Off-Grid Solar Calculators

Solar panels

Series vs Parallel Solar Calculator

Series connection adds voltage; parallel connection adds current. Cold-weather Voc is higher than the 25 °C label, so leave headroom under the controller’s max Voc.

Inputs

V
A
V
A

Results

String Voc (STC)
120.0V
Array Isc (STC)
20.0A
Array nameplate
1,728W

Recommended gear

Engineering methodology

Series connection adds voltage: string Voc = module Voc × modules in series. Parallel connection adds current: array Isc = module Isc × parallel strings. Nameplate watts ≈ Vmp × series count × Imp × parallel count. If Vmp or Imp is omitted, the tool uses typical crystalline ratios of about 0.82×Voc and 0.93×Isc. Values are STC; cold mornings raise Voc.

Frequently asked questions

Why is cold-weather Voc higher than the label?

The Voc temperature coefficient is negative. Cells colder than 25 °C produce higher open-circuit voltage. Always apply the datasheet cold-temperature correction before comparing a string to an MPPT’s max Voc. This calculator uses 25 °C STC labels only.

Series vs parallel: which is better for an MPPT?

Series raises voltage into the controller’s MPPT window and keeps current (and cable size) down. Parallel raises current and needs thicker wire. The controller’s max Voc and max input current are hard limits either way.

Do three parallel strings need fuses?

Typically yes. Under NEC 690.8/690.9, three or more equal parallel strings can backfeed more than 1.56 × Isc into a faulted string. Use the combiner-fuse calculator and the module’s maximum series-fuse rating.

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