About the Inverter Input Current Check
Inverter input current analysis verifies that the DC input current from the solar strings stays within the inverter's maximum DC input current rating — preventing overcurrent damage to the inverter's DC input terminals and internal components.
Formula
Total DC input current = Isc_panel × parallel strings per MPPT input
- Isc_panel
- Panel short-circuit current at STC (A)
- parallel strings per MPPT
- Number of strings connected to the same MPPT input
How to calculate it
- 1Find inverter maximum DC input current per MPPT channel from the datasheet.
- 2Calculate total Isc for strings connected to each MPPT: strings_per_MPPT × panel Isc.
- 3Under standard conditions, operating current ≈ Isc × 0.95. But at very high irradiance (1,100–1,200 W/m²), current can briefly exceed Isc at STC.
- 4Ensure total input current per MPPT ≤ inverter max input current per MPPT.
- 5If exceeded: split strings across more MPPT inputs or choose an inverter with higher input current rating.
Worked example
A 5 kW inverter with 2 MPPT inputs, max 12 A per MPPT. Panels: Isc = 10 A. Each MPPT has 1 string of 8 panels: input current = 1 × 10 = 10 A per MPPT — within the 12 A limit. If 2 strings were connected to one MPPT: 2 × 10 = 20 A — exceeds the 12 A limit, risking overcurrent.
What you can calculate
- Voc check
- MPPT range
- Isc × 1.25
- DC/AC ratio
Frequently asked questions
What happens if DC input current exceeds the inverter limit?
Exceeding the inverter's maximum DC input current can damage input protection diodes, MOSFETs, and associated components — potentially causing inverter failure. The inverter may enter an overcurrent protection state, shutting down and requiring a reset. Repeated overcurrent events significantly shorten inverter life.
Why does high irradiance cause overcurrent in solar systems?
Short-circuit current (Isc) scales almost linearly with irradiance — at 1,200 W/m² (possible briefly during cloud-edge concentration events), Isc is 20% above its STC value at 1,000 W/m². String design must account for this, particularly in high-altitude or reflective-environment sites where irradiance spikes above 1,000 W/m² are common.
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