Which high-power inverter power supply is better?
In the process of photovoltaic power station construction, how to use a small investment to obtain a large income (power generation), and what type of high-power inverter power supply is selected has become a very important link. It is better.
With the boom in the photovoltaic market, photovoltaic companies have sprung up like bamboo shoots after a rain, and products of different brands have uneven performance in actual power generation and user experience.
So how do you choose a high-power inverter power supply suitable for your power station? Here are six problems that cannot be avoided when purchasing an inverter for your reference.
1. Inverter type (string/centralized, 220V/380V/480V)
To choose an inverter, first choose the basic type of inverter according to the specific application environment.
At present, the inverters on the market are basically divided into three types: centralized inverters, string inverters, and micro inverters.
Centralized inverters are mainly used in large ground power stations with a voltage level of 315V, which is suitable for high-voltage grid connection;
String inverters, also known as distributed inverters, are mainly used in various barren hills, industrial and commercial or home roofs. The power station is generally not large, and it is integrated into the national grid through full or surplus power grid connection;
Micro-inverters, the main application method is directly integrated on the battery board, suitable for small family power stations, currently there are few domestic applications.
At present, most of the construction of distributed photovoltaic power plants in the country in full swing use string inverters. However, according to the specific grid connection requirements, the string inverter has three different voltage levels for everyone to choose.
First of all, grid-connected inverters with 220V output voltage are generally used in household photovoltaic power stations. Most of these power stations use the form of self-generated and self-used surplus power to be connected to the national grid. Secondly, grid-connected inverters with 380V output voltage are mainly used in various industrial and commercial rooftop power stations and small centralized power stations with villages as the unit in many places in China. Most of these power stations are integrated into the national grid in the form of full grid connection. The latter is a grid-connected inverter with 480V output voltage. This type of inverter is mainly used in 10KV medium-voltage grid-connected barren hills and tidal flat power stations.
Seeing this, you should be able to basically determine which type or voltage level of high-power inverter power supply to use in your power station, and this is just a step forward in the Long March. Next, the editor will take you to a more detailed inverse Change the multiple choice questions.
2. General parameters: power size, number of MPPT channels/number of input channels, efficiency, voltage range
After selecting the basic type of the inverter, the next step is to check whether the basic parameters of the inverter or meet their own requirements according to the project situation.
First of all, you must confirm how much inverter your photovoltaic power plant is suitable for.
Generally, the installation capacity of the power station is calculated based on the use area of the land or roof. The angle of inclination and bracket installation method should be considered in the calculation, and the principle of avoiding shadows as much as possible. Sometimes the power generation capacity of a power station is not very consistent with the power level of the inverter. For example, a roof can install 87 265W modules, and the entire power station capacity should be about 23.06KW, but there is no inverter with the corresponding power size on the market. Device. In this case, we will first look at the over-distribution capacity of the inverter at a power level lower than the power station capacity (we will focus on the sixth point). If the lower level does not meet the requirements, look for an inverter with a higher level.
Secondly, it is necessary to examine how many MPPT and input channels the inverter has.
The number of inverter MPPT circuits determines the power generation of a photovoltaic power station to a large extent, especially when the power station has problems such as shadow shading, different component orientations, and inconsistent performance of components, and as the life of the power station becomes longer (components Attenuation) The advantage of high power generation of MPPT will be more obvious. The number of inverter input channels often determines whether a photovoltaic power station is easier to design with panels, and save cables and other auxiliary materials.
Later, examine the power generation capacity of the inverter.
The power generation capacity of the inverter is a very comprehensive category, which is related to the heat dissipation of the inverter, component performance, failure rate and many other aspects, but the more intuitive parameters are nothing more than efficiency and voltage range. .
At present, the efficiency values marked in the inverter specifications are mainly two kinds of greater efficiency and weighted efficiency. The greater efficiency refers to the inverter's conversion efficiency when all internal and external environments including DC voltage reach a better state, that is to say, the greater conversion efficiency is an instantaneous efficiency. In the actual operation of the power station, the inverter will not always work at the "higher efficiency" load point. Its input voltage and load point will change with the irradiance and temperature. It can be said that the inverter with "larger conversion efficiency" and high In the actual application of the device, the power generation amount may not be large, so the actual gimmick of "higher efficiency" hyped by many companies is more. Weighted efficiency refers to the comprehensive efficiency obtained on the basis of full consideration of external light and the efficiency of each power point of the machine. It is more scientific to examine the performance of the inverter based on this.
The weighted efficiency reflects the power generation capacity of the inverter in a unit time in the vertical direction, and the voltage range mainly reflects the continuity of the inverter power generation time in the horizontal direction.
The lower the lower limit of the inverter's working voltage range, the earlier the inverter will start and the later the shutdown, which can effectively extend the daily power generation time; the higher the upper limit of the working voltage range, the more the inverter can withstand peak power generation. It is not easy to derate or even shut down when the light is stronger, and the operation is more stable.
As the core equipment in the photovoltaic system, the inverter not only undertakes the tasks of power generation tracking and direct-to-ac conversion, but also shoulders the important responsibility of protecting the power generation system and the power grid. As the "CPU" of the photovoltaic power generation system, the inverter must have active detection and prevention functions. When the grid fails or a component fails, the inverter uses current sensors and voltage sampling, and the "CPU" makes judgments and instructs the "actuating mechanism" The contactor or circuit breaker is disconnected to protect the safety of people, power grids, and equipment.
Generally, the basic protection functions of grid-connected inverters include: input over-voltage and under-voltage protection, input over-current protection, short-circuit protection, over-heat protection, lightning protection; grid-connected protection includes: output over-voltage protection, output over-current protection, Over-frequency, under-frequency protection and anti-islanding protection.
Among them, the more important one for photovoltaic grid connection is the anti-islanding protection. When the power grid is interrupted due to a fault, if the system cannot detect the power failure of the grid in time and continue to deliver power to the grid, then the photovoltaic system can become an independent power supply system at this time. This phenomenon is called the islanding effect. There are generally two reasons for the formation of islands: one is that the high-power inverter does not detect the fault after the power grid fault detection device operates; the other is that the natural environmental factors cause the grid line to fail. The islanding phenomenon will affect the entire power grid equipment and user equipment, and even damage the equipment.
High-power inverter power supplies are generally installed outdoors. They are often exposed to weather conditions such as exposure to the sun, high temperature, high humidity, and salt spray. In addition, they also emit a lot of heat when they work. Therefore, the cooling solution of the inverter is particularly important. Inverter heat dissipation design will comprehensively consider the heat dissipation effect, protection, installability, maintainability, and the economic cost paid.
At present, the general heat dissipation methods in the industry include forced air cooling, natural cooling, and water cooling. The water cooling method is mainly used in large-scale centralized inverters and has fewer applications. For air cooling and natural cooling, there are a lot of discussions in the industry at present, but in essence, there is no difference between the advantages and disadvantages of the two heat dissipation methods, but the difference between whether they are more suitable.
First look at forced air cooling. This is a traditional heat dissipation method. Fast heat dissipation is its main advantage. However, in harsh environments, the fan has a high failure rate, high noise, and high power consumption. Next, look at natural cooling. Low failure rate, low noise, and high protection level are its main advantages, but it has extremely high requirements for heat sink design and software control technology.
From the perspective of inverters, household single-phase inverters have lower power levels, less heat dissipation and are used in homes. I prefer to recommend forced air cooling. For small and medium-sized three-phase inverters (5-20KW), due to its high heat dissipation requirements, the installation location is generally easier to maintain, so forced air cooling is recommended. For large string inverters above 50KW, if air cooling is selected, it will produce greater noise and more power consumption, so natural cooling is recommended when the control technology is more advanced.
Due to the attenuation of module power, dust shielding and line loss, and the difference in lighting conditions in different regions, in order to optimize the system revenue, experienced design engineers will match the total capacity of photovoltaic modules to the inverter Larger capacity, this situation is called over-provisioning. Appropriate overconfiguration can improve the overall revenue of the power station system.
The overmatching capacity of the inverter is generally related to the number of input channels of the machine and the larger DC input power that can be undertaken. According to Moso inverter technicians, the current standard brand inverters will reserve some overmatches when designing The margin is generally about 1.1 times.
6. After-sales service capability
The latter problem facing the purchase of an inverter is the after-sales problem. The first thing to look at after-sales issues is the warranty period. At present, the domestic inverter industry generally adopts a 5-year warranty, and some poverty alleviation projects will also propose a 6-year or 8-year warranty. The second thing to pay attention to is the response speed of the inverter supplier's after-sales service. Whether the inverter can quickly resume power generation after the inverter fails is a big issue directly related to the power generation of the photovoltaic power station.
The latter question about after-sales service capability is also a more important one. Observe the operating conditions of the inverter supplier’s business. If a business is at risk, the business may not be there after five years. What about the after-sales service of the machine? ? This situation has occurred more than once in China. When a machine with a warranty period is found to be sold by a manufacturer, it is impossible to find that the manufacturer has gone bankrupt, or if the manufacturer switches to the machine warranty. Therefore, it is recommended that you purchase inverters to focus on several listed companies.
In a photovoltaic power station system, the cost of the inverter is less than 8%, but it is the decision maker of power generation efficiency. In a photovoltaic power station, when the components and other accessories are completely the same, choose different inverters, and the total power generation of the system There is a difference of 5% to 10%. After the system is installed into functional power generation, the inverter becomes the decisive factor. Therefore, it is very important to choose the inverter. The above six-point inverter selection suggestions hope to help more photovoltaic colleagues.