What Is the DC-AC Ratio?
The DC-AC ratio (also called the clipping ratio or inverter loading ratio) compares the total DC capacity of your solar panels to the AC output capacity of your inverter.
Example: 9 kWp of panels connected to a 7 kW inverter = a DC-AC ratio of 1.29.
A ratio of 1.0 means the inverter is perfectly matched to the panel capacity. A ratio above 1.0 means the panels can theoretically produce more DC power than the inverter can convert — any excess is 'clipped' and lost.
So why would anyone size this way intentionally? Because in most real-world conditions, a panel array never operates at its nameplate capacity. Temperature, diffuse light, orientation, and soiling all reduce actual DC output. In Switzerland — with its significant cloud cover, alpine micro-climates, and winter snow periods — a panel array operates at peak STC (Standard Test Conditions) output on relatively few hours per year.
→ Still unsure if the maths add up? Check your personal payback period — it takes 60 seconds.
Why Switzerland Favours Mild Oversizing
In Swiss conditions, a DC-AC ratio of 1.1 to 1.3 is widely considered optimal:
- More energy harvested on low-irradiance days: an oversized array generates meaningful DC output even under diffuse light conditions, pushing the inverter closer to its efficient operating range
- Morning and evening harvest: the array starts producing usable AC power earlier in the morning and later in the evening than a 1:1 system
- Cost efficiency: adding extra panels is cheaper per kWp than upsizing the inverter; a modestly oversized array can increase annual yield by 5–12% with minimal additional clipping loss
- Alpine irradiance peaks: at high altitude, irradiance can exceed STC conditions due to snow reflection; clipping at these moments is acceptable given the total annual gain
VSE NA/EEA-CH: The Swiss Grid Connection Standard
Every grid-connected solar installation in Switzerland must comply with the VSE NA (Niederspannung Anschlussempfehlungen) and its photovoltaic supplement, the EEA-CH. Key points relevant to inverter sizing:
- Maximum AC output: the inverter's rated AC output must not exceed the maximum feed-in capacity agreed with your local grid operator (Verteilnetzbetreiber)
- Anti-islanding: inverters must comply with the VSE disconnection requirements to protect grid workers — all major European inverters (Fronius, SMA, SolarEdge, Kostal, Solplanet, Sungrow) are certified
- Power factor: VSE requires reactive power capability within defined cos φ limits
- Feed-in limitation: some Swiss grid operators impose a maximum feed-in cap (Einspeisebegrenzung) on residential systems — this is separate from inverter sizing but interacts with the DC-AC ratio decision
If your grid operator caps feed-in at, say, 3.68 kW (a common limit for single-phase connection), sizing a larger inverter above that cap wastes money unless you have high self-consumption from a heat pump or EV charger.
Common Inverter Models and Swiss Grid Certification
| Inverter | Type | Common DC-AC range in CH | VSE certified |
|---|---|---|---|
| Fronius Primo/Symo | String | 1.1–1.4 | Yes |
| SMA Sunny Boy / Tripower | String | 1.0–1.35 | Yes |
| SolarEdge Home Hub | Optimiser-based | 1.0–1.25 | Yes |
| Kostal Plenticore Plus | Hybrid | 1.1–1.3 | Yes |
| Solplanet ASW | String | 1.0–1.25 | Yes |
| Sungrow SH series | Hybrid | 1.1–1.4 | Yes |
| Deye SUN-6K | Hybrid | 1.1–1.35 | Check model |
How to Evaluate the DC-AC Ratio in a Quote
When you receive an installer quote, locate the panel total (kWp) and the inverter rated AC output (kW). Divide panel kWp by inverter kW. Then ask:
- What clipping loss does the simulation estimate annually? (A good Polysun report will show this)
- Does this ratio comply with the grid operator's feed-in cap for this connection?
- Is there room to add panels later without replacing the inverter?
A ratio above 1.35 without clear justification for Swiss alpine conditions (high snow reflection, very sunny south-facing roof) warrants a detailed explanation from the installer.
Three-Phase vs Single-Phase Inverters in Switzerland
Most Swiss family homes with loads above 10 kW (heat pumps, EV chargers, large appliances) benefit from a three-phase inverter. Single-phase inverters are fine for small systems (under 5 kWp) but create phase imbalances in Swiss three-phase connections above certain loads — something local grid operators may flag during inspection.