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| In depth interpretation of household energy storage inverter and layout of relat |
| Release time:2022-12-13 14:42:06| Viewed： |
In depth interpretation of household energy storage inverter and layout of related enterprises!
1、 Type of energy storage inverter
1. Technical route: DC coupling and AC coupling
Optical storage system, including solar modules, controllers, inverters, batteries, loads and other equipment.
At present, there are mainly two technical routes: DC coupling and AC coupling. AC or DC coupling refers to the way that solar panels are coupled or connected to energy storage or battery systems. The connection type between the solar module and the battery can be AC or DC. Most electronic circuits use direct current, solar modules generate direct current, and batteries store direct current. However, most electrical appliances operate on alternating current.
Optical storage system
1) The hybrid photovoltaic+energy storage system, that is, the direct current from the photovoltaic modules, is stored in the battery pack through the controller, and the grid can also charge the battery through the bidirectional DC-AC converter. The collection point of energy is at the DC battery terminal.
In the daytime, photovoltaic power generation first supplies the load, and then charges the battery through the MPPT controller. The energy storage system is connected to the power grid, and the excess electricity can be connected to the grid; The battery is discharged at night to supply the load, and the insufficient part is supplemented by the power grid; When the power grid is cut off, photovoltaic power generation and lithium battery only supply power to the off grid load, and the load at the grid connected end cannot be used.
When the load power is greater than the photovoltaic power generation power, the grid and photovoltaic can simultaneously supply power to the load. Because both photovoltaic power generation and load power consumption are not stable, it depends on the battery to balance the system energy. In addition, the system also supports the user to set the charging and discharging time to meet the user's power demand.
Operating principle of DC coupling system
Hybrid photovoltaic+energy storage system The hybrid inverter integrates the function of off grid connection to improve the charging efficiency. For safety reasons, the grid connected inverter will automatically shut down the power supply of the solar panel system during power failure. The hybrid inverter allows users to have the functions of off grid and grid connection at the same time, so they can use power even during power failure.
The hybrid inverter simplifies energy monitoring, and important data such as performance and energy production can be checked through the inverter panel or connected intelligent equipment. If the system has two inverters, they must be monitored separately. DC coupling reduces the loss of AC-DC conversion. The charging efficiency of the battery is about 95-99%, while the AC coupling is 90%.
The hybrid inverter is economical, compact and easy to install. It may be cheaper to install a new hybrid inverter with DC coupled battery than to retrofit the AC coupled battery to the existing system, because the controller is cheaper than the grid connected inverter, and the switch is cheaper than the distribution cabinet. The DC coupled scheme can also be used as a control inverter integrated machine, saving both equipment costs and installation costs.
Especially for medium and small power off grid systems, DC coupled systems are very cost-effective. The hybrid inverter has a high degree of modularization, and it is easy to add new components and controllers. You can easily add additional components with a relatively low-cost DC solar controller.
The hybrid inverter is designed to integrate storage at any time, which makes it easier to add battery packs. The hybrid inverter system is relatively compact, using high-voltage batteries, with smaller cable size and lower loss.
Composition of DC coupling system
Composition of AC coupling system
However, Hunni is not suitable for upgrading the existing solar system, and the installation of systems with large power is complex and expensive. If users want to upgrade the existing solar system to include battery storage, choosing a hybrid inverter may complicate the situation, while the battery inverter may be more cost-effective, because choosing to install a hybrid inverter requires a comprehensive and expensive rework of the entire solar panel system.
The installation of systems with higher power is more complex, and it will be more expensive because more high-voltage controllers are required. If more electricity is used in the daytime, the efficiency will decrease slightly due to DC (PV) to DC (batt) to AC.
2) The coupled photovoltaic+energy storage system, also known as the AC modified photovoltaic+energy storage system, can realize that the DC power generated by the photovoltaic modules is converted into AC power through the grid connected inverter, and then the excess power is converted into DC power through the AC coupled energy storage inverter and stored in the battery. The energy collection point is at the AC end.
Including photovoltaic power supply system and battery power supply system. The photovoltaic system is composed of photovoltaic array and grid connected inverter, and the battery system is composed of battery pack and bidirectional inverter. These two systems can operate independently without interfering with each other, or they can form a micro grid system separated from the large power grid.
Operating principle of AC coupling system
Coupled home photovoltaic+energy storage system
The AC coupling system is 100% compatible with the power grid, easy to install and expand. Standard household installation components can be used. Even relatively large systems (2KW to MW) are easy to expand and can be combined with grid connected and independent generator sets (diesel units, wind turbines, etc.).
Most series solar inverters above 3kW have dual MPPT inputs, so long string panels can be installed in different directions and tilt angles. At higher DC voltage, compared with DC coupling systems that require multiple MPPT charging controllers, AC coupling is easier to install large systems with lower complexity, so the cost is lower.
AC coupling is suitable for system transformation, and the efficiency of using AC load in daytime is higher. The existing grid connected photovoltaic system can be transformed into an energy storage system with low input cost. When the power grid is cut off, it can provide users with safe power guarantee. Compatible with grid connected photovoltaic systems from different manufacturers.
Advanced AC coupling systems are usually used for larger scale off grid systems, and string solar inverters are combined with advanced multi-mode inverters or inverters/chargers to manage batteries and power grids/generators.
Advanced AC coupling systems are usually used for larger scale off grid systems, and string solar inverters are combined with advanced multi-mode inverters or inverters/chargers to manage batteries and power grids/generators.
The AC coupling charging efficiency is lower, which is expensive for small systems. The energy entering the battery in the AC coupling must be converted twice. When the user starts to use the energy, it must be converted again, so as to add more losses to the system. Therefore, when the battery system is used, the AC coupling efficiency is reduced to 85-90%. AC coupled inverter is expensive for small systems.
Off grid home photovoltaic+energy storage system is generally composed of photovoltaic modules, lithium batteries, off grid energy storage inverter, load and diesel generator. The system can realize direct charging of photovoltaic cells through DC-DC conversion, and can also realize bidirectional DC-AC conversion for battery charging and discharging.
In the daytime, photovoltaic power generation first supplies the load, and then charges the battery; The load is supplied by discharging the battery at night. When the battery is insufficient, the load is supplied by the diesel generator. It can meet the daily power demand in non grid areas. It can be combined with diesel generator to supply load or charge battery. Most of the energy storage inverters of the separated grid have no grid connection certification, and even if the system has a grid, it cannot be connected to the grid.
Off grid inverter
Off grid home photovoltaic+energy storage system
2. Applicable scenarios of energy storage inverter
The energy storage inverter has three functions, including peak shaving, standby power supply and independent power supply.
From a regional perspective, peak shaving is the demand of Europe. In Germany, for example, the electricity price in 2019 has reached 2.3 yuan/kWh, ranking first in the world. In recent years, the electricity price in Germany continues to rise. In 2021, the electricity price of German residents will reach 34 euro cents/kilowatt hour, while the photovoltaic/photovoltaic distribution and storage LCOE will be only 9.3 euro cents/14.1 euro cents/kilowatt hour, 73%/59% lower than the residential electricity price. The difference between the residential electricity price and the electricity cost of photovoltaic distribution and storage will continue to grow.
The household photovoltaic distribution and storage system can reduce the electricity cost, so users have strong power to install household storage in high electricity price areas.
Electricity price of residents in 2019
German kilowatt hour electricity price level (euro cents/kilowatt hour)
In the peak shaving market, users often choose hybrid inverters and AC coupled battery systems, which are more cost-effective and easier to manufacture. Off grid battery inverter chargers with heavy transformers are more expensive, and hybrid inverters and AC coupled battery systems use transformer free inverters with switching transistors. These compact lightweight inverters have lower surge and peak power output ratings, but are more cost-effective, cheaper, and easier to manufacture.
Standby power supply is required by the United States and Japan, while independent power supply is just required by the market, including South Africa and other regions. According to EIA, the average power outage time in the United States in 2020 will exceed 8 hours, mainly due to the dispersion of American residents, aging of some power grids and natural disasters.
The application of household photovoltaic distribution and storage system can reduce the dependence on the power grid and increase the power supply reliability at the user side. The photovoltaic energy storage system in the United States is large and equipped with many batteries, because it needs to store electricity to cope with natural disasters.
Independent power supply is just the demand of the market. In South Africa, Pakistan, Lebanon, the Philippines, Vietnam and other countries, where the global supply chain is tight, the national infrastructure is not enough to support people's power consumption. Therefore, users need to equip household photovoltaic energy storage systems.
Power outage duration per capita in the United States (hours)
In June 2022, South Africa will start six level power rationing, and many places will be cut off for six hours a day
The hybrid inverter as a standby power supply has certain limitations. Compared with dedicated off grid battery inverter, hybrid inverter has some limitations, mainly due to limited surge or peak power output during power failure. In addition, some hybrid inverters have no backup power supply capacity or have limited backup power supply, so they can only backup small or necessary loads such as lighting and basic power circuit in case of power failure, and many systems will have 3-5 seconds delay during power failure.
The off grid inverter provides very high surge and peak power output, and can handle high inductance loads. If the user plans to supply power to high surge equipment such as water pumps, compressors, washing machines and electric tools, the inverter must be able to handle high inductive surge loads.
Output power comparison of hybrid inverter
2、 DC coupled hybrid inverter At present, most photovoltaic energy storage systems in the industry use DC coupling to achieve the integrated design of optical storage, especially in the new system, the hybrid inverter is easy to install and the cost is low.
When adding new systems, the use of optical storage hybrid inverter can reduce the equipment cost and installation cost, because one inverter can achieve the integration of control and inverter. The controller and switch in the DC coupling system are cheaper than the grid connected inverter and distribution cabinet in the AC coupling system, so the cost of the DC coupling scheme is lower than that of the AC coupling scheme.
In the DC coupling system, the controller, battery and inverter are serial, closely connected and less flexible. For the newly installed system, PV, battery and inverter are designed according to the user's load power and power consumption, so they are more suitable for DC coupling.
DC coupled hybrid inverter products are the mainstream trend, and major domestic manufacturers have layout.
In addition to Yuneng, all major domestic inverter manufacturers have laid out hybrid inverters, among which Shangneng Electric, Goodway and Jinlang have also laid out AC coupling inverters, with perfect product forms. Deye's hybrid inverter supports AC coupling on the basis of DC coupling, providing convenience for installation for users' demand for stock transformation.
Sungrow Power, Huawei, Shangneng Electric and Goodwin will arrange energy storage batteries, and the integration of battery inverters may become a trend in the future.
Layout of major domestic inverter manufacturers
Three phase high-voltage products are the driving force of companies, and Deye focuses on low-voltage product market. At present, most of the mixed inverse products are within 10KW, most of the products below 6KW are single-phase low-voltage products, and most of the products below 5-10KW are three-phase high-voltage products. Deye has developed many high-power low-voltage products, and the low-voltage 15KW products launched this year have started to sell.
Hybrid inverter products of domestic inverter manufacturers
The maximum conversion efficiency of domestic inverter manufacturers' new products is about 98%, and the off grid switching time is generally less than 20ms. The maximum conversion efficiency of Jinlang, Sungrow Power and Huawei products has reached 98.4%, and the maximum conversion efficiency of Goodwin has also reached 98.2%. The maximum conversion efficiency of Hemai and Deye is slightly lower than 98%, but the switching time of Deye is only 4ms, far lower than 10-20ms of peers.
Comparison of maximum conversion efficiency of hybrid inverters of various companies
Comparison of switching time of hybrid inverters of different companies (ms)
The main products of domestic inverter manufacturers are mainly aimed at the three major markets of Europe, the United States and Australia. In the European market, Germany, Austria, Switzerland, Sweden, the Netherlands and other traditional photovoltaic core markets are mainly three-phase markets, preferring products with higher power. The traditional manufacturers with advantages are Sunshine and Goodwin. Jinlang has accelerated its catch up and is favored by users with its price advantage and the introduction of high-power products above 15KW.
Italy, Spain and other southern European countries mainly need single-phase low-voltage products. Goodway, Jinlang and Capital Airlines performed well in Italy last year, each accounting for about 30% of the market. The main demand of the Czech Republic, Poland, Romania, Lithuania and other Eastern European countries is three-phase products, but the price acceptance is low. Therefore, Capital Airlines performs well in this market with its low price advantage. In the second quarter of this year, Deloitte began to ship 15KW new products to the United States. The United States has a large energy storage system and prefers higher power products.
Domestic inverter manufacturers' hybrid inverter products are targeted at the market The battery inverter split type is more popular with installers, but the battery inverter integrated machine is the future development trend. Optical storage hybrid inverter is divided into hybrid inverter sold separately and battery energy storage system (BESS) sold together with inverter and battery.
At present, under the condition that the dealers have mastered the channel, the direct customers are relatively concentrated, and the products of the separated cell and inverter are more popular, especially in regions outside Germany. The main reason is that the installation is convenient and easy to expand, and it is convenient to reduce the procurement cost. If one of the batteries or inverters cannot supply, it can find a second supply, and the delivery is more secure. Germany, the United States and Japan are all in one.
The all-in-one machine can save a lot of after-sales trouble, and has certification factors. For example, the certification of the fire protection system in the United States needs to be linked to the inverter. At present, the technology trend is towards all-in-one machine, but the split type is more acceptable to installers in terms of market sales. Most domestic manufacturers began to layout battery inverter integrated machine.
Capital Airlines Xinneng, Guruiwat, Kehua and other manufacturers have chosen this mode. In 2021, the sales volume of energy storage batteries of Capital Airlines Xinneng will reach 35100 pcs, a 25 fold increase compared with 20 years; In 2021, the sales volume of Guruiwat's energy storage batteries will be 53000 sets, an increase of 5 times over 20 years.
The excellent quality of Arrow energy storage inverter drives the continuous growth of battery sales. In 2021, Arrow batteries will ship 196.99MWh, with a revenue of 383 million yuan, twice the revenue of energy storage inverter. The customer has a high degree of recognition for the inverter manufacturers that make batteries, because they have a good cooperation relationship with the inverter manufacturers and have confidence in the products.
The proportion of revenue of new energy storage battery of Capital Airlines increased rapidly The revenue of energy storage battery of Arrow will account for 46% in 2021
In the DC coupled system, the high voltage battery system is more efficient, but the cost is higher in the case of high voltage battery shortage. Compared with the 48V battery system, the working voltage range of the high-voltage battery is 200-500V DC, which has lower cable loss and higher efficiency. Because the solar panel usually operates at 300-600V, similar to the battery voltage, an efficient DC-DC converter with very low loss can be used.
The price of high-voltage battery system is higher than that of low-voltage system, while the price of inverter is lower. At present, the demand for high-voltage batteries is strong and the supply is insufficient, so it is difficult to buy high-voltage batteries. In the case of a shortage of high-voltage batteries, the cost of using low-voltage battery systems is lower.
DC coupling between solar cell array and inverter
DC directly coupled to compatible hybrid inverter The standby power output of hybrid inverters from major domestic manufacturers is not limited in case of power failure, so they are applicable to off grid systems. The power of the standby power supply of some products is slightly lower than that of the normal power range, but the power of the standby power supply of Goodway, Jinlang, Yangguang Power Supply and Hemai New products is the same as that of the normal value, that is, the power is not subject to more restrictions during off grid operation, so the energy storage inverters of domestic inverter manufacturers are applicable to off grid systems.
Comparison of standby power supply of hybrid inverter products of domestic inverter manufacturers
3、 AC coupled inverter The DC coupling system is not suitable for retrofitting the existing grid connected system. The DC coupling mode mainly has the following problems: First, the DC coupled system has the problems of complex wiring and redundant module design when retrofitting the existing grid connected system; Second, the delay of parallel and off network switching is long, and the user's electricity experience is poor; Third, the intelligent control function is not comprehensive enough and the control response is not timely enough, which makes it difficult to realize the microgrid application of the whole house power supply. Therefore, some enterprises choose the AC coupling technology route, such as Yuneng.
AC coupling system makes product installation easier. Yuneng realizes bidirectional energy flow by coupling the AC side and the photovoltaic system, which eliminates the connection of the photovoltaic DC bus and makes the product installation easier;
hrough the combination of software real-time control and hardware design improvement, the millisecond level switch between parallel and off network is realized; Through the output control of the energy storage inverter and the innovative combination design of the power supply and distribution system, the microgrid application of the whole house power supply under the control of the automatic control box is realized.
The maximum conversion efficiency of AC coupled products is slightly lower than that of hybrid inverters. Jinlang and Goodway have also laid out exchange coupling products, mainly for the stock transformation market. The maximum conversion efficiency of AC coupling products is 94-97%, which is slightly lower than that of hybrid inverters, mainly because the modules need to be converted twice before being stored in batteries after power generation, reducing the conversion efficiency.
Comparison of AC coupling products of domestic inverter manufacturers
Comparison of AC coupling products of domestic inverter manufacturers
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