Research and demonstration of 20kW wind and solar complementary coupling power supply in Xiangmao Township, Tibet

: In this paper, through technological research and development, we will improve the existing technology of domestic wind / light complementary power stations, apply wind power generation equipment with a single unit capacity of 5kW and 10kW in Xiangmao Township, Naqu City, Tibet, and optimize the system design. The completed power station will supply power to 42 herdsmen in Xiangmao Township through centralized power supply, and use the form of wind and light complementary coupling power generation to reduce the construction cost of the power station and improve the reliability of the system, It will provide a scientific basis for the next promotion and application of wind and solar projects.


Introduction
Xiangmao township of Naqu County is located in the area with abundant solar energy resources from the central and eastern part of Naqu to Changdu on the surface of Himalayas.It has long sunshine time, large annual total radiation and stable resources.Due to geographical reasons, the remote villages and towns in Naqu city are not covered by the power grid, and these areas are remote and poor areas.Due to the lack of conventional energy, less coal and oil, the electricity and other domestic energy of towns and herdsmen need to be imported from other regions, and the cost is relatively expensive, As shown in Figure 1.Xiangmao Township, Naqu County, Naqu City, 4683 meters above sea level, is located 72 kilometers south of Naqu County, Tibet, with 272 villagers from 42 households in the village.According to our investigation, the village has used the solar household system with a capacity of 150W as early as 1999, but many household systems have been unable to use due to the long history.Zongrege village, Xiangmao Township, is dominated by animal husbandry, of which 42 households live relatively concentrated.According to the field measurement, these herdsmen live within a radius of 800 meters, and the other 20 households live very scattered, with a distance between households of more than 300 meters.Some villagers do not use electricity, but still use candles or butter for lighting, and some even use firewood for heating and lighting, The lack of electricity has restricted the local economic development and the improvement of people's production and living conditions.This village urgently needs to solve the problem of electricity.According to the local solar energy resources and wind resources, solar power stations with complementary wind and solar energy coupling are used to solve the problem of power consumption.Working principle: in the daytime, under the irradiation of sunlight, solar cells generate direct current; Driven by the wind, the alternating current generated by the wind turbine is rectified and turned into direct current; Part of the direct current generated by solar energy and fan is transmitted to the inverter through their respective controllers to convert into current and supply it to users, and the other part is stored after charging the battery; When sunlight or wind energy is insufficient, the battery sends power to the inverter through the DC control system, which is converted into AC for AC load [4].

Solar module design
According to the provisions of GB50797-2012 code for design of photovoltaic power stations, in the photovoltaic array, the electrical performance parameters of each photovoltaic module in the same photovoltaic module string should be consistent.In this paper, a total of 32 165Wp solar panels are used, which are connected by 8 series as a group, 4 groups and a charging circuit.The output charging circuit is 4 channels, and the actual power output of the photovoltaic array is 5.28kW, as shown in Figure 3[5-6].

Control and inverter design
The controller is a control unit connecting the solar photovoltaic module array and the energy storage battery pack.It charges the battery by controlling the current and voltage, and has the function of protection and monitoring.Photovoltaic inverter is mainly used to convert DC power supply into AC power supply.The inverter configured in the system of this power station adopts dc220v power supply.The function of the inverter is to convert DC power from solar cells into AC power for AC loads.The controller is matched with the photovoltaic module, and the capacity of the inverter should be determined according to the actual load, with additional consideration of capacity reduction at high altitude [8].
The inverter capacity in this paper is 30KVA.Inverter is the core equipment of photovoltaic power station, and the load is mainly motor inductive load.The impulse current of motor load is large when starting.Considering the guarantee of actual power supply, it is generally 1.2-5 times.A total of 3 sets of 10KVA off grid inverter equipment are selected for this project, and the power supply mode of two for use and one for standby is adopted, as shown in Figure 5[9].

Battery pack design
In this paper, the DC voltage of the power station system is designed according to dc220v.In this project, the discharge depth coefficient of the battery is 0.7, the efficiency is taken as 90%, and the continuous rainy days are considered as 2 days.The 20kW off grid photovoltaic power station generates an average of 4.6 hours of electricity per day.Based on the calculation of 2-day daily electricity consumption, the batteries in this paper are installed in two groups, with 108 batteries in each group, a total of 216 batteries, single batteries of 800ah/2v, and the net weight of the whole battery group is about 14.47 tons, as shown in Figure 6 [10][11].
Fig. 6 Site photo of battery pack

Benefit analysis
The 20kW wind solar complementary coupling power station demonstrated in this project is located in Xiangmao Township, Naqu City, Tibet.The power station is expected to generate 34310 kWh per year.According to the actual data, the average annual power generation in recent years is about 36100 kWh.According to the average on grid electricity price of Naqu City, Tibet is 0.7 yuan / kWh (regardless of dry season, wet season and peak valley level), and the annual income is 36100 kWh × 0.7 yuan/degree =25270 yuan ≈ 25000 yuan.After the completion of the project, the daily electricity consumption of 272 people in 42 households has been solved, and their living conditions have been improved.This is of great significance to solve the problem of electricity consumption of farmers and herdsmen in Naqu power free area of Tibet, improve the quality of life of farmers and herdsmen, build a harmonious and prosperous Tibet, promote the stability and prosperity of Tibet, and promote the construction of a new socialist countryside in Tibet.The social benefits of the project are very significant.According to the calculation of 4 tons of standard coal consumed per 10000 kwh of electricity, 0.5 tons of dust and 10 tons of carbon dioxide emitted into the atmosphere, it is equivalent to saving 14.4 tons of standard coal per year, and reducing 1.8 tons of polluted dust and 36 tons of carbon dioxide emissions at the same time.

Fig. 5
Fig.5 Site photos of controller and inverter

Fig. 7
Fig.7 Photos of on-site implementation of transmission lines