Solar Panel & Inverter Sizing Estimator

Estimate required solar array wattage, panel count, and inverter size from daily energy usage, peak sun hours, and system loss assumptions — with a PASS/FAIL check for your selected inverter.

System Details

Daily Energy Usage

kWh

Peak Sun Hours

hrs

System Loss Percent

Panel Wattage

Selected Inverter Size

Live Results

Required Solar Array

9,000W

PASS

Selected inverter: 10.00 kW

Number of Panels

22.5

Recommended Inverter Size

9.00kW

Input Summary

Daily Energy Usage30.00 kWh

Peak Sun Hours4.00

System Loss Percent20%

Panel Wattage400 W

Selected Inverter Size10.00 kW

Solar sizing calculations follow standard PV design principles. Always verify final design with local electrical code and manufacturer specifications.

How to Use This Solar Panel & Inverter Sizing Estimator

Enter daily energy usage. Input your average daily electricity consumption in kilowatt-hours (kWh). Use utility bills, a Load Calculation Tool total, or smart-meter data — a typical U.S. home uses 25–35 kWh per day. This value drives the required solar array size.
Enter peak sun hours. Specify the average peak sun hours for your location — the equivalent hours per day when solar irradiance reaches 1,000 W/m². Most U.S. sites fall between 3.5 and 6 hours; consult NREL PVWatts or local solar maps for your latitude and climate.
Set system loss percent. Enter the total system derate factor as a percentage. The default 20% accounts for inverter efficiency, wiring losses, soiling, temperature derating, and shading. Increase this value if your site has partial shade, long wire runs, or older equipment.
Enter panel wattage. Input the rated wattage of your chosen solar module in watts — common residential panels range from 350 W to 450 W. The calculator divides required array wattage by panel wattage to estimate the number of modules needed.
Select inverter size and review PASS/FAIL. Enter your planned inverter size in kilowatts to run a PASS/FAIL check against the recommended minimum. PASS means the selected inverter meets or exceeds the calculated requirement. Review warnings for low sun hours, high system losses, and large inverter sizes before finalizing your design.

Formulas & Example

This calculator uses standard PV sizing formulas. System losses are applied as a multiplier on required array wattage so daily production meets your energy target.

Loss Multiplier = 1 + (System Loss % ÷ 100)

Required Array (W) = (Daily Usage kWh × 1,000) ÷ Peak Sun Hours × Loss Multiplier

Panel Count = Required Array (W) ÷ Panel Wattage (W)

Recommended Inverter (kW) = Required Array (W) ÷ 1,000

PASS/FAIL = Selected Inverter kW ≥ Recommended Inverter kW

Worked Example

A home using 30 kWh/day in a region with 4 peak sun hours, 20% system losses, and 400 W panels:

Daily Usage = 30 kWh
Peak Sun Hours = 4
System Loss = 20%  →  Loss Multiplier = 1.20
Panel Wattage = 400 W

Required Array = (30 × 1,000) ÷ 4 × 1.20 = 9,000 W
Panel Count = 9,000 ÷ 400 = 22.5 panels
Recommended Inverter = 9,000 ÷ 1,000 = 9 kW

Result: ~9,000 W array, ~23 panels, 9 kW inverter

Pair this tool with the Load Calculation, Generator Sizing, Transformer Sizing, Motor FLA, and Voltage Drop calculators for a complete electrical and renewable energy design workflow.

Frequently Asked Questions

How many solar panels do I need?▾

Divide the required solar array wattage by your panel's rated wattage. For example, a 9,000 W array using 400 W panels needs approximately 22.5 panels — round up to 23 modules for a practical installation. Required array wattage equals daily energy usage (in Wh) divided by peak sun hours, multiplied by a loss factor (typically 1.20 for 20% system losses). Use the Load Calculation Tool to determine daily kWh if you don't have utility data.

What affects solar output?▾

Solar output depends on peak sun hours (latitude, climate, and season), panel orientation and tilt, shading from trees or structures, soiling and snow accumulation, module temperature derating, inverter efficiency, and wiring losses. System loss percent bundles these derates into a single multiplier — 15–25% is typical for well-designed residential systems. Sites with heavy shade or poor orientation may need 30% or higher loss factors.

What is inverter sizing?▾

Inverter sizing matches the inverter's AC output rating (in kW) to the DC array size. A common rule of thumb sizes the inverter at 100% of the array's DC wattage — a 9 kW array pairs with a 9 kW inverter. Some designs intentionally undersize the inverter (DC-to-AC ratio > 1) to capture more energy during low-light hours, while others oversize for future expansion. This calculator recommends inverter kW equal to required array watts divided by 1,000.

What are system losses?▾

System losses are the combined efficiency reductions between sunlight hitting the panel and usable AC power reaching your loads. They include inverter conversion losses (typically 2–4%), wiring and connector losses (1–3%), temperature derating (5–15% in hot climates), soiling (2–5%), shading, and mismatch between modules. The loss multiplier (1 + loss percent ÷ 100) increases required array size so daily production meets your energy target despite these derates.

Should I oversize my inverter?▾

Moderate inverter oversizing (10–20% above calculated kW) provides headroom for future load growth and handles brief peak production. However, significantly oversizing increases equipment cost without proportional energy gain — inverters clip output above their rated AC capacity. Undersizing (DC-to-AC ratio of 1.1–1.3) is a valid strategy in sunny climates to improve morning and evening harvest. Always confirm inverter sizing with the manufacturer's DC input limits and local interconnection requirements.

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