Solar Panel Sizing Calculator
List your appliances with watts and daily hours, choose your location and battery type, then see how many solar panels and what size battery bank you need for your van, boat, or off-grid cabin. Nothing uploaded.
Appliances
Location
Days of autonomy ?
Number of panels needed
Learn more: off-grid solar system sizing
Why guessing your solar size is expensive
Undersizing your solar system leaves you short of power on cloudy days or during heavy use. Oversizing means you spend money on panels and batteries you do not need. The right size depends on three things: your daily energy use (Wh), how many useful sun hours your location gets, and how many cloudy days your battery needs to cover. This calculator handles all three and also accounts for the 20% efficiency losses that are common in real-world solar installations - so the panel size it recommends will actually meet your needs.
How to size your off-grid solar system
First, list your appliances with their wattage and average daily hours - include a fridge, lights, phone, laptop, and any pumps or fans. Second, set your location and sun hours by picking a region preset or entering custom peak sun hours. Third, choose battery chemistry (LiFePO4 gives 80% usable capacity; AGM and lead-acid give 50%) and system voltage (24V or 48V for smaller cable runs). Finally, set days of autonomy using the slider - results show panel W, battery Ah, charge controller A, and panel counts for 100W/200W/400W panels.
FAQ
How many solar panels do I need for a van build?
A typical van with a fridge, laptop, lights, and phone charging uses around 300-500Wh per day. At 4 peak sun hours per day you need at least 100-150W of panels before losses. Add a 20% efficiency buffer and you need 120-180W. Two 100W panels covers most builds; larger builds or high-consumption setups benefit from 400W+.
What battery size do I need for 2 days autonomy off-grid?
For 2 days without sun at 400Wh/day on a 12V LiFePO4 system: 400 x 2 / 0.80 DoD / 12V = 83Ah. Round up to a 100Ah battery. For AGM or lead-acid (50% DoD) you would need 133Ah. The calculator does this automatically based on your appliance list and chemistry choice.
What is depth of discharge and why does it matter?
Depth of discharge (DoD) is how much of your battery capacity you can safely use without reducing its lifespan. LiFePO4 lithium batteries tolerate 80% DoD. AGM and lead-acid batteries should only be discharged to 50% to preserve their cycle life. Using more than the recommended DoD shortens battery lifespan significantly.