Solar Inverter Sizing Calculator
Size a solar inverter from total panel wattage.
Calculate DC-to-AC ratio, oversizing tradeoffs, and get string inverter or microinverter recommendations.
Recommended Inverter Size
Solar Inverter Sizing
The inverter converts DC from panels to AC for your home or grid. Sizing it correctly balances cost vs. potential clipping (lost energy when panel output exceeds inverter capacity).
The DC-to-AC ratio (DC/AC ratio): DC/AC ratio = Panel wattage / Inverter wattage
| DC/AC Ratio | Interpretation |
|---|---|
| 1.0:1 | Inverter exactly matches panel rating — no oversizing |
| 1.1-1.2:1 | Conservative — minimal clipping, slightly larger inverter |
| 1.2-1.35:1 | Standard for most installs — small clipping, balanced cost |
| 1.35-1.5:1 | Aggressive oversizing — saves on inverter, accepts 1-3% clipping |
| Over 1.5:1 | Substantial clipping risk — usually only for off-axis sites |
Why oversize panels relative to inverter?
- Panels rarely produce rated output — STC ratings are lab conditions
- Real-world output is 75-85% of nameplate due to:
- Module mismatch
- Wiring losses
- Soiling (dirt, leaves)
- Off-angle sun
- Inverters operate at peak efficiency at 50-90% of rated capacity
- A larger panel array + smaller inverter = more energy per dollar
Clipping example:
- 8 kW DC panels with 6.5 kW AC inverter = 1.23:1 ratio
- On a perfect noon day, panels output 7.5 kW
- Inverter clips to 6.5 kW
- Lost: 1 kW × 1 hour = 1 kWh
- Annually: ~30-100 kWh of clipping (≈$5-15/year at $0.15/kWh)
- Inverter saved: ~$500-800 vs. larger size
Inverter type comparison:
1. String inverter (centralized):
- All panels feed one inverter
- Cheapest per watt
- Simpler maintenance (one big box)
- Single point of failure
- Whole string drops if one panel shaded
- Best for: simple unshaded roofs, large arrays
2. Microinverters (one per panel):
- Each panel has its own micro
- More expensive ($0.20-0.35/W premium)
- Per-panel monitoring
- Shading on one panel doesn’t affect others
- 25-year warranties common
- Best for: complex roofs, partial shade, modular expansion
3. Power optimizers + string inverter:
- Hybrid: string inverter with DC optimizers per panel
- SolarEdge dominant brand
- Per-panel performance, central inverter
- Mid-range cost
- Best for: shade tolerance + cost balance
4. Hybrid inverters (battery-ready):
- Solar inverter with battery integration
- Required for backup power systems
- ~30% premium over standard string inverter
- Best for: any system planning future battery
Sizing recommendations:
| Array Size | String Inverter | Microinverter Option |
|---|---|---|
| Under 4 kW | 3.0-3.5 kW string | All micros |
| 4-6 kW | 4.5-5.0 kW string | Either |
| 6-8 kW | 6.0-7.0 kW string | Mostly string |
| 8-12 kW | 8.0-10 kW string | String preferred |
| 12-20 kW | 11-15 kW dual-MPPT | String required for cost |
| Over 20 kW | Multiple string or 3-phase | String only |
Other considerations:
- Oversizing more than 30% voids many manufacturer warranties
- Future expansion: size inverter for ~10% more than initial array
- Battery-ready: hybrid inverters cost ~30% more but save replacement later
- Local code: some jurisdictions require AC disconnect at inverter