Installing more module power than the inverter's rated power — oversizing — is standard and recommended practice. Done well, it increases annual generation and makes better use of the inverter. Done badly, it causes excessive clipping, overheating and even loss of warranty. The key is the DC/AC ratio, called FDI (inverter sizing factor) in Brazil.
What the DC/AC ratio is and how to calculate it
The DC/AC ratio is the ratio between the modules' peak power (DC) and the inverter's rated power (AC):
DC/AC ratio = module DC power (kWp) ÷ inverter rated AC power (kW)
Example: 6.6 kWp of modules with a 5 kW inverter → ratio = 6.6 ÷ 5 = 1.32. Some manufacturers state the limit as the maximum allowed DC/AC ratio in the datasheet — never exceed that ceiling, or you risk losing the warranty.
Recommended range and clipping
For most Brazilian projects, a ratio between 1.1 and 1.35 is the sweet spot: it uses the hours of weak irradiance (morning, late afternoon, cloudy days), when the inverter would otherwise be idle. Above that, clipping begins: at irradiance peaks the inverter "cuts" the excess power it cannot convert. A little clipping is acceptable and even desirable; too much is energy thrown away.
Hybrid inverters and some modern string models accept higher ratios (1.5 or more) because they have thermal headroom and multiple MPPTs — always check the manual.
Factors that weigh on the decision
Use a higher ratio when local irradiance is moderate, when there are unfavourable orientations, or when the goal is to maximise annual energy with a cheaper inverter. Use a more conservative ratio when irradiance is very high (Brazil's Northeast), when there is thermal risk (hot roof, poor ventilation around the inverter) or when the customer prioritises peak generation for instant self-consumption.
DC/AC ratio ranges and expected effect
| Ratio | Situation | Effect |
|---|---|---|
| < 1.0 | Undersized array | Idle inverter, wasted capital |
| 1.1 – 1.2 | Conservative | Almost no clipping; ideal at high irradiance |
| 1.2 – 1.35 | Recommended | Best annual generation in most cases |
| 1.35 – 1.5 | Aggressive | More clipping; only with an inverter that supports it |
| > 1.5 | Risky | High clipping and possible loss of warranty |