RV OWNER’S FIELD GUIDE · SOLAR & POWER
Solar Panel Sizing & Installation Guide
Most solar installs fail the owner not because the panels are bad, but because the system was sized to the roof instead of the actual daily power draw. Here’s how to size it correctly before you buy anything.
Start With Daily Watt-Hours, Not Panel Wattage
Add up the watt-hours every 12V device draws per day — a compressor fridge (600–900 Wh), CPAP (30–60 Wh), lighting (100–200 Wh), water pump and fans (100–150 Wh), plus anything run through the inverter. A boondocking-focused rig commonly lands between 1,500 and 3,000 Wh/day. That number, not roof space, is what sizes the system.
Rule of thumb: panel watts ≈ daily Wh ÷ peak-sun hours ÷ 0.75. The 0.75 covers real-world losses: heat, flat roof mounting, dirt, wiring and charging. At 4–5 peak-sun hours, that means 1,500 Wh/day needs about 400–500W, 2,000 Wh/day needs about 550–650W, and 3,000 Wh/day needs 800W or more. Add more for cloudy stretches or winter sun.
Battery Bank Comes Second
Panels charge the bank; the bank is what actually gets you through the night and cloudy stretches. Size usable capacity to 1.5–2 days of draw with no sun at all. With lithium (100% usable) that’s simpler math than with AGM (50% usable) — see our battery chemistry comparison before you buy.
Undersized panels with an oversized bank just means slow recovery. Oversized panels with an undersized bank means wasted capacity on clear days. They have to be sized together.
What Installation Actually Involves
Roof mounting and sealing (a bad panel seal is a future roof leak, not a solar problem), wire routing sized for the run length to avoid voltage drop, a charge controller matched to panel voltage and battery chemistry, and correct fusing/breakers at every stage from panel to controller to battery. Skipping the fusing is the most common corner cut — and the most dangerous one.
OUR SOLAR PICKS
Panels, controllers & mounting
Rigid 12V panel from our shop
Flexible panel for curved or low-clearance roofs
Bluetooth MPPT controller, sized to your array
For arrays up to about 700W on a 12V bank
Larger rigid 12V panel from our shop
Seal bracket feet and roof penetrations with a self-leveling lap sealant rated for your roof membrane (EPDM, TPO or fiberglass)
Sealed roof entry for solar cables
Want it installed? We do that. Request an Appointment · Remote consult · All our solar picks →
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