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Solar power

RV solar power, sized to your rig

By Justin Champion· Boondocked 200+ nights· Updated June 2, 2026

Most first-night-off-grid power problems aren't gear problems. They're sizing problems. People buy a panel and a battery before they know what they actually run, and the system either dies on night two or costs twice what it needed to. This is the comprehensive version: how solar really behaves on an RV roof, how to size it to your loads, and a calculator that does the math on your setup.

Key takeaways

  • Loads first. The amp-hours you actually run is the only number that drives the whole system.
  • Panels never make their rated watts. Plan on 70 to 80% of nameplate on a good day, less when hot or cloudy.
  • The battery is the bottleneck. Solar refills it, but the usable bank is what gets you through the night.
  • Headroom beats peak. Size for a cloudy day at your real latitude and season, not the brochure photo.
  • Generators are insurance, not a plan. They earn a place for bad stretches, never the lead role.

The four numbers behind every off-grid power system

Boondocking power means running your rig for days without plugging in. Every watt you use comes out of a battery, gets put back by the sun or a generator, and runs out if you got the sizing wrong. Four numbers decide whether your weekend works, and they only work in this order.

01 Loads
amp-hours / day
What you actually run.
02 Battery
usable capacity
What gets you through the night.
03 Solar
wattage
What refills the bank by sunset.
04 Generator
backup
For cloudy stretches and emergencies.

Start with your loads, not your panels

Add up what you run and for how long. The fridge dominates. A 12V compressor fridge runs through roughly 30 to 60 amp-hours a day in moderate weather, and its appetite is weather-driven: its compressor duty cycle climbs from about 30 to 40% at 70°F to 50 to 70% once it's above 90°F, per bench tests at Build A Green RV and the model data summarized by LetsRV. Lights, a water pump, phone charging, and a vent fan add another 20 to 30 amp-hours. That sum, in amp-hours per day, is the number every other decision hangs off. Rooftop AC and induction cooking aren't loads you trim around the edges. They're a different system entirely, and usually a generator conversation.

How much solar do you actually need?

Here's the part the brochures skip. A 200-watt panel is a 200-watt panel only in a lab. The rating on the sticker is measured at Standard Test Conditions: a cool 25°C cell under 1000 W/m² of light. A panel bolted flat to a hot RV roof runs 25 to 40°C hotter than that, which alone costs 6 to 15% of output, so real-world production lands around 70 to 80% of nameplate on a clear day, per A1 SolarStore and the NOCT breakdown at The Green Watt. Size against the smaller number and you're never disappointed.

The other half of the equation is how many hours of usable sun you get, and that swings hard by place and season. The desert Southwest is a different planet from the Pacific Northwest in January.

WhereSummer peak sun hoursWinter peak sun hours
Arizona / desert SW~7.4~6.0
US average~5 to 6~3 to 4
Seattle / PNW~6.0~1.5

Peak-sun-hour figures from The Green Watt and IntegrateSun. The takeaway: a system that's perfect for March in Quartzsite can fall short by half on a cloudy December day in Oregon. Size for where and when you actually camp.

The rough method is simple. Take your daily amp-hour draw, divide by your worst realistic peak-sun-hours number, and that's the panel amps you need, then pad it. The calculator below does this properly, with the derating and a margin built in, so you don't have to.

The battery is the real bottleneck

Solar refills the bank. It doesn't power the rig directly in any way you should plan around. So the bank's usable capacity, not its sticker number, is what gets you through the night. And usable capacity depends entirely on chemistry. AGM batteries should only be drawn down about 50% before damage starts, so a 100Ah AGM is really 50Ah usable, and it's good for roughly 300 to 600 cycles. LiFePO4 gives you 80 to 100% usable and 3,000 to 6,000 cycles, per the chemistry comparisons at MANLY Battery and Battery Tender. That is the single fact behind most "my battery died too fast" stories. Size the bank to carry you through one cloudy day without the sun refilling it. One day of margin is the floor. Two is comfort.

When a generator earns its place

A generator is insurance, not a plan. It earns a spot for cloudy stretches and heavy loads like air conditioning, never as the daily lead role. A Honda EU2200i covers most rigs' backup needs and stays under most public-land quiet-hour limits during the day. If yours runs more than an hour or two on a normal day, something upstream was sized wrong, and the fix is more battery or more panel, not more fuel.

Field report · Moab, March 2025

Our first long dry-camp stretch outside Moab, I sized solar off the vendor's "good for off-grid" sticker and skipped the load math. 200 watts on the roof, a 200Ah AGM bank. On paper it looked fine. Two cloudy mornings in, the bank was at 40% and the fridge was the thing we were rationing.

The panel wasn't the problem. The 200 watts was really making about 150 in that heat, the AGM only handed back 100 of its 200 amp-hours, and two low-sun days never let it catch up. We never knew our real daily draw until it was already a problem. That trip is the reason this whole page exists, and the reason the calculator sizes to the cloudy day instead of the brochure.

Justin · 22ft travel trailer · 200Ah AGM, 200W roof solar at the time

Run your numbers

Solar calculator

Size your solar in about 60 seconds

Tell us what you run and we'll size the panel to your worst realistic sun day, not the brochure. It accounts for the real-world derating and battery chemistry, then points you at the battery math.

Power · boondocking.ai

Solar calculator

Tell us your rig, your loads, and your typical site. We'll size the panels and battery your real setup needs, not the brochure answer.

About 90 seconds.

Section 1 of 3

Your rig

Pick the closest match. We use this to set realistic load defaults.

Section 2 of 3

Your daily loads

Check what you actually run. We'll use sensible hours for each. You can tweak the assumptions below.

Section 3 of 3

Your climate

Pick the day you'd be sizing for. Most boondockers should pick Mixed.

Auto-set from above. Drag to override.
4.0 hrs
2 (PNW winter) 7 (desert summer)
Start the Battery calculator →

The mistakes that put people on night two with a dead bank

Sizing solar before sizing loads. Buying a 400W kit because a video said so puts the math in the wrong order. Confusing nameplate with usable capacity. Half your AGM bank is off-limits. Sizing for the average day. A rainy weekend is not the day to plan around the average. Treating the generator as a daily plan. Daily runs are a sizing-failure signal. Mounting flat and forgetting it. Flat panels are fine in summer, but a tilt toward a low winter sun can claw back a meaningful chunk of a short day.

RV solar, frequently asked

How many watts of solar do I need for my RV?
It depends on your daily amp-hour draw and where you camp, not on a one-size number. A weekend rig running a 12V fridge, lights, a fan, and chargers pulls roughly 60 to 100 amp-hours a day, which usually needs somewhere between 200 and 400 watts of panel once you account for real-world output and a cloudy-day margin. Run the calculator above for your actual setup.
How much solar does it take to run an RV refrigerator?
A 12V compressor fridge uses about 30 to 60 amp-hours a day, more in hot weather as the compressor runs harder. Replacing that on a typical sunny day takes roughly 100 to 200 watts of panel on its own, before you add lights, water pump, and charging. The fridge is almost always the single biggest load in the rig.
Will RV solar panels work on a cloudy day?
Yes, but at a fraction of normal output, often 10 to 25% of a clear day depending on how heavy the cloud is. That's exactly why you size the battery bank to carry you through a cloudy day on its own and treat solar as the refill, not the supply. Plan for the bad day and the good days take care of themselves.
Do I need an MPPT or a PWM charge controller?
For anything beyond a small trickle panel, MPPT is worth it. An MPPT controller harvests meaningfully more from the same panels, especially in cold or low-light conditions, and it lets you wire higher-voltage arrays. PWM is cheaper and fine for a single small panel matched to a 12V battery, but most boondocking setups should default to MPPT.
How many batteries do I need to go with my solar?
Size the bank to your daily draw plus a day of margin, then translate to nameplate by chemistry. If you draw 100 amp-hours a day and want one cloudy day of buffer, that's about 200 usable amp-hours, which is roughly 400Ah of AGM or about 200 to 250Ah of LiFePO4. The Battery calculator does this handoff from your solar result.
Can solar alone run my RV air conditioner?
Rarely, and never cheaply. Running AC off-grid means a large lithium bank, a lot of panel, and usually a generator for the hot afternoons. Most boondockers plan around not running AC, choosing elevation and shade instead. If AC off-grid is a hard requirement, it changes the whole system and the budget.
Should I tilt my RV solar panels?
In summer, flat-mounted panels are close enough that most people don't bother. In winter, when the sun sits low and the days are short, tilting panels toward the sun can recover a real chunk of a weak solar day. If you do most of your boondocking in shoulder seasons or winter, tilt brackets earn their keep.
Is RV solar worth it for boondocking?
For anyone boondocking more than a handful of nights a year, yes. Solar is what lets you stay out without running a generator all day or driving to shore power. The trick is sizing it right the first time so you don't overspend on panels you don't need or underspend and get stranded. That's the whole point of the calculator.

Sources: real-world panel output and STC vs NOCT from A1 SolarStore and The Green Watt. Fridge consumption from Build A Green RV and LetsRV. Peak sun hours from The Green Watt and IntegrateSun. Battery chemistry from MANLY Battery and Battery Tender.