Solar System Sizing Calculator

About the Solar System Sizing Calculator

Sizes the solar array (kW) needed to offset a target daily energy consumption, given local peak sun hours and a performance ratio.

How to use this calculator

1. Enter your daily energy use in \(kWh\).
2. Enter your average sun hours per day.
3. Choose a performance ratio, which accounts for real-world losses.
4. Read the required array size in \(kW\).

The formula explained

The formula computes the solar array size in \(kW\) needed to produce your daily energy use. It divides daily energy demand by the product of sun hours and performance ratio.

• kW = required solar array size in kilowatts
• \(daily\\ kWh\) = your electricity use each day in kilowatt-hours
• \(sun\\ hours\) = average peak sunlight hours per day
• PR = performance ratio, a decimal that accounts for system losses

Step by step method

1. Write down your daily energy use in \(kWh\).
2. Multiply your sun hours by your performance ratio.
3. Divide daily \(kWh\) by that result to find the array size in \(kW\).

Worked example

Problem. A home uses \(30\\,kWh\) per day, has \(5\) sun hours per day, and a performance ratio of \(0.8\). Find the solar array size.

1. Use the formula \(kW = \frac{daily\\ kWh}{sun\\ hours \\times PR}\).
2. Substitute the values, \(kW = \frac{30}{5 \\times 0.8}\).
3. Compute \(5 \\times 0.8 = 4\), then \(30 \\div 4 = 7.5\), so the system size is \(7.5\\,kW\).

Tips and common mistakes

• Make sure the sun hours are average peak sun hours, not total daylight hours.
• If you use a lower performance ratio, the calculator will give a larger, more realistic system size.

Frequently asked questions