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[en] Highlights: • A solar-driven photo-electrochemical system (S/EC/PS) was first constructed. • Solar spectrum was fully used for the dye decolorization, power supply and thermal. • The electricity needed for EC was offered by the hybrid system. • In comparison with S/PS, decolorization time of S/EC/PS shorten 50%. • PV panels has lower working temperature due to the water cooling. - Abstract: This study presents a new solar-driven hybrid system that integrated a photo-electrochemical reactor with a photovoltaics (PV) panel for azo dyes’ decolorization and electricity generation. Full spectrum of sunlight is utilized to optimize the color removal of Acid Red 26 (AR26) in this hybrid system. Persulfate (PS, S2O42−) was selected as the photochemical oxidant and Ti/IrO2-Ta2O5 electrode was used as the anode. Experiments were made to evaluate the efficiency of decolorization and the performance of PV panels in different reaction conditions outdoors. The results showed that the synergistic effect of two processes was observed for the AR26 decolorization. Comparing with the solar/persulfate process or the electrochemical process alone, the complete color removal time by the hybrid system decreased up to 50% and 44.4% respectively. In this system, the water layer in the flow channel cooled PV panels by absorbing the far infrared spectrum of sunlight, and the increased temperature of wastewater from 7 °C to 16 °C enhanced the decolorization efficiency of AR26. Moreover, the generated electricity by PV panels could satisfy the energy demand of electrochemical oxidation.
[en] Highlights: • PV-T driven air-conditioning systems can cover 60% of the domestic heating demand. • PV-T air-conditioning systems can cover up to 100% of the domestic cooling needs. • The importance of high resolution energy performance simulations has been demonstrated. • The LCOE of PV-T air-conditioning varies between 0.06 and 0.12 €/kW h. - Abstract: Solar energy can play a leading role in reducing the current reliance on fossil fuels and in increasing renewable energy integration in the built environment, and its affordable deployment is widely recognised as an important global engineering grand challenge. Of particular interest are solar energy systems based on hybrid photovoltaic-thermal (PV-T) collectors, which can reach overall efficiencies of 70% or higher, with electrical efficiencies up to 15–20% and thermal efficiencies in excess of 50%, depending on the conditions. In most applications, the electrical output of a hybrid PV-T system is the priority, hence the contacting fluid is used to cool the PV cells and to maximise their electrical performance, which imposes a limit on the fluid’s downstream use. When optimising the overall output of PV-T systems for combined heating and/or cooling provision, this solution can cover more than 60% of the heating and about 50% of the cooling demands of households in the urban environment. To achieve this, PV-T systems can be coupled to heat pumps, or absorption refrigeration systems as viable alternatives to vapour-compression systems. This work considers the techno-economic challenges of such systems, when aiming at a low cost per kW h of combined energy generation (co- or tri-generation) in the housing sector. First, the technical viability and affordability of the proposed systems are studied in ten European locations, with local weather profiles, using annually and monthly averaged solar-irradiance and energy-demand data relating to homes with a total floor area of 100 m2 (4–5 persons) and a rooftop area of 50 m2. Based on annual simulations, Seville, Rome, Madrid and Bucharest emerge as the most promising locations from those examined, and the most efficient system configuration involves coupling PV-T panels to water-to-water heat pumps that use the PV-T thermal output to maximise the system’s COP. Hourly resolved transient models are then defined in TRNSYS, including thermal energy storage, in order to provide detailed estimates of system performance, since it is found that the temporal resolution (e.g. hourly, daily, yearly) of the simulations strongly affects their predicted performance. The TRNSYS results indicate that PV-T systems have the potential to cover 60% of the combined (space and hot water) heating and almost 100% of the cooling demands of homes (annually integrated) at all four aforementioned locations. Finally, when accounting for all useful energy outputs from the PV-T systems, the overall levelised cost of energy of these systems is found to be in the range of 0.06–0.12 €/kW h, which is 30–40% lower than that of equivalent PV-only systems.
[en] Highlights: • Four double pressure low temperature Kalina cycle systems are introduced. • Pinch temperature difference is set for all the heat exchangers via an iterative method. • All the introduced cycles are optimized from thermodynamic point of view. • Levelized cost of electricity as the thermoeconomic criterion is calculated. • By increasing the heat source temperature both thermal and exergy efficiencies improve. - Abstract: In this paper four configurations of double pressure Kalina cycle system are presented and optimized all of which are modifications of Kalina cycle system 11. In order to set the exact pinch temperature difference an iterative method is applied. Prior to the optimization, the base cycle is validated by comparing the result with a reference. The heat transfer fluid of the inlet stream is supposed to be the product of combustion at 3 different temperatures, 383.15 K, 413.15 K and 443.15 and the results are compared at the base case and the optimum conditions. In order to present a thorough evaluation, thermoeconomic analysis is also presented in which levelized cost of electricity is selected as the criterion. Different decision variables can be defined for the cycles based on the cycle’s degrees of freedom. Pressure levels, mass flow rate and ammonia concentration of the base stream and split ratio are the decision variables. Exergy efficiency is considered as the objective function and the innovated double pressure Kalina cycles as well as the base Kalina cycle are compared. Results show that the Kalina cycle system named 112b is the most efficient cycle at the base condition. It is also shown that by increasing the heat source temperature the exergy efficiency and the purchased equipment cost at the optimum condition rises while the levelized cost of electricity lowers. Thermoeconomic evaluation indicates that at both base and the optimum conditions, the levelized cost of electricity of the base cycle is less.
[en] Highlights: • SAPG with concentrating and non-concentrating collectors has been compared. • Non-concentrating collectors could be superior to concentrating collectors in SAPG. • Using non-concentrating collectors is more effective in low latitude. - Abstract: The preheating of the feedwater in a Regenerative Rankine Cycle power plant with solar thermal energy, termed Solar Aided Power Generation, is an efficient method to use low to medium temperature solar thermal energy. Here, we compared the use of medium temperature (200–300 °C) energy from concentrating solar collectors (e.g. parabolic trough collectors) to displace the extraction steam to high temperature/pressure feedwater heaters with that from low temperature (100–200 °C) non-concentrating solar collectors (e.g. evacuated tube collectors) to displace the extraction steam to low temperature/pressure feedwater heaters of the power plant. In this paper, the in terms of net land based solar to power efficiency and annual solar power output per collector capital cost of a Solar Aided Power Generation using concentrating and non-concentrating solar collectors has been comparted using the annual hourly solar radiation data in three locations (Singapore; Multan, Pakistan and St. Petersburg, Russia). It was found that such a power system using non-concentrating solar collectors is superior to concentrating collectors in terms of net land based solar to power efficiency. In some low latitude locations e.g. Singapore, using non-concentrating solar collectors even have advantages of lower solar power output per collector capital cost over using the concentrating solar collectors in an SAPG plant.
[en] Highlights: • The integrated framework that combines IDA with energy-saving potential method is proposed. • Energy saving analysis and management framework of complex chemical processes is obtained. • This proposed method is efficient in energy optimization and carbon emissions of complex chemical processes. - Abstract: Energy saving and management of complex chemical processes play a crucial role in the sustainable development procedure. In order to analyze the effect of the technology, management level, and production structure having on energy efficiency and energy saving potential, this paper proposed a novel integrated framework that combines index decomposition analysis (IDA) with energy saving potential method. The IDA method can obtain the level of energy activity, energy hierarchy and energy intensity effectively based on data-drive to reflect the impact of energy usage. The energy saving potential method can verify the correctness of the improvement direction proposed by the IDA method. Meanwhile, energy efficiency improvement, energy consumption reduction and energy savings can be visually discovered by the proposed framework. The demonstration analysis of ethylene production has verified the practicality of the proposed method. Moreover, we can obtain the corresponding improvement for the ethylene production based on the demonstration analysis. The energy efficiency index and the energy saving potential of these worst months can be increased by 6.7% and 7.4%, respectively. And the carbon emissions can be reduced by 7.4–8.2%.
[en] Highlights: • A normal four-stroke cycle followed by a skip cycle without gas exchange is tested. • The normal and skipped mode results are compared at equal power levels. • The throttle valve is opened wider, thereby resulting in a higher volumetric efficiency. • The pumping work during the gas exchange decreases significantly. • The fuel consumption (BSFC) is reduced by approximately 14–26% under part load conditions. - Abstract: The efficiency decrease of spark ignition (SI) engines under part-load conditions is a considerable issue. Changing the effective stroke volume based on the load level is one of the methods using to improve the part-load efficiency. In this study, a novel alternative engine valve control technique in order to perform a cycle without gas exchange (skip cycle), is examined. The goal of skip cycle strategy is to reduce the effective stroke volume of an engine under part load conditions by skipping several of the four stroke cycles by cutting off the fuel injection and simultaneously deactivating the inlet and exhaust valves. To achieve the same power level in the skip cycle, the cylinder pressure level reaches higher values compared to those in a normal four stroke cycle operation, but inherently not higher than the maximum one at full load of normal cycle. According to the experimental results, the break specific fuel consumption (BSFC) was reduced by 14–26% at a 1–3 bar break mean effective pressure (BMEP) and a 1200–1800 rpm engine speed of skip cycle operation, in comparison to normal engine operation. The significant decrease in the pumping work from the gas exchange is one of the primary factors for an increase in efficiency under part load conditions. As expected, the fuel consumption reduction rate at lower load conditions was higher. These experimental results indicate a promising potential of the skip cycle system for reducing the fuel consumption under part load conditions.
[en] Highlights: • Optimum performance of PV/battery/fuel cell/grid hybrid system under load uncertainty. • Employing information gap decision theory (IGDT) to model the load uncertainty. • Robustness and opportunity functions of IGDT are modeled for risk-averse and risk-taker. • Robust strategy of hybrid system's operation obtained from robustness function. • Opportunistic strategy of hybrid system's operation obtained from opportunity function. - Abstract: Nowadays with the speed that electrical loads are growing, system operators are challenged to manage the sources they use to supply loads which means that that besides upstream grid as the main sources of electric power, they can utilize renewable and non-renewable energy sources to meet the energy demand. In the proposed paper, a photovoltaic (PV)/fuel cell/battery hybrid system along with upstream grid has been utilized to supply two different types of loads: electrical load and thermal load. Operators should have to consider load uncertainty to manage the strategies they employ to supply load. In other words, operators have to evaluate how load variation would affect their energy procurement strategies. Therefore, information gap decision theory (IGDT) technique has been proposed to model the uncertainty of electrical load. Utilizing IGDT approach, robustness and opportunity functions are achieved which can be used by system operator to take the appropriate strategy. The uncertainty modeling of load enables operator to make appropriate decisions to optimize the system’s operation against possible changes in load. A case study has been simulated to validate the effects of proposed technique.
[en] Highlights: • Coupled heating of ground-coupled heat pump and heat compensation unit is proposed. • Borehole numbers can be reduced to 40% of the conventional design. • Seasonal average heating coefficient of performance is improved from 2.41–3.30 to 4.39–4.70. • Hourly heating capacity of ground-coupled heat pump is increased by 19–65%. • Payback period is only 1 year compared with the system assisted by boiler. - Abstract: The heat compensation unit with thermosyphon has been developed to eliminate the annual soil thermal imbalance of ground-coupled heat pump in heating-dominant buildings. But the issues on heating capacity deficiency at peak heating loads and on the high borehole investment are still unsolved in this non-coupled system. In this paper, a coupled operation of the heat compensation unit and ground-coupled heat pump system is proposed. That is, the heat compensation unit reheats the borehole outlet fluid and improves the temperature of the fluid entering the evaporator of heat pump during the heating season. By doing so, it can enhance the heating capacity at peak loads and reduce the number of boreholes required. The heat compensation required by the heat compensation unit in the non-heating season is also reduced, increasing the system efficiency. To demonstrate the effectiveness of the coupled system against the non-coupled one, the system models are built in TRNSYS to analyze the system reliability, efficiency and economy. Results show that, while the number of boreholes is reduced to 40%, the coupled system can maintain the soil thermal balance and meet the indoor heating demand. For the coupled system with different numbers of boreholes (40–100%), the seasonal average heating COPs of the ground-coupled heat pump and heat compensation unit are 4.39–4.70 and 3.67–3.80, respectively. The hourly heating capacity of the ground-coupled heat pump is also increased by 19–65%. The annual system COP of the coupled system is about 2.48–2.61, which is higher than that of 1.82–2.45 for non-coupled one. Compared to the conventional Boiler assisted ground-coupled heat pump system, the payback period of the coupled system is only 1 year.
[en] Highlights: • A numerical model is developed to evaluate performance of earth to air heat exchanger. • The cooling/heating potential of earth to air heat exchanger is investigated in hot-dry and cold climates. • The more performance of earth to air heat exchanger in hot-dry climates compared to cold climates. • The high efficiency of earth to air heat exchanger for pre-heating in both hot-dry and cold climates. - Abstract: In order to examine and compare the efficiency of earth to air heat exchanger (EAHE) systems in hot-arid (Yazd) and cold (Hamadan) climates in Iran a steady state model was developed to evaluate the impact of various parameters including inlet air temperatures, pipe lengths and ground temperatures on the cooling and heating potential of EAHEs in both climates. The results demonstrated the ability of the system to not only improve the average temperature and decrease the temperature fluctuation of the outlet air temperature of EAHE, but also to trigger considerable energy saving. It was found that in both climates, the system is highly utilized for pre-heating, and its usage is unfeasible in certain periods throughout the year. In winter, EAHEs have the potential of increasing the air temperature in the range of 0.2–11.2 °C and 0.1–17.2 °C for Yazd and Hamadan, respectively. However, in summer, the system decreases the air temperature for the aforementioned cities in the range of 1.3–11.4 °C and 5.7–11.1 °C, respectively. The system ascertains to be more efficient in the hot-arid climate of Yazd, where it can be used on 294 days of the year, leading to 50.1–63.6% energy saving, when compared to the cold climate of Hamadan, where it can be used on 225 days of the year resulting in a reduction of energy consumption by 24.5–47.9%.
[en] Graphical abstract: The Figure shows the variations of volume fractions, granular temperatures, solid temperatures and carbon molar fractions of coal and biomass particles with time at x/R = 1/2 and z = 0.2 m. From the figure, an inverse relationship is shown between molar concentration of carbon and solid temperature. This is because the high temperature has a positive effect on carbon oxidation. For biomass particles, the granular temperature and the solid temperature increase with the volume fraction decreased in section a. In the sections b and c, the granular temperature has a similar trend with the volume fraction of particles. The granular temperature reflects the fluctuating intensity of particles, which indicates that the change of solid volume fraction can cause the granular temperature an increase and correspondingly influences the reaction process. For coal particles, the temperature of coal tends to be steady and the carbon produced by coal is fully consumed. - Highlights: • The KTGM model is developed for multi-component particle phases to simulate the coal/biomass co-gasification in ICFB. • A typical core-annulus flow structure in an inner combustor and the bubble motion in an outer gasifier are captured. • The change of solid volume fraction results in an increase of the granular temperature. • The high reaction temperature promotes the fluctuating velocity of fuel particles. • The granular temperature of biomass particles is higher than that of coal particles in the whole computational domain. - Abstract: A multi-fluid Eulerian model with the kinetic theory of granular mixture (KTGM) is employed for multi-component particles to simulate the coal/biomass co-gasification process in the internal circulating fluidized bed (ICFB). The hydrodynamic characteristic and chemical reaction kinetics are analyzed. The simulations with the KTGM model are in good agreement with experimental data. The instantaneous variables of volume fraction of particles, molar fraction of gas, molar concentration of carbon and temperature are described for the coal/biomass co-gasification process. The time-averaged distributions of volume fraction and velocity for both coal and biomass particles are given. The profiles of granular temperature with solid volume fraction and temperature are also discussed. The results reveal that the granular temperatures of both biomass and coal particles are obvious at a high temperature and a low solid volume fraction. Biomass particles have a higher granular temperature compared to coal particles.