How to Size a Solar Generator for Your RV
Most "what size solar generator do I need" articles are written by the companies selling the generator — so the answer tends to be "bigger than you probably need." Here's the actual methodology, independent of any brand, broken into three separate sizing questions that get conflated far too often.
The three numbers you actually need
- Continuous power (watts) — can the generator/inverter run everything you want running at once, indefinitely? This is about your appliances' running wattage, summed up.
- Surge power (watts) — can it survive the instant a motor-driven appliance (almost always your air conditioner) kicks on, which draws far more than its running wattage for a second or two?
- Energy capacity (watt-hours) — how much total energy can the battery hold, which determines how long you can run things between charges (from solar, shore power, or driving).
Conflating these is the single most common mistake: a generator can have plenty of running-watt capacity and still trip or shut down the moment your AC compressor starts, because that's a surge problem, not a continuous-power problem.
Step 1: Add up your running watts
List every appliance you'd actually run off the unit and its running wattage (on the nameplate, or in the manual). Common values, as a sanity check — not gospel, check your own appliance:
| Appliance | Typical running watts |
|---|---|
| RV air conditioner (13,500–15,000 BTU) | 1,200–1,600 W |
| Refrigerator (compressor-cycle) | 100–600 W (varies a lot — RV vs. residential-style) |
| Microwave | 600–1,200 W |
| Lights + device charging | 50–200 W |
| Converter/charger (replenishing house batteries) | 300–600 W |
Sum whatever you'd realistically run simultaneously — not everything you own, just your worst-case "running at the same time" scenario. Add a safety margin (commonly 15–25%) on top for efficiency losses and headroom. This total is your minimum continuous power rating.
Step 2: Check your surge requirement separately
Take your single largest motor-driven load — almost always the AC — and multiply its running watts by roughly 2–3x to estimate its surge draw (see our running vs. surge guide for why). Replace that one appliance's contribution to your Step 1 total with this surge number; everything else stays at its running value, since non-motor loads don't have the same startup spike. This total is your minimum surge rating — check it against the generator's surge spec, not just its continuous spec.
Step 3: Size energy capacity separately from power
Power (watts) and energy (watt-hours) are different questions. A battery rated for plenty of running watts can still run out of charge in a few hours if its watt-hour capacity doesn't match your actual daily use. See our battery capacity guide for the daily-use estimate and buffer math.
Step 4: Size solar panels to replenish that battery
Panel wattage should be sized to realistically recharge your battery capacity within the sun hours you actually get — not just "bigger is better." See our panel wattage guide.