Detailed explanation of three different grid conne

2022-08-11
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Detailed explanation of three different consolidation modes of photovoltaic power generation

State Grid encourages and cooperates in the application of distributed photovoltaic power generation, and allows the owners of photovoltaic power stations to adopt three settlement modes, namely, spontaneous self use mode, spontaneous self use surplus power or complete self use. Local power companies will encounter some obstacles in the process of actual operation. These problems are mainly caused by the owners of photovoltaic power stations' lack of understanding of power transformation and distribution systems. This article will focus on some practical problems encountered in the operation of the above three types of merger, and make some elaboration on the specific merger scheme

1. Completely spontaneous self use mode

this mode is generally used when the power load on the user side is large, and the power load continues, and there is little shutdown or semi shutdown in a year, or even during the holiday, the power maintenance load of the user is enough to absorb most of the power generated by the photovoltaic power station

for such systems, due to the low-voltage side, if the user can't absorb the electricity, it will be sent back to the upper level through the transformer. However, the design of distribution transformer is not allowed to be used for reverse power transmission (it can be used for short-term reverse power transmission, such as debugging, but not for a long time). Its initial power flow direction is designed to be fixed. Therefore, it is necessary to install anti countercurrent devices to avoid the reverse transmission of power

for some users who cannot ensure that their own power consumption can continue to consume photovoltaic power, or the production of projects that cannot ensure sustainability, it is recommended not to adopt this way of consolidation

this mode is recommended for photovoltaic power stations with a single unit below 500kW and a distribution transformer on the user side, because the increased investment required to boost the voltage accounts for a large proportion of the investment

2. Self generated residual power supply mode

for most users who are optimistic about distributed generation, choosing self generated residual power supply is the most ideal mode, so that they can not only get a higher price for self generated electricity, but also sell electricity when they can't use it. However, there is a lot of resistance in the actual operation process. The reason is the asymmetric information between photovoltaic practitioners and local power companies, and the lack of mutual understanding of each other's professional knowledge. This is also why this mode has become the most difficult part of the photovoltaic electricity price policy and the national new deal

when photovoltaic power generation is in the mode of self use surplus electricity, users (or "investors") hope that the generated electricity will be consumed within the enterprise as much as possible. When it can't be used, it can be sent into electricity, so as not to waste this part of light. The volt electricity is calculated according to the consumption of 2 lights per month. But what power companies want most is for users to simply choose whether to use it spontaneously or boost it. Because, for local power companies, it is necessary to increase some workload: Calculation of regional distribution capacity (allowing reverse power transmission load), increase of managed power points (pure self generation and self use can be managed by reducing the standard), cumbersome electricity consumption measurement of users after the transformation of forward and reverse electricity meters (it is necessary to obtain the user's actual electricity load curve and electricity consumption through the numerical conversion of electricity meter 1 and electricity meter 2) Increase the workload of meter reading, etc

of course, in essence, power companies cannot obtain the price difference between the purchase and sale of electricity used by users spontaneously, which is a real loss for local power companies. It not only increases the workload, but also has no practical benefits. Therefore, various reasons will be set to let investors not choose this consolidation scheme. However, as long as it is technically fully explained that this is the surplus power supply scheme allowed by the State Grid Corporation of China, and there is a reasonable design draft, the local power company cannot easily refuse the application of investors

many photovoltaic power station owners believe that as long as the photovoltaic power users can't absorb it at the third place of the meter (400V side), they can directly send it back to the 10kV side (or 35kV) through the distribution transformer. But in fact, this is not allowed, which violates the power flow design of power distribution, and may cause abnormal voltage and power factors on the 400V side. At the same time, some protective equipment may also lose its function

in fact, for distributed power stations, the cost difference between using boost and low-voltage side parallel is that the electro-hydraulic servo universal experimental machine is a high-precision experimental instrument combining light, machinery and electricity, which is not too large, because the low-voltage side also needs to choose an inverter with a transformer (of course, kW series inverter can also be selected); Although the transformer is added when boosting, the inverter without isolation transformer can be selected, and the comprehensive cost is about the same. It only increases the cost of integrated automatic protection system and local dispatching transmission. However, in the same plant area, for power stations with a scale above MW, boosting voltage will guarantee power quality to a certain extent, and users do not have to bear any risks

of course, this parallel form is not suitable for projects where the user's incoming bus is more than 35kV. At this time, 10kV or 35kV is completely the bus in the user's factory, and the bus connected substation is 110kV or 220kV, so it can generally be directly fed back. Because such substations can operate in both directions in the initial power flow design

it is also not applicable to small-scale power users (including families and small businesses) with 400V (or below) entering the house, because its 400V bus is shared with other power users, and the reverse power transmission does not directly cross the transformer, but is consumed on the 400V bus (which can be borrowed in principle). Of course, on the 400V bus, the total installed capacity of photovoltaic and other distributed power generation will be controlled (such capacity ratio has no fixed value, which is determined according to the load situation in the local 400V ring, and the installed capacity of distributed power generation can also be increased by adding regional regulation and energy storage support)

the biggest drawback of this operation mode is that its income model cannot be fixed, the proportion of spontaneous self use and the proportion of surplus electricity are always changing, the assessed value of the power station financing and sale will be discounted compared with the actual output, and even the management cannot obtain a reasonable asset value because of worrying about the future operation of power users

3. Completely selling electricity mode

in the past decade of the great development of photovoltaic power generation, direct selling electricity has always been the mainstream of photovoltaic applications. Because its financial model is simple and relatively reliable, it is willing to be favored by capital

this form of consolidation is not only applicable to the future distributed fixed electricity price projects, but also a good choice to choose the direct desulfurization electricity price to sell electricity (of course, the desulfurization electricity price in this region is required to be no less than 0.4 yuan). This is always shorter than the benefit period of distributed power stations in the future

moreover, we cannot avoid one thing - photovoltaic is a capital driven industry, which belongs to fixed income long-term investment. In the stage of pursuing development, most enterprises are unlikely to hold photovoltaic power stations, even now many owners of photovoltaic power stations are in their hands. Therefore, the transfer market of photovoltaic power stations will be a big enough cake in the future, and services for both buyers and sellers will become hot businesses, such as insurance services, evaluation services, testing services, operation and maintenance services, third-party guarantee services, etc

finally, investors can only decide which way to choose as the merger mode of photovoltaic power stations

personal investment household power station

although there is no transformer problem in household photovoltaic power station, its principle is similar. When consolidating and settling accounts, you can choose the second and third methods. At present, the second method should be the main one, because in order to obtain the subsidy of additional fixed electricity price from the government (the four regional fixed electricity price being formulated by the government) in addition to the desulfurization electricity price given by the power company, you must apply to the development and Reform Commission and other departments. At present, there is no simplified procedure for household power stations, which takes a long time and takes a lot of energy

concept of power and electricity

the concept of power and electricity is often mentioned in the industry. In fact, these are two different concepts, and sometimes they are not very standardized, but in order to reduce misunderstandings, I want to explain: people often say that power generally refers to instantaneous load, that is, power; However, it is recommended to use the professional term load

in the popular sense, electricity refers to the cumulative measurement calculated from the known instantaneous value. For purely self generated and self used projects, we need to pay attention to the power load of users, that is, the daily power load curve, especially the frequency and duration of the minimum value. For the project of self generated surplus electricity, we need to pay attention to the power consumption of users. We need to obtain the monthly peak, valley, flat and sharp electricity measured separately and use it to calculate the proportion of self used electricity after photovoltaic power generation in the future

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