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Van Power Sizing Calculator
Check the devices you plan to run, set the hours, and get a recovery-first battery and solar estimate. Sized for your typical day, not your worst one.
- 8 years full-time · 100,000 miles across all 48 states
- No email, no upsell · every output labeled Estimate
Your devices
Check the devices you use. Drag the slider to set hours per day.
Add a device not listed:
All outputs are Estimate. Your real usage depends on specific devices, temperature, and behavior. Use these as a starting point for planning, not a final specification.
How we calculate your estimate#
One principle drives every number on this page: size for your typical day, not your worst one. If you size for the absolute worst day you’ll ever have, you’ll buy battery and panels you almost never use. Size for typical and have a charging backup (alternator on driving days, or the option to plug in occasionally), and the math gets a lot smaller and a lot cheaper.
The numbers above come from three simple formulas:
Watts per device × hours per day, summed across every checked device. The watt values are typical draws; your specific laptop or fridge will differ, but these are reasonable starting points.
Daily use × 1.5. Lithium batteries perform best when you don't drain them below 20%. A 1,000 Wh battery really gives you about 800 Wh of usable capacity, plus you want margin for cloudy days.
Daily use ÷ 4 peak sun hours, with a 25% buffer. Four hours is conservative: desert Southwest gets more, Pacific Northwest and winter Northeast get less. The buffer covers angle, shade, dirt, and wiring losses.
What the tiers mean#
Phone, lights, fan. A small portable station and alternator charging cover you. Solar is optional.
Add a laptop and occasional hotspot. A 1,000–1,200 Wh station with 100–200W solar handles most days.
Full-time fridge, laptop workstation, Starlink. A 2 kWh-class station with 300W+ solar plus alternator charging handles this with margin.
Premium 2 kWh+ tier. Elite 300, DELTA 3 Ultra Plus (expandable to 11 kWh), or Apex 300 (expandable to roughly 20 kWh on one unit) all handle this load with real margin. A DIY fixed install isn't needed at this draw and isn't worth the build cost unless you specifically want one.
Use an expandable system (DELTA 3 Ultra Plus or Apex 300) or build a DIY fixed-battery install. Induction-everything builds and large remote offices land here.
Common questions#
Are these watt numbers accurate for my specific device?
They're typical values, labeled Estimate. A gaming laptop pulls more than a Chromebook. A Dometic CFX65 averages 20–25W in Florida summer and 10–12W in mild weather: same fridge, very different daily draw. Check your device's label or manual for actual numbers and adjust the slider to match. (Those fridge figures aren't guesses; see our real-world measured data.)
Why doesn't the fridge default to 24 hours?
Because the compressor doesn't run 24/7, not even in 100°F heat. The fridge is plugged in around the clock, but the compressor cycles on and off to hold temperature. Running a Dometic CFX65DZ for eight years, the worst I've seen is the equivalent of 8–10 hours of compressor runtime on a brutal hot day, and more like 4–5 hours in mild weather. The calculator models the compressor at ~60W times hours of actual runtime, so the 6-hour default works out to ~360 Wh, a realistic typical day, not a spec-sheet worst case. If you chase desert summers, push the slider toward 10.
Why 60W here when you measured the fridge at 45W?
Because they answer different questions, and only one of them belongs in a daily total. 45W is a spot reading off the meter while the compressor is running, on 12V at the low setting. Measured 60W is a planning figure for this calculator. Estimate It isn't a separate reading: it's what our long-run hourly averages come out to once you divide them by the compressor runtimes above. Mild weather lands near 59W, a typical day 60W, serious heat 59W. The same number falls out of all three, which is why I trust it for planning even though no meter ever showed it.
The gap between 45 and 60 is real and I'm not going to paper over it. The likeliest explanation is that the 45W came off the low setting, while years of averages were collected with no mode recorded and probably not on low. Timing the compressor across a full hour is what would settle it, and I haven't done that yet. Both figures, and the reasoning, sit on the real-world power data page.
Should I size my battery for worst-case or average use?
Typical. The principle at the top of this page applies here directly: typical-day sizing plus a charging backup beats worst-case sizing almost every time. The exception is if you regularly spend a week or more parked in one spot with no driving and no shore power. That's a recovery problem, not a capacity problem, and the answer is more solar (or a generator on standby), not more battery.
Do I really need solar?
Depends on how often you drive. If you move every day or two, alternator charging covers moderate loads on its own and solar is a nice supplement. If you sit in one spot for three days or more, solar is the thing keeping you out of the red. Heavy use or extended off-grid stays want both: alternator for driving days, solar for the days you don't move.
What about shore power or generator charging?
This calculator assumes off-grid use. If you regularly plug in at campgrounds or have access to outlets, your battery and solar needs drop significantly. Fast-charging stations can refill in 1–2 hours from a wall outlet, which changes the math entirely.
How do I size my inverter?
By your highest single-device draw (peak watts), not your daily total. The results panel shows this as "biggest single draw." If you run an induction cooktop at 1,500W, you need an inverter rated for at least 1,500W continuous, regardless of whether you use 500 Wh or 2,000 Wh per day. Most portable stations above 1,000 Wh include a 1,500–2,000W inverter, so in practice this only rules out the smallest stations.
Now watch it play out over a week#
A daily number tells you what you burn. It cannot tell you what happens on day four of an overcast stretch, because it has no memory of day three.
Take the watt-hour figure above into the 7-Day Off-Grid Simulator. Same measured data, but it runs an hour at a time across a full week and shows you whether you actually make it, or the exact hour you don’t.
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