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: in useful sun (4–5 peak-sun hours average across seasons), you need roughly 1 watt of panel for every 4–5 Wh of daily draw to keep pace, plus headroom for cloudy days and charge losses. 2,000 Wh/day realistically wants 400–600W of panel.
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.