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), 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.
Formula and source
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.
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