String TLs: Your Commercial Solution

1GW Ground-mounted Smart PV Plant in Ningxia, China
Contributed by Charlie Saginaw

Although transformerless (TL) string inverters were established in the residential market, the advent of 20, 30 and 40+ kW sizes have allowed these versatile units to replace central inverters in commercial and utility scale projects.  

For many years the common design conception for medium to large scale solar systems called for the use of central inverters. Depending on the size of the system, an entire project could be tied into a single large inverter. Driven by advancements in power electronics manufacturing, it is now possible for the largest solar fields in the world to be comprised entirely of smaller string inverters. These advancements have resulted in aggressive pricing on a dollar-per-watt basis as well as DC/AC conversion efficiencies approaching 100%.  

String inverters can also offer developers increased design flexibility, energy yield, decreased downtime and an easier installation. String Tls allow large systems to be cut into smaller subarrays, each tied to their own inverter. Furthermore, each inverter has 2-3 maximum power tracking inputs. Together this results in optimized production on a string and sub array level. By comparison, central inverters are forced to operate at a level equal to the voltage produced by the lowest voltage input. String Tls will dramatically increase energy harvest in the presence of shading and module soiling.

The use of string inverters on the sub array level also minimizes the amount of downtime and lost revenue a system will experience due to equipment failure. When a central inverter stops operating the entire array is lost. Not easily replaced, central units often require a technician to visit the site and make necessary repairs. A malfunctioning string inverter can easily be replaced with a backup unit held onsite or nearby. The dramatically smaller size of a string Tl compared to a central inverter makes installations and maintenance far easier without the need for large cranes or other heavy lifting equipment.

According to GTM research “in the long term, we believe that string inverters will take a large but minority share of the utility-scale market.” As illustrated in the graph below, the cost gap is narrowing, string inverters become an increasingly attractive option because of their distributed design and lower O and M costs.

US Inverter Factory-Gate Average Sale Prices ($/W AC). Source: GTM Research

Special attention should be paid to Huawei as they quickly become one of the industry leaders.  Coming from the world of telecommunications, Huawei seeks to leverage their manufacturing prowess to eliminate common failure points in the world of string Tls.

The rise of Huawei solar inverters can in part be contributed to the demand for simple and reliable PV systems, and the insistence that manufacturers provide bankable, long-term solutions. Huawei goes above and beyond their competition in regards to market demand, resulting in a product offering that adds significant value to today's commercial solar EPCs and contractors. Huawei’s value proposition is validated by their strong market position. In 2015, Huawei held the top spot in total MW AC shipped globally.

 

PV Inverter Shipments

What differentiates Huawei from the rest of the pack? Attention to detail. Huawei looks to eliminate every possible point of failure for unsurpassed reliability.  For example, their product has three MPPTs, each with two string inputs. This both minimizes performance draw-down from shading or mismatch and enhances monitoring.. By only having two inputs per MPPT, Huawei was able to do away with DC fusing entirely because each string is rated to handle reverse current from the other string. Similarly, Huawei eliminated fans as the primary cooling method for their inverters by applying their extensive knowledge of heatsink design. Perhaps the greatest failure-mitigation measure is that Huawei’s engineering team eliminated LCD screens on their inverters.

Most representative of Huawei’s commitment to unsurpassed reliability is the quality standards they are bringing to the PV market. In telecommunications, “five nines” is the uptime standard that systems must achieve. This translates to a 99.999% uptime rating for their TL inverters. A commitment to reliability and uptime to this degree was unheard of in the world of solar up until this point.

Curious to learn how Huawei inverters can add value to your next commercial project? Check out the products we carry HERE or Contact your CivicSolar account manager for more information.

 

Published
3 years ago
Written by
Conor Walsh
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Products
Inverter
Support keywords
transformerless
String TL
Commercial Inverters