Add battery back-up power option to existing grid-tied PV and solar systems: Page 3 of 14

August 05, 2013 //By Mark Mays
Add battery back-up power option to existing grid-tied PV and solar systems
Mark Mays of OutBack Power explains how to add a battery back-up power option to existing grid-tied PV and solar systems.
invested into a solar energy system and would like to have backup power, a grid/ hybrid inverter/charger with battery back-up is the best choice. Solar energy can still be sold back to the grid, while having the security of knowing your PV based renewable energy system will still provide power during an outage until the electrical grid is back up and running.
Why not purchase a grid/hybrid inverter from the start? For those staring at their roof full of PV modules when the grid goes down, fully inoperable while the hours without power turn into days, and sometimes even weeks, that very same question is probably being asked many times over. Some may not have realized they would be without the PV power on their roofs when they bought their grid-tied system. Maybe they thought it would never happen to them. Finally, the relatively modest extra cost of a smarter grid-interactive inverter/charger and batteries may have initially discouraged them.

Figure 2 -Typical Grid/Hybrid System

Adding energy storage through AC-coupling: For the owners of these more common grid-tied, grid-dependent inverters, there is a way to tie in a battery-backup inverter system using a method called AC Coupling. It typically requires adding a load center with circuit breakers and electrical connections for the building’s critical loads. This allows a point at which the grid-tied (GT) inverter and the battery-based (BB) inverter to “couple” and share their energy to the loads. In a normal mode of operation with grid power available, the energy from the PV array flows through the GT inverter to the critical load panel, with any excess energy flowing through the load panel to the BB inverter, and on out to the grid (see Figure 3).


Figure 3 – Current path when grid power is present.

When grid power is lost, the BB inverter activates an internal transfer switch which opens its connection to

Design category: 

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