude regions, the power generation improvements are usually <3%, and the payback period extends to >45 years. The deployment of hydrogel PV cooling in high-latitudes should be evaluated carefully due to suboptimal cooling effects and the risk of freezing. Overall, this research establishes a theoretical foundation for the applications of hydrogel PV cooling and paves the way for its global deployment. • A theoretical model of hydrogel evaporative cooling for photovoltaic is proposed. • The proposed theoretical model can guide the design of hydrogel structures for photovoltaic cooling. • Hydrogel photovoltaic cooling achieves a 10.2 °C annual average temperature drop and a 6.28% power boost in Singapore. • Hydrogel photovoltaic cooling is efficient in both low and mid latitudes but less viable in high latitudes. [ABSTRACT FROM AUTHOR]

A significant challenge is to determine the specific services Battery Energy Storage System (BESS) should provide to maximize profits. This study investigates the most profitable markets and sizes of BESS with utility-scale solar Photovoltaics (PV) power plants using techno-economic analysis frameworks. The objective is to maximize profitability in energy and frequency markets, focusing on primary regulation and day-ahead markets for Sweden and Germany. The inputs are historical market prices and frequency data, as well as real measurement PV power data. The results show that adding a BESS to an existing PV park does not result in a lower payback period than if implementing a stand-alone BESS. However, the payback period differs between Sweden and Germany during 2023, i.e., being 1.8 and 6.8 years, respectively. This is explained by the lower frequency market prices for Germany compared to Sweden. The technical results indicate that the BESS energy capacity after 10 years of operation is approximately 83% for Germany, whereas, for Sweden, it is around 87%. Also, combining the operating of BESS on primary regulation and day-ahead markets showed a 6-year payback period with a slight increase in loss of energy capacity (from 83 to 80%) for Germany. Moreover, combining various PV-BESS sizes showed a discrepancy in economic and technical metrics for the BESS in Germany, resulting in a best-case of a 6-year payback period. A sensitivity analysis, which examines a drop in the frequency control prices in the future relative to 2023 (by 20% and 50% for Germany and Sweden, respectively), reveals an increase in the payback period for both countries by approximately 1 year. [Display omitted] • Utilized PV data, historical market prices, and frequency data for BESS feasibility. • In 2023, BESS payback is 2 years in Sweden, 7 years in Germany on primary regulation. • Adding energy arbitrage optimization to BESS in Germany reduces payback by 1 year. • Limited synergy between BESS operating on primary regulation combined with solar PV plants. • Limited energy reservoir requirement with solar PV plants description. [ABSTRACT FROM AUTHOR]

Multi-terminal DC distribution network is regarded as a promising solution to integrate DC loads, energy storages, and renewable generators with different voltage and current levels. However, the rapid over-current variation, large over-current magnitude, and widespread use of power switches make it difficult to ride through the power quality issues including DC voltage sags, swells, as well as second-order voltage ripples. To strengthen the fault ride-through capability, superconducting magnetic energy storage (SMES) and series-connected custom devices are expected as promising solutions. This paper proposes a SMES-based modular interline dynamic voltage restorer (MIDVR) for multi-line DC device protections. It is mainly comprised of N modular converters to realize the voltage sag and swell compensation capabilities and the second-order voltage ripple suppression, where all the modular converters share one power-supplying SMES. The working principle, control strategy, capacity estimation, and universal extension methodology of the SMES-MIDVR concept are presented and technically verified by a MW-class edge-data-center-based DC simulation network. A kW-class experimental SMES prototype is established and tested to prove the feasibility and practicability of the SMES-MIDVR. Finally, the techno-economic analysis shows that the static and dynamic payback periods are only 7.82 and 16.13 years in IDC damage ratio is 0.175, which proves the SMES-MIDVR has both technical and economic advantages in renewable-based multi-terminal DC distribution network. • A novel topology of superconducting magnetic energy storage (SMES) based modular interline dynamic voltage restorer (MIDVR). • SMES-MIDVR can share one SMES unit and protect multiple loads with different voltage and current levels. • A kW-class prototype is verified for its well-suppression capabilities of voltage sags, swells, and second-order ripples. • Varying-axial-gap optimization of magnet structure enhances 44.5% the SMES capacity. • SMES-MIDVR has both technical and economic benefits for multi-terminal DC distribution network protection. [ABSTRACT FROM AUTHOR]

In the current era of the world, electricity has become a basic need of every individual. Therefore, the global energy demand has doubled from 77 trillion kWh to nearly 155 trillion kWh since 1980. However, despite the rising energy demand in developing countries, the per capita energy consumption only grew by about 14% globally. It is mainly because of the rural and remote areas where grid supply infrastructure is unavailable or inaccessible. Therefore, a solar-based microgrid (MG) can be considered an alternative energy solution. These MGs with energy storage support can be considered a viable solution because of the intermittent nature of solar photovoltaic (PV). In this regard, this paper describes the design, development, and deployment of a solar rooftop microgrid (SRMG) at the commercial building of BITS Pilani, India. Further, a comprehensive economic analysis is performed using a novel method of levelized cost of energy (LCOE) and payback period, and the results are compared with the traditional method's results. In order to improve the reliability of the SRMG, a demand side management (DSM) strategy is developed and implemented. It can effectively cater the unbalance between load and generation by shifting the non-critical loads to unused solar PV generation hours. It was found from the results that a significant energy of BESS is conserved which is reflected by the high state of charge (SOC) value. The developed design, economic analysis, and proposed DSM make the SRMG an economical and reliable energy solution. • The solar rooftop microgrid (SRMG) is designed by considering rural and remote areas' economic and reliability constraints. • Economic viability of the SRMG is estimated using the novel method of levelized cost of energy (LCOE) and payback period. • A demand side management (DSM) strategy is developed and implemented on the deployed SRMG to enhance its reliability. [ABSTRACT FROM AUTHOR]

Photovoltaic thermal heat pump technology has outstanding cogeneration ability by utilizing renewable energy to be accepted as a decarbonization pathway in the residential sector. However, existing photovoltaic thermal heat pumps consume higher energy under better external heat source conditions. To address this problem, a novel direct-expansion photovoltaic thermal heat pump/power heat pipe compound cycle system for heating and power generation as well as refrigeration, whose core equipment was a photovoltaic thermal module with straggled honeycomb fluid channel pattern on the serpentine arrangement, was proposed, manufactured, and studied with the method of experiment. The thermoelectric performance was compared between the heat pump and power heat pipe cycle modes, investigated under typical weather conditions, and discussed in contrast to the literature. The results showed that the average photoelectric conversion efficiency and coefficient of photothermal performance of the PVT modules, as well as COP of the novel system were 10.6%, 51.0%, and 6.19, respectively, at the average ambient temperature of 27.0 °C, average solar radiation intensity of 581 W/m2 and water temperature of 18.3–55.6 °C. And daily average COP s of the novel system under sunny, cloudy, and overcast conditions were 15.12, 7.40, and 3.17, respectively. The conclusion drawn from the experimental results is that the COP of the novel system was 10.0%–60.0% higher than that in the literature under similar outdoor conditions. The payback period of the additional cost of the novel system compared with the existing direct-expansion photovoltaic thermal heat pump was within 2.5 years. The novel system represents a practical response to the need to achieve total decarbonization of the residential sector. • A novel photovoltaic thermal compound cycle system was proposed. • The average COP of the novel system for 21-day in summer was 6.19. • The COP at sunny, cloudy, and overcast conditions were 15.12, 7.40, and 3.17. • The COP of the novel system is 10–60% higher than that of literatures. • The payback period of additional cost of the novel system was within 2.5 years. [ABSTRACT FROM AUTHOR]

Hydrogen is one of the potential candidates to replace fossil fuels to meet net zero emissions target. This study reports a detailed techno-economic and environmental assessment of hydrogen production through ammonia decomposition. The case study is based on a multiple catalytic packed bed reactor with intermediate heating system. Aspen plus® and MATLAB® were linked to evaluate economic and environmental impact of the process. The process parameter like furnace temperature, flue gas recirculation, ammonia decomposition temperature, market ammonia supply pressure, ammonia decomposition pressure, hydrogen purification unit's pressure and equivalence ratio, and economic parameters of capital expenditure (CAPEX) and operating expenditure (OPEX) were considered. The overall thermal efficiency of the developed process is found to be 79%. The levelized cost of hydrogen (LCOH) is estimated and found to be 6.05 USD/kg of H 2 based on CAPEX and OPEX. A major contribution of up to 62.2% to LCOH comes from the price of feed Ammonia. Based on 25-year plant life with 10% discounted rate the plant is economically viable, with a return on investment of 23.7%, in a payback period of 3.58 years. Global warming potential of the process is also carried out. [Display omitted] • Techno-economic and environmental assessment on ammonia decomposition was carried out. • Overall thermal efficiency of H 2 production from NH 3 decomposition process is 79%. • LCOH of H 2 production from NH 3 decomposition process is 6.05 USD/kg of H 2. • Ammonia price alone contributes up to 62.2% of LCOH. • GWP analysis of H 2 production from NH 3 decomposition process is 0.66 kg of CO 2 /kg of H 2. [ABSTRACT FROM AUTHOR]

Highlights • Dynamic simulation model of a novel vehicle to net zero energy building layout. • System environmental and thermo economic analysis coupled with electric vehicle. • Investigation of the electric vehicle charging effects on the system performance. • The system is economically feasible only with a small capacity storage system. • Electric vehicle allows one a significant equivalent CO 2 emissions reduction. Abstract This paper analyses the energy, environmental and economic performance of a future scenario where electric vehicles are connected to efficient buildings powered by building integrated flat-plate photovoltaic/thermal collectors, equipped with electric energy storage. The produced renewable electricity and thermal energy are exploited for building electrical and thermal applications. The surplus of produced electricity is stored into the electrical battery and used to charge the electric vehicle. The proposed system is modelled and dynamically simulated within the TRNSYS environment, where special attention is paid to the design of suitable system control strategies, aiming at optimizing the exploitation of the solar energy for electricity and heating purposes. To this aim, a sensitivity analysis is also carried out to find out the optimal system configuration. A case study analysis, relative to the weather zone of Naples (South Italy), is conducted to evaluate the energy, economic and environmental feasibility of the investigated scenario. Simulation results show that, with respect to a reference system, a remarkable reduction of electricity from the grid is achieved, corresponding to a primary energy saving equal to 57.66%. A reduction of 51.63% of CO 2 emissions and a simple pay payback period equal to 11.64 years are achieved. [ABSTRACT FROM AUTHOR]

• We devise a model to site and size the vehicle-to-grid facilities in a microgrid. • We develop a scalable methodology to solve the proposed optimization model. • We conduct case studies on a 14 and 37-bus systems for a horizon of 5 years. • We assess the impact of uncertainty and technical parameters on the proposed plan. • We show that the vehicle-to-grid technology improves the economics of microgrids. In this paper, we propose a new optimization model for investment planning for Vehicle-to-Grid (V2G) technology in a microgrid. The V2G technology allows the microgrid to take advantage of temporal arbitrage in the electricity market, and hence, improve economic viability of electric vehicles. We present both a mathematical model and a custom solution methodology for this problem. The proposed stochastic model is a very large-scale mixed-integer nonlinear programming problem, and thereby, we develop an algorithm that provides high-quality solutions. A case study for 14-node and 37-node microgrid test systems for a planning horizon of five years is presented, and a thorough sensitivity analysis for effects of uncertainty, investors preferred payback period, market price fluctuations and electric vehicles arrival and departure rates is discussed. The simulation results show that investing in the V2G technology can considerably improve the long-term economics of the microgrid, but the obtained profit and the payback period can vary from one plan to another. [ABSTRACT FROM AUTHOR]

Highlights • Off-grid housing in different climates under current and future global warming climates. • Off-grid housing with PV battery only is not economically feasible in heating dominated regions. • PV battery systems hybridized with a petrol generator for off-grid housing become feasible. • Grid-connected net zero energy housing is more attractive than off-grid housing. Abstract This study evaluates the feasibility of off-grid operation of fully electric housing under current and future global warming climates through case studies using building simulations. The case studies were carried out for two house types with different sizes and construction materials, under two typical occupancy patterns (occupied full day and evening only), in seven cities chosen to be representative of a broad range of climates. The study examined three operational scenarios: off-grid operation using PV and batteries; off-grid operation with PV, battery and petrol generator; and grid-connected net zero energy operation. Results show that for the houses being powered by electricity only in warm and moderate climates, large PV battery systems are required to achieve off-grid housing using PV and batteries only, and that payback periods are longer than 15.8 years under current and projected future climates considering replacement cost of battery storage, and projected inflation, discount rate and electricity price escalation rate. Off-grid operation with PV and batteries is economically unviable in heating dominated regions. The study shows that when a PV battery system is hybridized with an on-site petrol generator, the payback periods can be reduced significantly, and it may become economically feasible to operate off-grid with PV, battery and generator for both house types under most occupancy scenarios in moderate and warmer climates, but may still not be economically viable in colder climates. The case study also demonstrates that a grid-connected net zero energy home is economically feasible for all seven cities studied, and more economically attractive than a fully off-grid house under both current and projected future climates, even without subsidies for solar feed-in tariffs. [ABSTRACT FROM AUTHOR]

This paper investigates the opportunity for a Battery Energy Storage System (BESS) to participate in multiple energy markets. The study proposes an offline assessment to calculate the maximum annual revenues to reach the optimum stack of services through deterministic simulations. The markets include wholesale energy markets (day-ahead and intraday), ancillary services (frequency regulation and reserve), and the capacity mechanism. The study case performed on the French markets shows that frequency services overperform the other markets, where the long-term capacity market has the least potential. Moreover, providing multiple services maximizes the battery's revenues, for example, participating in joint energy and reserve markets showed a 76% increase in annual profits. Furthermore, a novel operation approach was proposed to enhance the performance of these joint markets, by indirectly utilizing energy products as frequency reserves. The results demonstrate that the proposed formulation allows a revenue increase of ∼23% compared to the conventional framework for the provision of frequency regulation with BESSs. Additionally, the joint markets have been shown to be economically viable with 6.2 years payback period after considering battery degradation and depreciation cost. • Modeling of wholesale markets for energy, frequency services, and capacity. • Novel direct/opposite operation framework for joint energy and reserve markets. • Economical assessment of a storage system providing stacked services and products. • Sensitivity analysis of the activation ratio for frequency services on the revenues. [ABSTRACT FROM AUTHOR]

The use of renewable energy and storage systems in energy sharing communities relieves the strain on the grid and reduces the cost of electricity, making the design of community energy management strategies particularly important. In this paper, a shared energy storage operation strategy considering the time-of-use tariff is proposed for the grid-connected PV-BESS system of hybrid building community including factories, offices and dormitories. Aiming at maximizing the photovoltaic self-consumption ratio, minimizing the payback period and power transportation loss, the system is optimized by non-dominated sequencing genetic algorithm II to obtain the optimal battery capacity of each building under the designed strategy. The results show that when the total battery capacity of the community is determined, the photovoltaic power generation of each building and the building load are the main factors that affect the allocation of battery capacity, and the proportion of battery allocation in each building changes little when the values of other influencing parameters are changed. The photovoltaic array area of the building, the difference between peak and valley electricity price and the power input and output limits of the grid are the main factors affecting the optimal battery capacity and system performance. When the photovoltaic array area increases from 65% to 80%, the difference between peak and valley price increases from 0.52RMB/kWh to 0.82RMB/kWh, and the grid power output limit increases from 7500 kW to 9000 kW, the total optimal battery capacity is increased by 9.8%, 20%, 2.2%, the corresponding payback period is increased by 4%, 3.1%, 2%, the photovoltaic self-consumption ratio is increased by 3.3%, 1.9%, 0.2%, and the electricity transportation loss is increased by 6%, 21%, 2.4%, respectively. On the contrary, when the grid power input limit increases from 5500 kW to 7000 kW, the optimal total battery capacity, the corresponding payback period, photovoltaic self-consumption ratio, and power transport loss are reduced by 2.8%, 2.5%, 0.3% and 3.3%, respectively. This study provides theoretical guidance for community battery capacity optimization and energy scheduling design under the peak-valley policy of power grid. • A shared energy storage operation strategy considering the TOU tariff is established. • Considering economy, technology and environmental protection, multi-objective optimization of the system is carried out. • A mixed community model is established to analyze the factors affecting the allocation of battery capacity. • The influence of four important factors on the optimal battery capacity and system performance is analyzed. [ABSTRACT FROM AUTHOR]

The light-duty vehicle market has seen some adoption of hybrid electric vehicles that is not reflected in the heavy-duty market. The major challenges associated with the heavy-duty segment are: (i) greater emphasis on economic viability, (ii) reluctance to take on risk associated with new technologies, and (iii) numerous diverse applications that preclude a one-size-fits-all approach to hybrid-electric powertrain design. To overcome these challenges, a model-based framework is required that enables the exploration and optimal design of powertrain architectures for diverse applications while capturing the impact of hybridization on the economics of ownership under different economic scenarios. This paper demonstrates such a framework that incorporates powertrain simulation and battery degradation models to predict fuel consumption, electrical energy consumption, and battery replacements. These results are combined with economic assumptions to enable the exploration of a large design space (which spans powertrain design & control variables, noise variables, and economic scenarios) from a total cost-of-ownership perspective to provide better insights to vehicle integrators, component manufacturers, and buyers of heavy-duty hybrid electric vehicles. The methodology is applied to series plug-in hybrid electric and extended-range electric powertrain architectures for medium duty truck applications. The results show that under the assumptions made, economically favorable solutions for series plug-in hybrid electric medium-duty trucks exist in the 2020 time-frame for the NY Composite Truck drive cycle, while for the HTUF Refuse Truck and HTUF Class 6 P&D Truck drive cycles, feasible solutions are not obtained until 2025 and 2030 time-frames respectively. [ABSTRACT FROM AUTHOR]

• Uncertainty-based optimal energy retrofit methodology is developed for building heat electrification. • Energy flexibility and climate adaptability are taken into account. • The revenue from smart grid accounts for 1.1% of total cost savings. • 88% lifespan carbon emission reduction is achieved with an average payback period of around 3 years. • Retrofitted air-source heat pumps can mostly meet the future cooling demand in light of global warming. To reach net zero emissions by 2050, the UK government relies heavily on heat degasification in buildings by using heat pump technology. However, existing buildings may have terminal radiators that require a higher operating temperature than what heat pumps typically provide. Increasing the size of radiators and thermally insulating building envelopes could be a potential solution, but the feasibility of these practices is uncertain due to space constraints and high retrofit costs. This study investigates the feasibility and potential benefits of incorporating air-source heat pumps into existing gas boiler heating systems to meet heating demands. The proposed probabilistic optimal air-source heat pump design method enhances energy flexibility and climate adaptability, taking into account a wide range of uncertainty sources and multiple flexibility services (e.g., energy and ancillary services). Heating systems of three educational buildings at the University of Cambridge are used as a testbed to assess and validate the effectiveness of the proposed method, under future climate scenarios and projected decreases in heating demand due to climate change. Results indicate that the best retrofit alternative of the hybrid heating system reduces carbon emissions by 88%, total costs by 54% over its lifespan, and has an average payback period of around 3 years. Air-source heat pumps can meet the majority of the heating demand (around 80%) with gas boilers used for "top-up" heating during high demand. Furthermore, air-source heat pumps' design capacity can fulfil future cooling demand even if retrofit optimization is initially focused on meeting heating needs. [ABSTRACT FROM AUTHOR]

• The increased flexibility and economic benefit provided by P2H integration is assessed on the DA spot market and balancing market. • The increased profitability of P2H investment is evaluated in terms of net present value and payback period. • Key factors influencing the economics of P2H are identified and their impacts are quantified. Integrating power-to-heat (P2H) assets in combined heat and power plants (CHPs) is an attractive option, which can improve the flexibility in CHPs. This paper compares the potential benefits of integrating an electrical boiler (EB) and a heat pump (HP) in a CHP from providing flexibility services in both the day-ahead market and the frequency regulation market. An optimization model is developed for the operation of P2H assets and the CHP to maximize the profit. A case study is carried out using the data of a real CHP and electricity prices of Nord Pool. It is found that when an EB or a HP is integrated, the annual profit of the studied CHP from providing frequency regulation can be increased by 3.1 % (EB) or 27.7 % (HP) respectively compared to the CHP without P2H. Despite the high capital cost, a HP can increase the net present value up to 21.8 %, and achieve a payback period of 3 year, which are better than an EB (0.8 % and 5 year). Sensitivity analysis shows that prices of fuel and electricity have significant impacts on the net present value and payback period for the integration of P2H assets. Even though the increase of the fuel price decreases the NPV, it can lead to a decline in the payback period. Meanwhile, the increase of the electricity price results in a large growth in the profit and NPV, but a big reduction in payback period. [ABSTRACT FROM AUTHOR]

The hybridization of middle-temperature solar heat with traditional coal-fired power plants has profound and realistic implications for China. Most solar hybrid power plants, which differ from solar-only power plants, are not designed to include a thermal storage system to maintain system performance at nominal conditions during off-design solar radiation periods. Thus, a proper solar field size is an important design parameter. An excessively large field is partially useless under high solar irradiance, whereas a small field mainly reduces the work output and leads to the poor utilization of invested capital. This paper presents an economic optimization of the solar multiple (SM) for typical solar–coal parabolic trough plants with different unit scales (200–600 MW). The thermal performance for each solar hybrid power plant demonstrates that the methods to calculate the annual solar electricity produced with SM varies. Once the annual electric energy generation is identified, the levelized cost of energy (LCOE) and payback period (PP) for each case can be calculated. Thus, the optimized SM values yielding a minimum LCOE value or PP can be obtained. Furthermore, the influences of local solar radiation resources and turbine operation load conditions on the economic optimization of a system are estimated. Results indicate that the optimization of the solar field size is promising for the economic improvement of a solar–coal hybrid system. The results may also provide a theoretical reference for investors and government officials in designing a solar–coal hybrid project. [ABSTRACT FROM AUTHOR]

This paper documents the magnitude of energy savings achievable in the field by retrofitting existing packaged rooftop air conditioner and heat pump units (RTUs) with advanced control strategies not ordinarily used for RTUs. A total of 66 RTUs on 8 different buildings were retrofitted with a commercially available advanced controller for improving operational efficiency. The controller features enhanced air-side economizer control, multi-speed fan control, and demand-controlled ventilation. Of the 66 RTUs, 18 are packaged heat pumps and the rest are packaged air conditioners with gas heat. The eight buildings cover four building types and four climate conditions. Based on the performance data collected for approximately 1 year, the normalized annual energy consumption savings ranged between 22% and 90%, with an average of 57% for all RTUs. The average fractional savings uncertainty was 12% at 95% confidence level. Normalized annual electricity savings were in the range between 0.47 kW h/h (kW h per hour of RTU operation) and 7.21 kW h/h, with an average of 2.39 kW h/h. RTUs greater than 53 kW and runtime greater than 14 h per day had payback periods less than 3 years even at electricity price of $0.05/kW h. [ABSTRACT FROM AUTHOR]

This paper examines the cost-effectiveness of subsidies (feed-in tariffs and renewable energy credits) paid for by electricity consumers to support the uptake of roof top photovoltaic (PV) systems by households in Australia. We estimate annual payback periods, and then regress these against the actual uptake of household PV and associated emission reductions, creating a relationship not apparent in other research. Sensitivity analysis reveals that the declining cost of PV panels had most impact on PV uptake followed by feed-in tariffs, renewable energy credits and the increasing cost of household electricity tariffs. Our modelling shows that feed-in tariffs were higher than necessary to achieve the resultant levels of PV uptake and that the low cost of PV panels and comparatively high electricity tariffs are likely to result in a continuing strong uptake of household PV in Australia. Our modelling shows that subsidies peaked in 2011 and 2012, with payback periods of three to four years, having since increased to five to six years. Emission reduction costs are expected to reduce from over AU$200 per t CO 2 e in 2013 to between AU$65 and AU$100 per t CO 2 e in 2020. Household PV reduced Australia’s emissions by 3.7 million t CO 2 e in 2013 (1.7% of Australia’s total emissions) and is expected to reach eight million tonnes (3.7% of Australia’s total emissions) by 2020. [ABSTRACT FROM AUTHOR]

Concentrating solar power is an important technological option to gradually increase the share of energy produced by renewable energy sources. Central power towers and parabolic trough collectors, are currently the most mature technologies globally installed. While the former technology requires less land area to produce the same power output, the latter operates at lower temperatures thereby requiring less demanding materials. In this paper, we investigate by dynamic modeling the potential of both technologies in the same plant configuration. We find more stable day-to-day annual power profile for a configuration of a 29 MWe tower and 25 MWe of north–south oriented parabolic trough collectors compared to single technology plants. This results in a higher maximum capacity factor of 18% at 925 W/m 2 direct normal irradiance and discounted payback of 9 years at a cost of electricity of 248 Euro/MWh compared to a standalone plant based on parabolic trough technology. In this way, the advantages of both concentrating technologies can be utilized and aid towards wider utilization of solar energy. • Assessment of power plant based on combined solar power tower and parabolic trough collector technologies. • Increased day-to-day performance by concurrently utilizing the collecting efficiencies of both technologies. • Optimum tower-to-trough ratio was found at 29/25 MWe for a case study plant providing at least 50 MWe. • 9 years discounted payback period of the combined power plant compared to 15 years of the north–south oriented trough-only. [ABSTRACT FROM AUTHOR]

In the context of a rapid and massive deployment or renewable energy and in particular solar photovoltaic, it is necessary to develop methods and tools to guide this deployment. To this end, this work proposes a multicriteria approach for evaluating the suitability of a building to be equipped with photovoltaic (PV) systems (PV suitability). In the present case, technical (roof complexity), economic (payback period), environmental (CO 2 reduction), energetic (self-consumption), as well as social (heritage constraint) criteria are considered. These criteria are evaluated for each building of the Greater Geneva Agglomeration (GGA), a cross-border French–Swiss territory of nearly 270 000 buildings. A multicriteria method, ELECTRE TRI, makes it possible to sort these buildings into three categories, A, B, and C, that correspond to "very high," "high," and "moderate" PV suitabilities, respectively. Large differences are observed within the 210 municipalities of the GGA since some of them have almost no A-ranked buildings whereas others comprise more than 70% of these buildings. It is shown that, by prioritizing the A-ranked buildings, almost 50% of the annual electricity consumption of the Geneva Canton could be produced by PV systems. Finally, the method developed here offers a decision-aiding tool that could be used at a territory scale to achieve energy transition goals in terms of solar PV deployment. • Large-scale evaluation of the suitability of buildings to be equipped with photovoltaic systems (PV suitability). • Simple labeling of PV suitability: A (very high), B (high), C (moderate). • Multidisciplinary and multicriteria approaches considering social, economic, energetic, environmental, and technical criteria. • A cross-border territory (data from two countries, three administrative regions, 270 000 buildings). • Decision support for massive urban deployment of PV systems. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Motor vehicles represent one of the widely owned assets in the US. A vehicle’s ownership cost includes fixed expenses to purchase and own the vehicle and variable costs to use and operate the vehicle. Policymakers, analysts and consumers are interested in understanding the total ownership costs of various vehicle types and technologies so as to understand their relative consumer preference and valuation. Plug-in hybrid electric vehicles are an advanced technology vehicle that is presently in limited production, but whose relative cost of ownership is not well-defined. A few studies have attempted to calculate the costs and benefits of PHEVs but none consider the cost and benefits of PHEVs at a level of detail comparable to what has been performed for other vehicle technologies. In order to understand the costs and benefits of PHEVs purchase and use, this study constructs a comprehensive ownership cost model. The model is then used to analyze different PHEV designs within four vehicle classes. This study then performs a sensitivity analysis to understand the sensitivity of total ownership cost and payback period to model parameters and the modeled components of ownership costs. Results show that a more comprehensive PHEV ownership cost model has a lower net cost of ownership than studies to date, resulting in a shorter payback period and higher consumer preference. [Copyright &y& Elsevier]

Abstract: Photovoltaic (PV) is one of the promising solar energy applications. Measured data can give the realistic performance of PV systems under actual operating environments for product selection and system design. This paper studies a grid-connected PV system installed in an institutional building. Technical data including available solar radiation and output energy generated were systematically recorded and analyzed. The performance of the PV system is elaborated in terms of energy, environmental and financial aspects. Feed-in-tariff (FIT) schemes with high electricity selling price can encourage the deployment of PV system. The monetary payback period (MPBP) for the PV system was computed to be 72.4years when the electricity buying price is equal to the electricity selling price. If carbon trading was considered, the payback was shortened to 61.4years. The embodied energy payback period (EEPBP) was estimated to be 8.9years. The findings would be useful for planning grid-connected PV installations and applicable to other spaces with similar architectural layouts. [Copyright &y& Elsevier]

Abstract: Energy recovery from flue gases in thermal treatment plants is an integral part of municipal solid waste (MSW) management for many industrialized nations. Often cogeneration can be employed for both enhancing the plant profitability and increasing the overall energy yield. However, it is normally difficult to justify traditional cogeneration in tropical locations since there is little need for the heat produced. The main objective of this article is to investigate the opportunities and potentials for various types of absorption technologies driven by MSW power plants for providing both electricity and cooling. Results show that cogeneration coupling with thermally driven cooling is sustainably and economically attractive for both electricity and cooling production. The thermally driven cooling provides significant potential to replace electrically driven cooling: such systems are capable of providing cooling output and simultaneously increasing electricity yield (41%). The systems are also capable of reducing the fuel consumption per unit of cooling in comparison with conventional cooling technology: a reduction of more than 1MWfuel/MWcooling can be met in a small unit. MSW power plant coupled with thermally driven cooling can further reduce CO2 emissions per unit of cooling of around 60% as compared to conventional compression chiller and has short payback period (less than 5years). [Copyright &y& Elsevier]

Abstract: Combined heating and power (CHP) systems may be considered for installation if they produce savings over conventional systems with separate heating and power. For a CHP system with a natural gas engine as the prime mover, the difference between the price of natural gas and the price of purchased electricity, called spark spread, is an indicator as to whether a CHP system might be considered or not. The objective of this paper is to develop a detailed model, based on the spark spread, that compares the electrical energy and heat energy produced by a CHP system against the same amounts of energy produced by a traditional, or separate heating and power (SHP) system that purchases electricity from the grid. An expression for the spark spread based on the cost of the fuel and some of the CHP system efficiencies is presented in this paper as well as an expression for the payback period for a given capital cost and spark spread. The developed expressions allow determining the required spark spread for a CHP system to produce a net operational savings over the SHP in terms of the performance of system components. Results indicate that the spark spread which might indicate favorable payback varies based on the efficiencies of the CHP system components and the desired payback period. In addition, a new expression for calculating the payback period for a CHP system based on the CHP system capital cost per unit of power output and fuel cost is proposed. [Copyright &y& Elsevier]

Abstract: This paper discusses specific models and analyses to select the best cogeneration planning solution in the presence of uncertainties on a long-term time scale, completing the approach formulated in the companion paper (Part I). The most convenient solutions are identified among a pre-defined set of planning alternatives according to decision theory-based criteria, upon definition of weighted scenarios and by using the exceeding probabilities of suitable economic indicators as decision variables. Application of the criteria to a real energy system with various technological alternatives operated under different control strategies is illustrated and discussed. The results obtained show that using the Net Present Cost indicator it is always possible to apply the decision theory concepts to select the best planning alternative. Other economic indicators like Discounted Payback Period and Internal Rate of Return exhibit possible application limits for cogeneration planning within the decision theory framework. [ABSTRACT FROM AUTHOR]

Abstract: A model for a ground-source heat pump (GSHP) fitted with a variable-speed compressor was developed. A frequency inverter (FI) was used to modulate the GSHP capacity for improving the part-load performance of the system. Year-round dynamic simulations were made using TRNSYS for a general office based on the weather conditions in Hong Kong (HK), Kunming (KM) and Beijing (BJ). Different control schemes for the part-load control were tried and the results compared. It was found that the adoption of a variable-speed part-load control to the GSHP in both the cooling and heating mode operations was better. A reduction in the compressor energy input by minimum 27% could be achieved although a slight increase in the borefield fluid circulating pump energy consumption was inevitable. The peak borefield fluid temperatures were also reduced which allowed the borehole lengths to be shortened by at least 4% and the initial cost lowered accordingly. An economic analysis indicated that with the reduced borehole lengths, the payback periods were no longer than 0.4months. This highlighted the merit of employing a variable-speed part-load in a GSHP system as the initial cost might also be saved besides the running costs under a wide range of climatic conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A Multi-generation energy hub is proposed based on power, heat, cold, and hydrogen. • Strong eco-exergy and enviro-exergy analyses are presented. • Optimal operating conditions are sought using a robust multi-objective optimization. • Optimal outputs: 21.42 MW power, 26.81 MW heat, 8.89 MW cold, and 11.96 kg/h hydrogen. • The payback period is approximately 5 years at the optimal conditions. In this study, a new configuration of a multi-generation energy system is proposed based on waste heat recovery from a regenerative gas turbine cycle (as the driver cycle) for running a district heating heat exchanger, a Rankine cycle, an ejector refrigeration cycle, and a proton exchange membrane electrolyzer cycle. In the first phase of the study, a thorough parametric model of the system is developed in EES software based on the eco-exergy and enviro-exergy analyses. The second phase is focused on the optimal operation of the system utilizing a robust multi-criteria optimization in Matlab software. Results of the parametric study showed that: (i) the share of fuel, capital, and environmental penalty costs rates in the system's total cost rate are respectively 46.95%, 29.38%, and 23.67%, at the optimal conditions. (ii) although the design variables of the bottoming cycles are not effective on the amount of pollutants, they have a significant effect on the enviro-exergy assessment criterion. The optimal system productions are included 21.42 MW of power, 26.81 MW of heat, 8.89 MW of cold, and 11.96 kg/h of hydrogen. The energy and exergy efficiencies are found to be 89.75% 35.21%, respectively. In such conditions, the payback period is approximately 5 years, demonstrating the economic feasibility of the proposal. Recovering the waste heat of conventional cycles to develop an energy production hub with minimal energy loss is one of the most important challenges in the energy matrix and relying on the results of the present study, it can be concluded that the proposed system has done this task well. [ABSTRACT FROM AUTHOR]

• Three LCPV panels were fabricated and tested at Brunel's outdoor test facility. • Performance indices such as energy output and payback period have been presented. • LCPV systems were compared against the flat PV systems in terms of energy output. • The best LCPV system for the UK's climate is presented. Low concentrating photovoltaic (LCPV) systems offer viable solution for generating higher energy output per unit cell area compared to a typical flat PV panel, making them potential candidates for building retrofit. However, the best LCPV geometry for a given location is yet to be identified. The current study investigates the technical, economic and environmental feasibility of three geometrically equivalent LCPV designs installed at a building within Brunel University London (UK). The studied LCPV systems comprised of Asymmetric Compound Parabolic Concentrating (ACPC), Compound Parabolic Concentrating (CPC) and V-Trough optical concentrators with the post-truncation geometric concentration ratios of 1.53, 1.46, 1.40 respectively. The performances of the prototypes have been monitored every 15 min over 10 months and analyzed on hourly, daily, and monthly basis. Performance parameters such as reference yield, array yield, performance ratio, electrical conversion efficiency and the generated energy output per unit area have been derived and presented. Payback periods have been estimated in two separate scenarios. Measurements have showed that the ACPC integrated LCPV achieved the highest annual optical efficiency generating the highest amount of electrical energy per unit cell area of 246.2 kWh/m2 compared to CPC-LCPV, V-Trough-LCPV and conventional flat modules which produced 224.6 kWh/m2, 196.1 kWh/m2 and 185.4 kWh/m2 respectively. One particular conclusion of the study is that the ACPC based LCPVs perform better in locations where diffuse component of solar radiation is predominant as in the case of the UK. Consequently, ACPC based LCPV modules are recommended for the building retrofit in such locations. [ABSTRACT FROM AUTHOR]

• Energy investment of prosumer industrial SMEs is analysed considering costs trends. • A multiple-year methodology is applied with weekly pattern optimisation. • This framework allows to make energy investments with economic evolution awareness. • An automotive industry case willing to invest in new energy equipment is studied. • The results expose the suitability of industrial SMEs for an active energy role. The market is searching for solutions to reduce emissions in the energy sector by increasing the consumer efficiency and flexibility and integrating renewable sources. Prosumers are suited to this role and are increasingly considered crucial to any such solution. Small-and-medium enterprises (SMEs) that need to upgrade their energy infrastructure, due to equipment obsolescence or external pressures to adopt greener technologies, face difficulties in integrating new energy management strategies given the investment required and the payback periods. Industrial SMEs traditionally seek to make on-off investments with fast returns, exploiting the obtained equipment for its whole lifetime. Therefore, this paper presents a novel methodology to determine the optimal sizing and operation of the energy infrastructure for an industrial SME transitioning to a prosumer model to improve its economic perspectives, considering the exploitation of the infrastructure for its complete lifetime. The energy and economic profiles of SMEs are analysed and their energy infrastructure modelled in order to define the sizing and operation optimisation problem. Operation of the equipment is optimised considering weekly cycles along multiple years, obtaining the net present value of the investment. The proposed methodology, which employs direct search and linear programming techniques, enable industrial SMEs to undertake informed energy investment actions. A real manufacturing plant is described, characterized and used as the basis for a case study. The results show the economic feasibility of installing new energy equipment in SMEs, obtaining payback periods less than five years and final investment value of more than ten times the initial expense. [ABSTRACT FROM AUTHOR]

• The decision-making framework streamlines emission-neutral microgrid deployment. • A novel price-based demand shifting technique is developed to contribute energy savings. • A decomposition approach is employed to decouple the investment and operation problems. • Challenges and solution schemes for emission-neutral microgrids are discussed. • Financial feasibility of microgrid projects with green resources is explored and verified. Energy and global climate change crises are correlated issues since energy generation currently contributes to nearly 40% of global greenhouse gas emissions, and inevitably the escalating energy demand realization exacerbates the ongoing undesirable circumstances. As a viable solution against the concerns above, microgrid deployments with low-emission on-site resources have been receiving increasing attention from power decision-makers. Thus, this study scrutinizes the technical and financial sustainability of deploying a net-zero emission multi-carrier microgrid and determines the optimal generation configurations. Besides, the proposed emission-neutral multi-carrier microgrid model provides insights into the economic prominence of renewable energy incentives together with regulations for the short-term deployment of green resources. The objective of the proposed model is to minimize the multi-carrier microgrid deployment costs associated with the investment, operation, maintenance, energy demand shifting, monthly peak demand charge, emission, and reliability. Furthermore, load prioritization and a novel demand shifting of demand response schemes are propounded to maintain at least the continuous flow of energy for high-prioritized loads. The customer multi-carrier microgrid deployment problem is disintegrated into an investment master problem and an operation subproblem. The results indicate that notable electrical peak mitigation of about 7–23% is procured by employing the demand response scheme. Furthermore, the sensitivity analysis illustrates that renewable penetration of 30% along with dispatchable resources is required to procure the targeted share of green resources within microgrids. Finally, the economic and environmental merits of the proposed emission-neutral multi-carrier microgrid are ensured with savings and the discounted payback period of 131% and 3.977 years, respectively. [ABSTRACT FROM AUTHOR]

Liquid air energy storage (LAES) is increasingly popular for decarbonizing the power network. At off-peak time, ambient air after purification is liquefied and stored; at peak time, the liquid air is discharged to generate power. One of the key challenges for the LAES system is the lower economic benefit as peak electricity is usually the only source of income, leading to a longer payback period of ~15 years. To address this issue, this paper, for the first time, proposes a multifunctional LAES system, which not only generates peak electricity but also provides pure oxygen and heating. The proposed system is composed of an air separation unit (ASU), a nitrogen liquefaction unit (NLU) and a power generation unit (PGU). Thermodynamic and economic analyses are carried out on the proposed system. Compared with the baseline LAES system (NLU + PGU), the multifunctional LAES system has a lower round trip efficiency of ~0.39 due to the extra electricity consumption by the ASU. However, it shows a much better economic performance with additional benefits from pure oxygen and heating. In a project life-span of 30 years, the multifunctional LAES system (10 MW/80 MWh) has a short payback period of ~5.7 years. Furthermore, it has a savings-to-investment ratio of 3.12, which is ~153% higher than that of the baseline LAES system. Investigation on the system operation strategy suggests that the ASU should operate at full time. The proposed system provides a feasible way to improve the economic benefits of the LAES system, thus promoting its wide applications. [ABSTRACT FROM AUTHOR]

• Hydraulic Power Recovery Turbine (HPRT) as energy recovery application in refinery. • H 2 S removal process with Selexol® solvent is studied for energy recovery with a HPRT. • A performance prediction model for HPRTs handling viscous liquids is proposed. • The system in the case study allows to recover 2966 MWh saving 10.3 TJ (205 TOE) • The best PayBack period of this energy efficiency intervention is about 7 years. Chemical plants like oil refineries involve energy intensive processes. Several energy efficiency interventions are being performed in oil refineries to meet the latest emission targets, but few of them are related to the energy recovery from process liquids. In this paper, an energy recovery study of an Italian oil refinery is presented: specifically, a Hydraulic Power Recovery Turbine (HPRT), coupled with the shaft of the feed pump used in the same process, is used to replace a Pressure Reducing Valve (PRV). The machine is installed in the H 2 S removal process and it exploits the Selexol® solvent. A new model that predicts the Best Efficiency Point (BEP) of the HPRT in turbine mode when handling liquids different from water is discussed and validated through operational BEP data. The HPRT supplies 349.3 kW to the feed pump, leading to a yearly electric energy recovery of 2966 MWh and a maximum PayBack Period (PBP) close to 9 years considering the installation, the Carbon Dioxide Equivalent (CDE) allowances and both operational and maintenance costs. The obtained PBP is quite high, but the installation costs would be fairly lower if the HPRT is already considered in the design phase of the chemical process. [ABSTRACT FROM AUTHOR]

• Grid-connected photovoltaic battery systems are simulated under dynamic electricity tariffs. • Reference sizing combinations are obtained via system techno-economic analysis. • High self-sufficiency leads to more schedulable production, sold energy and less battery usage. • Subsidies impact the revenues obviously especially in high self-sufficiency cases. • Partial grid parity could be achieved under the current market conditions. Battery storage provides an effective solution to alleviate the burden of the intermittent photovoltaic production on the grid and increase photovoltaic penetration in residential houses. Despite several existing work dedicated to the evaluation of photovoltaic battery system, the research on system sizing and operation strategy of the household system still has substantial areas to be explored such as techno-economic analysis under different electricity tariffs and comprehensive parametric analyses. In this paper, the mathematical model of a photovoltaic battery system is developed to investigate system performance, based on the various economic and technical indicators. This study demonstrates that the integration of battery energy storage could increase the value of self-consumption and self-sufficiency rates while making payback period longer. Substantial photovoltaic battery systems have been simulated under practical dynamic electricity tariffs in a typical electricity market. Eight cases with different technical performances from the recommended reference combinations are compared and studied in detail. The energy flows among photovoltaic, battery bank, grid and household user are discussed, revealing that systems with high self-sufficiency rate lead to more schedulable photovoltaic production, sold electricity and lower battery usage rate than those with high self-consumption rate. Besides, the entire lifecycle economic analysis indicates that a higher self-sufficiency rate refers to higher initial investment but shorter payback period and larger profit. The revenues breakdown of the cases shows that subsidies have a significant impact, especially for cases with high self-sufficiency rate. The levelized cost of electricity of photovoltaic and photovoltaic battery systems ranges from 0.373 to 0.628 CNY/kWh, demonstrating the possibility of partial grid parity under the current situation in Shanghai. [ABSTRACT FROM AUTHOR]

• Potential scenarios of adopting UHS in different parts of China were reviewed. • Planning schemes for HPES in three different regions of China were presented. • Peak shaving and renewable energy consumption capabilities of HPES were discussed. • Application prospect of applying UHS in different parts of China was analysed. Underground Hydrogen Storage (UHS) is regarded as a promising approach to achieve seasonal energy storage in the future, due to its synergy with surplus renewable energy generation. This paper proposes the idea of implementing an Integrated Energy System (IES) with UHS and other hydrogen related technologies, called Hydrogen Penetrated Energy System (HPES), and presents an intelligent planning procedure applicable to the HPES. Depleted oil/gas fields and salt caverns are selected as the study objects to explore the ability of UHS to achieve seasonal peak shaving, facilitate the renewable energy, and improve the energy system efficiency. Firstly, three regions in China are analysed in terms of geological conditions, resource endowment and load characteristics, to illustrate the feasibility of building a HPES in each of the analysed region. A two-stage planning method for the HPES is proposed and a detailed UHS model is established where the process of cushion gas accumulation is emulated and the influence of the diurnal temperature range is considered. Comprehensive case studies are subsequently carried out for typical cities or regions in Eastern, Northern and North-eastern China and the results demonstrate that the HPES can lower the cost, improve the energy efficiency and reduce the level of carbon dioxide emission to some extent. A lateral comparison also shows that the combination of salt cavern UHS and offshore wind power has a broad application prospect in the east coast of China, and the investment in the HPES scheme for Jintan can be recovered within 8 to 9 years. In addition, compared with the benchmark scheme without UHS and large penetration of renewables, the HPES scheme for Jintan can improve the primary energy efficiency by 22.26% and 27.75% in the first decade and second decade, reduce the carbon dioxide emission by more than 96%, and consume an average level of 95.85% of the offshore wind power. Although the investment payback period of HPES cases in north and northwest China is relatively long (20 years or more), significant return and benefits can be obtained in the long term. [ABSTRACT FROM AUTHOR]

• A multi-parameter method to assign schools' affordable retrofit is established. • 60% primary energy and 42% global cost reduction potentials are recorded. • Comfort conditions can worsen though the cost and energy consumption are reduced. • Various parameters are crucial to determine an applicable retrofit scenario. • Being in the cost-optimal range is not making an action reasonable. The majority of the buildings was built before the energy efficiency prospering in the construction sector. Hence, they are consuming an enormous energy amount that can be preserved considerably by applying some not even advanced retrofit measures. Schools' low budget is a problem that managers are encountered. Thus the high retrofit cost can prevent taking proper actions. However, considering the measures leading to higher energy efficiency with appropriate cost and payback period, together with taking the lifespan of buildings and the economic benefits during this extended period, would make the actions attractive. This research aims at defining a multi-parameter approach to distinguish energy efficient measures with proper cost, payback period and CO 2 emission for primary school buildings' retrofit. It is following the concept of cost-optimal building retrofit introduced by the EPBD-recast. To assess the proposed approach, two typical school buildings were considered as case studies, the model was created and validated by real consumptions, and then some measures were applied to the envelope, mechanical and lighting system. After driven cost-optimal measures, the comfort analyses were conducted and some of the measures were excluded due to worsening the comfort conditions. The results indicate that, in the suitable cost-optimal scenarios, the potential of primary energy savings and CO 2 emission reductions are approximately 60%, and savings for global cost would amount to more than 42%, while the payback periods are less than seven years. [ABSTRACT FROM AUTHOR]

• Embodied energy impact on the energy life cycle analysis of buildings is assessed. • Energy and carbon pay-back largely vary if the embodied values are considered. • Embodied energy plays a critical role on the estimation of wall insulation. The implementation of energy efficiency measures is an effective way to gain energy savings in the Italian residential sector. This paper assesses the embodied energy impact related to the envelope insulation and evaluates the energy and carbon payback of the efficiency measures. The proposed method consists of (1) an estimation of the baseline operational energy consumption, (2) simulations of realistic retrofit solutions and, (3) the assessment of the 'retrofitting' embodied energy and the energy and carbon payback time calculation. The payback is based on the comparison between the saved operational energy and the embodied energy of the materials selected for insulation. Ten Italian cities are analysed, and the results show a deep dependence on the climate zone. In Northern Italian cities, envelope insulation gains relevance as the energy and carbon payback periods are shorter, about 3 years against the 84 years for the Southern city of Palermo. The optimal thickness is estimated for the city of Milan considering the building's typology, the insulation materials, and the energy payback. This study shows how the total energy savings can be used as a criterion to obtain design indications. [ABSTRACT FROM AUTHOR]

• Cogeneration system proposal for a building in Pisa for sized and undersized modes. • Energy costs of the proposed system are evaluated and contrasted for Iran and Italy. • Proposed system payback period is obtained and analyzed for Iran and Italy by NPV. • For under-sized system, electricity cost is about 37% more than in sized system. • If natural gas price is taken the same as Iran, the payback period reduces by 6.4%. The objective of the present paper is sizing of a technically optimum and economically feasible cogeneration system to supply heating, cooling and electricity to a reference building in the city of Pisa, Italy, for different months of the year. This cogeneration system is proposed in two operational modes, sized and under-sized, so that the effect of natural gas and electricity consumption costs on the system design can be achieved. To this end, the amount of energy consumption and cost of various types of the proposed cogeneration systems based on reciprocating engines are computed and compared. Afterward, in the proposed systems, for understanding the effect of the costs of the energy carriers in different countries on the rate of payback period, a comparison is conducted on the payback period between Iran and Italy. In the end, a sensitivity analysis is performed in Iran and Italy to survey the effect of any change in the cost of investment, natural gas, and electricity on the payback period. The results indicated that although the costs of gas and electricity are comparatively lower, the payback period is longer for Iran, which can be blamed on Iran's higher discount rate (~50%). The results of sensitivity analysis showed that if the natural gas cost in Italy equals that of Iran, there would be a 6.4% reduction in the payback period and if the electricity cost consumption in Iran is taken equivalent to the cost of electricity in Italy, a decrease of 25% will appear in the payback period. [ABSTRACT FROM AUTHOR]

• The optimal BtM process has efficiency of 53.3% and a payback time of 4.8 years. • The SOE-BtM increases efficiency to 66.0% and payback time to 11 years. • The waste heat of gasification process 50% less than the state-of-the-art and zero-power export cases. • The payback time can be shorter than 5 years. The purpose of this paper is to assess techno-economically the integration of solid-oxide electrolysis in biomass-to-methanol processes: (1) The hydrogen produced by electrolysis can be used to adjust the composition of syngas from gasification to increase the conversion of carbon in biomass, (2) the oxygen as a byproduct of electrolysis can be used in the gasifier to avoid expensive air separation units, and (3) the overall process can be thermally integrated. Two integration concepts are proposed with different sizing methods of the electrolyzer: (1) the case of full conversion of carbon in biomass, in which a large electrolyzer is driven by the electricity purchased from the grid, and (2) the case of zero power exchange, in which only part of the carbon in biomass is converted reaching self-sufficiency of electricity. The three cases including the state-of-the-art biomass-to-methanol process are investigated to identify (1) possible trade-offs between efficiency and costs, and (2) under which conditions, these concepts become economically viable. With a reference methanol production of 100 kton/year, the results show that there is an optimal design for the state-of-the-art case, which offers an efficiency of 53.3% due to steam cycles and a payback time of 4.8 years. For the integrated concepts, there are sharp trade-offs between the system efficiency and methanol production cost rate. The case of full carbon conversion can reach an energy efficiency of 64.5–66.0% but results in a longer payback time of over 11 years. The case of zero-power exchange can achieve a similar efficiency as the state-of-the-art case with a slightly increased payback time of over 5.5 years. The payback time of the full carbon conversion case can be shorter than 5 years with a reduction in stack cost and electricity price, and an increase in stack lifetime. [ABSTRACT FROM AUTHOR]

• Life Cycle Impact Assessment of rooftop PV systems throughout Europe is conducted. • Their environmental impact is calculated for their whole life cycle. • Depending on the electricity mix PV's aren't environmental positive in all cases. • The energy return on energy invested ranges from 1.64 to almost 5. • The systems break even in 5 to 11 years in most European Countries. Global energy demand is constantly increasing and recent projections show that this trend is going to continue with an average increase of 1.2% up to 2040. Since the building sector has emerged as a large energy consumer, in an effort to combat this trend, governments worldwide introduced various policies. The utilization of solar energy conversion systems are at the forefront of attention as they are considered carbon dioxide neutral and can be used in order to cover both electricity and heating load demands. Thus, these systems need to be thoroughly investigated taking into consideration the variations in the solar potential and the differences that exist in the electricity mix throughout Europe both in terms of cost, as well as of emissions, in order to assess their sustainability. In the current work a complete life cycle impact assessment is conducted for typical 4 kWp photovoltaic systems throughout Europe, and their environmental impact, sustainability, energy return on energy invested and payback period are calculated. The results highlight that although residential photovoltaic systems are considered "clean" and have a relatively low environmental impact throughout their life cycle, depending on the installation location and local electricity mix this might not be the case in the coming years. The energy return on energy invested ranges from 1.64 to almost 5 depending on location, while their simple payback period is less than 11 years in most cases, and as low as 5, without any subsidy. [ABSTRACT FROM AUTHOR]

• Techno-economic assessment of residential power-to-heat-to-power storage. • The integration with a solar PV system in a dwelling in Madrid is considered. • Electricity savings beyond 70% and payback periods lower than15 years are possible. • Payback periods lower than 10 years are possible when using an absorption chiller. • Additional fuel savings of 20% are possible due to the consumption of exhaust heat. This article assesses whether it is profitable to store solar PV electricity in the form of heat and convert it back to electricity on demand. The impact of a number of technical and economic parameters on the profitability of a self-consumption residential system located in Madrid is assessed. The proposed solution comprises two kinds of heat stores: a low- or medium-grade heat store for domestic hot water and space heating, and a high-grade heat store for combined heat and power generation. Two cases are considered where the energy that is wasted during the conversion of heat into electricity is employed to satisfy either the heating demand, or both heating and cooling demands by using a thermally-driven heat pump. We compare these solutions against a reference case that relies on the consumption of grid electricity and natural gas and uses an electrically-driven heat pump for cooling. The results show that, under relatively favourable conditions, the proposed solution that uses an electrically-driven heat pump could provide electricity savings in the range of 70 – 90% with a payback period of 12 – 15 years, plus an additional 10 – 20% reduction in the fuel consumption. Shorter payback periods, lower than 10 years, could be attained by using a highly efficient thermally driven heat pump, at the expense of increasing the fuel consumption and the greenhouse gas emissions. Hybridising this solution with solar thermal heating could enable significant savings on the global emissions, whilst keeping a high amount of savings in grid electricity (>70%) and a reasonably short payback period (<12 years). [ABSTRACT FROM AUTHOR]

• A novel emissions trading system model is proposed. • Aspects of resilience and the energy mix are modeled. • Introducing the trading scheme engenders significant CO 2 reductions for Japan. • Detailed economic feasibility analysis is undertaken to establish payback periods. • CO 2 price sensitivity effects identified for model outcomes. The issue of climate change and the development of international agreements around carbon targets such as the Paris agreement have engendered the prospect of a carbon constrained future. As a result, individual nations who are signatory to the Paris Agreement have developed ambitious carbon reduction targets in order to restrict temperature rises to two degrees Celsius compared to pre-industrial levels. To achieve these ambitious goals, nations have a variety of policy approaches at their disposal including feed in tariffs, fossil fuel restrictions, carbon capture and storage, renewable portfolio standards and carbon trading regimes. This study investigates carbon trading, and, using Japan as a case study assesses the economic feasibility and environmental efficiency of a carbon trading scheme underpinned by renewable energy deployment. The model employed uses an optimization approach, cognizant of technological, geographic and economic constraints. Findings identify that such an approach incorporating the 47 prefectures of Japan could engender a 42% reduction in emissions without resilience constraints and 34% incorporating a best-mix, resilient approach. Both approaches prove feasible at moderate carbon prices, considering international norms. The findings underpin policy implications for a future national Japanese emission trading scheme to improve previous single prefecture attempts which did not engender carbon trading. [ABSTRACT FROM AUTHOR]