The First String Inverter Brand with Over 100GW Deployment Globally
10 years of Huawei Smart PV journey
24 Jul 2020
Introduction: Within the PV industry, it is widely believed that SMA invented string inverters while Huawei make them thrived.

String Inverters: A Great Reverse Deduction

Staring across the endless Gobi Desert, the President of Huawei Smart PV was dazzled by the "blue sea" stretching out before him.

In 2013, following more than three years of technical research and buildup, Huawei Network Energy (now renamed as Huawei Digital Power) began launching Huawei inverters. Quite quickly, Huawei central inverters installed hundreds of MWs in the Chinese market. Through this process, the head of the business realized that he needed to visit project sites in order to acquire more specific and real customer problems.

A few days later, he arrived at the Qinghai Huanghe hydropower PV plant 3000 kilometers away from Huawei headquarter in Shenzhen.

Qinghai is a sparsely populated city known for its vast amounts of loess soil. Driving to a PV plant usually involves a journey of dozens or hundreds of kilometers. In the foreseeable future, the available manpower will be unable to fulfill the requirements of increasingly enlarged PV plants. By then, we will exceed the limit to which manpower can be of support.

Back in 2013, industry research on the weather resistance of inverters was still in its infancy. During the onsite visit, the head of Huawei inverter business discovered that the dust prevention door needed to remain open in summer in order to dissipate heat, which then necessitated the removal of dust every night. Even in winter, dust accumulated inside the device. As such, every device require two people to maintain and clean dust each night everyday throughout the year, which was a source of great frustration among O&M personnel. In addition, the O&M of central inverters required professional knowledge. Faulty central inverters could only be repaired once a professional O&M personnel arrived at the site, a time-consuming process which negatively impacted the power generation of the PV plant.

To address these problems, Huawei began to wonder and research on what kind of inverters are needed for the PV industry.

Solar inverter technology originated from SMA, a German company. In 1991, SMA produced its first solar inverter, which took the form of a small string inverter. By 2002, SMA had launched its first container inverter. At that time, Huawei had not yet entered the PV business.

From a technical roadmap perspective, SMA decided to develop string inverters first, before moving on to central inverters, and this development path formed the technical roadmap for the entire solar inverter industry. As SMA inverters are originally manufactured and produced in Germany, the costs of string inverters have not been lowered much.

The PV industry has developed rapidly since 2010, and the costs of inverters have been reduced to approximately 0.2 USD/watt. Following a visit to German enterprises during the early days, Huawei realized that German enterprises possessed sophisticated equipment techniques, and has very regulated and impressive production lines. Many Huawei employees also believed that central inverters would be the trend.

To be prudent, Huawei assigned two teams to work on different technical solutions. At that time, Huawei tended to use string inverters to win the European market, and use central inverters to explore the Chinese utility PV plant market.

Following the Qinghai trip, the management of Huawei PV business decided to ditch the central inverter entirely however and in search of a completely new model.

The ever-increasing cost of manpower, paired with existing O&M expenses, became a major problem that restricted the levelized cost of energy (LCOE) for PV plants. In addition, the number of central inverter MPPTs was insufficient at that time, and could not provide a solution to the PV string mismatch problem. Over the years, the mismatch problem became increasingly serious, and the energy yield decreased at a faster rate. More importantly, as central inverters did not have the capability to accurately locate faults, it was extremely difficult to determine which PV string was faulty in a PV plant the size of dozens of football fields. However, string inverters were also unable to completely solve these problems. The Danish industrial giant, Danfoss, which once promoted string inverters, cut off its PV business shortly after entering the Chinese market due to the prohibitive cost of string inverters, in addition to unresolved problems relating to the grid connection harmonics of utility PV plants.

It seemed that Huawei had reached a dead end. However, as a company known for developing effective solutions and solving customers’ problems, Huawei instead used reverse deduction to address customer needs:

1. Detection capabilities for small PV arrays or PV strings must be available.
2. Troubleshooting time must be short.
3. Manpower, especially professional technical personnel who often travel back and forth between multiple PV plants, must be freed.
4. The PV string mismatch problem needs to be solved to improve energy yields.
5. The cost cannot be too high.

While it seemed that none of the products available at that time could meet these requirements, Huawei engineers, famed for their problem solving abilities, expanded products into product packages.

They chose string inverters that satisfied the preceding conditions and transplanted Huawei's telecom business experience to the PV field.

Low power string inverters are used, enabling the number of inverters to increase. As such, successfully controlling the fault rate becomes key to the success of this solution. By the end of 2018, and owing to Huawei's strict manufacturing and testing standards, the overall failure rate of Huawei's 3 million sets of inverters delivered globally was at only 3‰, far lower than any other inverters in the industry. Such an ultra-low failure rate stems from Huawei's large amount of R&D investment. Huawei launches a new quality product every year, each of which must pass verification and testing, such as heat dissipation and dust prevention as basic requirement. In addition, Huawei operates the only rocket-triggered lightning and explosion tests in China, with the costs of outdoor lightning tests often exceeding 150,000 USD and serving as a reminder of the great importance Huawei attaches to product quality.

In the beginning, Huawei's decision to eliminate fuses resulted in many confused observers. From an O&M perspective, Huawei did not wish to include any vulnerable parts in the solution, and instead opted to make the entire PV plant maintenance-free by removing components that are prone to faults, such as fuses and fans. As such, Huawei adheres to its concept of simplicity. "Less is more" leaves simplicity to customers while Huawei handles all the troubles. With less time, less equipment, and less O&M, energy yields and user experience are improved.

In addition to hardware, Huawei also operates a software team comprised of hundreds of members, over 80% of whom are PhDs. This team is dedicated to solving the grid connection algorithm problems of utility PV plants. Soon, even PV plants at GW level could use string inverters and have no trouble in grid connection, which demonstrates the ability of the team. We could see Huawei working very hard to integrate its superior ICT technologies into building Smart PV plants.

With enhanced string inverters as the core, the loaded smart PV plant management system was first applied in the mountain PV plants of Quyang.

Huawei Smart PV Solution 1.0 made its industry debut in 2014, and demonstrated how the centralized control center remotely detects and locates PV module faults, site intrusion, and power generation for each array.

Excited by the success of this new technology, industry insiders began promoting the "No intelligence, no PV" slogan after the debut.

The smart PV era has just began.

(to be continued)