The energy storage inverter integrates the functions of photovoltaic grid-connected power generation with energy storage power stations. When the electric energy is abundant, the energy is stored, and when the electric energy is insufficient, the stored energy is output to the grid, which plays the role of peak cutting and valley filling.
It is one of the main directions of development in the future. The photovoltaic inverter is the control center of the photovoltaic power generation system, which can convert the direct current generated by the module into alternating current to achieve grid-connected or load use.
A photovoltaic inverter is mainly composed of power conversion modules, microcomputer control modules, EMI modules, protection circuits, monitoring modules, man-machine interaction modules, etc. Its development depends on the development of electronic circuit technology, semiconductor device technology and modern control technology.
1. Power modularization accelerates serial penetration
Photovoltaic inverters can be divided into centralized inverters, cluster inverters and solar microinverter according to the working principle. Due to the different operating principles of various inverters, the application scenarios are also different.
- Centralized inverter
First confluence, then inverter, mainly applicable to the large centralized power station scene with uniform illumination. The centralized inverter first converts the multiple parallel series to the DC input, tracks the maximum power peak, and then converts centrally to AC.
The unit capacity is usually more than 500kw. Because the centralized inverter system has high integration and high power density, the cost is low. Mainly used in large plants with uniform sunshine, desert power stations and other large centralized photovoltaic power stations.
- Series inverter
First inverter, then convergence, mainly suitable for small and medium-sized roofs, small ground power station and other scenarios. The series inverter is based on the modular concept, and the maximum power peak tracking of 1-4 groups of photovoltaic series is carried out separately.
The DC inverter generated by it is first alternating current, and then the convergent voltage boost and grid connected, so the power is relatively small.
However, the application scenario is more abundant, which can be applied to various types of power stations such as centralized power stations, distributed power stations and rooftop power stations, and the price is slightly higher than that of centralized power stations.
Direct inverter grid-connected, mainly suitable for household and small distributed scenarios. The purpose of the micro inverter is to track the maximum power peak of each photovoltaic module separately, and then merge into the AC power grid through the inverter.
Compared with the first two inverters, its volume is the smallest, the power is the smallest, the general power is below the 1kw inverter. It is mainly suitable for distributed household use and small distributed industrial and commercial roof power stations, but the price is high and it is difficult to maintain once there is a failure.
2. The proportion of distributed generation increased
Distributed pv system is the preferred series solution, and the increase in the proportion directly drives the increase in the share of series. The centralized photovoltaic power station has a large investment, a long construction period, a large land area, and is mainly built on the large ground with uniform light. It can make full use of abundant and stable solar energy resources in the open.
Through the construction of large-scale photovoltaic power stations, access to high-voltage transmission systems to supply long-distance composite, power generation will be directly transmitted to the grid.
The power grid purchases all the electricity at the benchmark price of photovoltaic power generation and agrees to allocate power to the user. Distributed photovoltaic power stations have a low investment threshold, fast construction, small footprint and flexible installation. It is the main direction of photovoltaic development in the future.
Distributed generation refers to the power supply system located near the user's location, and the electricity produced by it can not only be used by users for their own use and nearby use, but also send excess power to the local distribution network.
Because solar energy resources have the characteristics of dispersion and low energy density, it has the natural advantages of distributed power generation.
Due to the low threshold of centralized investment, the willingness of high electricity price users such as parks, large industries, and industrial and commercial enterprises to use distributed power generation is constantly strengthening, which directly promotes the gradual increase of the market share of series inverters.
3. Series inverter MPPT has significant advantages
The series inverter has the advantages of high power generation, high reliability, high safety and easy installation and maintenance. When a component is blocked by a shadow or fails because it has multiple MPPT, it will only affect the power generation of the corresponding few strings.
Damage can be minimized, the array mismatch loss is small, and the efficiency is higher, and it is gradually applied to the large power station market. The main reason why series inverters have not been able to replace centralized inverters on a large scale before is the high cost.
The maximum power of a single machine is also limited by power devices and line layout. However, thanks to the iterative upgrade of core components such as upstream IGBT and MOSFET, the superposition power module technology continues to develop, and the single power density of cluster inverters continues to improve.
The price is falling rapidly, the cost performance is prominent, and more and more large power stations choose to use the series inverter scheme. New and replacement demand accelerates the explosion of the PV inverter market.
Different from the 25-30 year service life of photovoltaic modules, the service life of electronic components such as IGBT used by photovoltaic inverters is generally 10-15 years, so the 3000w inverter needs to be replaced at least once during the operation cycle of the photovoltaic power station.
In 2010, the global photovoltaic new installed capacity reached 17.5 GW, and as photovoltaic power stations continue to enter the technical transformation period of stock, replacement demand will continue to grow.
4. Industrial chain development superimposes technological upgrading
The raw material cost rigidity of photovoltaic inverters is the core focus of cost reduction. The raw material cost of photovoltaic inverters accounts for more than 80%, mainly including electronic components, mechanism parts and auxiliary materials. Product pricing is mainly based on cost plus, brand positioning and local market competition situation and other factors.
● The continuous development of the industrial chain
China's manufacturing industry has developed rapidly, and most raw materials have been made by itself. The general materials market is fully competitive, and the purchase price has declined year by year. Integrated circuits and semiconductor devices due to the high technical threshold, is expected to drive further reductions in procurement costs.
● Electronic and circuit technology upgrades
In photovoltaic power generation applications, the cost of traditional silicon-based inverters accounts for about 10% of the system, but it is one of the main sources of system energy loss.
The conversion efficiency of photovoltaic inverters using SiC MOSFET power modules can be increased from 96% to more than 99%, the energy loss is reduced by more than 50%, and the cycle life of the equipment is increased by 50 times.
Thus, the system size can be reduced, the power density can be increased, and the service life of the device can be extended.
According to the penetration rate of energy storage in the ratio of various energy facilities, the demand for energy storage facilities is expected to exceed 140 GW in 2025. Generation side energy storage primarily addresses the volatility and absorption of grid connected renewable energy.
The energy storage on the distribution side mainly realizes the function of peak and frequency regulation. The application of energy storage systems on the power generation and distribution sides usually has the characteristics of large capacity, a large footprint and high investment cost.
It is mainly used in large-scale centralized ground power stations and power grid substations. The power side can be divided into home energy storage, industrial and commercial photovoltaic energy storage, which is mainly used to improve power generation income and reduce electricity costs.