The Complete RV Boondocking Power Guide: Sizing an Off-Grid System
Most boondocking power guides tell you to do a “power audit” and then hand you a calculator tool instead of actually walking through the math. This guide does the opposite — a full, real, worked example from your daily usage all the way through battery, solar, and inverter sizing, so you finish it with actual numbers instead of a link to someone else’s spreadsheet. Our Calculator can help!
Start With a Power Audit, Not a Panel Wattage Number
The biggest mistake in off-grid system sizing is starting with a panel wattage or battery amp-hour number you saw somewhere and working backward. The right starting point is always your own real daily energy use — everything else in this guide is derived from that one number, so it’s worth taking the time to get it right.
Step 1: Calculate Your Daily Watt-Hour Usage
List every device you’ll realistically run in a day of boondocking, its wattage, and how many hours you expect to use it. Multiply watts × hours for each device, then add them up.
A real worked example
| Device | Watts | Hours/day | Watt-hours |
|---|---|---|---|
| LED lighting | 40 | 5 | 200 |
| 12V compressor fridge | 60 | 8 (cycling) | 480 |
| Water pump | 50 | 0.5 | 25 |
| Vent fan | 40 | 6 | 240 |
| Laptop + phone charging | 65 | 3 | 195 |
| Microwave (inverter load) | 1,000 | 0.25 | 250 |
| CPAP or other medical device | 40 | 8 | 320 |
| Misc / buffer | — | — | 150 |
| Total | ~1,860 Wh/day |
Your list will differ based on your actual appliances — the method is what matters, not this specific total.
Step 2: Size Your Battery Bank From That Number
Convert your daily watt-hours to amp-hours by dividing by your system voltage (1,860Wh ÷ 12V ≈ 155Ah/day for a 12V system), then multiply by how many days of autonomy you want without full sun — 2–3 days is a reasonable target for most boondockers. At 2 days: 155Ah × 2 = 310Ah, which rounds up to a 300–460Ah lithium bank depending on the products available. For the fuller version of this specific calculation, including a quick-reference table by lifestyle, see our lithium battery sizing guide.
Step 3: Size Solar to Actually Recharge It
Sun hours matter as much as panel wattage
A battery bank is only as useful as your ability to recharge it. Using the formula panel watts = daily Wh ÷ (peak sun hours × 0.75), our 1,860Wh/day example at 6 peak sun hours needs: 1,860 ÷ (6 × 0.75) = 1,860 ÷ 4.5 ≈ 413W of solar as a bare minimum, before adding a buffer. Adding the standard 20–25% real-world buffer for cloudy days and panel losses brings that to roughly 500–520W. Tucson’s peak sun hours run higher than the national average most generic calculators assume, which means a Tucson-based boondocker can realistically expect faster recharge from the same array size than this formula would predict in a milder climate — a genuine, if easy-to-overlook, local advantage.
Step 4: Size Your Inverter for What You’ll Actually Run
Your inverter needs to be rated for your highest simultaneous AC load, not your average load. If your biggest single draw is a 1,000W microwave, you need an inverter rated comfortably above that continuous wattage, with headroom for the brief surge most appliances draw at startup — many manufacturers specify a separate, higher “surge” rating for exactly this reason. Undersizing the inverter for your peak load, rather than your average one, is one of the most common sizing mistakes we see (more on this in our guide to common RV solar installation mistakes).
Redundancy: What Happens on a Cloudy Day
Every calculation above assumes reasonably sunny conditions. A stretch of cloudy or monsoon weather can cut solar output significantly for a day or more, which is exactly what your autonomy-day buffer in Step 2 is meant to absorb. If your battery bank is sized with only one day of autonomy, a single overcast day can put you in a genuinely tight spot; sizing for 2–3 days gives you real breathing room without requiring a generator as a first line of defense. For the desert-specific version of this planning, see Boondocking in the Arizona Desert, and for a direct answer on trip duration under a given setup, see How Long Can You Boondock on Solar Alone?
Real Sizing Examples: Weekend, Extended, and Full-Time Boondocking
| Scenario | Daily use | Battery bank | Solar array |
|---|---|---|---|
| Weekend boondocking | ~900–1,200Wh | 100–150Ah | 250–350W |
| Extended boondocking (1–2 weeks) | ~1,800–2,500Wh | 300–460Ah | 500–800W |
| Full-time boondocking | ~3,500Wh+ | 460Ah+ | 900W+ |
These are realistic starting ranges, not guarantees — your actual appliances and habits are what determine your real number, which is why Step 1 is worth doing properly rather than skipping to a table like this one.
How Our Three Packages Map to These Numbers
Our Weekender package (800W solar, 460Ah lithium) comfortably covers weekend-to-extended boondocking for most RVers. The Glamper (1,200W solar, 600Ah lithium) is built for extended and heavier-use boondocking, including regular inverter use. The Monster (2,500W solar, 300Ah at 48V — note the different amp-hour math at higher voltage) is our full-time, home-like-habits package, sized for RVers who want AC-assist and heavy appliance use without hookups.
Key Takeaways
- Start from your actual daily watt-hour usage, not a panel wattage or battery amp-hour number you saw elsewhere.
- Battery bank size comes from your daily use × your target autonomy days; solar wattage comes from that same daily use divided by your real peak sun hours.
- Size your inverter to your highest simultaneous load with surge headroom, not your average daily draw.
- Tucson’s above-average peak sun hours are a genuine advantage for solar recharge speed, though they come paired with heat considerations for battery placement.
FAQ
How many days of autonomy should I actually plan for?
Two to three days is a reasonable default for most boondockers; full-time RVers or those camping somewhere with less reliable sun may want to size closer to 3–4 days.
Do I need a generator if I size my system correctly?
A well-sized system with adequate autonomy reduces how often you’d need one, but a generator remains a reasonable backup for extended cloudy stretches or if you want to run high-draw appliances without depleting your battery bank.
Can I boondock indefinitely with the right solar setup?
For most usage patterns, yes, as long as you’re getting reasonably regular sun to keep the battery bank topped off — water and holding tank capacity are usually the practical limits on boondocking duration before power is.
Is this sizing method different in Arizona than elsewhere?
The method is the same everywhere — what changes is the actual peak-sun-hour number you plug into it, and Tucson’s number runs higher than a lot of the country, which works in your favor for solar recharge specifically.
Ready to size a system for how you actually boondock?
Get a free quote and we’ll run this exact calculation against your real usage and roof space before recommending anything. You can also use our free Calculator to help!