Sizing Your Solar System: Panel & Battery Calculators Simplified

Planning your solar setup can feel overwhelming—but it doesn’t need to be. Whether you're powering a fridge in your 4WD, lights at a campsite, or going fully off-grid, this guide will walk you through how to calculate the right size solar panel and battery system for your needs.

⚡ Step 1: List What You Want to Power

Start by listing all the devices you plan to run and how long you’ll run them each day.

? Step 2: Size Your Battery Bank

To find the right battery size, convert watt-hours to amp-hours (Ah) using the formula:

Battery Ah = (Total Wh ÷ Battery Voltage)

For a 12V system:
1490 Wh ÷ 12V = 124 Ah/day

Now consider depth of discharge (DoD)—most lithium batteries can safely discharge up to 80-90%, while AGM is about 50%.

✅ So, a 150Ah lithium battery or 250Ah AGM battery would be suitable.

☀️ Step 3: Size Your Solar Panels

To recharge your battery daily, divide your energy needs by average sun hours (e.g. 5 peak sun hours/day in most of Australia):

Solar Panel Wattage = Daily Wh ÷ Sun Hours

1490 Wh ÷ 5 hrs = 298W

Add a buffer for inefficiencies (clouds, shading, regulator losses):
298W × 1.3 = ~388W

✅ So, aim for at least 400W of solar to replenish your battery daily.

? Quick Reference Table

? Bonus Tips

• Go modular: Combine 2x 200W panels instead of 1x 400W for flexibility.

• Add a safety margin: If you're camping in winter or shaded areas, go 20–30% higher in solar and battery size.

• Don’t forget your inverter: Make sure your battery can handle the surge draw (especially for fridges or kettles).