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In this work, a novel enhanced deep borehole heat exchanger (EDBHE) was proposed to improve heat extraction efficiency based on the jet grouting method. By means of this technology, a soilcrete zone with high thermal conductivity was built near the wellbore. To analyze the feasibility and efficiency of this method, we firstly constructed a validated deep borehole heat exchanger (DBHE) model based on the field experimental data. Numerical simulations were carried out to investigate the 30-year production performance of EDBHE. Results demonstrated that the jet grouting method is an efficient way for improving thermal output of DBHE. It is evaluated that the average annual heat production rate over a 30-year heating period of EDBHE is 463.2 kW, which is 1.27 times as that of DBHE. Sensitivity analyses indicate that the heat production rate and outlet temperature mainly depend on the height and radius of the artificial soilcrete zone. However, thermal output is not sensitive to thermal conductivity of the soilcrete zone due to the higher thermal resistance of the geological formation. For the experimental site used in this work, the recommended height, radius, and thermal conductivity of the soilcrete are 1000 m, 1.0 m, and 50 W/m °C, respectively.

Increasing levels of wind energy in modern electrical power system is initiating a need for accurate analysis and estimation of transient stability of wind turbine generation systems. This paper investigates the transient behaviors and possible direct methods for transient stability evaluation of a grid-connected wind turbine with squirrel cage induction generator (SCIG). Firstly, by using an equivalent lump mass method, a three-mass wind turbine equivalent model is proposed considering both the blades and the shaft flexibility of the wind turbine drive train system. Combined with the detailed electromagnetic transient models of a SCIG, the transient behaviors of the wind turbine generation system during a three-phase fault are simulated and compared with the traditional models. Secondly, in order to quickly estimate the transient stability limit of the wind turbine generation system, a direct method based on normal form theory is proposed. The transient models of the wind turbine generation system including the flexible drive train model are derived based on the direct transient stability estimation method. A method of critical clearing time (CCT) calculation is developed for the transient stability estimation of the wind turbine generation system. Finally, the CCT at various initial mechanical torques for different dynamical models are calculated and compared with the trial and error method by simulation, when the SCIG stator terminal is subjected to a three-phase short-circuit fault. The results have shown the proposed method and models are correct and valid.

This paper describes a method that was applied as a part of the creation of a wind map for the Czech Republic. The method (abbreviated VAS/WindAtlas) combines an interpolation method (VAS) with the Wind Atlas methodology applied by using the microscale model WAsP. While WAsP eliminates the site-specific effects around measurement sites to provide generalised wind conditions (GWC), VAS interpolates the GWC over the entire domain and takes into account the general increase of wind speed with altitude. As a result, an altitude-dependent generalised wind map is provided. Then, a final high-resolution calculation is performed by WAsP. The VAS/WindAtlas method is considerably more simplified and less computationally demanding than approaches employing more complex numerical models, but it requires a sufficiently dense network of wind measurements, a thorough data quality evaluation and careful corrections that compensate for the known limitations of the applied data and methods. A comparison of the original wind map with new independent wind measurements, which were obtained after the wind map calculation, was performed with a detailed analysis of the expected errors and uncertainties at the validation sites. The presented VAS/WindAtlas method proved to be good solution to estimate wind resources of Czech Republic.

The metropolitan cities of developed countries comprise more than 50% of the global population and consume over 60% of the world's energy. Many governments plan to enhance their energy infrastructure and the electricity supply–demand reliability of their energy sources. Among them, South Korea's government has developed electricity generation facilities, most of which use renewable resources such as photovoltaic and wind energy. This study determines the optimal renewable electricity generation configuration for one of the largest metropolitan cities in South Korea, Busan metropolitan city. A simulation using 2013 Busan electricity demand data produces this optimal configuration, which includes photovoltaic panels, wind facilities, converters, and batteries with $0.399 of COE (Cost of Electricity) and 100% of renewable fractions. Both the study's practical limitations and implications are discussed.

This paper explores the possibility of a development project with a geothermal well doublet in the Pisa plain, Italy. The performance of the system has been evaluated with a 3-dimensional field-scale nu- merical model that simulates the evolution of temperature and pressure conditions in the aquifer, under different exploitation scenarios. Coupled groundwater flow and thermal transport processes in the reservoir are considered together with non-Darcy fluid flow in the wellbores, and heat exchange be- tween boreholes and surrounding rock formations. Calculations are performed with a parallelized version of the wellbore-reservoir simulator T2Well. This code allows for the efficient modeling of coupled hydraulic-thermal processes over a domain about 40 km2 wide and 1.5 km thick. Simulation results indicate that the energy of the reservoir is sufficient for the designed extraction rate (between 80 and 150 m3/h), but also suitable for much larger rates, up to 250 m3/h. Although aimed at assessing the long-term performance of a specific system, this modeling approach could be profitably applied for the design of similar projects elsewhere.

Hazelnut shell ash was investigated as a new base catalyst for the transesterification of used cooking sunflower oil to biodiesel. To understand its catalytic properties, the prepared ash was characterized by EDX, XRD, TGA/DTA, Hg porosimetry, N2 physisorption, FE-SEM, and basic strength measurements. The effects of the catalyst loading in the range of 1–5% of the oil weight and the methanol-to-oil molar ratio of 6:1–18:1 on the kinetics of the fatty acid methyl esters synthesis were established. Moreover, the leaching and reusability of the catalyst were assessed. The obtained results revealed that hazelnut shell ash was mostly composed of K, Ca, and Mg. The highest ester content (98%) was achieved at the catalyst loading of 5%, the methanol-to-oil molar ratio of 12:1, and the reaction time of 10 min. The contribution of homogeneous catalysis because of the catalyst leaching was confirmed but did not determine the overall reaction rate. The catalyst can be reused after the recalcination at 800 °C for 2 h achieving the high methyl esters content (>96%) in 30 min after three subsequent runs. The overall reaction followed the pseudo-first-order kinetics with respect to triacylglycerols. A linear relationship between the apparent reaction rate constant and the catalyst loading and the methanol-to-oil molar ratio was determined. The determined value of the reaction rate constant was 0.0576 dm6/(min•mol2).

Tools and experience on solar thermal cooling system sizing and design are still limited, as less than one thousand plants have been built until now. In this paper, a design tool for mid-size thermal solar cooling systems is presented. The tool consists of a model realised in TRNSYS and validated using the data of a real solar air conditioning system installed in the green building of Shanghai Research Institute of Building Science. Characteristic features of the system are the use of adsorption chillers driven by low-temperature solar heat from U-type and heat pipe evacuated solar collectors. The model has subsequently been employed for a technical analysis: the most relevant parameters have been varied and figures of merit calculated. An energy analysis has been performed for 6 reference cities, differing for climates and latitudes, highlighting the possibility to use only renewable energy for cooling purposes. Eventually, the systems have been compared with reference ones. Comparison highlighted that considerable savings in primary energy and CO2 emissions can be achieved: 0.97 MWh per installed square meter of solar collectors and up to 22 tons of CO2 annually, thus indicating a great potential for increasing energy efficiency and reduce CO2 emissions.

Understanding of hydraulic heterogeneity of the reservoir is the basis for Enhanced geothermal systems (EGS) optimization. This, however, is challenging, as there are limited well tests available for reservoir characterization. To overcome this challenge, this study developed a methodology for determining hydraulic parameters by integrating the induced micro-seismic data collected during the hydraulic stimulation, and tracer test data in the subsequent trial production period for the first time. The spatio-temporal distribution of induced micro-seismicities is indicative of the hydraulic diffusivity distribution, and is subsequently converted into the heterogeneous distribution of permeability and porosity, by quantitative calibrating models outputs with tracer test observations. This approach was verified and applied to the Habanero EGS, Australia, where the accuracy in calibrating the tracer test responses was improved by over 50%, attributed to the constraints of micro-seismic data. The well placement was then optimized based on new insights of hydraulic parameters in the reservoir. As a result, the electrical power efficiency was increased by 5.59 times in 30 years. The wide existence of tracer and induced micro-seismic data promotes the generality of this methodology to improve the reservoir characterization and well placement optimization for the sustainable development of EGS.