Short answer: most mistakes come from guessing daily watt-hours and assuming panels make their rated watts. Measure your loads, use real sun hours for where and when you camp, and size the controller, wire and battery as one system.
| If you need… | Look for |
|---|---|
| Guessing energy use | Do a load audit with the daily energy calculator |
| Using rated watts | Plan on roughly 70–80% of panel rating in good sun |
| Summer sun hours for winter trips | Use winter peak sun hours for your area |
| Controller sized to the panels, not the array | Amps = array W ÷ battery V × 1.25 (MPPT guide) |
| Ignoring cold Voc | Series strings rise above rated Voc on cold mornings |
| Thin cables | Voltage drop wastes power; use the wire size calculator |
| Battery too small | Store at least one day of use, more for cloudy stretches (battery bank calculator) |
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.
Add up daily watt-hours, divide by peak sun hours for your season, then divide by a derate of about 0.75. The result is the panel watts you need.
Panels are rated in lab conditions. Heat, sun angle, dirt and wiring losses usually cut real output to around 60–80% of rating.
Not by itself, but a large battery with a small array may rarely reach full charge. Size them together using the solar and battery calculators.
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