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Solar Panel Array Sizing Calculator

Quick answer

Size the full PV array: panel count from daily kWh, array watts, series string sizing from inverter voltage window, and roof area with mounting row spacing.

Figures are estimates from this calculator’s standard formula — adjust the inputs in the tool below for your exact number.

How Does the Solar Panel Array Sizing Calculator Work?

Panels = Daily kWh ÷ (Panel kW × Sun h × 0.75)

Array sizing chains three checks. Energy: panels = daily kWh/(panel kW x sun hours x 0.75 derate). String: series count must keep the string voltage inside the inverter's MPPT window at record cold and record heat. Area: each 400 W panel needs about 2 m2 plus 20-30 percent row spacing. Example: 12 kWh/day at 4.6 sun hours with 450 W panels gives 12000/(0.45 x 4.6 x 0.75) = 7.7 - so 8 panels, 3.6 kW array, about 22 m2 of roof. Snow and soiling add derate: heavy-dust regions lose 5-15 percent between cleanings, and snow-prone roofs need steep tilts or the winter harvest collapses - fold local reality into the 0.75 factor.

  1. 1

    Enter daily energy

    kWh your home uses per day.

  2. 2

    Enter panel watts and sun hours

    Nameplate and local average.

  3. 3

    Read array

    Panel count, kW, and roof area.

Use Cases

Designing rooftop systems before contacting installers

Checking quotes for undersized arrays

Planning ground mounts with row self-shading spacing

Common Mistakes

  • Sizing strings at STC voltage without the cold-weather Voc multiplier

  • Ignoring shading that cuts a whole string through bypass diodes

  • Forgetting winter sun hours are 30-50 percent below the annual average

FAQs

How do I size solar strings for an inverter?

String voltage = panel Voc x count x 1.12 (cold bonus). With 41.8 Voc panels and a 500 V inverter max: 500/(41.8 x 1.12) = 10 panels max; the MPPT minimum of 200 V needs at least 5. Design strings of 6-8 for margin.

How much roof area does a solar array need?

About 5 m2 per kW including spacing: a 6 kW array needs 30-32 m2 of usable roof. South-facing planes are ideal; east-west splits lose 10-15 percent yield but often fit more panels.

Should I oversize the array relative to the inverter?

Yes, commonly 110-130 percent DC/AC ratio: the inverter clips midday peaks but harvests more in morning, evening, and winter. Above 1.35 the extra panels mostly clip and permit rules may intervene.

What tilt angle should I use?

Rule of thumb: latitude +/- 10 degrees - steeper for winter-biased harvest, flatter for annual average. At 30 degrees latitude, 40 degrees tilt maximizes December while 25 degrees maximizes the yearly total.

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