Inverter AC coupling is the process of tying in an additional battery based, off-grid inverter/charger into an existing solar power system. This setup allows the system to provide backup power during grid outages.
Understanding AC Coupling
In a standard grid-tied solar system, your solar panels produce DC power, which is then converted to AC power by a grid-tie inverter (either a central string inverter or micro-inverters). This AC power is typically used to power your home or sent back to the grid.
However, most standard grid-tied systems shut down during a power outage for safety reasons (to prevent backfeeding the grid while utility workers are making repairs). This means you lose power even if the sun is shining.
How AC Coupling Provides Backup Power
AC coupling addresses this by adding a second inverter – an off-grid inverter/charger – and a battery bank. This system works alongside your existing grid-tie inverters.
Here's a simplified breakdown:
- Your existing grid-tie inverter(s) convert solar DC power to AC power as usual.
- This AC power is fed to the AC-coupled inverter/charger.
- The inverter/charger can then use this AC power to:
- Charge the connected battery bank.
- Directly power essential loads in your home via a dedicated circuit.
- When the grid goes down, the AC-coupled inverter/charger creates its own stable AC mini-grid. Your existing grid-tie inverter(s) can then synchronize with this mini-grid and continue producing power, which is used by the home or stored in the batteries.
- Power from the battery bank is also converted to AC by the off-grid inverter/charger to supply power when solar production is insufficient or at night during an outage.
Key Components of an AC Coupled System
- Existing Grid-Tie Inverter(s): String inverter or micro-inverters attached to solar panels.
- Additional Off-Grid Inverter/Charger: The central component for managing backup power. It converts battery DC to AC and manages charging from solar or the grid (when available).
- Battery Bank: Stores energy from solar or the grid for use during outages.
- Critical Loads Sub Panel: A critical loads sub panel is necessary for this application. This is a separate electrical panel that contains only the circuits you want to keep powered during an outage (e.g., lights, refrigerator, specific outlets). The AC-coupled inverter system powers only this sub panel.
Benefits
- Adds Backup Power: Keeps essential systems running during utility outages.
- Utilizes Existing Solar Array: Allows your existing solar panels to continue generating power during an outage (when synchronized with the off-grid inverter).
- Flexibility: Can often be retrofitted to an existing grid-tied solar system.
In essence, AC coupling is a method of integrating battery storage and backup power capabilities into a standard grid-tied solar system using an additional inverter operating on the AC side of the power flow.
