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DC:AC Ratio — Why Your Solar Panels Should Be Bigger Than Your Inverter
Most homeowners assume you match your panels exactly to your inverter — a 5kW inverter needs exactly 5kW of panels. This is wrong. Professional solar design uses a higher DC capacity than AC inverter output, intentionally. Here's why.
What Is the DC:AC Ratio?
The DC:AC ratio (also called the Inverter Loading Ratio or ILR) is:
DC:AC Ratio = Total Panel Wp ÷ Inverter AC Output (W)
A 5kW inverter with 5,500Wp of panels = 5,500 ÷ 5,000 = 1.10 ratio
Why Oversize the Panels?
1. Panels Rarely Produce at STC Nameplate
STC (Standard Test Conditions) = 1,000 W/m² irradiance, 25°C cell temperature. In the Philippines, panels regularly reach 55-65°C, losing 12-16% of output. A "5kW system" at STC produces closer to 4.2-4.4 kW in real Philippine heat conditions.
2. Morning and Evening Production
In the early morning and late afternoon — when irradiance is below 200-300 W/m² — a 1:1 system leaves the inverter underloaded. A 1.25:1 system starts producing useful power earlier in the morning and later in the afternoon, capturing more total daily energy.
3. Inverter Clipping is Minimal
At peak solar noon, if panels produce more than the inverter's rated output, the inverter "clips" — it operates at maximum output and lets the panel excess go unused. This clipping is typically only 1-3% of annual energy and is far outweighed by the gains in shoulder hours.
Recommended DC:AC Ratios for the Philippines
DC:AC Ratio | Context | Notes |
|---|---|---|
1.0 – 1.1 | Cloudy locations, limited roof space | Conservative — use when space is tight |
1.1 – 1.25 | Standard Philippine residential | Recommended range for most installations |
1.25 – 1.5 | East/West split arrays, commercial | Suitable when panels face different directions |
>1.5 | Generally not recommended | Excessive clipping, may void inverter warranty |
Practical Example
A homeowner with a ₱8,000/month bill needs approximately 5kW.
Inverter: Deye 5kW (5,000W AC rated)
Target DC:AC = 1.1 → Panel target: 5,000 × 1.1 = 5,500 Wp
Using 550W panels: 5,500 ÷ 550 = 10 panels
Result: 5,500 Wp DC / 5,000W AC = 1.1 ratio ✓
This is exactly the configuration shown in our Solar Quotation Tool — 10 panels × 550W = 5,500 Wp with a 5kW inverter.
Engr. Jason Morales — Founder, SolarEnergyPH