Pillar page
Solar generator for an RV
Short answer: size the trip, not the battery. Multiply your declared watt-hours per night by the nights, subtract the recharge you can genuinely credit each day, divide by 0.765, and check startup surge separately. Everything below is that arithmetic, written out.
Most RV power advice starts from a capacity number and works backwards to a story. This page does the opposite: it publishes the equations used by the free RV weekend check, states the assumptions behind each constant, and marks the points where the method refuses to answer.
- 01Mission energyDoes the whole trip close?Nights × declared Wh per night, minus credited recharge, against usable energy after inverter losses and a retained reserve.
- 02Daily loopDoes each day pay for the night before?Credited recharge per day against the declared daily need. A trip can finish on stored energy while the loop stays open — those are different verdicts.
- 03Peak and startupDoes anything trip at the moment it starts?Declared running watts plus the worst declared startup surge. Never inferred from average energy: undeclared means unproven, and unproven means no product is named.
The four equations
01 — Daily energy need
daily_wh = Σ (device watts × hours per day) · or a directly declared Wh/day
Declared per device. Nothing is inferred from an appliance category, and an undeclared device is not silently assumed to be zero.
02 — Mission energy
mission_wh = (daily_wh × nights) − (credited_recharge_wh_per_day × nights)
Credited recharge counts solar, alternator and shore power only at the figure you declare. Trips are scoped from 1 to 7 nights; beyond that the answer is an installed-system question.
03 — Usable capacity
required_capacity_wh = mission_wh ÷ 0.765
0.765 = 0.85 AC delivery × 0.90 retained reserve. It is a planning factor, not a manufacturer claim, and it is applied identically to every candidate.
04 — Conservative system peak
peak_w = max over devices of ( starting_w(i) + (continuous_w − running_w(i)) )
Simultaneity is included: one device surges while everything else keeps running. Running watts are used only when explicitly declared. If any running or starting figure is missing, the peak is unproven and no exact product is named.
Where the method abstains
- Undeclared startup surge. No surge figure, no product. A compressor or air conditioner that starts is an instantaneous event that average energy cannot model.
- An open daily loop. A trip can finish on stored energy while each day still costs more than it recovers. Those are separate verdicts and we publish both.
- Air conditioning without shore power. Usually a generator or hybrid question. We say so rather than sizing a battery into a bad answer.
- TT-30 above the planning ceiling. Past 2,880 W of continuous demand the pedestal, not the battery, is the constraint.
Run it on your own trip
Worked cases and further reading
- Decision case RV-01 — two nights, no shore power, every peak declared
- Portable power station for an RV: what it covers and what it never will
- Portable power station for a travel trailer, including TT-30 arithmetic
- The published methodology behind every verdict
- All guides, diagnostics and research
Frequently asked questions
- How many watt-hours do I need for an RV weekend?
- Add the watt-hours each device uses per day, multiply by the number of nights, then subtract the recharge you can actually credit each day. Divide the remainder by 0.765 to account for inverter losses and a retained reserve. A typical no-air-conditioning weekend lands between 600 and 1,200 Wh per night, but the figure that matters is the one you declare for your own loads.
- Can a solar generator run an RV air conditioner?
- Only with a declared running wattage and a declared startup surge, and usually only with a soft start and a large battery. Without those declared figures the check abstains: a roof air conditioner can draw two to three times its running watts for a fraction of a second, and no capacity number predicts that.
- What does a TT-30 pedestal actually allow?
- 120 V times 30 A is 3,600 W of nameplate capacity. We plan against 2,880 W as a conservative ceiling, which is a planning figure and not an electrical code limit. Anything above that is an architecture question, not a battery question.
- Why do you sometimes refuse to recommend anything?
- Because a missing fact is not a small fact. If startup surge is undeclared, if the daily recharge loop stays open, or if the trip needs an installed system, we say so and name the measurement to take. Naming a product on top of an unknown would be a guess wearing a number.
- Is solar or an alternator the better recharge path?
- Whichever one you can actually credit. Solar depends on panel area, season and shade; alternator charging depends on drive time and the charger you have. The check credits only the recharge you declare, so both paths are compared on the same daily watt-hour basis.