Energies2013, 6(12), 6413-6422; doi:10.3390/en6126413 (doi registration under processing) - published online 10 December 2013 Show/Hide Abstract
Abstract: A laboratory-scale passive hybrid power system for transportation applications is constructed and tested in this study. The hybrid power system consists of a fuel cell stack connected with a diode, a lithium-ion battery pack connected with a DC/DC power converter and another diode. The power converter is employed to regulate the output voltage of the battery pack. The dynamic responses of current and voltage of the stack to the start-up and acceleration of the load are experimentally investigated at two different selected output voltages of the DC/DC converter in the battery line. The power sharing of each power source and efficiency are also analyzed and discussed. Experimental results show that the battery can compensate for the shortage of supplied power for the load demand during the start-up and acceleration. The lowest operating voltage of the fuel cell stack is limited by the regulated output voltage of the DC/DC converter. The major power loss in the hybrid power system is attributed to the diodes. The power train efficiency can be improved by lowering the ratio of forward voltage drop of the diode to the operating voltage of the fuel cell stack.
Energies2013, 6(12), 6391-6412; doi:10.3390/en6126391 - published online 4 December 2013 Show/Hide Abstract
Abstract: Under the Biofuels Obligation Scheme in Ireland, the biofuels penetration rate target for 2013 was set at 6% by volume from a previous 4% from 2010. In 2012 the fuel blend reached 3%, with approximately 70 million L of biodiesel and 56 million L of ethanol blended with diesel and gasoline, respectively. Up to and including April 2013, the current blend rate in Ireland for biodiesel was 2.3% and for bioethanol was 3.7% which equates to approximately 37.5 million L of biofuel for the first four months of 2013. The target of 10% by 2020 remains, which equates to approximately 420 million L yr−1. Achieving the biofuels target would require 345 ktoe by 2020 (14,400 TJ). Utilizing the indigenous biofuels in Ireland such as tallow, used cooking oil and oil seed rape leaves a shortfall of approximately 12,000 TJ or 350 million L (achieving only 17% of the 10% target) that must be either be imported or met by other renewables. Other solutions seem to suggest that microalgae (for biodiesel) and macroalgae (for bioethanol) could meet this shortfall for indigenous Irish production. This paper aims to review the characteristics of algae for biofuel production based on oil yields, cultivation, harvesting, processing and finally in terms of the European Union (EU) biofuels sustainability criteria, where, up to 2017, a 35% greenhouse gas (GHG) emissions reduction is required compared to fossil fuels. From 2017 onwards, a 50% GHG reduction is required for existing installations and from 2018, a 60% reduction for new installations is required.
Energies2013, 6(12), 6373-6390; doi:10.3390/en6126373 - published online 4 December 2013 Show/Hide Abstract
Abstract: This paper presents the findings from an undergraduate research project concerning the energy efficiency, consumption, and generation of a 1000 ft2 (92.9 m2) solar house. The results were compared to a home of similar size and layout, built using traditional construction methods. The solar house was modeled after the Chameleon House: Missouri University of Science and Technology’s 2013 entry in the U.S. Department of Energy Solar Decathlon. The efficiency of the design was analyzed using Energy-10 Version 1.8 software. For this comparison, a fictional American couple was created and a breakdown of their energy-use habits was recorded to accurately depict the magnitude of energy consumption. A 71% energy savings was forecasted using the Energy-10 software through the incorporation of various energy-conserving strategies in the home’s design. In addition, if a 9.1 kW photovoltaic array is also installed on a home of this size, it is possible to fully offset the energy consumption of the home. The forecasted energy usage and production detailed in this report shall be used for analyzing the integrity of the design of the Chameleon House as well as future solar houses constructed by the Missouri S&T Solar House Team.
Energies2013, 6(12), 6352-6372; doi:10.3390/en6126352 - published online 4 December 2013 Show/Hide Abstract
Abstract: This paper describes a frequency domain approach for evaluating the impact of tower shadow and wind shear effects (TSWS) on tie-line power oscillations. A simplified frequency domain model of an interconnected power system with a wind farm is developed. The transfer function, which relates the tie-line power variation to the mechanical power variation of a wind turbine, and the expression of the maximum magnitude of tie-line power oscillations are derived to identify the resonant condition and evaluate the potential risk. The effects of the parameters on the resonant magnitude of the tie-line power are also discussed. The frequency domain analysis reveals that TSWS can excite large tie-line power oscillations if the frequency of TSWS approaches the tie-line resonant frequency, especially in the case that the wind farm is integrated into a relatively small grid and the tie-line of the interconnected system is weak. Furthermore, the results of the theoretical analysis are validated through time domain simulations conducted in the two-area four-generator system and the Western Electric Coordinating Council 127 bus system.
Energies2013, 6(12), 6335-6351; doi:10.3390/en6126335 - published online 4 December 2013 Show/Hide Abstract
Abstract: In this paper a new bucket configuration for a Savonius wind generator is proposed. Numerical analyses are performed to estimate the performances of the proposed configuration by means of the commercial code COMSOL Multiphysics® with respect to Savonius wind turbine with overlap only. Parametric analyses are performed, for a fixed overlap ratio, by varying the slot position; the results show that for slot positioned near the blade root, the Savonius rotor improves performances at low tip speed ratio, evidencing a better starting torque. This circumstance is confirmed by static analyses performed on the slotted blades in order to investigate the starting characteristic of the proposed Savonius wind generator configuration.
Energies2013, 6(12), 6322-6334; doi:10.3390/en6126322 - published online 3 December 2013 Show/Hide Abstract
Abstract: In this paper we propose a new method to evaluate the effects of nationwide conservation voltage reduction (CVR) on peak-load shaving, using substation operating results management system (SOMAS) data. Its evaluation is based on a national CVR factor, which is defined as the weighted average of CVR factors associated with all transformer banks and weighting coefficients are determined by the reconstructed loads corresponding to each transformer bank. To make use of the data resulting from nationwide CVR without installing additional measuring devices, we adopt a linearized static-load model with a linearizing parameter. SOMAS data are used to evaluate the effects of nationwide CVR on peak-load shaving in the Korean power system. Evaluation results show that the national CVR factor of the Korean power system has small values in the summer season and large values in the winter season. This means that the effect of nationwide CVR on peak-load shaving in the Korean power system presents stronger benefits during winter months.