Lightning, Ice Baths and Sandblasting: Inside the Quest for World’s Most Reliable String Inverter

Huawei is obsessed with failure.

Or, to put it more precisely, the Chinese string inverter manufacturer is focused on pinpointing any possible source of failure in its products that need to endure at least 25 years in some of the world’s harshest conditions. It uses that information to ensure that its inverters achieve industry-leading reliability.

Not far from its corporate headquarters in Shenzhen, China, Huawei has a sprawling Global Compliance & Testing Center. The GCTC can mimic, and even exceed, the harsh conditions Huawei’s string inverters may encounter when they are deployed in large-scale solar power plants.

Huawei is the largest inverter manufacturer in the world. The company expects global shipments to reach between 30 and 35 gigawatts this year. The testing center ensures that those inverters are top quality.

“The GCTC is something that only a very few big companies could attempt to do in-house,” said Bates Marshall, vice president and general manager for North America Smart PV Plant Solutions at Huawei. “The reason we have this type of capability is because reliability is the single most important attribute of our products. It’s part of our DNA.”

Huawei’s roots are in the telecommunications industry, and it is currently the third-largest smartphone company in the world. The GCTC is one of 16 Huawei R&D centers across the globe. One of the reasons Huawei entered the inverter business was because it saw an enormous gap in the market, and therefore an opportunity to leverage its research prowess to improve the reliability of string inverters.

“We saw that the reliability outcomes in the PV market were very poor,” said Marshall, who pointed to Huawei’s long history of producing sturdy telecommunications infrastructure, like 4G LTE base stations. “We knew that we could bring this reliability expertise into PV and make a big impact. And we deliver that quality by leveraging this GCTC capability that already existed.”

Finding the weak points

String inverters that find their way into the Huawei GCTC are essentially subjected to torture. For example, because string inverters could very well be hit by lightning over the course of their decades of outdoor operation, the GCTC literally creates lightning with gold.

Huawei takes an inverter and places it on a tower outside. “From that tower, we launch a rocket into the cloudy sky that trails a gold thread,” said Marshall. “We will actively seek to trigger lightning, and that lightning bolt will strike the rocket and the gold wire and go down into the inverter, and we will look at the effect.”

When they’re not being shocked by lightning, Huawei’s string inverters undergo a range of other tests meant to mimic the worst possible stresses and conditions they might encounter.

One test involves a week in a chamber that can reach temperatures as low as -40 degrees Celsius. But over the course of the test, the inverters aren’t simply left to chill. They’re doused with water, left to freeze and then warmed up to thaw out. All the while, Huawei powers the inverters on and off and connects and disconnects them from loads in order to gauge their resilience and reliability.

Other tests involve sandblasting inverters and mimicking the low-pressure environment they would encounter in high-altitude environments. All of these experiments are done in addition to the battery of mandatory standards testing that all inverters are required to comply with in different regions of the globe, such as the UL 1741 inverter standard and National Electric Code requirements in the U.S.

But satisfying standards is just the very beginning. The GCTC also looks to always push the envelope, given Huawei’s obsession with reliability. That means constantly developing new tests, some of which have resulted in design changes, such as ditching the external fans usually found in inverters.

“In our [string inverter], one of the characteristics that is unique is that it’s passively cooled. Instead of forced air fans like most of the competitors use, our design relies on a patented heat sink on the back to remove heat,” said Marshall.

“We have to think of things like, what would happen if a customer plants trees next to the inverter and it’s dropping leaves on it over the next 25 years?” added Marshall. To test for that scenario, the researchers at the GCTC fill the inverter heat sink up with leaves and then run an array of experiments to ensure the inverter will still function properly.

More reliable, by design

The wide range of tests that are done at GCTC have positively impacted projects in the field that face trying conditions. According to a study conducted by international engineering firm TUV, Huawei’s string inverters installed at a major 220-megawatt site have an availability of at least 99.99 percent across the board. This compares very favorably to industry norms of around 99.5 percent availability.

Huawei’s inverters installed around the world are seeing stable performance in trying conditions, from being doused with salt mist in the Philippines to baking in extremely high-temperature project sites in Jordan and Delhi. Customers report to Huawei that energy yields for projects are consistently higher than they would be for central inverters.

Many of the tests Huawei conducts at the GCTC simply could not be applied to central inverters. Why? String inverters are much smaller than central inverters, which are so big that they are often transported on an oversized flatbed trailer -- as opposed to string inverters, which can be carried around by two people.

The size of central inverters makes it impractical to run them through the litany of rigorous tests that Huawei can do with its string inverters. “If you think about subjecting them to the same environmental conditions, it’s an impossibly different task for the central inverter,” said Marshall. “It’s one of the reasons that the reliability outcomes of the central inverters are so much worse.”

For Huawei, reliability is also enhanced by the architecture of its string inverters. Put simply, some of the components most likely to fail on a central inverter just don’t exist on Huawei’s string inverters -- think of it as addition by subtraction.

“One of the fundamental things we have done is remove those elements that fail in competitors' devices,” said Marshall, whether it’s fans, the filters for the fans, or DC fuses on the inputs. “For example, our devices don’t have unnecessary LCD screens because there are no LCD screens that will last out in the sun for more than 10 years.”

When it comes to inverters, less really can be more.