Daily Solar Power Balance Calculator
Will you have enough power tomorrow? Model your expected solar harvesting against daily appliance consumption and forecast your battery state-of-charge tonight.
The Engineering Physics of RV Daily Power Balance
Most boondockers who wake up to dead RV batteries do not suffer from broken equipment — they suffer from a Daily Power Balance Deficit. The fundamental law of off-grid boondocking is:
Daily Solar Harvesting (Wh) ≥ Daily Appliance Consumption (Wh) + System Inefficiency Losses (15–20%)
Why Peak Sun Hours (PSH) Differ From Daylight Hours
A location may have 14 hours of sunlight in June, but only 5.5 Peak Sun Hours. One Peak Sun Hour equals 1,000 Watts per square meter of solar irradiance. Early morning and late afternoon sun passes through much thicker atmosphere at a severe angle, producing a fraction of your panel's rated wattage.
Flat Roof Derating: The RV Solar Tax
Commercial solar arrays are angled toward the sun. RV solar panels are almost always mounted flat to prevent wind shear while driving. Flat roof panels suffer from a 15% to 25% cosine loss compared to tilted arrays, especially in spring, autumn, and winter when the sun tracks lower along the horizon.
Usable Battery Capacity Limits
- LiFePO4 Lithium: 80% to 90% usable depth of discharge (DoD). A 200Ah lithium bank provides approximately 160Ah (~2,000 Wh) of reliable energy before safety cutoff.
- Lead-Acid / AGM: Only 50% usable depth of discharge. Discharging an AGM battery below 50% causes permanent plate sulfation and drastically shortens cycle life.