Solar System Size Calculator

Solar System Size is evaluated from Monthly Electricity Usage, Peak Sun Hours per Day and Panel Wattage. The calculation reports Recommended System Size, Number of Panels Needed and Approximate Roof Area Required.

Results

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About the Solar System Size Calculator

Solar System Size is treated here as a quantitative relation between Monthly Electricity Usage, Peak Sun Hours per Day, Panel Wattage and Target Coverage and Recommended System Size, Number of Panels Needed, Approximate Roof Area Required and Estimated System Cost.

The calculator uses a multi formula configuration. Each reported value is read as a direct evaluation of the stored rules with the declared field formats and units.

Formula basis:
Daily usage = monthly kWh / 30 x coverage%
System kW = daily usage / (sun hours x 0.80 efficiency)
Panels = system kW x 1000 / panel watts
Cost = system kW x $3,000/kW (national average installed)

Interpret the outputs in the order shown by the result fields. Optional inputs affect only the outputs that depend on those variables.

Formula & How It Works

The calculation applies the following relations exactly as recorded in the metadata:

Daily usage = monthly kWh / 30 x coverage%
System kW = daily usage / (sun hours x 0.80 efficiency)
Panels = system kW x 1000 / panel watts
Cost = system kW x $3,000/kW (national average installed)

Each output field is produced by substituting the supplied inputs into the relevant relation and then applying the declared rounding or text format.

Worked Examples

Example 1: Average US home: 886 kWh/month, 5 sun hours, 400W panels, 100% coverage

Inputs

monthly_kwh: 886 peak_sun_hours: 5 panel_watts: 400 coverage_pct: 100
Recommended System Size: 7.38 kW. Number of Panels Needed: 19 panels. Approximate Roof Area Required: 333 sq ft. Estimated System Cost: $22,150

With Monthly Electricity Usage = 886, Peak Sun Hours per Day = 5, Panel Wattage = 400 and Target Coverage = 100 as the stated inputs, the result is Recommended System Size = 7.38 kW, Number of Panels Needed = 19 panels and Approximate Roof Area Required = 333 sq ft. Each value corresponds to the declared output fields.

Example 2: High-use home: 1,500 kWh/month, Phoenix (6.5 sun hours), 120% coverage

Inputs

monthly_kwh: 1500 peak_sun_hours: 6.5 panel_watts: 400 coverage_pct: 120
Recommended System Size: 11.54 kW. Number of Panels Needed: 29 panels. Approximate Roof Area Required: 508 sq ft. Estimated System Cost: $34,615

With Monthly Electricity Usage = 1,500, Peak Sun Hours per Day = 6.5, Panel Wattage = 400 and Target Coverage = 120 as the stated inputs, the result is Recommended System Size = 11.54 kW, Number of Panels Needed = 29 panels and Approximate Roof Area Required = 508 sq ft. Each value corresponds to the declared output fields.

Example 3: Small home / apartment energy: 400 kWh/month, 4.5 sun hours, 80% offset

Inputs

monthly_kwh: 400 peak_sun_hours: 4.5 panel_watts: 400 coverage_pct: 80
Recommended System Size: 2.96 kW. Number of Panels Needed: 8 panels. Approximate Roof Area Required: 140 sq ft. Estimated System Cost: $8,889

With Monthly Electricity Usage = 400, Peak Sun Hours per Day = 4.5, Panel Wattage = 400 and Target Coverage = 80 as the stated inputs, the result is Recommended System Size = 2.96 kW, Number of Panels Needed = 8 panels and Approximate Roof Area Required = 140 sq ft. Each value corresponds to the declared output fields.

Example 4: Net-zero new construction: 1,200 kWh/month (all-electric), 5.5 sun hours, 100%

Inputs

monthly_kwh: 1200 peak_sun_hours: 5.5 panel_watts: 420 coverage_pct: 100
Recommended System Size: 9.09 kW. Number of Panels Needed: 22 panels. Approximate Roof Area Required: 385 sq ft. Estimated System Cost: $27,273

With Monthly Electricity Usage = 1,200, Peak Sun Hours per Day = 5.5, Panel Wattage = 420 and Target Coverage = 100 as the stated inputs, the result is Recommended System Size = 9.09 kW, Number of Panels Needed = 22 panels and Approximate Roof Area Required = 385 sq ft. Each value corresponds to the declared output fields.

Common Use Cases

  • Calculate solar system size to meet home electricity needs
  • Determine how many panels are needed
  • Estimate solar installation size