Sizing an RV solar system for full-time boondocking is a math problem, not a guessing game. This guide walks through the four steps that matter: auditing your daily energy use, sizing the battery bank, sizing the solar array, and matching the inverter and charge controller. Follow them in order for a system that keeps the fridge cold through a week off-grid.
- Most full-time boondockers use 1.5 to 4.5 kWh per day without AC; air conditioning can double or triple that.
- Size the battery bank for 1 to 2 days of autonomy; a 100Ah 12V lithium battery holds about 1.28 kWh usable.
- Array watts = daily kWh / peak sun hours / 0.8; most full-timers need 600 to 1,200 W.
- Use an MPPT charge controller and a pure sine wave inverter rated ~25% above your largest simultaneous load.
- The 30% federal tax credit ended for installs after December 31, 2025. Verify state programs at DSIRE; rules change.
How Much Power Full-Time Boondockers Really Use
The fridge is the biggest daily draw in most RVs. A modern 12V compressor fridge pulls 40 to 60 W while running and cycles all day, totaling about 1 kWh daily. Our guide to running an RV fridge on solar has the full breakdown.
After the fridge: lights, vent fans, phones, laptops, water pump, and 40 to 60 W for Starlink during work hours. The microwave draws big watts but only for minutes, so it matters for inverter sizing, not daily energy. AC is in a league of its own: one 13.5k BTU unit can use more in an afternoon than everything else all day. Conservative: 1.5 to 2.5 kWh/day; moderate: 2.5 to 4.5; with AC: 6 to 10+.
Step 1: Build Your Daily Energy Budget
A power audit takes twenty minutes. List every device, note its watts from the label or a Kill-A-Watt meter, and estimate daily hours: watts x hours / 1,000 = kWh per day. Example audit for a couple working remotely:
| Device | Typical draw | Hours per day | Daily energy |
|---|---|---|---|
| 12V compressor fridge | 45 W average | 24 | 1,080 Wh |
| LED lights (six) | 30 W | 5 | 150 Wh |
| Roof vent fan | 30 W | 8 | 240 Wh |
| Phones and laptops | 65 W | 4 | 260 Wh |
| Starlink / router | 50 W | 6 | 300 Wh |
| Water pump | 60 W | 0.5 | 30 Wh |
| Microwave | 1,000 W | 0.25 | 250 Wh |
| Total | 2,310 Wh (2.3 kWh) |
Measure big loads instead of guessing, then add a 20 percent margin for phantom loads and inverter losses: 2.3 kWh becomes a 2.8 kWh design number. Try EXPLORIST.life’s power audit calculator, and see our off-grid cabin sizing guide for stationary builds.
Step 2: Size Your Battery Bank
Multiply your daily energy by the cloudy days you want to ride through. One day of autonomy works if you chase sun and carry a generator; two days is the comfortable full-time number. At 2.8 kWh/day, two days means 5.6 kWh of usable storage.
A 100Ah 12V lithium battery gives about 1.28 kWh usable; a 100Ah AGM gives only ~0.6 kWh, since draining lead-acid below 50 percent kills it. So 5.6 kWh needs four 100Ah lithium batteries (5.12 kWh) versus roughly nine AGMs. See our lithium vs AGM comparison and off-grid battery count guide.
Pros
- Nearly 100% of rated capacity usable, versus ~50% for AGM
- 3,000 to 5,000 cycles; Battle Born’s 100Ah 12V carries a 10-year warranty
- Charges faster and holds voltage steady under heavy loads
- About half the weight of lead-acid for the same usable energy
Cons
- Costs more upfront: ~$800 to $950 per 100Ah 12V versus $200 to $300 for AGM
- Needs a lithium-compatible charger profile on older converters
- Cannot charge below freezing without heating or low-temperature cutoff
Stay at 12V for arrays up to ~1,200 W, since the rig already runs on 12V. Above that, wire pairs in series for 24V. Our 13.5 kWh battery runtime guide shows what the biggest banks power through a night.
Step 3: Size Your Solar Array
The array must replace your daily use on an average day: array watts = daily kWh / peak sun hours / 0.8, where 0.8 covers heat, angle, dust, and wiring losses. Peak sun hours are equivalent hours of full sun, and they vary widely by region and season.
| Region | Typical peak sun hours | Sizing note |
|---|---|---|
| Desert Southwest | 5.5 to 6.5 | Size for December, not June |
| South, Southeast, Midwest | 4 to 5 | Summer haze trims output |
| Pacific Northwest, Northeast | 3 to 4 | Winter can drop to 2; plan for your worst month |
Example: 2.8 kWh/day in Arizona winter at 5 sun hours = 2,800 / 5 / 0.8 = 700 W, so install 800 W for margin. The same load in a Pacific Northwest winter needs 1,400 W, which will not fit most roofs. Compare rigid, flexible, and portable RV panels for the type decision, and cross-check with EXPLORIST.life’s camper panel sizing guide.
Step 4: Pick the Inverter and Charge Controller
Add up the watts you might run at once and multiply by 1.25: microwave (1,000 W) + fridge kick (150 W) + laptops and fans (200 W) = 1,350 W, so a 2,000 W inverter covers it. Always buy pure sine wave. For AC, see our RV air conditioner solar guide.
Go MPPT, not PWM: 15 to 30 percent more harvest. Size by amperage: array watts / battery voltage. An 800 W array on 12V pushes ~62 A (800 / 12.8), so buy a 60 to 100 A controller. Victron SmartSolar is the boondocking favorite; Renogy Rover is the budget pick. Add a shunt-based battery monitor, fuses on every positive run, and a DC-DC charger for alternator charging.
Three Real Boondocking System Recipes
Match these to the three usage bands above, adjusted with your own audit numbers.
| Weekend warrior | Full-time moderate | Full-time plus AC | |
|---|---|---|---|
| Daily use | ~1.5 kWh | ~2.5 to 3.5 kWh | ~6 to 8 kWh |
| Solar array | 400 W rigid | 800 to 1,000 W rigid | 1,600 W or more |
| Battery bank | 200Ah lithium (2.56 kWh) | 400Ah lithium (5.12 kWh) | 800Ah lithium (10.24 kWh) |
| Inverter | 1,000 to 2,000 W | 2,000 W pure sine wave | 3,000 W plus soft start |
| Charge controller | 30 to 40 A MPPT | 60 to 100 A MPPT | 100 A MPPT or dual |
| Typical DIY cost | $1,500 to $2,500 | $3,500 to $6,000 | $7,000 to $10,000 |
The moderate build is the sweet spot where most long-term boondockers settle. The AC build rivals a small cabin system; it works only if the audit says you need it and the roof fits the panels.
What It Costs in 2026 and the Tax Credit News
A 400 W panel-and-controller kit runs $600 to $1,500 before batteries; Renogy’s 400 W premium RV kit with 40 A MPPT controller shows what that buys. Full-time lithium setups typically land between $3,000 and $10,000 DIY, plus 30 to 50 percent for professional install. Our 2026 RV solar cost breakdown prices each component.
Incentive warning: the federal 25D credit ended for systems installed after December 31, 2025, so 2026 installs do not get the 30% credit. Some states still offer rebates or tax exemptions, but programs change, so verify at DSIRE. Also read whether going off-grid is legal where you park.
Related Guides
- RV air conditioner solar watts: running watts, surge, soft starts
- Best RV solar panels for 2026: rigid vs flexible vs portable
- RV solar setup costs in 2026, component by component
- Lithium vs AGM RV batteries: cost per usable kWh
- Running an RV fridge on solar, the biggest daily load
- Off-grid cabin solar sizing, same audit method
- 5 kW off-grid solar cost in 2026
- Batteries needed off-grid: bank sizing math
- Is going off-grid legal? Rules for RVs and land
- Home battery size for outages
- How long a 13.5 kWh battery lasts on real loads
Can I run my RV air conditioner on solar while boondocking?
Yes, with ~1,500 W+ of panels, 5 kWh+ of lithium, a 3,000 W inverter, and a soft start kit. Most users run it a few afternoon hours, not all night.
How many solar panels do I need for full-time boondocking?
Most full-timers without AC need 600 to 1,200 W: daily kWh / peak sun hours / 0.8. Measure the roof before buying.
How long do RV solar batteries last?
Quality lithium: 3,000 to 5,000 cycles, roughly 8 to 12 years full-time; Battle Born’s 100Ah 12V carries a 10-year warranty. AGM: 3 to 5 years.
Should my RV system be 12V or 24V?
Stay 12V under ~1,200 W of panels; move to 24V for bigger arrays to halve amperage. Keep all bank batteries the same age, type, and capacity.
Can I start small and add panels later?
Yes: buy an MPPT controller rated for the future array, leave roof space and wiring capacity, and add matching panels later.
Ready to compare real solar prices?
Get free, no-pressure quotes from vetted local installers and see what solar costs for your roof.
