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SUMMARY This work reports a newly proposed system for electrical energy storage. The new system combines a direct open nitrogen (cryogen) expansion cycle with a natural gas-fuelled closed Brayton cycle and the CO2 produced in the system is captured in the form of dry ice. Thermodynamic analyses are carried out on the system under the baseline conditions of 1 kg s−1 natural gas, a combustor operating pressure of 8 bars and a cryogen topping pressure of 100 bars. The results show that the exergy efficiency of the proposed system is as high as 64% under the baseline conditions, whereas the corresponding electricity storage efficiency is about 54%. A sensitivity analysis has also been carried out on the main operating conditions. The results indicate that the baseline performance can be enhanced by increasing the gas turbine (GT) inlet temperature, decreasing the approach temperature of the heat exchange processes, operating the combustor at an optimal pressure of ∼7 bars and operating the cryogen topping pressure at ∼90 bars. Further enhancement can be achieved by increasing the isentropic efficiency of the GT and the liquefaction process. The results of this work also suggest that the power capacity installation of peak-load units and fuel consumption could be reduced by as much as 50% by using the newly proposed system. Further work is suggested for an economic analysis of the system. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An uninterruptible power supply (UPS) system based on supercapacitor and liquid nitrogen (LN2) hybridization is first introduced in this paper. Of the newly designed UPS, the supercapacitor reacts instantaneously once the main supply fails, and it also starts the LN2 power system to produce continuing electricity for the customer. This hybrid UPS system is of environment cleanness, long life time, easy maintenaince, etc. A 10kW model is analyzed in this study. A two-stage nitrogen expander is designed with the rated speed of 900rpm as the long time power generation device of the LN2 cycle. The UPS starting process calculation is carried out. The results reveal that commercial supercapacitors could fulfill this request. This UPS could be a competent choice for the UPS application. Further discussion indicates the LN2 power system could be used widely from UPS to low carbon vehicles. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a new type of solar energy based power generation system using supercritical carbon dioxide and heat storage. The power generation cycle uses supercritical carbon dioxide as the working fluid and integrates the supercritical carbon dioxide cycle with an efficient high-temperature heat storage. The analysis shows that the new power generation system has significantly higher solar energy conversion efficiency in comparison to the conventional water-based (steam) system. At the same time, the heat storage not only overcomes the intermittent nature of solar energy but also improves the overall system efficiency. The study further reveals that the high temperatures and high pressures are favorable for solar energy storage and power generation. Moreover the expander and the heat storage/regenerator are found to be the key components that determine the overall system performance. [Copyright &y& Elsevier]

Highlights: [•] Techno-economical and social analysis of energy storage is conducted for commercial buildings. [•] Methodologies for demand analysis, technical, economical and social evaluations are developed. [•] An illustrative example is analyzed for three kinds of energy storage systems. [Copyright &y& Elsevier]