PV Inverter Loading Ratio (DC:AC) and Clipping Onset

The array-to-inverter power match: the inverter loading ratio (DC nameplate over AC rating, the DC:AC or ILR).

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Details, formula, and sources

With the cost-optimal band (commonly 1.1 to 1.3) and the clipping onset as a fraction of STC nameplate. An array is deliberately oversized so it fills the inverter's ceiling for more of the day, but push it too far and the inverter clips every clear-day peak. The clipping ceiling is fixed by the inverter; raising the array lowers the fraction of nameplate at which it bites - the diminishing return that puts the sweet spot near 1.2. A sizing sanity check, not a clipping-loss model.

ilr = dc_kw / ac_kw; clip_dc_kw = ac_kw / inv_eff; clip_fraction = clip_dc_kw / dc_kw; verdict by band (< 1.1 oversized, 1.1-1.3 optimal, > 1.3 undersized).

The inverter loading ratio (ILR / DC:AC ratio) and NREL inverter-sizing guidance (clipping begins where the array DC output exceeds P_ac / eta_inv), by name; the relations are public.

The loading-ratio definition and the clipping-onset relation are public; NREL inverter-sizing guidance is free at nrel.gov.

Estimate. AHJ and licensed professional govern.

Field names used by the API: dc_kw, ac_kw, inv_eff, ilr, clip_dc_kw, clip_fraction

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