Reviewed by: David Chen, CFA • Renewable Energy Analyst
Determining the right solar system size is the first step toward energy independence. This professional solar system size calculator helps you estimate the total kilowatt (kW) capacity and number of panels required based on your energy consumption and local sun peak hours.
Solar System Size Calculator
Solar System Size Calculator Formula:
System Size (kW) = (Annual Usage / 365) / (Sun Hours × Efficiency)
Panels Required = (System Size × 1000) / Panel Wattage
Source: NREL Solar Resource Data | Energy.gov Guide
Variables:
- Monthly Usage (kWh): The total electricity consumed by your home in a typical month.
- Daily Peak Sun Hours: Not just total daylight, but the equivalent hours when solar intensity is 1,000 W/m².
- Panel Wattage: The rated output of a single solar panel (usually 300W to 450W).
- Efficiency Factor: Accounts for real-world energy losses (e.g., heat, inverter conversion, dust).
Related Calculators:
- Solar Payback Period Calculator
- Solar Battery Capacity Estimator
- Electricity Bill Savings Calculator
- Roof Pitch Solar Angle Calculator
What is a Solar System Size Calculator?
A solar system size calculator is a technical tool designed to translate your energy consumption habits into physical infrastructure needs. By analyzing your monthly kilowatt-hour (kWh) usage alongside regional climate data, it determines the total capacity your home requires to offset its carbon footprint or eliminate electricity bills.
Understanding your system size is crucial for budgeting. A system that is too small won’t cover your needs, while one that is too large may result in wasted investment costs and extended payback periods.
How to Calculate Solar System Size (Example):
- Determine your annual consumption (e.g., 900 kWh/month × 12 = 10,800 kWh/year).
- Find your daily consumption (10,800 kWh / 365 days ≈ 29.58 kWh/day).
- Identify local sun hours (e.g., 5.0 hours).
- Divide daily consumption by sun hours and adjust for 80% efficiency: (29.58 / 5) / 0.8 ≈ 7.39 kW.
- Divide by panel wattage (400W) to find panel count: (7.39 × 1000) / 400 ≈ 19 panels.
Frequently Asked Questions (FAQ):
How many solar panels do I need for a 2000 sq ft house? Most 2,000 sq ft homes require a system between 5kW and 10kW (approximately 15 to 25 panels), depending on energy usage.
Does sun hours mean daylight hours? No. Peak sun hours refer to the duration when solar radiation reaches 1kW/m². 10 hours of daylight might only equal 4.5 peak sun hours.
Should I size my system for 100% offset? Most experts recommend sizing for 90-100% of your current usage, accounting for future needs like electric vehicles (EVs).
What efficiency loss should I assume? A standard assumption is 20% loss (0.80 efficiency factor), which covers inverter losses, temperature coefficients, and wiring.