This article proposed a model improvement method based on the second-order RC equivalent circuit model, which was carried out under testing conditions of missing temperature sample and fewer discharge current sample. And a BP neural network was constructed to predict the terminal voltage error of the model in a wide range of temperature and current rates, in order to achieve dynamic compensation of the model. This method can avoid the loss of cycle life caused by repeated charging and discharging experiments of lithium-ion batteries. The simulation and experimental results indicate that the proposed small sample data expansion method is feasible; The battery model with an additional controllable voltage source has better adaptability at different temperatures and current rates, improving the accuracy of the model. Through model analysis, batteries are screened to form a cascade utilization energy storage system, and combined with battery models to achieve SOC prediction and heat warning. The model has practical engineering significance for the application of new energy generation battery energy storage systems.

Through simulating the mechanical motion equation of synchronous generator, this paper proposed voltage-controlled virtual synchronous generator, designed the prime mover regulation and excitation regulation control strategy, and simulated the rotational inertial of synchronous generator, so as to improve the active support ability of renewable energy for power grid operation stability. This paper proposed five control characteristics evaluation indicators including active power-load coefficient, active power frequency regulation coefficient, reactive power voltage regulation coefficient, primary frequency regulation stable time, and reactive power voltage regulation stable time. In addition, based on Matlab/Simulink’s electromagnetic transient simulation and verification model of voltage-controlled virtual synchronous generator, the influence of different key control parameters on the performance of voltage-controlled virtual synchronous generator active frequency regulation and reactive power regulation under small disturbances, quantitative analysis the trends and laws of key indicators were analyzed. The virtual inertial, damping parameters, reactive power integral parameter and droop parameter optimization parameter range were given for engineering application. Finally, the interactive resonance mechanism of voltage-controlled virtual synchronous generators was studied by establishing the parallel grid-connected system model of multiple voltage-controlled virtual synchronous generators. The critical parameters, oscillation frequency and multi-generators parallel oscillation mode of multiple voltage-controlled virtual synchronous generators grid-connected system were obtained.

Aiming at the high-efficiency OTEC application, a 3 kW radial-inflow turbine using R134a was constructed. In addition, a 3D CFD simulation was carried out to research the turbine performance and analyze the variable conditions. Finally, the influences of radial clearance and the number of rotor blades on the performance of radial-inflow turbines are analyzed. It is indicated that the performance of the designed turbine is satisfactory with a theoretical isentropic efficiency of 84.96%. The results show that the optimal rotational speed of turbine increases with the increasement of inlet pressure. When the rotational speeds deviate from the optimal value, the turbine efficiency decreases. The results also indicate that the increasement of inlet pressure increases the output work of turbine. With the increasement of rotational speed, the flow rate gradually decreases. In terms of optimization, the radial clearance between the nozzle and the rotor makes the working fluid flow more uniform at the nozzle outlet. Finally, the turbine performance is improved by increasing the number of rotor blades to 8.

Increasing the current of the silicon heterojunction（HJT） solar cell is expected to further improve its efficiency. Transparent conductive oxide film （TCO） is an important functional layer that affects the current of the HJT solar cell. In this paper, the characteristics of TCO films are firstly introduced, including the effects of doping elements, doping ratios and preparation techniques on the film properties. Moreover, the influence of film properties on the performance of HJT cells is summarised. Finally, the latest progress and development trend of TCO film application are described. Increasing the cap layer or adopting multilayer TCO film structure is expected to improve the characteristics of TCO films and solar cell performance. It is expected to guide the optimization of TCO films characteristics, so as to further improve the efficiency of HJT solar cell and accelerate its industrialization process.

In order to overcome the drawbacks of low thermal efficiency and poor sustainable performance, this paper proposes a novel strategy using metal pipes and backfilling the borehole with permeable materials. The heat transfer process under different geo-materials and the soil temperature response are investigated through physical model tests. The results show that the energy efficiency coefficient （EEC） of a metal pipe increases with the increased permeability of the geo-materials. Compared with clay, the EEC of gravel with a hydraulic conductivity of 1.04×10 ^-3 m/s increases by 72.31%, indicating the aquifer is a suitable geological setting for the application of the proposed technology. The monitoring of soil temperature display that the higher the hydraulic conductivity the slower the temperature change of the aquifer is, implying a higher thermal diffusion which in turn improves heat transfer efficiency. The EEC of the heat exchanger with a heating power of 100 W increases by 73.08% compared to 50 W, indicating the effects of thermally induced heat convection are more significant at a higher thermal load.

Different shapes of solar chimney （SC） systems have different effects on the heat collection characteristics of the system. A 10° circular SC numerical simulation model and a test bench were established. The comparision betweenthe numercial simulation and the test results showed that the relative error was less than 4%, which ensured the correctness of the model and numerical simulation method. The same numerical simulation method was used to calculate the 0° circle, 0° square and 10° square SC models, and the results of different systems were compared. The results show that the uniformity of the surface temperature field of the absorber varies with different system structures, and the influence of the chimney shadow on the surface temperature field of the 10° square absorber is the least. Compared with the fluid velocity in the chimney, the 10° square has a higher velocity gradient, which is more conducive to determining the turbine position. The total enthalpy difference of the fluid in the chimney of different systems is different, and the total enthalpy difference of the 10° square is larger. Compared with the 0° circular SC system, the collector efficiency of the other three SC systems is increased by 11.328%, 43.705% and 66.061%, respectively, and the mass flow rate is increased by 59.36%, 8.39% and 39.04%.

In response to the problem that the previous digital twin modeling of the wind turbine is limited by different research purposes or the function of a single software, which makes it challenging to establish the whole model of the wind turbine, a new wind turbine twin modeling method is proposed. The method first relies on the FAST wind performance module to build the steady-state and the random turbulent wind model, the real-time wind speed model of wind farms. Then the aerodynamics module and the structural dynamics module are used to build the geometric and dynamics models of critical components such as wind turbine blade and towers respectively. Finally, the wind turbine electrical system model and control strategy were built in Simulink, which resulted in a complete twin model of the wind turbine. The twin modeling approach was validated for WindPACT 1.5 MW doubly-fed wind turbine and Fuhrländer 2.5 MW doubly-fed wind turbine at a wind farm, and the results showed that the twin model has a high accuracy of all essential production parameters compared to the design standard and actual operation data under different wind speed models. In addition, the feasibility and validity of the twin model were further demonstrated by real-time simulation of the wind turbine digital twin system and twin simulation of the unmeasurable data in the field.

In this paper, a typical rural area in northern Shaanxi province was investigated, Monte Carlo simulation was used to generate aggregated shiftable load curves on the basis of family clustering, and a comprehensive evaluation from the perspectives of time, energy, and randomness was given. The results show that the volume of cooking load is large but the time range to be shifted is small, while the volume of laundry load is small but the time range to be shifted was large. Overall, domestic hot water load is more comprehensive in the above three aspects, the heat storage properties of water tank makes the shiftable load potential more significant.

Response surface methodology （RSM） is used to study the relationship between three physical properties of biomass seedling pot density, drop breakage rate and pressure breakage rate of buckwheat straw and molding pressure, dosage of binder and holding time. MOPSO optimization algorithm is used to carry out three response optimization analysis of process parameters. The experimental results show that when the pressure is 8-12 MPa, the amount of binder is 60%-90%, and the pressure holding time is 11-14 min, the seedling pot density can reach above 1.041 g/cm ³, and the drop damage rate and pressure damage rate are below 2.97% and 2.65%, respectively. When the optimal molding parameters are pressure 11.73 MPa, binder dosage 60.5% and holding time 12.7 min, the seedling pot density reaches 1.168 g/cm ³, and the drop damage rate are 2.52% and 2.58%, respectively.

Accurate identification of solar cell model parameters has a great impact on PV module power prediction and maximum power point tracking, and it must be ensured to have high accuracy. Traditional intelligent algorithms can achieve a certain degree of parameter identification, but they all suffer from the problems of insufficient accuracy, slow convergence, and easy to fall into local optimality. To address such problems, a solar cell model parameter identification method based on the improved pelican optimization algorithm （IPOA） is proposed. In this algorithm, the population individuals are closely connected, and the position is updated by mutual learning of randomness, which has better effect than the traditional algorithm in engineering applications. At the same time, for the characteristics of this algorithm, a position updating strategy based on Jaya algorithm is introduced to make the candidate solutions of the population more optimal; the decreasing factor is improved to make the model better in the later stage of the iteration. The Lévy flight strategy is added, which effectively improves the algorithm accuracy. IPOA has good results under different solar irradiance, and the discrimination results fit well with the actual curves, indicating that IPOA can accurately and effectively identify the solar cell model parameters in different environments.

Based on continuous heating air source heat pump hot gas bypass defrost technology, this study proposes a segmental defrosting continuous heating air source heat pump system and investigates its performance in an enthalpy difference lab. The results show that lower ambient temperature or lower relative humidity or higher condensing temperature will reduce the average heating capacity of the segmental defrosting system. The change of compressor suction pressure in the process of segmental defrosting is 698.5 kPa smaller than that of reverse cycle defrost, and the change of discharge pressure is 238.9 kPa smaller than that of reverse cycle defrost. The defrosting sequence from top to down takes more time for each coil, while the defrosting sequence from down to top takes basically the same time for each coil, top to down defrosting sequence reduces total defrosting time by 55 s compared to top to down defrosting sequence, but has an impact on“secondary frosting”. Compared with the traditional reverse cycle defrost system, the segmental defrosting system has the advantages of short defrosting time and continuous heating, high COP, and less impact on the system. The switching of valves during defrosting will cause some local pressure fluctuations and energy loss in this system, which needs to be further optimized.

To investigate the application prospects and energy harvesting characteristics of two tandem cylinder with different diameter ratios in the field of wind vibration power generation,the vibration response and energy conversion characteristics of a two tandem cylinder system with different diameters are investigated under the condition of L/ D=1.5, where the upstream cylinder is fixed and the downstream cylinder only vibrates in the transverse direction. The results indicate that the downstream cylinder exhibits both vortex-induced vibration and galloping vibration response, and the diameter ratio affects the vibration response and force characteristics of the downstream cylinder, which leads to the change of the lock-in velocity range. The galloping exhibits a harvesting power two times larger than the vortex-induced vibration. The energy conversion efficiency can be about 30% in the vortex-excited vibration region, but only 10% in galloping region. Based on these analysis results, the advantage of d/ D=0.8 energy conservation is more notable at low reduced velocity, but at high reduced velocity, the advantage of d/ D=0.6 energy conservation become more significant.

This paper conducts a test study on the hot spot temperature of modules prepared by current mainstream module products, especially large-size cells, and specifically analyzes the key influencing factors affecting the hot spot temperature. The hot spot temperature of the shaded cells is determined by the power dissipated per unit area Φ _q, i.e., it is related to the number of cells in a single string, the cell leakage current, and the distribution of the cell leakage current. The non-uniform heating at the cell leakage point is the main reason for the high local temperature of the hot spot. At the same time, this paper discusses the hot spot risk control of modules with a relatively large number of single-string cells. The control of cell leakage current value at reverse bias voltage can effectively reduce the hot spot temperature. The screening of cells based on the temperature difference between cell leakage point and non-leakage area at reverse bias voltage can further control the hot spot risk.

Under the background of ‘dual carbon’, based on the comprehensive target domain of wind power forecasting error and smoothing fluctuation, a control strategy is proposed to compensate both the prediction error and smoothing fluctuation of wind power. Firstly, the allowable range of prediction error and wind power fluctuation is determined more strictly than that of the national standard, and the comprehensive target area is established. The target domain is divided into internal and external parts, using improved complete ensemble empirical mode decomposition with adaptive noise （ICEEMDAN） and technique for order preference by similarity to an ideal solution （TOPSIS）to calculate the scope of super capacitor and battery, which bear the part with the larger change rate and the smooth part respectively. And then, the hybrid energy storage batteries acting on the target domain are divided into four groups, and the states are switched according to the charge/discharge power. Finally, a wind farm in Xinjiang was taken as an example for simulation analysis, and a comprehensive comparison of various decomposition methods and energy storage configuration methods was made to prove the effectiveness of the proposed strategy.

Conventional PV power stations can only rely on local surface meteorological observation information for irradiance forecasting, and it is difficult to tap the spatio-temporal correlation characteristics of wide area photovoltaic resources around the power station for these kinds of stations, which limits the forecasting accuracy of irradiance and PV power. To solve the above problems, this paper proposes a mapping method for the spatial distribution of wide area irradiance around PV power station based on satellite remote sensing, and establishes an ultra-short-term spatio-temporal correlation forecasting model for surface irradiance based on graph convolutional network （GCN）. The method makes full use of multi-channel satellite data and considers the spatio-temporal correlation characteristics to improve the ultra-short-term prediction accuracy of surface irradiance. The feasibility of the inversion model of surface irradiance is verified through the simulation analysis of a photovoltaic station, and the progressiveness of the corresponding spatial-temporal correlation prediction model is also proved.

Firstly, the application scale of wind power blades at home and abroad and the trend of decommissioned wind power blades are introduced, and the international common disposal methods of decommissioned wind power blades（stacking, burying, and recycling） and their advantages and disadvantages are described. Secondly, the typical recycling methods of waste blade materials, namely mechanical recycling, thermal recycling, and chemical recycling, are systematically introduced, and the technical characteristics of the above three typical recycling methods are compared. Thirdly, the typical cases of product remanufacturing using retired wind power blades are summarized, including the preparation of recycled composite plates, the manufacture of concrete aggregates, the preparation of 3D printing consumables, etc. Finally, aiming at the difficult cutting performance of common wind power materials such as glass fiber composites and carbon fiber composites, the recycling processing technology and equipment of wind power blades are introduced, including cutting processing technology and equipment, crushing and crushing processing technology and equipment, etc.

The large-scale implementation of solar photovoltaics （PV） changes the types and characteristics of the underlying surface and gradually changes local ecological succession. Their impact on local climate and ecosystem has been widely studied in recent years. This scientific question is the important foundation for designing climate-ecosystem-friendly PV stations and developing sustainable renewable energy. This paper summarizes the existing research methods including field observation and numerical simulation, and the results show that the implementation of PV significantly impacted local radiation, temperature, humidity, and wind speed. By increasing the biodiversity, changing the growth of the vegetation, as well as changing the physical and chemical properties of soil in the PV station, large-scale implementation of PV will protect the ecologically fragile area from soil erosion, and the local ecosystem will benefit from windbreak and sand fixation. However, the existing studies are localized. The principle of these changes can be partly explained by the changes in radiation balance and the water-energy cycle process. Further observational studies about large-scale PV stations and urban PV systems should be explored to reveal the critical role of factors and processes such as conversion efficiency and evapotranspiration. The payoff of ecological benefits during the construction and operation of PV stations should be valued to prevent desertification, ecological damage, and soil pollution.

This paper researches the optimal control method and SOC balance strategy of distributed battery energy storage system, and proposes a cooperative control strategy based on SOC balance. The multi-agent system （MAS） theory was used to realize the cooperative control of battery energy storage system, and the multi-agent distributed algorithm was used to realize the adaptive allocation of power instructions,and then realized SOC dynamic equalization. Aiming at the slow convergence of traditional multi-agent algorithm,a distributed algorithm based on model predictive control （MPC） was proposed. MPC was used to optimize the traditional multi-agent algorithm and improve the convergence speed. Finally, the effectiveness of the proposed strategy and the advantages of the algorithm in convergence speed are verified by simulation with the actual energy storage power data.

The error of solar energy resource parameters from ERA5 reanalysis data is evaluated based on parameters from data of 40 ground observation stations around China. The results show that the regression equations’ coefficient of determination （ R ²） of the monthly surface global horizontal irradiance from ERA5 data against that from stations is 0.999. The maximum and average root mean square error （RMSE） between data from ERA5 and stations are 8.7 MJ/m ² and 4.9 MJ/m ², and the maximum and average relative root mean square error （RRMSE） are 2.4% and 1.0%. The maximum and average error of inter-annual variability （IV） between data from ERA5 and stations are 19 MJ/m ² and 3 MJ/m ², and the maximum and average error of percentage inter-annual variability （PIV） are 0.5% and 0.1%. The maximum and average error of stability between data from ERA5 and stations are 0.013 and 0.003, and the maximum and average percentage errors are 2.9% and 0.8%. ERA5 data is validated in this study to be of good consistency with the observation stations data, and application of ERA5 data to solar energy resource assessment in China is feasible.

In this study, the comprehensive energy efficiency of bifacial photovoltaic vertical shading system is studied experimentally and theoretically. Firstly, a bifacial photovoltaic vertical shading power generation model based on EnergyPlus is established, and the accuracy of the model is verified through experiments. Then, combined with the energy consumption of air conditioning and lighting, a comprehensive energy efficiency model of bifacial photovoltaic vertical shading system is established. Finally, based on the verified model, the impact of climate conditions, overhang width and installation tilt angle on the comprehensive energy efficiency of the system is analyzed by using three evaluation indicators： net energy consumption （ Q _NEC）, self-consumption rate （SCR） and self-sufficiency rate （SSR）. The results show that the net energy consumption decreases with the increase of the inclination angle, and the energy saving rate can reach 71.25% at the maximum. The variation tendency of self-satisfaction rate is basically consistent with photovoltaic power generation, and the trend of self-consumption rate is highly consistent with net energy consumption.