PV Module Quantity Calculator

Professional Notes

Target DC capacity and module power

The calculator converts your target array size to watts and divides by the module’s STC rating to estimate the minimum module count. For example, a 50 kW target using 545 W modules needs 50,000 ÷ 545 = 91.74, rounded up to 92 modules so the nameplate capacity is not short. If you are constrained by roof area, adjust the target size until the area output aligns with your usable footprint.

DC oversizing and performance adjustments

Many systems oversize DC versus inverter AC capacity to improve energy yield in low irradiance. A DC/AC ratio of 1.10–1.30 is often used, but clipping losses and export limits must be checked. The loss factor input applies a practical allowance for temperature, soiling, wiring, mismatch, and degradation. If you already apply losses elsewhere, keep this factor conservative to avoid double counting.

String count and electrical practicality

When you enter modules per string, the tool reports the number of full strings and any remainder modules. This supports early screening against inverter MPPT range and maximum DC voltage. Verify cold-weather open-circuit voltage using temperature coefficients and your minimum design temperature. Also consider voltage drop, combiner capacity, and how many MPPT inputs are available as string counts increase.

Area estimation and layout allowance

Area is estimated from module length × width × quantity, then increased by the layout allowance for walkways, tilt spacing, parapets, and maintenance access. A 10–25% allowance is common for rooftops, while ground mounts may need more due to row spacing and shading control. Fire setbacks, drainage paths, and roof obstructions can reduce usable space, so treat the result as a planning figure.

Procurement buffer and cost roll-up

Spare percentage adds extra modules for breakage, future replacements, and commissioning failures. The cost section totals module, mounting, and labor components so you can compare scenarios quickly. For budgeting, confirm unit rates with supplier quotes and local labor productivity, then include logistics, duties, and a contingency for site-specific constraints.

FAQs

What if my target size is in kWp?

Enter the kWp value as the target DC capacity. The calculator treats it as nameplate DC at STC, then converts it to watts internally for the module quantity and related outputs.

Should I use module power at STC or NOCT?

Use the datasheet STC rating for sizing. If you want a more conservative count, increase the loss factor or reduce target capacity to reflect operating conditions and temperature effects.

How do I pick modules per string?

Start from inverter limits: MPPT voltage range and maximum DC voltage. Choose a string length that stays within limits in cold weather and still reaches MPPT range in hot conditions.

Why does the calculator round up modules?

Rounding up ensures the design meets or exceeds the target capacity after dividing by module rating. It also prevents ending up short due to fractional module counts.

What layout allowance should I assume?

For simple flat rooftops, 10–20% is common. Complex roofs, higher tilt angles, and maintenance corridors can push it higher. Ground mounts often require larger allowances for row spacing.

Does the estimate include inverter and BOS items?

This tool focuses on module quantity, strings, area, and a basic cost breakdown for modules, mounting, and labor. Add inverters, cabling, protection, and permitting separately for a full project estimate.