• Energy Research
• Closed Access close
• Open Source close
• IT close
• Energy Conversion and Management close

In the present work, an experimental study on a lab-scale adsorption refrigerator, based on activated carbon/ethanol working pair is reported. An extensive testing campaign has been carried out at the CNR ITAE laboratory, with multiple aims. First, the performance has been evaluated in terms of both COP and Specific Cooling Power (SCP), under different boundary conditions, including both air conditioning and refrigeration applications. Attractive SCPs, up to 180 W/kg and 70 W/kg for air conditioning and refrigeration, respectively, were measured. Under the same conditions, COP between 0.17 and 0.08 were obtained. In addition, different management strategies, namely, heat recovery between adsorbers and re-allocation of phase durations, were evaluated to identify their influence on the system. Both strategies confirmed the possibility of increasing COP and SCP up to 40% and 25%, respectively. Moreover, a design analysis based on the experimental results has been carried out, to suggest possible improvements of the system. The obtained results demonstrated the possibility of employing a non-toxic refrigerant like ethanol reaching performance comparable with other harmful refrigerants like ammonia and methanol.

Abstract Demand response and real-time pricing of electricity are key factors in a smart grid as they can increase economic efficiency and technical performances of power grids. This paper focuses on incorporating price-responsive customers in day-ahead scheduling of smart distribution networks under a dynamic pricing environment. A novel method is proposed and formulated as a tractable mixed integer linear programming optimization problem whose objective is to find hourly sale prices offered to customers, transactions (purchase/sale) with the wholesale market, commitment of distribution generation units, dispatch of battery energy storage systems and planning of interruptible loads in a way that the profit of the distribution network operator is maximized while customers’ benefit is guaranteed. To hedge distribution network operator against financial risk arising from uncertainty of wholesale market prices, a risk management model based on a bi-level information-gap decision theory is proposed. The proposed bi-level problem is solved by recasting it into its equivalent single-level robust optimization problem using Karush–Kuhn–Tucker optimality conditions. Performance of the proposed model is verified by applying it to a modified version of the IEEE 33-bus distribution test network. Numerical results demonstrate the effectiveness and efficiency of the proposed method.

Abstract This paper presents a method for the capacity sizing of a small hydropower plant on the basis of techno-economical analyses of the flow duration curve. Seven technical and economical parameters were considered: the turbine type, the turbine dimensions, the annual energy production, the maximum installation height to avoid cavitation inception, the machine cost, the Net Present Value (NPV) and the Internal Rate of Return (IRR). A proper model was proposed to study the effects of the design operating conditions on these parameters. The model, applied to the flow duration curve, allowed to analyse the feasibility, the profitability and the performance of the plant in the available flowing range of the site. To verify the effectiveness of the proposed method, three sites having different flow duration curves were analysed.

Abstract The spread of wind turbines and photovoltaic modules for green electricity generation is stressing the need of installing large-scale electricity energy storage. Among the in-developing storage technologies, those which store electricity in the form of thermal energy are considered the most promising due to the absence of geological restrictions and long cycle life. In this context, the Authors of the present work, developed a large-scale electricity energy storage unit which uses air as working fluid and stores electrical energy as sensible heat in a man-made tank. As other thermal storage technologies, the proposed one does not suffer of geographical limitations, is characterized by long cycle life and can be assembled with decommissioned devices originally designed for gas turbine plants. In this work, the Authors analyse the plant energetic performance and the construction cost for different storage materials and plant management strategies. Results show that the thermo-physical properties of the storage medium and the charging tolerance affect the plant performance and costs. For these reasons, it is essential selecting the material based on the plant purpose: if the plant works with daily charge/discharge cycle, packed bed made up by limestone or masonry material is suggested while, for weekly charge/discharge cycles, aluminium oxide can be a better storage option.

A new hybrid hydrogen/hydrocarbon-driven motor-car is proposed which is equipped with a CO2-trap and which exhibits an energy absorption ability in its storage systems (with respect to their masses) much larger than that of a hydrogen- or battery-powered car. The principal idea is to use light metal hydrides (like MgH2) as energy storage facilities whose metallic atoms not only carry fuel atoms but, if is discharged, also the carbon dioxide from the burned hydrocarbons. In the opinion of the author, a system is presented for the first time which would be able to bind and collect the CO2 of a large number of diffuse CO2-sources for the purpose of its central disposal.

Abstract Biogas plants are an interesting solution for production of clean energy. Biogas produced in an anaerobic digester can be used locally to produce electric energy in an internal combustion engine or in a micro-gas turbine. A portion of the waste heat is used to keep the digester at a constant temperature which is a necessary condition for a correct operation of the digester. Generally, waste heat overcomes that necessary to keep the digester at the desired temperature and a big portion of this thermal energy is dissipated. Many solutions exist to increase the amount of heat recovered. In this study, the use of an absorption chiller to decrease the inlet temperature of a micro-gas turbine operating with biogas was considered. The advantage of this solution relies in a more stable operation of the micro gas turbine and an increase in the power output. The integration of the absorber chiller in the biogas plant and the effect of the ambient conditions were investigated in detail. The study was based on an existing plant operating near Pisa (Italy). A model of the system has been developed in AMESim and a numerical simulation has been performed. The effects of different temperature profiles, corresponding to different climate conditions, have been investigated both from the energy and economic points of view. The results showed that local climate conditions strongly influence the effectiveness and the profitability of the inlet turbine air cooling technique. In those climates where the temperatures are constantly high over the year, this technique may lead to interesting benefits and profitability.

Abstract Carbon dioxide capture and storage (CCS) is gaining widespread interest as a potential method to control greenhouse gas emissions from combustion processes of fossil fuels, especially in electric power plants. Retrofitting existing power plants with post-combustion CO 2 capture technologies, the most mature options today, has been suggested as a possible mean to reduce CO 2 emissions. After adding a carbon capture unit, both electricity and steam are required by the capture system, essentially forcing the power plant to operate in cogeneration. Instead of derating the base plant for post-combustion capture energy needs, steam could be generated in an external auxiliary unit designed specifically for the capture island. Since this auxiliary plant would be a new build, the plant could be designed for the particular heat load of the capture section in order to minimize efficiency losses and increase the energy saving. This paper examines the energy behavior of combined cycle power plants with CO 2 post-combustion capture, assuming that the reboiler duty is satisfied by steam extracted upstream the low pressure turbine or by an auxiliary biomass boiler. These options are also compared in terms of cost of electricity (COE) and capture cost per tonne of CO 2 avoided. The platform used to simulate the power plant is the commercially available software GateCycle; the CO 2 capture process is simulated using ChemCad software and assuming 90% CO 2 capture ratio with monoethanolamine (MEA 30 wt%) as absorbent.

Abstract A theoretical model of a regenerative blower used for the hydrogen recirculation of a Proton Exchange Membrane (PEM) fuel cell (FC) for automotive applications has been implemented and validated by means of experimental data. A momentum exchange theory was used to determine the head-flow rate curves, whereas the circulatory flow rate was determined through a theory based on the consideration of the centrifugal force field in the side channel and in the impeller vane grooves. The model allows a good forecast to be made of the blower behaviour, and only needs its main geometrical characteristics and some fluid-dynamic data as input. For this reason, the model could be very interesting, especially during the first sizing and the design activity of the blower.