• Energy Research
• other engineering and technologies close
• CN close
• IN close

AbstractAs a result of the global fuel crisis of the early 1970s, coupled with concerns for the environment, the use of biofuel has been on the increase in many regions throughout the world. At present, a total of approximately 30 billion (30×109) liters of biofuel are utilized worldwide annually, although most countries rely hugely on the first generation biofuel. The limitations of the first and second generation biofuel gave rise to current interest in algae as a promising alternative to these conventional biofuel sources. Algal biomass could provide a lion׳s share of the global transport fuel requirements in future. The present review highlights some important developments in, and potentials of algaculture as a major biomass resource of the future. However, the major constraint to commercial-scale algae farming for energy production is the cost factor, which must be addressed adequately before its potentials can be harnessed.

Linear power flow models are widely used in power system analysis. To control the maximum influence of linearization error on decision making, it is important to evaluate the worst-case linearization error (i.e., the error bound). This letter theoretically derives the error bound of linear power flow models based on the truncation error analysis of Taylor series expansion. A cold-start approach is proposed to restrain the error bound. Case studies show that 1) the proposed error bound is tight and effective and 2) the maximum linearization error can be successfully reduced using the proposed method.

<p>Increasing renewable energy penetrations bring complex feasibility and stability problems. Data-driven methods are applied in extracting and embedding these feasibility and stability rules in power system operations and planning. This paper presents a method of alternate support vector machine decision trees for rule extraction problems. The method has significant improvements to the classical decision-tree-based algorithms in terms of efficiency, stability and versatility. Finally, we apply the method to several power and energy system scenarios to show its effectiveness.</p>

In this study, a pilot scale of 100 t/year biodiesel production system, mainly consisting of a fixed-bed and a down-stream plug-flow reactors, was setup to test different feedstock oils, especially a kind of high-acidified oil, trap grease, for their feasibility as biodiesel feedstock in China. The tested oils include three kinds of typical oil from Guangdong Province, China: rapeseed oil, Chinese wood oil, and trap grease. At the same time the optimum residence time for a plug-now reactor to perform transesterification reaction was investigated in this study. At the temperature of 65 degrees C, methanol/oil molar ratio of 6:1 and KOH load of 1.2 wt% of oil, the optimum residence time was found to be 19 min. A type of ion-exchange resin was used to fill in the fixed-bed reactor and used as the esterification catalyst for pretreating on the high-acidified oil. For the fresh catalyst, the acid value of trap grease could be reduced from 114 mg KOH/g to about 2 mg KOH/g after 13 h at temperature 75 degrees C, catalyst load of 15 wt% of oil, methanol addition of 20 wt% of oil. The lifetime test for the catalyst indicated that its life is over 30 days. The quality of biodiesel derived from three feedstock oils is compared with newly published China BD100 standard of GB/T20828-2007. A comparison of the results reveals that the biodiesel generated through this system could satisfactorily meet China BD100 standard. It indicates that the designed process in this system has a good adaptability for different kinds of oil. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract This paper presents a solar photovoltaic/thermal (PV/T) system with triple-junction solar cells. The essential components of the system are a concentrator of high concentration ratio, a PV/T module and a tracking device. Plane-mirrors array structure is applied to the concentrator, which can provide PV/T module with a uniform light intensity distribution and an adjustable concentration ratio. The PV/T module is an integration of triple-junction solar cells and a heat exchange device, where the heat from triple-junction solar cells is collected and transported for thermal applications by fluid passing through. Considering both photovoltaic and thermal conversion, the total solar utilization efficiency is greatly increased. The simulation results show that the thermal conversion efficiency of this high concentration PV/T system in hybrid operation can achieve about 52%, which is approximately in agreement with the experimental result of 48%, meanwhile the theoretical photovoltaic conversion efficiency can reach 26%. The simulation results also reveal the effect of fluid flow rate on the thermal efficiency of high concentration PV/T system, which is quite opposite to that in non-concentration PV/T system.

Abstract Low efficiency of heat conduction and absorption is a key problem to restrict the application of phase change materials (PCMs). Foam metals, which work as random heat transfer networks, are often used to improve the thermal conductivity of PCMs. But further improvements are still required in engineering. Interestingly, random micro-channels also widely exist in natural heat and mass transfer systems (e.g., minor veins of leaves and blood capillaries) that always appear with ordered branching networks of macro-channels. But the ordered branching networks, which perform as efficient transfer networks, are rare in metal-foam-enhanced PCMs. Therefore, this work enhances the PCMs’ heat-absorption efficiency by constructing heat transfer networks mimicking leaf veins. Given the gap that there lack trusted design criteria to design the heat transfer networks, we propose an innovative optimization criterion mimicking the generating process of leaf veins. Combine the criterion with an original flexibility-oriented optimization framework, a generating design method is established. The optimization performance is discussed in point-area PCM structures. Compared with the metal-foam-enhanced PCM plate, the heat-absorption efficiency of the generating-based PCM plate is increased to 196.67% in concentrating heat from the PCMs, and the heat-absorption efficiency is also enhanced for more than 3.79 times in dispersing heat to the PCMs. With these improvements, the proposed method is applied in cooling high-power electronic devices which solves the overheating problem and prolongs the working time to 400.00%. Further applications can be expended to PCM-cooling systems, heat pump, collection and output of solar energy and waste heat, etc.