Although the search for new energy has a long history, environmental pollution and energy shortage around the world have forced people.
Scientists are making greater efforts to find and develop new energy sources. In the process of finding and developing new energy sources, people will naturally turn their attention to various possibilities.
Renewable alternative energy. Photovoltaic power generation is one of them. Although photovoltaic power generation has various limitations in practical application, with the light
With the decrease of photovoltaic power generation cost, the increase of mineral power generation cost and the decrease of mineral energy, the cost of photovoltaic power generation will one day be different from that of traditional power generation.
The cost of power generation is comparable. By then, photovoltaic power generation will gradually enter the commercialization stage. What will happen to the power grid after photovoltaic grid-connected power generation forms a scale?
What kind of influence is the problem to be discussed in this paper.
First, the basic principle of photovoltaic power generation
1. Composition of solar photovoltaic power generation system
Solar photovoltaic power generation system is mainly composed of solar photovoltaic battery pack, photovoltaic system battery controller, storage battery and AC /DC inverter.
Want parts. The core components are photovoltaic battery pack and controller. The function of each component in the system is: photovoltaic cell: photoelectric.
Conversion.
Controller: Process control acting on the whole system. There are many types of controllers used in photovoltaic power generation systems, such as two-point controllers and multi-point controllers.
Road sequence controller, intelligent controller, high-power tracking charging controller, etc. At present, most controllers with simple design are used in China.
Intelligent controllers are only used in communication systems and larger photovoltaic power plants.
Battery: The battery is a key component in the photovoltaic power generation system, which is used to store the electric energy converted from photovoltaic cells. At present, China has not.
Special battery for photovoltaic system, but conventional lead-acid battery is used.
AC -DC inverter: Because its function is AC -DC conversion, the most important indicators of this component are reliability and conversion efficiency. parallel in
The inverter adopts maximum power tracking technology to maximize the electric energy converted by photovoltaic cells into the power grid.
2. Solar photovoltaic panels:
Solar cells mainly use monocrystalline silicon as material. The pn junction in the diode is made of monocrystalline silicon. It works like a diode.
Only in diodes, the external electric field drives the holes and electrons in the pn junction, while in solar cells, it drives and affects the pn junction.
The motions of holes and electrons are solar photons and radiant heat (*). Also known as the photovoltaic effect principle. Current photoelectric conversion
The efficiency of photovoltaic cells is about 13%- 15% for monocrystalline silicon and1%-13% for polycrystalline silicon. At present, the latest technologies include
Photovoltaic thin film battery.
3. The classification of solar photovoltaic power generation system:
At present, solar photovoltaic power generation systems can be roughly divided into three categories: off-grid photovoltaic energy storage system, grid-connected photovoltaic power generation system and the mixed system of the first two.
A) Off-grid photovoltaic energy storage system. This is a common way of solar energy application. It has been used at home and abroad for several years. The system is relatively simple,
Has wide adaptability. The application scope is limited to a series of batteries, which are bulky and difficult to maintain.
B) In the photovoltaic grid-connected power generation system, when the power load is heavy and the solar power is insufficient, the power is purchased from the commercial power. When the load is small, it may not be used up.
Electricity, you can sell the excess electricity to the mains. On the premise of relying on the power grid, the system saves batteries, thus expanding the use.
Scope and flexibility, and reduce costs.
C) the mixed system of a and b is between the above two parties. This scheme has strong adaptability, for example, according to the power grid.
Peak and valley electricity prices to adjust their power generation strategy. However, its construction cost and operation cost are higher than the above two schemes. Second, photovoltaic power generation.
superiority
After entering the 1970s, due to the influence of two oil crises, photovoltaic power generation has been highly valued and developed very rapidly in the world. Congyuan
In the future, photovoltaic power generation will enter the power market with distributed power sources, partially replacing conventional energy sources. Whether in the near future, or in the near future, photovoltaic
Power generation can be used as a supplement to conventional energy sources to solve special application fields, such as communication and communication.
The power supply and the demand for domestic electricity in remote areas without electricity are of great significance from the perspective of environmental protection and energy strategy. Guangfufa
The advantages of electricity are fully reflected in the following aspects:
1. Clean enough. (If the battery scheme is adopted, the disposal of waste batteries should be considered. )
2. Absolutely safe. (The grid-connected voltage is generally below 220V.
3. Relative universality.
4. Real long life and maintenance-free.
5. Preliminary and practical.
6. Adequacy of resources and potential economy, etc.
Third, the limitations of photovoltaic power generation.
Everything has two sides. At present, there are too many articles introducing the advantages and advantages of photovoltaic power generation, so it is necessary to point out photovoltaic power generation here.
Some restrictions. Solar energy has the weakness of low energy density and poor stability, which is influenced by geographical distribution, seasonal variation and alternation of day and night.
The ring. The limitations of photovoltaic power generation include the following aspects:
1. Time limit. Because the condition of photovoltaic power generation is when the sun shines, photovoltaic power generation equipment can work normally to generate electricity. Therefore, this day
Night, spring, summer, autumn and winter have great influence on the load of photovoltaic power generation. In order to cope with this situation, the power grid must be equipped with
The generator with corresponding capacity is in the rotating standby state.
2. The geographical location is limited. Photovoltaic power generation equipment can only be attached to the installation and construction of buildings, which is the so-called photovoltaic roof local power supply.
If we leave the building to build photovoltaic power generation, it will greatly increase the cost or destroy the environment and ecology.
3. Limited meteorological conditions. Influence of climate on photovoltaic power generation. When photovoltaic grid-connected power generation is adopted without batteries, if it is over the city,
Great climate change will cause great fluctuation of power load; When the air quality above the city, such as air pollution or visibility, changes.
Bad weather, such as foggy and cloudy days, will reduce the online or real-time output of photovoltaic power generation.
4. Capacity transmission limit. After solving the cost problem of photovoltaic power generation, high-power, high-voltage and long-distance electricity is transported from desert areas to
In the load center, because photovoltaic power generation does not have the moment of inertia of traditional motors, governors and excitation systems, it will bring new economy to AC power grid.
And stability. Both AC and DC high-voltage and high-power are used for long-distance power transmission from desert areas, because of the above 1, 2, 3 bureaus.
Power rationing will greatly increase the transmission cost per kilowatt. This problem will be discussed below.
5. Low light energy conversion efficiency. Compared with the conversion efficiency of traditional energy sources (mineral energy, oil, hydropower, atomic energy, etc.). ), photovoltaic energy
The conversion efficiency of quantity is not satisfactory.
Fourth, the future prospects of photovoltaic power generation
The photovoltaic industry in China is growing at an annual rate of 30%. In recent three years, the average annual growth rate of total battery output in global solar is as high as 49.8%.
. According to Japan's new energy plan, EU's white paper on renewable energy and American photovoltaic plan, global photovoltaic power generation will be connected to the grid in 20 10.
The machine capacity will reach 15GW (15MW, which will still be less than 1% of the total installed capacity of global power generation), and the installed capacity of global photovoltaic power generation in 2030.
The production capacity will reach 300GW (by then, the output value of the whole industry may exceed 300 billion US dollars), and by 2040, the photovoltaic power generation will reach the global total power generation.
15%-20% quantity. According to this plan, from 20 10 to 2040, the compound growth rate of photovoltaic industry will be as high as more than 25% (see reference: 15).
. Among them, grid-connected applications will develop greatly, thus forming grid-connected power generation (about 46%), off-grid power supply (about 27%) and communication stations (about 2 1%).
Three main application fields (see reference: 16).
The energy of the sun is almost unlimited for human beings, but in fact, the resources that can obtain solar energy resources on the earth are limited.
Not as huge as some articles say. For example, when we install a solar water heater on the roof, we lose the installation of the sun.
The battery's chance. It will be unrealistic to build solar panels in other places except buildings and deserts, and it will not be worth the candle. This is not only
Just because the cost is huge, the problem is obvious The main problem is to leave buildings and deserts to build photovoltaic power stations.
Destroy the environment and ecology, and you will find that nothing grows under the solar panel. In a word, saving energy and reducing consumption is an eternal topic for human beings.
In a sense, while eliminating old technologies and products, it also wastes the energy used to produce these technologies and products. examination for going abroad
Inspectors often find that western developed countries still use products and equipment from the 1920s to 1930s on some occasions, not to protect "historic sites".
In a sense, this is saving energy. The replacement of old and new products and technologies is at the expense of energy consumption, and the products are updated too quickly.
Will accelerate the consumption of energy. Of course, an overall economic index is needed to judge energy consumption. Should we consider saving "used"
Energy "problem? (**)
On the other hand, the necessary condition for any advanced technology to enter the business is that the price can be accepted by the market. If the use cost is too high,
No matter how good the technology is, it will only stay in the laboratory or demonstration project stage.
The influence of grid-connected photovoltaic power generation on the future power grid
With the promulgation and implementation of China's Renewable Energy Law, the price of conventional energy is rising all over the world, and the price of oil is approaching $ 100.
Around the use of solar energy technology, business has developed very rapidly, among which photovoltaic grid-connected power generation technology has developed very rapidly. At present, photovoltaic power generation is limited.
The main factor is cost. The cost of solar photovoltaic power generation is high (more than 30 thousand yuan per kilowatt), and the cost of power generation is expensive (1.5 yuan/kilowatt).
More than). With the decrease of photovoltaic power generation cost and the increase of energy-consuming power generation cost, the cost of photovoltaic power generation will be the same as that of traditional power generation one day.
The electricity bill is comparable. By then, photovoltaic power generation will enter the stage of commercial application. In order to welcome this day early, we will
It is necessary to consider in advance the impact of photovoltaic grid-connected power generation on the technical, economic, policy and environmental benefits of existing power generation modes. Let's assume this first.
The time has come, and the existing power generation mode has not changed much. Then photovoltaic power generation will also bring us benefits.
What kind of problems will it cause to the existing power grid?
Because solar photovoltaic power generation is a kind of energy with low energy density, poor stability and poor regulation ability, the power generation is greatly affected by weather and region.
Grid-connected power generation will have a certain impact on the security and stability of power grid, economic operation and power supply quality. As for the impact.
It is not clear at present. We know that electric energy cannot be stored on a large scale at low cost at present, nor can it be produced on a large scale in the foreseeable future.
This warehouse. This makes the application of photovoltaic power generation restricted by physical factors and geography. But with technology and
With the development of the market, when the online capacity of photovoltaic power generation is equivalent to that of thermal power plants, hydropower plants, nuclear power plants and other power plants in the power grid.
When the equivalent sum becomes an indispensable part, photovoltaic grid-connected power generation will affect the existing power generation mode and the technology, economy, policy and environment of the power grid
Benefits bring the following problems: (If the photovoltaic grid-connected power generation system adopts the battery scheme, the advantages and benefits of photovoltaic grid-connected power generation will be great.
Discount. The battery system optimized for photovoltaic grid-connected power generation can partially solve the problems raised in the following points 1, 2 and 3. )
1. Influence of peak and valley load on power grid. Because the photovoltaic grid-connected power generation system does not have the ability of peak shaving and frequency modulation, it will affect the initial peak shaving and harmony of the power grid
Late peak load has an impact. The increase of photovoltaic grid-connected power generation system can not reduce the ownership of traditional rotating units, and the power grid must
Prepare a large number of rotating standby units for photovoltaic power generation system to solve the peak shaving problem of early peak and late peak. Photovoltaic grid-connected power generation system supplies power to power grid.
Electricity is at the expense of the reduction of the utilization hours of the unit. This is certainly not what power producers want to see.
2. The influence of day and night changes, time difference between east and west and seasonal changes on the power grid. Due to the periodicity of sunshine and load, photovoltaic grid-connected power generation.
The increase of electricity cannot reduce the demand for installed capacity of power grid.
3. Changes in meteorological conditions. When the photovoltaic roof of a city is connected to the grid to generate electricity to a certain scale, if the geography and meteorology change greatly,
The power grid will provide enough regional rotating standby units and reactive power compensation capacity for photovoltaic grid-connected power generation system to control and adjust the frequency of the system.
Speed and voltage. In this case, the power grid will ensure the safe and stable operation of the power grid at the expense of economic operation.
4. Long-distance photovoltaic power transmission. When photovoltaic grid-connected power generation can transmit electricity in a long distance economically and technically, because photovoltaic grid-connected power generation
Power generation without moment of inertia, governor and excitation system will bring new stability problems to AC power grid. If photovoltaic grid-connected power generation is formed
Large-scale use of high-voltage AC /DC transmission will bring stability and economic problems to the adjacent AC system of photovoltaic DC transmission system.
The transmission lines specially used for photovoltaic grid-connected power generation will restrict the utilization of desert solar energy because of their low efficiency. Used to borrow passage
Or the transmission line that transports the electric energy of photovoltaic grid-connected power generation system, because the load rate is low, it is very uneconomical. ) regardless of high pressure.
When AC or DC power transmission, photovoltaic grid-connected power station must be equipped with reactive power automatic regulator. As for the influence on the stability of power grid, there is no such influence at present.
See the mathematical model of photovoltaic power generation (including power supply model and load model) in power grid stability calculation for details. Photovoltaic grid-connected power generation is safe for the power grid.
It is not clear how much the impact of completely stable operation is.
5. The problem of reduced consumption; One of the main advantages of photovoltaic grid-connected power generation is that it can replace the consumption of fossil fuels. With the photovoltaic grid-connected power generation, the power generation is increased
Rotating standby or hot standby of rotating generator in power plant, therefore, the actual consumption reduction ratio of photovoltaic grid-connected power generation should be deducted from rotating standby or hot standby.
Energy loss caused by hot standby. The reduction efficiency of photovoltaic grid-connected power generation should consider the power generation of photovoltaic grid-connected power generation system.
The efficiency loss caused by the reduction of the company's equipment use time. Because the power system operates as a whole, the direction of photovoltaic grid-connected power generation
Power grid transmission will infringe the interests of other power producers, which is a problem that policy makers need to consider. This is because the power grid is considering
In the safe, stable and economical operation, not only hydropower plants are used as rotating standby. Therefore, the total amount of photovoltaic grid-connected power generation in the system.
The effective theoretical standard coal consumption should be multiplied by a coefficient less than 1 before reducing the standard coal consumption, and the auxiliary power loss of rotating standby units should be deducted in equal proportion.
6. Environmental protection; Whether the emission reduction effect brought by photovoltaic power generation should only consider sulfur dioxide and carbon dioxide emitted by thermal power remains to be studied.
Because when photovoltaic power generation is connected to the grid, when considering the safe, stable and economic operation of the grid, it is often not just the fire that reduces the output.
Power plants, and when considering rotation standby, it is not only hydropower plants that undertake the task of rotation standby (hydropower plants bear the loss of rotation standby tasks)
Smaller). Therefore, when considering the emission reduction contribution of photovoltaic grid-connected power generation system, it should also be multiplied by a coefficient less than 1 before the theoretical value.
This conclusion is not as optimistic as some articles say.
7. By the way, wind power also has environmental protection and ecological problems. Some environmentalists abroad point out that large wind power plants are often built in this season.
In the wind tunnel, this is often the best route for migratory birds to migrate.
Concluding remarks
The advantage of photovoltaic power generation lies in solving the energy power of communication, microwave and other equipment in off-grid areas and dispersing small-capacity electricity consumption in population areas.
And provide electricity for local buildings with conditions to build photovoltaic roofs. Load forecasting should be fully considered when planning the future power grid development.
Influence of grid-connected photovoltaic power generation and grid-connected photovoltaic power generation on power grid and its mathematical model. Off-grid photovoltaic power generation system can be used as online active variable load.
The model to be considered (here refers to the load that can be supplied by off-grid photovoltaic power generation system and municipal power grid in the city). Photovoltaic parallel connection
If the grid-connected power generation system is powered by 1 10V or 220V, the grid-connected photovoltaic power generation system can also be regarded as active and can be changed from negative to positive.
Load model. Through the above analysis, the long-term positioning of photovoltaic grid-connected power generation can only be used as an important supplementary means of power grid energy saving and consumption reduction. If it exceeds
This strategic positioning will lead to investment and additional energy waste, and the optimistic view on reducing pollution emissions will be greatly reduced.
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