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[en] An investigation of estimating clear sky insolation has been conducted. Some discrepancies have been found between the conventional method of estimation and the data. It has been noticed that the conventional method underestimates the insolation. A simpler, more elegant and more accurate 'universal' relationship has been derived for estimating the annual mean daily clear sky insolation as a function of the latitude and altitude of a given location. As part of this derivation, two simple and accurate correlations have been obtained, i.e. for extraterrestrial insolation and for atmospheric attenuation
[en] Highlights: • A solar thermoelectric with micro-channel heat pipe system was presented. • Mathematical model of the system was built. • Experiment and the simulation were compared to verify the model. • Performance of the system with different factors was analyzed. - Abstract: Micro-channel heat pipe can convert the low heat flux to the high heat flux by changing the ratio of the evaporator area to the condenser area and has a higher heat transfer performance than the common heat pipe. Combining the solar concentrating thermoelectric generation with micro-channel heat pipe can save the quantity of thermoelectric generation and reduce the cost significantly. In this paper, a solar concentrating thermoelectric generator using the micro-channel heat pipe array was designed, and the mathematical model was built. Furthermore, the comparison of the experiment and the simulation between the solar concentrating thermoelectric generator using the micro-channel heat pipe array and the thermoelectric generations in series was made. In addition, the performance on the different areas of selective absorbing coating, different concentration ratios, different ambient temperatures, different wind speed all were analyzed. The outcomes showed the overall performance of the solar concentrating thermoelectric generator using the micro-channel heat pipe array system.
[en] Highlights: • A technical solution to the power supply of wireless sensor networks is presented. • The low voltage produced by TEG is boosted from less than 1 V to more than 4 V. • An output current and voltage of TEG device is acquired as 21.47 mA and 221 mV. • The device successfully provides output power 4.7 mW in no electricity conditions. • The thermo-economic value of TEG device is demonstrated. - Abstract: Motivated by the limited power supply of wireless sensors used to monitor the natural environment, for example, in forests, this study presents a technical solution by recycling solar irradiation heat using thermoelectric generators. Based on solar irradiation and the earth’s surface-air temperature difference, a new type of thermoelectric power generation device has been devised, the distinguishing features of which include the application of an all-glass heat-tube-type vacuum solar heat collection pipe to absorb and transfer solar energy without a water medium and the use of a thin heat dissipation tube to cool the earth surface air temperature. The effects of key parameters such as solar illumination, air temperature, load resistance, the proportional coefficient, output power and power generation efficiency for thermoelectric energy conversion are analyzed. The results of realistic outdoor experiments show that under a state of regular illumination at 3.75 × 10"4 lx, using one TEG module, the thermoelectric device is able to boost the voltage obtained from the natural solar irradiation from 221 mV to 4.41 V, with an output power of 4.7 mW. This means that the electrical energy generated can provide the power supply for low power consumption components, such as low power wireless sensors, ZigBee modules and other low power loads
[en] A district space heating and cooling system using geothermal energy from bearing piles was designed in Shanghai and will be installed in two years before 2010. This paper describes the pile-foundation heat exchangers applied in an energy pile system for an actual architectural complex in Shanghai, 30% of whose cooling/heating load was designed to be provided by a ground-source heat pump (GSHP) system using the energy piles. In situ performance tests of heat transfer are carried out to figure out the most efficient type of energy pile and to specify the design of energy pile system. Numerical investigation is also performed to confirm the test results and to demonstrate the medium temperature variations along the pipes. The averaged heat resistance and heat injection rate of different types of energy piles are calculated from the test and numerical results. The effect of pile type, medium flow rate and inlet temperature on thermal performance is separately discussed. From the viewpoint of energy efficiency and adjustability, the W-shaped underground heat exchanger with moderate medium flow rate is finally adopted for the energy pile system
[en] Highlights: • A new method for design of segmented TEG is proposed. • Optimal length ratios for output power and efficiency are different. • Material properties, geometry and heat transfer all need to be considered. • This method is approved to be accurate and time-efficient. - Abstract: A comprehensive method for indicating the length ratio of segmented thermoelectric generator (TEG) is proposed to increase the output power and thermoelectric conversion efficiency. It is found that for a segmented TEG, there is an optimal length ratio corresponding to the highest maximum output power or thermoelectric conversion efficiency, which is not only dependent on the material properties but also the heat transfer conditions and geometry structure. The optimal length ratios corresponding to the output power and thermoelectric conversion efficiency are different. This method is also validated, and the error is within a reasonable range, indicating that this method can be used accurately and time-efficiently for the design of segmented TEGs.
[en] Highlights: • Thermodynamic analysis is presented for a LAES system combined with packed bed units. • The LAES system round-trip efficiency is in the range 50–62%. • Cold box inlet temperature and discharge pressure have significant influence on system performance. • LAES system has smaller air storage volume and higher ASED compared with A-CAES system. - Abstract: Energy storage is a key technology required to manage intermittent or variable renewable energy, such as wind or solar energy. In this paper a concept of an energy storage based on liquid air energy storage (LAES) with packed bed units is introduced. First, the system thermodynamic performance of a typical cycle is investigated and temperature distribution in cold boxes is discussed. Then, the effects of inlet temperature of cold boxes, charge and discharge pressures on thermal behaviors of LAES system are analyzed, as well as the system round-trip efficiency. Finally, an overall comparison between this LAES system and an adiabatic compressed air energy storage (A-CAES) system is conducted. The system could achieve a round-trip efficiency in the range 50–62% depending on the values of process conditions. The system round-trip efficiency decreases with the increase of cold box inlet temperature, and increases with the rise of charge and discharge pressures. Although the round-trip efficiency of the present LAES system is a bit lower than the A-CAES system, however, the air storage volume decreases and the air storage energy density (ASED) increases remarkably for the same operational conditions. The main conclusions draw from this work is beneficial for future LAES development in particular the combination with the packed bed units and the fit with the requirements for large-scale energy storage.
[en] Aim: Policy-makers typically track the rapidly evolving U.S. residential photovoltaic (PV) market by relying on price data reported by PV installers/integrators to incentive programs. Recent years have witnessed a shift toward third-party-owned (TPO) business models, in which the absence of a cash purchase price obscures data interpretation. Appraisals—often based on estimates of the average fair market value across a diverse fleet of systems—are one way TPO prices are reported. Scope: This study investigates residential PV system price drivers to improve the accuracy, consistency, and relevance of PV price-tracking efforts. Our econometric approach evaluates system price drivers using California Solar Initiative data, controlling for system, installer, and geographic variables. Conclusions: We find that reported prices for confirmed appraised systems are $1.13/W higher than non-appraised systems and do not respond to hypothesized price drivers. For non-appraised systems, we find preliminary evidence of market distortions based on the impact of the incentive level, module cost and household income on reported price. Further, unspecified installer heterogeneity—possibly due to differences in products, cost structure or reporting practices—is a substantial price driver. Using estimates, we develop a price model to approximate non-appraised system prices. -- Highlights: •This analysis evaluates residential PV price drivers using an econometric model. •Reported prices for appraised systems are $1.13/W higher than non-appraised. •Reported prices for appraised systems do not respond to expected price drivers. •We find some evidence of market distortions in non-appraised systems. •Installer heterogeneity is a substantial price driver for all systems
[en] Renewable energy generation is expected to continue to increase globally due to renewable energy targets and obligations to reduce greenhouse gas emissions. Some renewable energy sources are variable power sources, for example wind, wave and solar. Energy storage technologies can manage the issues associated with variable renewable generation and align non-dispatchable renewable energy generation with load demands. Energy storage technologies can play different roles in each of the step of the electric power supply chain. Moreover, large scale energy storage systems can act as renewable energy integrators by smoothing the variability. Compressed air energy storage is one such technology. This paper examines the impacts of a compressed air energy storage facility in a pool based wholesale electricity market in a power system with a large renewable energy portfolio
[en] Thermal energy storage system (TES) is developed to extend the operation of power generation. TES system is a key component in a solar energy power generation plant, but the main issue in designing the TES system is its thermal capacity of storage materials, e.g. insulator. This study is focusing on the potential waste material acts as an insulator for thermal energy storage applications. As the insulator is used to absorb heat, it is needed to find suitable material for energy conversion and at the same time reduce the waste generation. Thus, a small-scale experimental testing of natural cooling process of an insulated tank within a confined room is conducted. The experiment is repeated by changing the insulator from the potential waste material and also by changing the heat transfer fluid (HTF). The analysis presented the relationship between heat loss and the reserved period by the insulator. The results show the percentage of period of the insulated tank withstands compared to tank insulated by foam, e.g. newspaper reserved the period of 84.6% as much as foam insulated tank to withstand the heat transfer of cooking oil to the surrounding. The paper finally justifies the most potential waste material as an insulator for different temperature range of heat transfer fluid
[en] Wind and solar energy will play an important role in the decarbonization of the European electricity generation. However, high shares of these variable renewable energies (VREs) challenge the power system considerably due to their temporal fluctuations and geographical dispersion. In this paper, we systematically analyze transmission grid extensions as an integration measure for VREs in Europe. We show the effects of grid extensions for fundamental properties of the power system as a function of the penetration and mix of wind and solar energy. Backup capacity requirements and overproduction are reduced with a powerful overlay transmission grid. We determine the costs of the grid extensions in dependence of the VRE penetration and mix and find that the grid integration costs remain below 25% of the VRE investment costs for all conceivable VRE configurations. Furthermore, robust design features of future power systems in terms of grid geometry and flexibility requirements for backup technologies are identified. We apply a spatially and temporally highly resolved techno-economic model of the European power system for our analysis. - Highlights: ► Quantification of the advantages and costs of a European overlay transmission grid. ► Grid integration costs for VREs in Europe remain below 6€/MWh. ► Application of a detailed power system model to a wide parameter space.