Simulation of Vertical Solar Power Plants with Different Turbine Blades

The performances of turbine blades have a significant impact on the energy conversion efficiency of vertical solar power plants.In the present study,such a relationship is assessed by considering two kinds of airfoil blades,designed by using the Wilson theory.In particular,numerical simulations are conducted using the SST K−ω model and assuming a wind speed of 3–6 m/s and seven or eight blades.The two airfoils are the NACA63121(with a larger chord length)and the AMES63212;It is shown that the torsion angle of the former is smaller,and its wind drag ratio is larger;furthermore,the resistance is increased by about 66.3%on average.Within the scope of the study,the results show that the NACA63212 airfoil is better than the AMES63212 airfoil in terms of power,with an average improvement of about 2.8%.The simulation results have a certain guiding significance for selecting turbine blade airfoils and improving turbine efficiency.

Vertical power flow forecast with LSTMs using regular training updatestrategies

The strong growth of renewable energy sources as well as the increasing amount of volatile energy consumptionis leading to major challenges in the electrical grid. In order to ensure safety and reliability in the electricitygrid, a high quality of power flow forecasts for the next few hours are needed. In this paper we investigateforecasts of the vertical power flow at transformer between the medium and high voltage grid. Forecastingthe vertical power flow is challenging due to constantly changing characteristics of the power flow at thetransformer. We present a novel approach to deal with these challenges. For the multi step time series forecastsa Long-Short Term Memory (LSTM) is used. In our presented approach an update process where the model isretrained regularly is investigated and compared to baseline models. The model is retrained as soon as asufficient amount of new measurements are available. We show that this retraining mostly captures changesin the characteristic of the transformer that the model has not yet seen in the past and therefore cannot bepredicted by the model without an update process. To give more weight to recent data, we examined differentstrategies in terms of the number of epochs and the learning rate. We show that our new approach significantlyoutperforms the investigated baseline models. On average, we achieved an improvement of about 8% with theregular update process compared to the approach without update process.

Effect of blade pitch angle on aerodynamic performance of straight-bladed vertical axis wind turbine

Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.

Fabrication and characterization of a GaN/(4H)SiC vertical pn power diode using direct and interfaced epitaxial-growth approaches

We report the fabrication and characterization of a vertical pn power diode which is realized using two separate epitaxial-growth mechanisms： （a） p-GaN over p-（4H）SiC, and （b） p-GaN over n-（4H）SiC with A1N as the interface layer. In all of the cases, n＋-doped （4H）SiC serves as the cathode substrate. Pd（200 A）/Au（10000 A） is used for the anode contact while Ni（1000A） is used for the bottom cathode contact. The measured forward drop of the pn diode with A1N as the interface material is found to be around 5.1 V; whereas, it is 3 V for the other sample structure. The measured reverse-blocking voltage is found to be greater than 200 V.