Choose Easy or Advance Mode below, then set your array, battery voltage, and controller type. Formula: Voc (cold) = Panel Voc × Series Count × Cold Factor; Controller Current = Array Output ÷ (Battery Charge Voltage if MPPT, or Array Current if PWM) × (1 + Safety Margin).

Sizing Mode

Not sure what a field means? Tap the ⓘ next to its label.

Array Configuration

W
V
A
%

Cold-Weather Temperature Data

From your panel's datasheet — used for exact Voc-at-cold, instead of Easy Mode's flat 25% margin.

%/°C
%/°C

Battery Bank Voltage

Controller Type

MPPT tolerates a wide range of panel voltages and is more efficient. PWM is simpler and cheaper, but only works well when your panel string voltage stays close to your battery voltage — for more information, check our FAQs.

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Recommended Controller

Recommended Size
next standard rating
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Minimum Current
—
amps, with margin
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Minimum Voltage Rating
—
Voc at cold, volts
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Series versus parallel solar panel wiring Two panels wired in series combine into higher voltage with the same current. Two panels wired in parallel combine into higher current with the same voltage. Series wiring Panel 1 Panel 2 Array output Voc doubles, Imp same Parallel wiring Panel 1 Panel 2 Array output Imp doubles, Voc same

Standard Controller Sizes

Every commercially available size, checked against your minimum current above. Always round up to a size flagged Pass, never down.

Residential / RV scale
Commercial / industrial scale

This 60A / 80A split is a market convention, not a code requirement — sizes through 60A are typically consumer and RV-grade product lines, while 80A and up are typically commercial and industrial-grade lines.

Results are planning estimates based on the values you enter. Always verify against your panel and controller manufacturer's datasheets and applicable electrical code before purchasing or installing equipment.