Solar Panel Sizing Calculator

What is a solar sizing calculator?

A solar sizing calculator determines how many solar panels and what battery capacity you need to power a specific load. Whether you are building an off-grid cabin system, adding solar to a homelab, or sizing a portable solar setup for camping, this tool calculates the panel wattage and battery storage needed based on your daily energy consumption and location's solar availability.

Solar panel output varies dramatically by location, season, and weather. A 400W panel produces 400W only under ideal conditions (direct sunlight, optimal angle, cool temperature). Real-world output averages 3-6 peak sun hours per day depending on your latitude and climate. This tool uses these factors to calculate realistic system sizes.

How to use this tool

Enter your daily energy consumption (in watt-hours or kilowatt-hours), your location's average peak sun hours, and the desired days of autonomy (backup without sun). The tool calculates the recommended total panel wattage, battery capacity, and charge controller size. It accounts for system losses, panel degradation, and efficiency factors.

Solar system components

• Solar panels — convert sunlight to DC electricity. Common sizes: 100W-400W per panel.
• Charge controller — regulates power from panels to batteries. MPPT controllers are 15-30% more efficient than PWM.
• Battery bank — stores energy for use when sun is not available. Size depends on desired autonomy days.
• Inverter — converts DC battery power to AC for household devices. Must be sized for peak load.

Solar sizing tips

Oversize your solar array by 25-50% to account for cloudy days, panel degradation over time, and winter's shorter days. Place panels facing south (in Northern Hemisphere) at an angle equal to your latitude. Keep panels clean and shade-free — even partial shade drastically reduces output. Start by reducing your load (energy-efficient devices, LED lighting) before sizing the solar system, as it is cheaper to save a watt than to generate one.

Frequently asked questions

How many peak sun hours does my location get?

Peak sun hours vary by location and season. US Southwest: 5-7 hours. Northern Europe: 1-3 hours in winter, 4-6 in summer. Southeast Asia: 4-5 hours year-round. This is not total daylight hours — it is the equivalent hours of full-intensity sunlight (1,000 W/m2). Websites like PVWatts (NREL) or Global Solar Atlas provide precise data for any location.

How long do solar panels last?

Solar panels typically come with 25-30 year warranties and can last 30-40+ years. They degrade about 0.5% per year — a panel rated at 400W will produce about 350W after 25 years. Lithium batteries last 10-15 years. Charge controllers and inverters typically last 10-15 years. Budget for battery replacement at least once during the panel lifetime.