Solar Panel Calculator
Estimate how many solar panels you need for your daily energy use.
Roughly size a rooftop solar array from your energy use and local sunshine.
How the Math Works
The Solar Panel Calculator uses the formula: panels = daily kWh divided by (sun hours multiplied by panel kW multiplied by efficiency). This equation determines how many solar panels you need by comparing your total energy consumption to the output capacity of each panel. Your daily energy use in kilowatt-hours (kWh) is divided by the product of peak sun hours for your location, the panel's rated power in kilowatts (kW), and its efficiency rating. For example, if you use 30 kWh per day, have 4 peak sun hours, a 300-watt panel (0.3 kW), and 90% efficiency, you'd need approximately 30 ÷ (4 × 0.3 × 0.9) = 28 panels.
Practical Applications
To use this calculator practically, first gather your daily electricity consumption in kWh from past utility bills, then determine your location's average peak sun hours using online solar maps or weather data. Next, select a specific solar panel model to get its rated power output (typically 250-400 watts) and efficiency percentage from the manufacturer's specifications. Multiply these three values together (sun hours × panel kW × efficiency) to find each panel's daily output, then divide your total daily kWh usage by this number. This calculation may surprise you with the number of panels needed, so also consider your roof space availability and budget constraints before proceeding with installation.
Day-to-Day Use
This calculation helps you make informed decisions about solar energy investment and environmental impact in your daily life. By knowing exactly how many panels you need, you can accurately budget for the total system cost, plan your roof installation layout, and estimate your monthly electricity savings. Understanding this relationship also helps you evaluate whether solar power is financially viable for your household or if you need to reduce energy consumption first. Additionally, this knowledge empowers you to have informed conversations with solar installers, compare different panel technologies, and ultimately make the transition to clean, renewable energy more accessible and affordable for your home.
Worked example
30 kWh/day, 5 sun hours, 400 W panels, 80% efficiency → 1.6 kWh/panel → 19 panels (7.6 kW).
FAQ
What are peak sun hours?
The equivalent hours per day of full 1,000 W/m² sunlight — varies by location and season.