String Sizing & MPPT Analyzer
I Have These Panels & This Inverter — Make Me My Strings
Enter your inverter specifications, your panel specifications and the number of modules you own. The tool splits those panels into every possible string layout that fits — all in series, half in series and the halves in parallel, strings spread across MPPT trackers — checks cold-weather voltage, current per MPPT, DC input power and the DC/AC ratio, picks the best layout, and draws each one as a wiring diagram.
Inverter, Panel & Module Count
Adjust any value to recalculate. All results, diagrams and charts update automatically.
INVERTER SPECS
Generic example values - change them to your inverter's datasheet any time.
PANEL SPECS
The starred fields are cleared on every visit, so you always size with your actual panel datasheet. Vmp and Isc are optional - see below.
Every layout must use all of these. Cleared on each visit so mistakes don't carry over.
Optional & advanced values (defaults shown - change if you have exact numbers)
Modern / industrial inverters may legally allow a higher DC/AC ratio - widen the range if yours does. Cold-weather Vmax follows the record-low temperature (blank = 1.10 margin); untick "Include cold-weather Vmax derating" when your site is never really cold, and the check judges against the datasheet Voc only.
Your Best String Layout & Verdict
Enter your specs and module count - results update as you type.
The tool splits your panels into strings that fit your inverter safely and draws every layout below.
Best Layout
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Total Panels
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Total Capacity
-- kWp
DC/AC Ratio
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MPPTs Used
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Check-by-check verdict (best layout)
Recommendation
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How Your Panels Are Wired
What is a "string"?
A string is a row of panels wired one after another, end to end. Each panel adds voltage to the row, so a longer string means more voltage. In the drawing below, the boxes joined by a line are one string.
What is an "MPPT"?
MPPT is one of the tracker inputs on your inverter (most home inverters have 2, bigger ones 3–6). You plug one or more strings into each MPPT input. Strings on the same MPPT add up their current, which is why each tracker has its own voltage and current limits.
Here is your best layout, drawn panel by panel. One row of boxes joined by a line = one string. Strings that enter the same tracker are grouped inside one shaded panel. Click any row in the configuration table below to open its own wiring drawing.
Showing the best layout automatically.
I already have a layout in mind — is it safe?
Example: “10 panels in series” = S 10, P 1, MPPTs 1. The verdict updates as you type - if your layout is one of the possible configurations above it is highlighted in the table.
All Possible Configurations
Every way to split your modules into strings that fits this inverter. The best layout is highlighted. Click any row to view its wiring diagram.
| Layout | Strings | Panels | kWp | V (cold) | V (op) | A/MPPT (imp/isc) | DC/AC | Verdict |
|---|
0
Charts & Graphs
Charts & Graphs
Voltage Per String Size
Each bar is one possible string length (panels in series). Red is the voltage on a cold morning, blue the normal working voltage - red must stay under the inverter max, blue above the tracker start.
DC/AC Ratio Per Layout
How big your array is compared to the inverter. Green sits in the healthy range, amber above it (more clipping), slate below it (inverter over-specced).
Capacity Utilization
Your whole array vs how much DC power the inverter can accept. The dashed line is that limit - everything left of it is spare capacity for later.
Quick Answers (No Jargon)
tap for answers
Quick Answers (No Jargon)
tap for answers
Advanced Technical Analysis (For Engineers & Professionals)
Advanced Technical Analysis (For Engineers & Professionals)
How the analysis works. Given inverter limits (Vmax, MPPT Vmin window, Imax per MPPT, MPPT count, AC rating, optional max DC input) and panel electrical specs (Voc, Vmp, Isc, Imp, wattage), the tool enumerates every integer partition of your module count N into string sizes inside the valid window [min panels per string…max panels per string]. Each partition is then distributed across the MPPT trackers so that no tracker exceeds its parallel-string current limit. Every distinct arrangement becomes a row you can draw.
Key formulas and assumptions. String voltage (cold) = modules × Voc × cold factor, where the cold factor = 1 + 0.30%/°C × (25°C − record-low temperature), or the flat 1.10 planning margin when left blank (use your site's record low for final design). String operating voltage = modules × Vmp, which must exceed the MPPT start voltage. Parallel current per MPPT = strings-per-MPPT × Imp, which must not exceed Imax. DC/AC ratio = total DC capacity (kWp) / inverter AC rating (kW); the band is editable (default 1.15–1.35) because modern and industrial inverters often allow higher ratios. Rows outside the band are kept and marked as warnings rather than hidden. The DC input check compares the array's STC power against the inverter's max DC input - your datasheet value, or AC rating × the top of the band if you left it blank. Recommended ranking: fully valid layouts first, then closest to the middle of the DC/AC band, then fewer strings (longer series), then the fewest MPPT blocks used, then the most balanced wiring.
What the numbers mean for you. FITS means the layout passes every hard safety limit. FITS WITH WARNINGS means it passes voltage and current limits but sits outside your DC/AC band - either the inverter AC is oversized for the array or you should expect clipping. DOESN'T FIT means a hard limit is crossed (usually the inverter max DC input when you entered a datasheet value). The wiring diagram shows the physical connections: series strings carry one voltage that grows with each module, parallel strings combine their current into one MPPT input.
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Next: from a valid string design to a complete system
Your strings are electrically valid. Three things remain before it is a working system.
Real generation
Energy Yield Estimation
Check the finished design against real weather, month by month.
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Roof Space Checker
Confirm the panel count those strings need actually fits the available roof.
OpenBackup & storage
Battery Backup Calculator
Size storage for the loads that must keep running when the grid fails.
OpenEverything in one page
Open the Complete Setup Calculator
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