Photovoltaic inverter technology route and representative enterprises

Editor's note: Although the price per watt of photovoltaic modules in ground-based power stations is more than ten times that of inverters, inverters are the real core components of power stations.

In the previous article, it was mentioned that the future competition in the photovoltaic industry must not be a vicious competition of low prices, but a competition to improve the quality of electric energy and grid friendliness. In this competition, inverters will play an irreplaceable and important role!

In a photovoltaic system, the inverter carries the connection between the power generation side and the grid side, and transmits the real-time power generation information of the power station to the monitoring system and determines whether operation and maintenance is required.

Another aspect that illustrates the core position of inverters is their diverse technology routes. Compared with the component link, which is firmly dominated by crystalline silicon technology, the inverter industry is showing a flourishing trend. The industry has been arguing endlessly but there is no consensus. The key is that the functions involved in inverters are much more complicated than those of components. In addition, owners often choose different types of inverters according to different types of photovoltaic power stations.

This magazine has collected and compiled information and current status of several inverter manufacturers active in China for readers' reference.

Technical route 1: large centralized inverter

Representative companies: Sungrow Power Supply, TBEA, CSR, TMEIC

Large inverters are still the mainstream of ground-based power stations and are often used as comparison samples for inverters of other technical routes.

Sungrow: After meeting the performance and quality requirements, Sungrow's box-type inverter room began to pay more attention to details such as heat dissipation and dust prevention. Sungrow and Alibaba Cloud have cooperated to establish the "Smart Light Cloud" power station operation and maintenance management platform. "Photovoltaic power generation will enter the group power station management stage from single power station management. With the help of Alibaba Cloud, Smart Photovoltaic Cloud will provide customers with standardized operation and maintenance services and investment and financing references." Sungrow will integrate nearly 20 years of solar power station operation and maintenance management experience, system design capabilities and product technologies to provide users with smart operation and maintenance services. And through Alibaba Cloud's US data center, it can provide operation and maintenance services to overseas solar power stations.

TBEA: TBEA considers how to build smart power stations from the perspective of the power grid, including how to connect the power generation, transmission and distribution ends. At the same time, it provides channels, including cloud computing platforms, real-time model mobilization and centralized control. In addition, TBEA has also launched a single-machine 2MW solution, replacing two 500kW centralized inverters with 1MW modular parallel inverters.

CSR: CSR National Power Conversion Center has the most core IGBT technology, which is not available in other domestic enterprises. The new fourth-generation model starts with high power density and reduced operation and maintenance costs after the development of the efficiency, quality and low voltage ride-through functions of the first three generations.

TMEIC: TMEIC is the manufacturer of the world's first MW-class inverter and the inverter leader with a market share of more than half of Japan's ground-mounted power stations. In the past two years, TMEIC has continuously increased its investment in China. In 2014, it established a factory in Shanghai. In February 2015, the Yancheng factory opened and was named "Yancheng TMEIC Power Electronics Co., Ltd." It produces two types of photovoltaic inverters: 500kW and 630kW.

Technical route 2: Distributed solution

Representative companies: Hopewind Electric, Wuxi Sineng, Han's Inverter

The distributed tracking centralized inverter photovoltaic grid-connected solution (referred to as the "distributed solution") is based on the traditional photovoltaic combiner box, adding a DC/DC boost conversion hardware unit and an MPPT control software unit to form an intelligent photovoltaic controller to achieve decentralized tracking of multiple MPPTs, which can reduce efficiency losses caused by factors such as inconsistent component parameters, local shadows, and elevation angle differences; after the output voltage of the improved photovoltaic combiner box is increased to 820V-1000V, it is centrally inverted to the inverter, which can reduce AC/DC transmission losses and inverter heating losses. While achieving accurate MPPT tracking, boosting and reducing losses, the output power quality is guaranteed through centralized inversion.

This technology originated from Satcon in the United States. Currently, there are three companies in China that use this technology, namely Hopewind Electric, Wuxi Sineng, and Han's Inverter. Among them, Hopewind Electric was the first to apply the distributed solution in China. It has been more than two years and has accumulated a total of about 100MW.

Hopewind Electric's boost module uses Sic material MOS tube to replace the traditional IGBT module, achieving high frequency, high voltage and high temperature resistance, and high conversion efficiency; from the combiner box end, one MPPT tracking is achieved for every two parallel branches. At the same time, the product has zero voltage ride-through function, which is the first in China.

Technical route three: string inverter

Representative small-power string inverter companies: Sungrow Power Supply, Growatt, Ginlong, Sanjing Electric, and Sofar New Energy.

At present, small-power string inverters have not been developed in China due to the distributed situation. Except for rural photovoltaic poverty alleviation projects in some areas, they are still mainly sold in overseas markets.

Sungrow: In overseas markets, including Australia and the Netherlands, where the company's small-power string inverters are widely used, Sungrow launched a new small-power single-phase string inverter to the world in 2014. The power range covers 3-5kW, and the whole machine weighs only 9kg, which can be easily installed and carried by one person. It also has a remote real-time monitoring function, which is convenient for operators to diagnose and maintain power stations. This type of product has been widely used in rural household photovoltaic systems in Anhui and other places.

At the end of 2014, Ginlong launched the world's lightest commercial 2kW grid-connected photovoltaic inverter, weighing only 5.6KG, and successfully applied its products to the Eiffel Tower, a landmark building in Paris. For the domestic market, Ginlong prefers to provide overall solutions to meet user needs. The solution has recently been applied in the photovoltaic system on the roof of Fuda Bearing Group.

The inverters of Shouhang New Energy are used in Wuxi, Henan, Anhui and other places. They are intelligent, efficient and reliable, with IP65 protection level, and can be freely installed indoors or outdoors.

SAJ Electric is one of the companies that has taken a unique approach in the industry. In addition to its great success in the Netherlands, Pakistan and India, it is also at the international leading level in photovoltaic pumping systems.

Representative companies of medium-power string inverters: Huawei, Sungrow, KOSTAL

Huawei has carried out in-depth cooperation with industry giants such as Huanghe Hydropower, Zhongli Tenghui, China Minsheng Investment, Longi Green Energy Technology, and Aikon. Huawei has established a monitoring and operation and maintenance system for Huanghe Hydropower that integrates digital technology, the Internet, and photovoltaic power generation. In the demonstration power station, a 4G wireless system dedicated to photovoltaics is used, and Wifi covers the entire power station. Unmanned aerial vehicle inspections with set flight routes are configured to view the power generation status of components in real time. The monitoring personnel at the Xining headquarters of Huanghe Hydropower found that the power generation data transmitted through the photovoltaic cloud fluctuated. They checked the problematic component array in the background, and then found the problem through high-definition cameras and called on-site operation and maintenance personnel to deal with it. At present, Huanghe Hydropower already has 200MW of "centrally operated, remotely diagnosed, and maintained in real time" intelligent photovoltaic power stations. In the future, Huawei will strengthen how to provide services more comprehensively and intelligently rather than just the products themselves.

Sungrow: Since the first grid-connected photovoltaic power station in China in 2003, Sungrow has been widely used in landmark photovoltaic demonstration projects such as the Olympic Bird's Nest and the Shanghai World Expo. In 2014, it launched the world's most efficient string inverter series with an efficiency of over 99%. So far, this model has been used in many large power stations in Japan, the United States, Europe and China, with a shipment volume of over 20,000 units.

KOSTAL: In 2003, KOSTAL PIKO inverter was the first in the world to propose the design concept of three-phase multi-channel MPPT string inverter and applied it to its products. It is the earliest small 3MPPT three-phase string inverter in the world and has been widely used in the European market since 2005. At the same time, PIKO inverter has a flexible load control function. When the light meets the required power, the load is automatically turned on, which can reduce the demand on the power grid and improve the economic benefits of users. KOSTAL PIKO uses a DC electronic input switch, which can overcome the strong voltage, current shock and DC arcing of ordinary switches during opening and closing, and solve the DC voltage and current shock from the root, prevent the occurrence of secondary accidents, and extend the equipment life and system reliability.