RV solar sizing: daily energy and controller limits
Size RV solar from daily energy use and conditions at the intended location and season, then verify the panel and controller limits separately. Panel watts are a test-condition rating, not a promise of daily watt-hours. No one loss factor or series-versus-parallel rule fits every roof.
State the assumptions before dividing by panel watts
For an assumed 800-Wh daily demand, four equivalent full-sun hours and a chosen 75% delivered-energy factor, required array power is 800 ÷ 4 ÷ 0.75 = 266.7 W. Three hypothetical 100-W panels give 900 Wh under those assumptions, just 100 Wh above demand.
This example is not a site forecast. Halving the sun-hours assumption halves the estimated energy to 450 Wh while demand remains 800 Wh. Plan another charging source or reduce use when energy falls short; more battery capacity alone does not replace missing daily input.
PVWatts defaults are not an RV battery efficiency
The PVWatts loss documentation uses a 14% default system-loss estimate while treating inverter conversion efficiency separately. It also calculates temperature effects separately. Do not call a 75% RV planning allowance the official PVWatts default.
PVWatts’ interpretation guidance warns that nearby shade and other unrepresented conditions can overestimate energy. A movable RV under trees, roof accessories and seasonally changing campsites needs its own assessment rather than an annual residential output guarantee.
One controller has several independent limits
The SmartSolar 100/30 manual lists 100-V maximum PV open-circuit voltage, 30-A charge output and 35-A maximum PV short-circuit current. Its nominal PV power differs by battery system: 440 W at 12 V and 880 W at 24 V. Those figures must not be interchanged with another controller’s limits.
| Design item | Evidence |
|---|---|
| Cold string voltage | Panel coefficient and lowest design temperature |
| Parallel current | Array short-circuit calculation and controller limit |
| Battery charging | Actual chemistry, current and temperature permissions |
| Wiring and protection | Approved size, length, route and disconnect/fuse arrangement |
Choose layout from the actual panels and shadows
Series raises string voltage; parallel raises array current. Bypass diodes, panel mismatch and shadow geometry affect performance, so neither arrangement universally solves RV shade. Qualified design must preserve the corrected voltage and current limits.
Inspect what solar-ready includes before buying parts: connectors, cable ratings and installed controls require documentation. Use the complete battery-and-solar budget and the GP-PWM-30-UL’s different limits for the actual equipment.