1 L introduction
Around the world, the rapid population growth and industrialization degree to improve the energy shortage and environmental pollution have become the common serious problem facing the world today. Active development of new energy, protect the human survival environment has caused the world bank, the global environmental protection agency and the competent department of energy, including political leaders from all over the world. The development of new energy, the use of alternative energy sources and the development and utilization of space resources has become a social, environmental and sustainable development in driven by the necessary measures. In this form, solar photovoltaic technology has entered the rapid development stage.
Photovoltaic pumping system in the number of rapid growth in recent years, especially in Africa, South America, Australia and Asian countries grow quite large. At present, the world bank and the United Nations to promote photovoltaic pumping as solving the problem of remote areas people and water diversion and irrigation technology of choice.
Traditional photovoltaic pumping and lighting system will respectively independent photovoltaic pumping and photovoltaic lighting system, not only has the advantages of no noise, no pollution, full automation and high reliability, also makes photovoltaic array output power to the reasonable application of effective energy saving.
2 the system
Photovoltaic pumping and lighting integrated system structure as shown in figure 1, it is generally by the photovoltaic array pump, frequency converter, motor and battery. The control of the system can be divided into three parts, namely the MPPT (maximum power point tracking) control, DC/AC variable frequency control and charge and discharge control. Its main functions are: to provide motor pump load in sunny day maximum power output; In owe the sun early in the morning or evening in order to maximize power for battery charging; In the night, without sunshine has sufficient power battery will provide lighting load and stable dc power supply.
Figure 2 shows the photovoltaic pumping and lighting integrated circuit principle diagram of the system. Switch between each function of the system is made up of switch SW1 and SW2.
At present, the market of photovoltaic solar cells for monocrystalline silicon solar cell, polycrystalline silicon's market share is growing year by year, amorphous silicon has a place, but its market share only the teens. Solar cell output volt-ampere characteristic has strong non-linear, and sunshine intensity, environmental temperature, rain, fog and many other meteorological factors, when the environment remains unchanged, the output work area including current source area with high resistance properties, including low resistance characteristics of voltage source area. Considering the practical application of the system load frequency converter, a motor, water pump and accumulator, lighting features, generally only will photovoltaic cells used as voltage source, and a current source with high resistance properties become unstable working area. In choosing the system voltage level and installed capacity, pv cells can be divided into several groups in parallel connection, as shown in figure 2.
2.2 MPPT (maximum power point tracking) controller
According to the working principle of solar cells, when the light intensity, temperature and other natural conditions change, the output of the solar cell, will change according to the characteristics of the output power and maximum working point also change accordingly. In the practical application system, the radiation intensity of natural light, and light transmittance of atmosphere are still in the dynamic change of it brought difficulties to the application of photovoltaic system. In addition, the photovoltaic pumping system may be a dc motor, load motor can also be ac motor or other new type of motor. It is due to many unpredictable factors affecting the output of the pv array, makes in the actual system, there must be a adapter, to guarantee the harmony between the power and load, high efficiency, stable working condition. MPPT (maximum power point tracking) controller to meet the requirements of the adapter. Not only that, but it can also make pv pumping and lighting integrated application system can work in any sunshine intensity in the optimal state. Its main functions are: to detect the primary loop dc voltage and output current, calculate the power output of the solar cell array, and realize the maximum power point tracking; To implement special protection function, such as under voltage, over load, load is low, the well is dry.
2.3 DC/AC frequency conversion device
In recent years, due to the new FM speed regulation control theory and the development of power electronic components, to gradually catch up with the efficiency and reliability of ac speed regulation of dc motor. Traditional has also gradually been three-phase asynchronous motor brush dc motor and dc brush motor. In the actual application of motor frequency control of motor speed three phase asynchronous motor is designed. Thus the DC/AC inverter device become indispensable component. Considering the fan pump type load, VVVF modulation method is adopted in the frequency conversion device.
2.4 charge and discharge controller
When the sun light intensity decrease at some point, the maximum output power of pv arrays have been unable to continue to drive the pump pumping, main controller will switch SW1 state to start charging control circuit, to charging of lead-acid battery, and when the output voltage of photovoltaic array to zero when it gets dark, main controller will be closed discharge switch SW2, start lighting load. The charging control circuit is not only to complete the search of maximum power point of owe under the condition of strong light and a corresponding PWM switch T7 has driven charge, as well as complete lead-acid battery state of charge (SOC) detection and protection measures related to the battery.
3 application instance
October and November 1999, two 2.5 kw solar pv pumping and lighting comprehensive application system respectively installed on the campus of tsinghua university and xinjiang shihezi shibei springs. Has been running well so far. The measured data shows that under the condition of the sunny day, the average water for more than 60 m3, sunrise in strong sunlight, can reach more than 80 m3. Figure 3 and figure 4 shows the October 7, 1999, tsinghua university demonstration site measured rizhao power distribution curve and the pump flow curve. In the installation of the system in shihezi area of xinjiang water more than 10 m3 per hour on average. Not only solved the problem of the local irrigation, but also produced a strong demonstration effect.
4 our pv technology market and system promotion prospects
Our country is based on coal as main energy consumption. Than is given priority to with oil and gas energy consumption of the mainstream, the energy structure is not reasonable. In a long historical period, China had to develop energy, transportation, as the focus of the national economy development, excessive mining of energy resources and extensive use, do not hesitate to come at the expense of environmental pollution, tried to break through to the restriction of the national economy, energy and transport in our country now energy development is facing great challenges.
Solar photovoltaic technology in China since the 70 s, after the "purpose", ">", "five-year" three five-year plan research, had certain development. The existing six solar battery manufacturer, annual production capacity of 4.44 MW, the actual sales of 2.0 2.5 MW, is growing at 15% to 20% on average. Products are mainly for monocrystalline silicon photocell and amorphous silicon cell, other types of photovoltaic cells is still on the stage of development. Monocrystalline silicon solar cell conversion efficiency by 14%, laboratory as high as 20%. The stability of the single junction amorphous silicon solar cell efficiency is 5% - 5.5%, laboratory, highest efficiency is 8.35%.
So far, the total installed capacity of solar photovoltaic system in our country in more than 10 MWP, most used in traffic signal, communication and cathodic protection, etc., which accounts for about 60%, above the rest for sunshine resources rich in remote areas of west China. Practice proves that the photovoltaic technology in remote areas without electricity in our country (especially western) application promotion has a special role. In yuzhong county in gansu province in 1982 built the first 10 KWP photovoltaic power station, for more than 200 households farmers light; In 1992, gong of xinjiang county demonstration zone are all made of solar photovoltaic power, made use of solar energy to eliminate the first step in the condition of no electricity. Qinghai province since 1986 has 21000 sets of household photovoltaic system, and has built six village power station since 1990; Prior to the Tibet autonomous region wood building and planning building photovoltaic power station, a total of six, which in December 1998, the expansion of the successful amdo photovoltaic power station, the total installed capacity of 100 KWP, is the biggest solar photovoltaic engineering in our country.
In addition, household photovoltaic system (more than 50 wp in the following) in the country has more than 100000 sets. The world bank through the global environment facility (GEF) project loans and contributions to China, for China's solar photovoltaic demonstration and market development, the purpose is to the western region in China to promote (MWP) about 10 200000 sets of household photovoltaic system. The project under the organization of the setc have been launched.
According to the national solar photovoltaic development plan in 1996-2000, 2000 and 2020 in China's solar photovoltaic capacity reached 66 MWP and 300 MWP.
More than the fact that the use of solar energy in our country has just entered the early stage, has a great potential, especially in our country region vast, rich solar energy resources, the development and utilization of solar energy in the vast space, must pay attention to the development and utilization, China's energy to provide more choices for the future.
In addition, so far our country still has a population of more than 2800 without power, a scattered in remote backward poverty-stricken areas. Owning to the shortage of energy has not solve the problem of water diversion and irrigation, especially in the northwest region, because of the drought, desertification, grassland degradation situation more and more serious, ecological environment worsening, seriously hindered the development of rural economy. The northwest region of groundwater resources is rich, but the utilization rate is not high. The main reason is the lack of power supply. The northwest region of solar radiation intensity at the same time, the sunshine time is long, solar energy resources are abundant. Therefore, the use of solar energy photovoltaic pumping and lighting system development abundant groundwater resources, to solve the poor water without electricity, water and lighting problem of farming and animal husbandry, is an economical and feasible way.
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