The DC/AC ratio is the PV array DC nameplate capacity divided by the inverter AC rating. A ratio greater than 1 is common because the array rarely operates at STC nameplate output for long periods.
Why oversize?
Increasing the DC array can improve inverter utilization during mornings, afternoons and periods of reduced irradiance. It can therefore increase annual energy without increasing inverter AC capacity proportionally.
The trade-off: clipping
When the array could produce more than the inverter can convert, the inverter limits output. This is clipping. The designer should quantify whether the extra DC capacity produces enough additional useful energy to justify the added modules, structure and BOS cost.
What else must be checked?
- Maximum inverter DC input power.
- Maximum DC current per MPPT.
- String count and MPPT allocation.
- Module and inverter compatibility.
- Thermal and environmental conditions.
- Project energy target and economics.
Professional approach
Do not select a DC/AC ratio from a universal rule. Test several options in the actual simulation environment and compare clipping, yield, cost and electrical constraints.
Apply the concept
Use the corresponding GCC Solar Academy calculator after reading the article. For final engineering, verify the result against the actual equipment datasheet, installation method, governing standard and authority requirement.
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