DC/AC ratio
Ratio of a PV array DC nameplate capacity at STC to its inverter AC rating; also called inverter loading ratio (ILR).
The DC/AC ratio expresses how much module capacity is connected per unit of inverter capacity. A 1.3 MWp array feeding a 1.0 MWac inverter has a ratio of 1.3.
Ratios above 1 are standard because modules rarely deliver their STC rating: irradiance is below 1,000 W/m² most of the time, cell temperatures are usually above 25 °C, and there are DC wiring, soiling and degradation losses. Oversizing the array keeps the inverter, transformer and grid connection busy for more hours, raising AC-based capacity factor at the cost of some clipping.
Typical values:
- Residential rooftop: 1.0–1.3, constrained by inverter model limits and grid export caps.
- US utility-scale: median about 1.3 for new projects (Lawrence Berkeley National Laboratory, Utility-Scale Solar reports), higher for fixed-tilt than tracking plants.
- Grid-limited or PV-plus-storage plants: 1.4–1.6 or more.
The economic optimum rises as module prices fall relative to inverter and grid-connection costs, and is higher in cloudy climates and with east-west layouts, where the array seldom reaches peak output. It is lower with single-axis trackers in sunny regions, where output stays near peak for longer. Because capacity factors are sometimes quoted on DC and sometimes on AC basis, comparing plants requires knowing their DC/AC ratio.
Related terms
All terms →- Inverter clipping
Energy lost when the DC power available from a PV array exceeds the inverter AC rating, so the inverter caps output at its maximum.
- String inverter
An inverter that converts the DC output of one or more series strings of PV modules into grid-synchronised AC, typically with several independent MPPT inputs.
- Capacity factor
The ratio of the energy a power plant actually produces over a period to the energy it would produce running at full nameplate capacity for the whole period.
- Kilowatt-peak (kWp)
The DC power rating of a PV module or array under Standard Test Conditions; the conventional unit of installed solar capacity.
- String (PV)
A group of PV modules wired in series so that their voltages add up while the current stays that of a single module.