Solar Sizing Calculators
Free technical calculators for solar, battery and DC systems. Every result cites the NEC 2023 section it came from and shows the arithmetic behind it.
Solar Wire Tools
Solar Wire Tools7 tools
- Solar Wire Size CalculatorFind the right wire gauge for any DC circuit in a solar system.
- 12V Solar Wire Size CalculatorWire sizing for 12 volt solar, RV, van and marine circuits.
- 24V Solar Wire Size CalculatorWire sizing for 24 volt off-grid and cabin systems.
- 48V Solar Wire Size CalculatorWire sizing for 48 volt off-grid and whole-home systems.
- RV Solar Wire Size CalculatorWire sizing for RV, camper van and trailer solar builds.
- Battery to Inverter Wire Size CalculatorSize the highest-current cable in the whole system.
- Solar Panel to Charge Controller Wire Size CalculatorSize the run from the array to the controller, per NEC 690.8.
Solar Electrical Tools
Battery Tools
System Sizing Tools
System Sizing Tools4 tools
- Solar Inverter Sizing CalculatorSize an inverter from continuous load and motor surge.
- MPPT Charge Controller Sizing CalculatorMatch a controller to your array, including cold-weather Voc.
- Solar Panel Series & Parallel CalculatorWork out string voltage and current for any wiring layout.
- Solar Array Size CalculatorHow much array your daily energy use actually needs.
No calculator matches that. Try a voltage, a component, or clear the filter.
What these tools are built on
- Ampacity
- NEC Tables 310.16 and 310.17, with the correction and adjustment factors from 310.15 applied, not assumed.
- Protection
- 240.6(A) standard ratings, the 240.4(B) round-up and the 240.4(D) small-conductor caps, checked against the conductor.
- PV circuits
- Article 690 throughout: 690.7 cold-weather voltage, 690.8 maximum current, 690.9 device ratings.
- Everything else
- Manufacturer convention and the NREL PVWatts loss model, labelled as such wherever it appears rather than presented as code.
One shared calculation core, 122 automated tests, and cross-tool checks that stop two pages disagreeing about the same circuit. Methodology and limitations.
The order to size a system in
Most off-grid systems that disappoint their owners were sized in the wrong order. Each step produces the number the next one needs.
- 1Daily energy useEvery other number derives from this one.
- 2System voltage12, 24 or 48 V. Decides current everywhere, and current decides cable cost.
- 3Battery bankConsumption, autonomy and usable depth give capacity.
- 4Array and stringsReplace a day of use; survive the coldest morning.
- 5Charge controllerArray watts set the current, cold Voc sets survival.
- 6InverterContinuous load and surge; yields DC input current.
- 7Wire and protectionEvery current is now known. Size conductors, then devices.