Off-Grid Power Systems: Solar, Batteries, Inverters and Charging

Power is the section everything else on this site depends on. Cooling is a power problem. Connectivity is a power problem. Water pumping is a small power problem that becomes a large one when the pump runs dry at midnight because the bank was flat.

The category makes one error more often than all others combined: it starts with hardware. People arrive knowing they have four hundred watts of solar and two hundred amp-hours of battery, and no idea whether those two figures relate to what they actually run. They do not, usually. The order below is the order the decisions should be made in, and it is deliberately the reverse of how the market sells.

1. Establish the number

Nothing here works until you know your daily consumption in watt-hours.

• Off-grid load calculator — appliance list in, watt-hours per day out, plus bank and array sizes at 12V, 24V and 48V. Shows the full calculation.
• How many watts do you actually need off-grid? — the method behind the calculator, and the loads people leave out: inverter standby, compressor duty cycle in heat, always-on connectivity hardware.

2. Size the array

Our position, argued at length rather than asserted: array size beats battery expansion for shoulder-season resilience. Panels are cheaper per unit of usable energy than storage, and the failure mode people actually hit is three overcast days in October, not one hot night in July.

• Solar array sizing: panels or batteries first — the argument, with the working shown.
• Solar array and battery bank sizer — location-specific sun hours and a shoulder-season stress case.
• What a 400W solar setup actually runs — the most common array size on the road, and an honest account of what it covers.

3. Choose and size the storage

• LiFePO4 vs AGM vs lead-acid: the cost per cycle nobody calculates — purchase price is the wrong comparison. Cost per usable cycle is the right one.
• Battery bank sizing for shoulder-season camping — size for the worst week you will accept, not the average one.
• Lithium batteries below freezing — charging limits, self-heating, and the failure modes that void warranties.
• Retrofitting lithium into an older RV, costed — including the converter/charger replacement, DC-DC charger and wiring upgrade that quotes routinely omit.

4. Convert and charge it

• Inverter sizing for surge loads — why a 2000W inverter trips on a 900W appliance.
• Inverter surge sizing tool — continuous rating and surge rating, separately.
• MPPT vs PWM charge controllers — the efficiency claim, tested against real-world conditions rather than datasheets.
• Shore power, solar and generator: a three-source charging system — how the sources coexist without fighting each other.
• Inverter generators for backup: sizing, fuel cost and the CO sensor question — carbon monoxide is a genuine hazard here and is treated as one.

5. Pick the system voltage before you buy anything

This decision is made by default far more often than it is made deliberately, and it is expensive to revisit. Twelve volts is the path of least resistance because that is what the vehicle already runs, the appliances are cheap and the fittings are everywhere. It is also the reason a large build ends up with cable the diameter of a garden hose and a bank that will not physically fit anywhere sensible.

The rule of thumb that holds: once the array is heading past a kilowatt or the bank past four hundred amp-hours at 12V, twenty-four or forty-eight volts is almost certainly the right answer. Doubling the voltage halves the current, and current is what sets cable cost, connector cost, voltage drop and the size of every fuse and busbar in the system. The load calculator returns bank sizes at all three voltages side by side for exactly this reason.

6. Wire it properly

• DC wire gauge by run length and amperage — reference tables for the calculation people skip.
• DC wire gauge and voltage drop calculator — minimum AWG, actual drop, and the next size up.

Or buy it in a box

• Portable power stations vs installed systems — when the all-in-one genuinely wins, which is more often than installers admit and less often than the marketing claims.
• EcoFlow vs Jackery vs Bluetti in 2026 — rated versus usable capacity, cycle-life claims and pass-through charging limits.

Before you build

A substantial owner-installed electrical system changes what your policy covers. The moment a vehicle stops being stock is the moment standard cover stops reliably applying — see insuring a custom or converted vehicle. And if this build is part of a larger purchase decision, run the whole thing through the five-year cost of RV ownership before committing.

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