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Grid-tie inverters are typically sized at 1.0–1.25× the array DC wattage (DC/AC ratio). Oversizing DC relative to inverter AC rating allows morning/evening production without clipping midday peaks.
Inverter AC (W) = Array DC (W) / DC:AC ratio (1.1–1.3)When array output exceeds inverter AC rating, excess power is clipped. A 1.2 DC:AC ratio clips ~1–3% annually but reduces inverter cost. Higher ratios clip more but improve ROI in some climates.
Clipped energy ≈ Hours above rated power × (DC output − AC rating)Off-grid inverters must handle simultaneous load startup surges — well pumps and refrigerators draw 3–7× running watts for 1–3 seconds.
Inverter surge ≥ Max simultaneous startup surge (W)Updated: July 2026
18 × 400W panels = 7,200W DC. At 1.2 DC:AC ratio, select a 6,000W inverter. Expect ~2% annual clipping in sunny climates — acceptable tradeoff for lower inverter cost.
Running loads total 1,200W but well pump surges to 4,000W. Select a 2,000W continuous / 6,000W surge inverter. Add soft-start on pump to reduce surge requirement.
20 panels × 250W microinverters each rated 250W AC. Total AC capacity matches DC — no clipping but higher component count. Ideal for partial-shade roofs.
Panels rarely produce rated wattage due to temperature and soiling. A 1.15–1.25 DC:AC ratio is standard — the inverter runs more efficiently at partial load and costs less.
Motor startup surges trip undersized inverters instantly. A 1,500W running load with a 4,000W pump surge needs a 4,000W+ surge-rated inverter, not a 2,000W unit.
The inverter converts DC solar output to usable AC power and must handle array wattage and peak household loads. This calculator sizes grid-tie, hybrid, and off-grid inverters from panel array capacity, surge requirements, and acceptable clipping ratios.