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In this paper, the technologies of fermentation, gasification and pyrolysis of carbonaceous residues for the production of biohydrogen and other gaseous, liquid or solid fuels, are analysed. The energetic, economic and environmental advantages of linking these energy areas with the fuel cell engines are stressed. In addition, the current status of fuel cell technologies, namely their historic trends, basic electrode mechanisms, cell types, market drivers and leading issues, are reviewed.

Abstract Volumetric machines are the most suitable candidates to be used as expander in power units based on the Organic Rankine Cycle (ORC) thermodynamic concept, for waste heat recovery of Internal Combustion Engine in the on-the-road transportation sector. In particular, the technology of the Sliding Rotary Vane Expander (SRVE) shows intrinsic advantages thanks to their lower cost, shaping features, easier manufacturing and reliability and, generally speaking, very suitable operative conditions. Nevertheless, they show some disadvantages which are typical of volumetric machines, such as low capacity, limited expansion ratio and power lost by friction. Among the different technologies available to reduce the effects of these aspects (revolution speed increase, elliptical stators or with more complex geometries, tip blade optimization, rolling stators, etc.), the Dual-Intake Port (DIP) was assessed as a promising solution to enhance SVREs performance and operability. However, dual-intake port was still not conceived as design option. In this paper, a novel Sliding Vane Rotary Expander design concept involving a Dual Intake Port expander (DIP) option was developed and compared to the conventional Single Intake Port (SIP) one, under the same operating conditions. Thus, after an experimental comparison between SIP and DIP expanders, under the same conditions of mass flowrate, a theoretical expander model of the latter was validated on a set of experimental results. The model allows to outline the advantages of considering the dual port as a design option: for a specific flow rate and revolution speed, this option allows to reduce the friction losses, which represent a weak point of this volumetric machine. For a given mass flow rate of the working fluid, an additional feature is that it allows a sensible downsizing with respect to the SIP, with an axial dimension reduction up to 50%, ensuring additional weight and space saving. Despite the reduction of the dimensions, DIP produces a comparable mechanical power with respect to SIP, limiting the reduction to 8–10% of the SIP one with a 50% lower mechanical power loss due to friction. For the same flow rate, the added intake port determines a decrease of the intake pressure which is completely beneficial in terms of operating conditions of the overall recovery unit.

Liquid desiccants used for many industrial and domestic applications have to be reconcentrated for reuse. Instead of using thermal energy, a method is proposed in this paper to use mechanical energy for regeneration of weak desiccants. The osmotic pressure required to regenerate two such desiccants, namely calcium chloride and lithium chloride, for given operating conditions is predicted, and correlations are developed. It is found that the pressure required for calcium chloride is much less than that of lithium chloride for the same operating conditions.

We present performance studies of an earth air tunnel cum greenhouse technology in terms of instantaneous thermal efficiency. Analytical expressions have been obtained for heating/cooling conditions of a greenhouse. The results are in accordance with the experimental results obtained for the same system in Greece.

Abstract Rising penetrations of variable renewable generation in electric power systems can raise operational challenges. One is that renewables can increase the need for dispatchable generation with fast-ramping capabilities. This can be costly, because in many instances flexible generators can be more expensive than baseload units that have slower ramping capabilities. If ramping capacity is not available, renewable curtailment may be needed. An alternate solution to this need for ramping is to use energy storage. A question that this raises is how renewable and conventional generators and energy storage would interact in a market environment, and whether certain asset-ownership structures would result in more efficient coordination. To this end, this paper presents a multi-period market-equilibrium model of interactions between these different types of market agents. The impacts on renewable integration of conventional generators having limited ramping capabilities are studied through an illustrative case study. We also examine a variety of structures for the participation of energy storage in the market. We find that co-ownership and co-operation of renewable generators and energy storage brings about the best results from the perspective of alleviating market inefficiencies. Having energy storage directly controlled by the market operator or participating as an independent profit-maximizing firm is less efficient.

Abstract The Curved Slats Fixed Mirror Solar Concentrator (CSFMSC) is a solar concentrator with a static reflector and a moving receiver. An optical analysis using ray-tracing tools was presented in a previous study in function of three design parameters: the number of mirrors N, the ratio of focal length and reflector width F/W, and the aperture concentration Ca. However, less is known about the thermal behavior of this geometry. In this communication, the integrated thermal output of the CSFMSC has been determined in order to find the optimal values for the design parameters at a working temperature of 200 °C. The results were obtained for three different climates and two axial orientations (North–South, and East–West). The results show that CSFMSC can produce heat at 200 °C with an annual thermal efficiency of 41, 47, and 51%, dependent of the location considered (Munich, Palma de Mallorca, and Cairo). The best FMSC geometries in function of the design parameters are exhibited for medium temperature applications.

Abstract In this paper, a two-step design optimization framework is developed for four low-temperature geothermal combined heat-and-power plant configurations. The economic comparison, including off-design performance, has not been done before. The optimization tool is applied for an existing district heating system and for geothermal and meteorological conditions which are based on the Belgian situation. It is concluded that a combined heat-and-power plant results in an economically profitable project (net present value of 3.46 MEUR), whereas the stand-alone electrical power plant does not (net present value of −3.65 MEUR). Furthermore, the design for the series set-up is optimal, and the best connections during operation are the series and parallel connections for low and high heat demands, respectively. Also, a less detailed (high-level) control optimization model is developed for this series set-up, based on the part-load operating maps which are calculated from the detailed two-step optimization model results. The calculation time is much faster ( ∼ milliseconds) and the errors on the total revenues are smaller than 0.1%. The goal of this high-level model is to optimize the amounts of heat and electricity to produce, so that the plant can be used as a flexibility tool in energy markets driven by price signals for heat and electricity.