Solar Array Sizing Calculator - Panel Count Prompt from Daily kWh

How It Works

1. Enter Daily Energy Load

   Use utility bills, metered data, or a load audit for daily kWh. Historical annual averages are useful for grid-tied planning; off-grid planning needs seasonal and worst-month load review.

2. Choose Solar Resource Prompt

   Select a local regional row or enter a custom peak-sun-hour value from a current PVWatts, NSRDB, installer, utility, or measured source. The built-in rows are not site-specific solar-resource data.

3. Select Module Wattage Prompt

   Choose a local module wattage row or enter a custom nameplate value. Verify actual product data sheets for dimensions, current, voltage, temperature coefficient, listing, warranty, and compatibility before design use.

4. Set Loss and Tilt Multipliers

   Enter a combined loss multiplier and tilt multiplier. These are simplified prompts; the tool does not separately model azimuth, hourly weather, inverter clipping, soiling by month, shade, snow, albedo, or degradation.

5. Review Source-Aware Results

   Use the panel count, kW DC, annual/monthly shape, and module-area outputs as planning prompts only. Resolve PV modeling, roof layout, structural, NEC, utility, product, and AHJ source gaps before field or purchase decisions.

Built For

• Early conversations about how daily kWh, peak sun hours, and module wattage affect panel count
• Homeowners cross-checking whether a proposal's rough panel count is in the same order of magnitude as their load
• Installers or electricians capturing assumptions before running site PV modeling and product-specific design tools
• Off-grid planners exposing the need for worst-month solar resource, battery autonomy, generator, and controller review
• Project teams documenting that roof area, NEC, utility, product, and AHJ gaps remain unresolved

Features & Capabilities

Grid-Tied and Off-Grid Prompts

Grid-tied mode uses the entered load, solar-resource prompt, module watts, and multipliers. Off-grid mode adds battery round-trip efficiency but does not size battery capacity, charge controllers, generator backup, or worst-month reliability.

Simple Multiplier Chain

The tool uses daily kWh per module = peak sun hours x module kW x loss multiplier x tilt multiplier. Detailed PVWatts inputs such as azimuth, DC-to-AC ratio, inverter efficiency, albedo, soiling by month, and weather files remain external.

Monthly Shape Prompt

Monthly values redistribute the annual prompt through a fixed local fraction table. They are useful for conversation but are not NSRDB weather data or a monthly production model.

Module-Area Prompt

Roof area uses a fixed 17.5 square feet per module. It does not include actual module dimensions, fire setbacks, access pathways, roof obstructions, structural attachment, or racking layout.

Source Warnings in Export

CSV and PDF exports carry the PVWatts, NSRDB, NEC, UL, roof, product, utility, and AHJ gaps forward so the output is not mistaken for a permit-ready design.

Assumptions

• Daily load is an entered average kWh/day prompt.
• Peak sun hours are local row or custom prompts, not site-specific PVWatts or NSRDB output.
• Loss and tilt factors are user-entered multipliers, not separate modeled loss components.
• Panel wattage is a nameplate prompt; current product data controls design use.
• Off-grid mode only adds battery round-trip efficiency and does not size storage or reliability.

Limitations

• Does not run PVWatts, NSRDB, SAM, hourly weather, azimuth, inverter clipping, or shade modeling.
• Does not size batteries, charge controllers, strings, conductors, overcurrent protection, grounding, rapid shutdown, or inverters.
• Does not approve roof structure, waterproofing, fire setbacks, access pathways, or racking layout.
• Does not determine NEC compliance, product listing, utility interconnection, tariff treatment, inspection, or permission to operate.
• Does not replace qualified solar, electrical, structural, utility, product, insurer, owner, or AHJ review.

References

• PVWatts Calculator and PVWatts V8 API source pointers.
• NREL/NLR National Solar Radiation Database source pointer.
• NFPA 70 National Electrical Code PV system source pointer.
• UL 1741 inverter and interconnection equipment source pointer.

Frequently Asked Questions