Plan array sizing using capacity or energy targets. Check roof area, strings, and voltage limits. Print clean reports for bids, audits, and clients quickly.
| Scenario | Basis | Target | Panel W | PSH | PR | Panels | Total kWdc |
|---|---|---|---|---|---|---|---|
| Warehouse rooftop | DC size | 50 kWdc | 550 W | 4.5 | 0.80 | 92 | 50.6 |
| Office building | AC size | 40 kWac, ratio 1.20 | 500 W | 4.2 | 0.78 | 96 | 48.0 |
| Retail energy goal | Annual energy | 80,000 kWh/yr | 540 W | 5.0 | 0.82 | 71 | 38.3 |
Examples are illustrative; your results depend on your inputs.
Panel count converts a budget line into an installable scope. It sets procurement, pallet space, crane lifts, racking bays, and labor hours. A small sizing error at 500–600 W per module can shift dozens of panels, changing ballast weight, structural loading, and interconnection documents. Count also drives combiner quantity, homerun sizing, and how many rooftops or carport rows you must stage.
Three inputs dominate results: target capacity, module wattage, and the DC/AC ratio. A 40 kWac inverter with a 1.20 ratio implies 48 kWdc. With 550 W panels that is 88 modules, while 500 W panels need 96 modules. When you size by DC, PR and losses do not change panel count, but they strongly change energy forecasts and payback models.
For energy goals, the calculator estimates required DC size using annual kWh, peak sun hours, and effective PR. Example: 80,000 kWh/year with 4.5 PSH and 0.80 PR needs about 60.9 kWdc before rounding. Adding 3% losses reduces effective PR to 0.776 and increases required DC size. Treat PSH as a planning average; monthly production can vary, so a utility bill match should use conservative assumptions and irradiance where available.
Commercial rooftops rarely fit nameplate density. Setbacks, walkways, fire lanes, and HVAC access reduce usable area, so the spacing factor expands the footprint above pure panel area. If one module is roughly 2.6 m², 100 modules occupy about 260 m² before spacing. Using 1.15 raises that to 299 m². If you work in square feet, 1 m² equals 10.764 ft², so 299 m² is about 3,218 ft².
Voltage limits drive series length. Cold temperatures raise Voc, while high cell temperatures reduce Vmp and can fall below MPPT minimum. The tool estimates a safe series range, rounds module totals to complete strings, and flags near-limit conditions. It also approximates current per MPPT from Imp and Isc so you can spot overloaded inputs. Use these checks to reduce redesign cycles, then confirm with the inverter manual, site minimum temperature, and local code requirements.
Use DC sizing for procurement and racking. Use AC sizing when inverter capacity is fixed. Use annual energy when you have a kWh target and reliable PSH and PR assumptions.
Many commercial projects land between 0.75 and 0.88. Start near 0.80, then adjust for temperature, soiling, shading, wiring, and inverter clipping based on site studies.
Begin with 1.10 for tight layouts and 1.15–1.25 for typical roofs with walkways and setbacks. If fire lanes, parapets, or heavy HVAC exist, increase the factor.
Only when you size from an annual energy goal. Higher PSH increases expected production per kWdc, so less DC capacity is required to meet the same kWh target.
Rounding ensures the design meets or exceeds the target after integer module constraints. Stringing may round to complete series strings, which reduces imbalance and simplifies installation.
Yes, for planning-level counts and energy estimates. Replace roof area with available footprint, and use an appropriate spacing factor for row pitch, maintenance access, and tilt.
Engineering note: This tool provides planning-level estimates. Final designs should follow local codes, structural review, and manufacturer limits.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.