String inverter specialist Solis, which has a global network of service teams, has explored the possibility of connecting a single-phase inverter to the grid in the absence of a split-phase inverter while installing a solar photovoltaic (PV) system.
Highlighting a key technical detail that in many countries, the power grid structure entails a split-phase grid, Solis has analyzed how to tackle the issue if split-phase inverters are not available while installing a solar PV system. This article explains whether the conventional single-phase inverter could be connected to the grid in such cases. Additionally, problem areas that need to be considered have also been discussed.
120V/240 Vac split phase
120/240 Vac split phase is a type of single-phase, three-wired mid-point neutral power distribution system commonly found in the United States. It comes with a standard phase-neutral voltage of 120 Vac for residential and light commercial applications. The phase-to-phase (live-to-live) voltage is 240 Vac for heavy industrial loads such as compressors, refrigerators, and pumps. Because of the 120-0-120 voltage configuration, it is sometimes referred to as ‘dual-phase’, ‘2 phase or two-phase’, or even mistakenly, ‘single-phase 220 Vac’.
Figure 1: Wiring supply
Using a traditional single-phase inverter in a split-phase grid system
Customers in some regions often mistake 120/240 Vac for a single-phase 220 Vac grid. Therefore, the PV grid-connected inverter purchased turns out to be a single-phase inverter line and neutral (L+N), which could cause trouble during the installation process. However, there is no need to worry about it. The L+N structure single-phase inverter could still be used in the 120 Vac/240 Vac split-phase power grid.
Figure 2: Wiring topology
As shown in Figure 2, only the L+N wires of the inverter need to be connected with the two lines of the split-phase grid. Also, the polyethylene wire of the inverter is connected with its neutral.
This particular wiring method does not need any special setting of the inverter. Instead, only the local grid standard is needed to be set. The sequence of commands entails going to the main menu, followed by advanced settings, feeding in password 0010, selecting standard, followed by selecting standard code, and finally saving and sending.
While using the zero-injection function in this system, attention needs to be paid to the current transformer (CT) line entry method, which is different from the conventional thread method. The L2 cable on the CT needs to be looped, as shown in Figure 3.
Figure 3: The wiring topology of zero-injection function in split-phase grid
As demonstrated, a single-phase inverter can be connected to the split-phase power grid. However, this is an emergency solution for extreme circumstances. For the split-phase power grid, the grid-tied Solis U.S. version inverter is recommended.
For any further queries, you could contact Solis support engineers or visit their website for after-sales services.
This article is sponsored by solar inverter manufacturer Ginlong Technologies.
Image credit: Solis