AC Coupling vs DC Coupling
Two different ways to connect solar panels and batteries to your home. Understanding the difference helps you make the right choice.
What's the Difference?
The terms "AC coupling" and "DC coupling" describe where the battery connects in your solar system - either on the AC (alternating current) side or the DC (direct current) side.
AC Coupling
The battery has its own inverter and connects to your home's AC electrical panel. Solar and battery are separate systems that work together.
DC Coupling
The battery connects directly to the solar panels (DC side) and shares a single inverter. Everything flows through one central unit.
Think of it like plumbing: AC coupling is like having two separate water heaters that both feed into your home. DC coupling is like having one big water heater that handles everything.
AC Coupled Systems
In an AC coupled system, the solar panels have their own inverter, and the battery has a separate inverter. Both connect to your home's AC electrical panel.
How Power Flows in AC Coupled Systems
Solar to Home
Solar DC → Solar Inverter → AC → Home
Solar to Battery (Charging)
Solar DC → Solar Inverter → AC → Battery Inverter → Battery DC
Power converts DC→AC→DC (two conversions)
Battery to Home (Discharging)
Battery DC → Battery Inverter → AC → Home
Advantages
- + Easy to add batteries to existing solar
- + Mix different brands/equipment
- + Can expand each system independently
- + If one inverter fails, the other still works
Disadvantages
- - Lower efficiency (double conversion losses)
- - Two inverters = higher equipment cost
- - More complex wiring
- - More points of potential failure
Typical Efficiency:
When charging batteries from solar, AC coupling loses about 10-15% of the energy due to double conversion (DC→AC→DC). Round-trip efficiency is typically 85-90%.
DC Coupled Systems
In a DC coupled system, the solar panels connect directly to the battery through a charge controller, and a single hybrid inverter manages everything.
How Power Flows in DC Coupled Systems
Solar to Home
Solar DC → Hybrid Inverter → AC → Home
Solar to Battery (Charging)
Solar DC → Charge Controller → Battery DC
Power stays DC the whole way (no conversion loss!)
Battery to Home (Discharging)
Battery DC → Hybrid Inverter → AC → Home
Advantages
- + Higher efficiency (fewer conversions)
- + One inverter = lower equipment cost
- + Simpler wiring and installation
- + Better for new installations
- + Single monitoring system
Disadvantages
- - Harder to add to existing solar
- - Must use compatible equipment
- - If inverter fails, entire system is down
- - Solar array size limited by inverter
Typical Efficiency:
When charging batteries from solar, DC coupling loses only about 2-5% of energy. Round-trip efficiency is typically 92-97%.
Side-by-Side Comparison
| Feature | AC Coupling | DC Coupling |
|---|---|---|
| Number of Inverters | 2 (solar + battery) | 1 (hybrid) |
| Charging Efficiency | 85-90% | 95-98% |
| Equipment Cost | Higher | Lower |
| Retrofit Existing Solar | Easy | Difficult |
| System Flexibility | High | Limited |
| Wiring Complexity | More complex | Simpler |
| Single Point of Failure | No | Yes (inverter) |
Which One Should You Choose?
AC Choose AC Coupling If...
- You already have a grid-tied solar system
- You want to add batteries without replacing your inverter
- You want flexibility to mix equipment brands
- You plan to expand solar and battery independently
- Your existing solar inverter is still under warranty
DC Choose DC Coupling If...
- You're installing a new solar + battery system
- Maximum efficiency is your priority
- You want simpler installation and wiring
- You prefer a single monitoring platform
- You want lowest overall system cost
Real-World Example: The Efficiency Difference
Let's say your solar panels produce 30 kWh of excess energy that you want to store in batteries for later use.
AC Coupled (90% efficient)
27 kWh
stored in battery
Lost: 3 kWh (10%)
DC Coupled (97% efficient)
29.1 kWh
stored in battery
Lost: 0.9 kWh (3%)
Over a year: If you store 10,000 kWh in batteries annually, DC coupling saves you approximately 700 kWh compared to AC coupling. At $0.15/kWh, that's about $105/year in efficiency savings.
Rick's Recommendation
Here's my practical advice based on your situation:
Remember: the "best" system is the one that fits your specific situation and budget. Both coupling methods work well when properly designed.
Ready to Find the Right Battery?
Browse our directory of batteries compatible with both AC and DC coupled systems.