calc.engineer / Solar & Power / String Sizing

String Sizing v1.0.0

Calculates optimal solar panel string and MPPT configuration based on panel electrical specs, inverter/charge-controller MPPT limits, and site temperature extremes. Applies temperature coefficients to determine Voc at minimum temperature (cold) and Vmp at maximum temperature (hot), then computes the safe range of panels per string, maximum parallel strings, and total array wattage. Prevents over-voltage damage in winter and under-voltage MPPT dropout in summer. Essential for NEC 690.7 compliant residential and commercial solar design.

feeds wire_gauge →
Panel open circuit voltage (Voc) at STC in volts
Panel maximum power voltage (Vmp) at STC in volts
Panel short circuit current (Isc) at STC in amps
Panel maximum power current (Imp) at STC in amps
Maximum MPPT input voltage in volts
Minimum MPPT start/operating voltage in volts
Maximum MPPT input current in amps
Minimum expected site temperature in Celsius, default -10
Maximum expected cell temperature in Celsius, default 60
Voc temperature coefficient in %/C (negative for silicon), default -0.30
Fill in the inputs and Compute to see the structured result.

From an agent (MCP) or the API

curl -X POST https://calc.engineer/api/string_sizing \
  -H "Content-Type: application/json" \
  -d '{"panel_voc": …, "panel_vmp": …, "panel_isc": …}'

MCP: connect to https://calc.engineer/mcp and call string_sizing.

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