208V Three-Phase PV Interconnection

When making that leap to commercial service voltage, a little upfront knowledge of 208 three-phase can save time and problems down the line.

Designing a 208v Three-Phase Solar Project

As residential installers begin to win more jobs, small commercial projects become a natural next step. When making that leap to commercial service voltage, a little upfront knowledge of 208 three-phase can save time and problems down the line.

 

Three-Phase

 

Some single-phase inverters like Enphase, SMA SunnyBoy, and Fronius Primo inverters have a 208v and 240v setting single-phase. Solar contractors will typically want to use the same equipment they are familiar from residential installs on a new service voltage. To use single-phase inverters on 208 three phase service voltage, it is critical that the installer established balanced output on each leg of the three inverters. For example, if you have a ~15kw 208v three phase system you can NOT use (2) 7.7kw in 208v 3 phase because you throw off the voltage output. Instead, you would want to design around (3) 5kw sunny boy to balancing the output from each the three legs on each inverter. Nick Gilleland, Director of Solar at Davis Electric, explained, “my install team sets up each inverter in the 208v mode without a neutral.” 

 

SMA Sunny Boy Inverter Technical Data

 

Utility often requires expensive additional control equipment to make all three inverters shut off and some utilities won’t allow it at all.  Most AHJ will tack on extra requirements. For those reasons we typically recommend a installers design around dedicated 208v three phase inverters such as the Fronius Symo, Solectria or SolarEdge.