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Abstract Limiting the increase of global temperature requires electrification of the railway transport, which is relatively a distinct mode of transport in terms of economy, business and socialization of a country. However, battery complemented railway transport systems such as fuel cell hybrid railway propulsion systems are constrained by the high cost of the battery, and suboptimal performance of the fuel cell under varying loads. Optimized selection of battery can reduce its costs associated with sizing, life and utilization. Similarly, managing the load distribution between the battery and fuel cell can reduce the load variations concern for fuel cell. In this study, model-based selective characterization of the battery and fuel cell is done to identify the optimal features and constraints. Following characterization, the load allocation to battery and fuel cell is determined with the targets of collaborative utilization of optimal features and mitigation of constraints. Subsequently, considering this load allocation and results of characterization, conditions are proposed for reliable sizing and optimized selection of battery. The significance of the proposed conditions in reliable sizing is explored. Based on these conditions, certain commercially developed batteries are evaluated for optimized selection of battery. The results signify this study as a foundation for research on the reliable sizing and optimized selection of battery in fuel cell hybrid railway propulsion systems.

Abstract This paper presented a novel method of dissipating solar photovoltaic heat based on the technology of micro-heat-pipe array and the utilization of photovoltaic-cell waste heat. This novel technology solved the problems of low PV electrical efficiency and thermal failure caused by high cell temperature, greatly increased the comprehensive utilization efficiency of solar energy, and extended the service life of photovoltaic modules. One-year experiments were conducted to investigate the electrical and thermal performance of a forced-circulation, household-type photovoltaic/thermal system based on micro-heat-pipe array in Beijing, China. Test results showed that on the four typical days in different seasons, the average electrical efficiencies were 13.76%, 11.92%, 13.71%, and 14.65%; the average thermal efficiencies were 31.62%, 33.07%, 24.99%, and 17.24%; and the average total efficiencies were 45.38%, 44.99%, 38.70%, 31.89%, respectively. The system met the demand of power supply on sunny days and the demand of hot water between March and November, except in cloudy days. These experimental results can provide basis and reference for practical applications of the system.

Abstract Hybrid energy storage is a multi-modal approach to store and supply different forms of energy (electricity, heat, cold) simultaneously. This is an important sector coupling approach and enables large scale flexibility for a deep decarbonization of energy systems. Two different proposed energy storages – power-to-heat-to-X energy storage (PHXES) and pumped thermal energy storage (PTES) – are investigated in detail in this work towards their potential towards a hybrid deployment. The techno-economic analysis includes thermodynamic flowsheet simulations and unified cost estimations based on the used equipment. It is shown that the main input data set (e.g. working fluid selection, turbomachinery efficiency, pinch temperatures) has a strong influence on storage roundtrip efficiency in the thermodynamic simulations, but also on storage costs. Cost decrease and performance increase can be conflicting development targets, and it is not clear if future energy systems rather require technologies with the highest storage efficiencies or if low cost is an important prerequisite. PHXES and three variants of PTES are implemented into a simplified energy system model of the city of Hamburg that comprises the electric load and heat demand of the district heating system. Two scenarios (fossil benchmark and 80% decarbonization) are used to select the technologies and their capacities that allow the most cost-effective energy supply solution by a linear-programming optimization procedure. Large scale renewable power generation and hybrid energy storage play the major roles in the decarbonization scenario. PHXES with a storage capacity of 69 GWh, hot water storage (3.6 GWh) and a battery system (430 MWh) are part of the cost-optimal solution. A cost sensitivity analysis shows that a total cost reduction of 60–80% is required for PTES to become competitive in this model scenario.

This paper presents a robust model predictive control strategy for improving the supply air temperature control of air-handling units by dealing with the associated uncertainties and constraints directly. This strategy uses a first-order plus time-delay model with uncertain time-delay and system gain to describe air-conditioning process of an air-handling unit usually operating at various weather conditions. The uncertainties of the time-delay and system gain, which imply the nonlinearities and the variable dynamic characteristics, are formulated using an uncertainty polytope. Based on this uncertainty formulation, an offline LMI-based robust model predictive control algorithm is employed to design a robust controller for air-handling units which can guarantee a good robustness subject to uncertainties and constraints. The proposed robust strategy is evaluated in a dynamic simulation environment of a variable air volume air-conditioning system in various operation conditions by comparing with a conventional PI control strategy. The robustness analysis of both strategies under different weather conditions is also presented.

Abstract Four power generation options covering the spectrum of methods of fossil fuel power generation were used as the base cases to determine the resultant increase in base case levelized generating costs resulting from CO2 capture from the flue gas of a 500 MWc power station by liquid scrubbing technology. Suitable liquid scrubbing technology for CO2 capture was investigated only for end of pipe treatment, after upstream FGD (where applicable), for each of the options of a 500 MWe power station from coal and natural gas at a coastal site in the Netherlands. The three coal options were based on pulverised fuel, IGCC, and coal combustion in a mixture of oxygen and recycle gas respectively, whilst the natural gas option was based on a sulphur free NGCC. Only commercially proven liquid scrubbing technology screened in economic and technical terms. Inhibited MEA (monoethanolamine) was the most acceptable for the conventional pulverised coal fired power station, the IGCC coal fired power station and the NGCC plant. Selexol® was the most suitable for combustion of coal in the recycle mixture. In all cases pre treatment was necessary to remove traces of NOx and/or SO2 which otherwise would cause solvent degradation. As a consequence of CO2 capture, drastic reductions of both acid gases and particulates occur. The reduction in overall generating efficiency over the four options ranged from 2.4 to 13.5 per cent corresponding to an increase in power station nameplate capacity of 540 to 740 MWe to achieve a net export of 500 MWe after CO2 capture and regeneration. Investment costs increased substantially by between 52 to 108 per cent in terms of $/kWso. Over the range of options the resultant levalised base case generating costs increased from 22 to 108 per cent. The conventional PF coal power station showed an increase from 53.4 to 80.38 mills/kWhso and the natural gas (sulphur free) NGCC plant showed an increase from 32 to 50.24 mills/kWhso. In the case of the non conventional combustion of coal in recycle gas the cost increased from 83 to 101 mills/kWhso. Because the base case selected for the coal based IGCC plant required CO2 to be captured at almost atmospheric conditions, rather than at higher pressure, the costs were seriously distorted and are not readily comparable with the other options. The nett parasitic effect was not only to substantially increase investment costs but also to substantially increase the basic cost of electricity irrespective of the type of fuel and method of power generation. The balance between a CO2 tax and CO2 capture cannot be inferred without taking into cognisance the additional cost of CO2 disposal.

Abstract The use of photovoltaic solar power generation is rising as worldwide energy demand increases. Therefore, reliability, safety, life cycle, and improved efficiency of photovoltaic plants have all become a major concern in research nowadays. In this context, monitoring systems are necessary to guarantee the required operating productivity and to avoid overpriced maintenance costs. This paper studies the non-ideal operating conditions for grid-connected photovoltaic plants and proposes an anomaly detection methodology that combines the advantages of the 2-sigma, short-window simple-moving average control charts with shading strength and irradiance transition parameters to detect early deviation in photovoltaic plant operational data. The key aspect of proposed methodology is that it requires neither historical data for model training procedure nor parameters from previous simulation. Only instantaneous meteorological and electrical parameters are required. The efficiency of the condition monitoring methodology has been validated through experimental results conducted in actual operating conditions. Results demonstrated that the proposed methodology is effective to identify non-ideal operating conditions for grid-connected photovoltaic plants, i.e., (i) normal operating condition, (ii) natural dynamic shading, (iii) artificial dynamic shading, and (iv) artificial static shading. Moreover, a low-cost and non-invasive internet-of-things-based embedded architecture is proposed to monitor photovoltaic plant operation in real-time.

Abstract The combined production of electricity, heat and cold by a polygeneration system connected to a district heating and cooling network can provide high energy utilization efficiency. The inherent complexity of simultaneous production of different services and the high variability in the energy demand make combined cooling and heating systems performance highly dependent on the operational strategy. In this paper, an operational optimization method based on the moving average of real-time measurements of energy demands and ambient conditions is proposed. Real energy demand data from a district heating and cooling network close to Barcelona, Spain, are used to test the method. A complex polygeneration system is considered, consisting of an internal combustion engine, a double-effect absorption chiller, an electric chiller, a boiler and a cooling tower. A detailed modelling of the system is provided, considering partial load behavior of the components and ambient conditions effects. Results of the real-time optimal management are discussed and compared to traditional operational strategies and to the ideal optimal management achievable with perfectly accurate forecast of energy demands. Moreover, the optimal width of the window adopted for the moving average of real-time data is identified.

Abstract The relative merits of a thermosyphon heater for domestic water heating are brought to light with special emphasis to Libyan weather conditions. The experimental performance of this type of heater was studied by the authors for a brief period and reported in an earlier study. In the present study, year-round experimental performance is reported. Measurements performed all over the year showed that water is heated to a maximum temperature of 66°C while the minimum temperature during six months was as high as 50°C. The picture is no less bright from an overall efficiency point of view. Efficiency ranges as high as 40 to 50%. Hourly measurements on various days showed that the water temperature has an increasing trend, irrespective of the fluctuating solar radiation pattern on a cloudy day.

Abstract In this paper, a three-dimensional numerical simulation was carried out to characterize a high-ash coal gasification in a pressurized, oxygen-blown, two-stage E-Gas entrained flow gasifier. The Tabas coal was used as a high-ash feedstock, with 32 wt% ash and was compared with the Illinois #6 low-ash coal, with 10 wt% ash. The computational model was conducted in ANSYS FLUENT 14 based on the conservation equations described in the Eulerian–Lagrangian approach. Also, four heterogeneous combined with seven homogeneous reactions were solved via the finite rate and eddy-dissipation/finite rate model, respectively. Two different parametric analyses were conducted to characterize the gasification process in the E-Gas gasifier. These analyses cover the effects of the O2/Coal ratio and coal slurry water content on the gasifier performance characteristics such as the exit temperature, main species mole fractions, carbon conversion, high heating value, yield syngas fraction and cold gas efficiency. It was found that using the higher ash content coal decreases the cold gas efficiency about 5%, limits the gasifier economical operating range, and reduces the exit temperature, yield syngas and total higher heating value.