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Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2018;140(7):071201-071201-9. doi:10.1115/1.4039023.

This study deals with thermodynamic analyses of an integrated wind thermal energy storage (WTES) system. The thermodynamic analyses of the proposed system are performed through energy and exergy approaches, and the energy and exergy efficiencies of the components in the system and overall system are determined and assessed. The magnitudes of irreversibilities are determined, and the impacts of different parameters on the performance of the system are identified. The overall energy and exergy efficiencies of the proposed system and its subsystems are computed as well. The energy and exergy efficiencies of the overall system are defined and obtained as 7.0% and 8.6%, respectively. WTES plants with combined molten salt energy storage application can run continuously, and can provide electrical power for both on-grid and off-grid systems. By converting the wind power into a permanent energy source, the WTES offers a practical solution that can meet the electrical demand of the regions where the climate conditions are feasible for consistent, environmentally benign and cost-effective electric power, and it can be considered as a potential energy solution.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2018;140(7):072001-072001-6. doi:10.1115/1.4038964.

Mixing of fresh (river) water and salty water (seawater or saline brine) in a controlled environment produces an electrical energy known as salinity gradient energy (SGE). Two main conversion technologies of SGE are membrane-based processes: pressure retarded osmosis (PRO) and reverse electrodialysis (RED). Exergy calculations for a representative river-lake system are investigated using available data in the literature between 2000 and 2008 as a case study. An exergy analysis of an SGE system of sea-river is applied to calculate the maximum potential power for electricity generation. Seawater is taken as reference environment (global dead state) for calculating the exergy of fresh water since the sea is the final reservoir. Aqueous sodium chloride solution model is used to calculate the thermodynamic properties of seawater. This model does not consider seawater as an ideal solution and provides accurate thermodynamics properties of sodium chloride solution. The chemical exergy analysis considers sodium chloride (NaCl) as main salt in the water of this highly saline Lake with concentration of more than 200 g/L. The potential power of this system is between 150 and 329 MW depending on discharge of river and salinity gradient between the Lake and the River based on the exergy results. This result indicates a high potential for constructing power plant for SGE conversion. Semipermeable membranes with lifetime greater than 10 years and power density higher than 5 W/m2 would lead to faster development of this conversion technology.

Commentary by Dr. Valentin Fuster

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