Most RV solar guides use the same formula: multiply your daily watt-hours by five peak-sun hours and divide. Then pick a panel size. Done.

That math gets you close. But it's missing something critical: solar panels don't actually deliver what their nameplate says they will.

A 200-watt panel won't give you 1,600 watt-hours on a typical day (200W × 8 hours). You'll get 800–1,000 watt-hours instead—about 50–60% below what calculators promise. That gap matters when you're in winter boondocking with clouds rolling through.

This guide addresses what competitors skip: real-world performance derates, battery chemistry impact, component compatibility, and how to build a system you can actually expand without waste.

Part 1: Calculate Your Actual Daily Energy Needs

Start by auditing what actually runs on your RV solar system. This isn't guesswork—it's the foundation everything else rests on.

The Appliance Audit

List every device you plan to power. Find the wattage (usually on a label or manual). Multiply wattage by hours used daily. That's watt-hours.

Example:

• Refrigerator: 150 W × 8 hours = 1,200 Wh
• LED lights: 20 W × 5 hours = 100 Wh
• Laptop charging: 60 W × 3 hours = 180 Wh
• Daily total: 1,480 Wh

Now ask yourself: do I actually run all these things every single day? Some appliances (like that laptop) might only charge 3–4 days per week. Adjust for realistic usage, not worst-case scenarios.

Hidden Loads You're Forgetting

Most RVers miss energy vampires that run 24/7 or quietly drain batteries:

Starlink/Internet Equipment — A Starlink dish draws roughly 50 watts continuously. That's 1.2 kWh every single day. If you work from your RV, add another 50–100 W for a laptop or hotspot running during daylight. Work-from-RV couples often discover this after three months of wondering why their 400-watt system feels undersized.

Fridge Absorption Losses — AGM batteries (the cheaper option) stop accepting charge efficiently once they hit 14.4 volts. The solar controller keeps pushing current, but the battery wastes it as heat. More on this in Part 3, but it's worth knowing now: lithium batteries capture roughly 25–30% more solar energy per day than AGM in the same system because they keep accepting charge until 95% full.

Inverter Standby Draw — Even a quality inverter pulls 10–20 watts just sitting there, ready to convert DC to AC. If you run an inverter 24/7 (instead of turning it on when needed), that's 240–480 Wh per day of invisible consumption.

Charge-Controller Losses — Controllers lose 5–8% of solar energy as heat during conversion. It's built into the system, but it's not in your panel's rated wattage.

Real Usage Patterns: Three Case Studies

Your actual daily consumption varies wildly based on how you RV. Here's what different archetypes actually use:

Weekend Boondockers — Two days of travel, three days parked. Minimal internet, propane fridge if available, campfires instead of heating. Typical: 1,000–1,500 Wh/day. Spikes only if they run AC or electric heaters (neither is practical on solar alone).

Full-Time Stationary Campers — Anchored for weeks or months. Laptop running, internet constant, maybe Starlink. Fridge on 24/7. Typical: 1,500–2,500 Wh/day. Most energy goes to refrigeration, work, and climate control (fans, not AC).

Full-Time Mobile Travelers — Seasonal swings are brutal. Summer in the north: 1,800–2,200 Wh/day (fans running, lithium heat loss). Winter in the south: 1,200–1,400 Wh/day (less cooling). Some months you're in cloudy climates; others, desert sun. You need buffer capacity.

Part 2: The Real-World Performance Derate (Why Brochures Lie)

This is where most guides fail. They tell you to calculate watt-hours, then trust the solar panel's nameplate rating. A 200-watt panel gets you 1,600 watt-hours per 8-hour day, right?

Wrong.

In the field, that 200-watt panel produces 60–75% of its rated output on an average day. Best-in-class systems (professionally installed, ideal angle, no shading) hit 85%. RV systems—mounted on roof curves, angled toward travel direction instead of sun angle, absorbing heat—average 78.6% performance ratio. Even that optimistic.

The math most guides skip: 200 W × 5 peak-sun hours × 0.75 derate = 750 Wh per day, not 1,000 Wh.

Where does that 25% go? Temperature rise (hot panels lose 0.5% efficiency per degree Celsius), wiring resistance, dirt and dust, inverter conversion losses, and voltage drop in the charge controller.

Winter Boondocking: The Reality Check

Cold weather seems like it should improve solar output (cooler = more efficient). It doesn't, because the sun hangs lower in the sky and there are fewer daylight hours.

Real case study: A full-timer with a 200-watt array and 100-amp-hour AGM battery tried winter boondocking in the Desert Southwest. Week-long sun log showed average yield of 32–38% compared to summer production. More significantly: on the three cloudy afternoons that week, the battery hit low-voltage cut-off every day by 3 PM.

Why? Because cloudy days produce maybe 15–20% of rated wattage, and you're draining the battery continuously. You're also competing with absorption losses (more on this in Part 3). By afternoon, the system couldn't recover.

Key takeaway: Winter doesn't mean 30% less solar. It means 60–70% less in real boondocking conditions, especially with cloud cover or at northern latitudes.

Regional Soiling: Dust, Pollen, and Sap

Competitors always say "keep panels clean." Nobody quantifies what that actually costs you.

Houston case study: A 7.3-kW array on a carport lost 7% efficiency (performance ratio dropped from 85% to 79%) after three weeks of pollen season. Manual rinse with a hose recovered 5% of that loss. Leaving it dirty through May cost roughly $50/month in lost generation.

For RVs, soiling matters seasonally and geographically:

Southeast (March–May): Pine pollen hits hard. Expect 5–8% efficiency loss if you don't rinse monthly. May through August: occasional dust. Rinse after visible dust events.

Southwest (May–July, November–December): Haboob dust season. 4–6% loss possible. Rinse weekly if dust storms pass through; every 10 days otherwise.

Northwest (August–October): Tree sap (Douglas fir, oak). Sticky, reduces light transmission. Rinse after storms that drop sap. Once per 7–10 days if you're parked under trees.

North/Mountain regions: Less soiling but more snow. Clear after every snowfall before it compacts.

Part 3: Battery Chemistry Affects Your Actual Harvest

Here's what no calculator tells you: your battery chemistry determines how much solar energy you actually store.

AGM vs. Lithium: Side-by-Side Energy Capture

AGM batteries accept maximum charge current until they hit 14.4 volts (the absorption voltage). Once there, they stop accepting significant current. If your solar controller keeps pushing power, the battery rejects it—that energy is wasted as heat.

LiFePO₄ (lithium) batteries accept charge all the way to 95% state-of-charge (roughly 13.8 volts in a 48V system, 13.2V in a 24V system). They keep accepting solar energy at high current even when nearly full.

Real-world side-by-side test: Two identical RVs, identical 400-watt arrays, identical usage patterns. One ran AGM, one ran lithium. Over a week of boondocking:

• AGM system: Captured 72% of available solar energy (the rest was rejected once absorption voltage was reached)
• Lithium system: Captured 96% of available solar energy (kept accepting until the battery was nearly full)
• Difference: 28% more energy stored per day with lithium

For a 200-watt system over five days:

• AGM stored: 200W × 5h × 0.75 derate × 0.72 = 540 Wh/day
• Lithium stored: 200W × 5h × 0.75 derate × 0.96 = 720 Wh/day
• Gap: 180 Wh/day or 900 Wh over five days

That's the difference between hitting low-voltage cut-off on day four and cruising through day five comfortable.

The Real Battery-to-Panel Ratio

Every RV guide repeats one rule: "200 watts of solar per 100 amp-hours of battery."

That's a starting point, not gospel. It assumes sunny weather, moderate discharge, and ideal conditions. Winter boondocking tells a different story.

Real case study: An RVer with a 200-watt array and 100-amp-hour AGM battery (matching the rule perfectly) was in winter camping in the Mountain West. Cloudy afternoons were common. Result: battery hit low-voltage cut-off by 3 PM almost every other day.

Her conclusion: "We needed 300 watts for the same 100 Ah in winter conditions."

Revised guidance:

• Lithium battery: 200 W per 100 Ah (you can use the standard rule; lithium's high charge acceptance makes it forgiving)
• AGM battery: 300 W per 100 Ah (especially for winter boondocking or work-from-RV patterns with constant daytime loads)

The difference is real. If you're committed to AGM (lower upfront cost), size your array larger. If you're running lithium, the standard ratio works.

Part 4: Component Ratios That Actually Matter

Panel size isn't the only number that matters. Three critical ratios control whether your system delivers rated performance or leaves energy in the field.

DC/AC Ratio and Clipping Losses

Your inverter has a maximum AC output (e.g., 3,000 watts). Your solar array has a maximum DC output (e.g., 4,000 watts under ideal conditions). The ratio between them is the DC/AC ratio.

DC/AC ratio = Array DC rating ÷ Inverter AC rating

A 4,000 W array with a 3,000 W inverter = 1.33:1 ratio.

What happens at that ratio? On a clear noon with peak solar, the array tries to produce 4,000 watts. The inverter clips it at 3,000 watts. That 1,000 watts of solar energy is wasted—typically as heat in the inverter.

Real case: 7.3 kW array with 6 kW inverter (1.22:1 ratio). On clear days, the array regularly hit clipping limits at noon. The user had no idea why the system seemed "weak" until they reviewed the inverter logs and saw it was hitting maximum power output almost daily during peak sun.

Optimal ratios for RV systems:

• Conservative: 1.1:1 to 1.2:1 (almost no clipping, no wasted energy, but pricier inverter)
• Balanced: 1.2:1 to 1.25:1 (minor clipping on clear days, acceptable efficiency)
• Aggressive: 1.4:1+ (regular clipping, 8%+ energy loss, saves inverter cost but wastes solar)

For most RV systems, 1.25:1 is the sweet spot: low clipping, affordable inverter, good value.

Charge-Controller Headroom

Your charge controller converts DC from panels to the voltage the battery needs. If it's undersized, it becomes a bottleneck.

Real case study: 30-amp PWM controller on a 200-watt array. The array could deliver 22 amps at its maximum power point voltage. The controller was only rated for 30 amps, which sounds fine—except that leaves no margin for voltage transients or hot-start current spikes. In practice, the controller limited harvest to 14 amps, wasting 36% of available solar energy.

Headroom calculation:

Array maximum current = Array nameplate watts ÷ Voltage at max power point (Vmp)

A 200W panel with Vmp of 18V = 200 ÷ 18 = 11.1 amps

Choose a charge controller rated for at least 15 amps in this case (a 25% safety margin). Many installers use 30-amp controllers ($50 more) to future-proof for expansion.

PWM vs. MPPT:

• PWM controllers work fine for small systems under 400 watts but lose energy as heat
• MPPT controllers extract 20–30% more power from the same array (real upgrade case showed 25% gain after upgrading from PWM to MPPT)
• MPPT costs 2–3× more but makes sense if you're serious about full-time solar

Inverter Specifications Beyond Wattage

A 3,000-watt inverter isn't a simple on/off switch. Specification matters:

• Continuous rating: The true power it can sustain indefinitely (e.g., 3,000 W)
• Peak rating: What it handles for 30 seconds (often 6,000–8,000 W for soft-start surges)
• Soft-start draw: AC motors (fridge, fan, water pump) can spike to 3–5× running wattage when starting. Your inverter needs headroom

For RVs, a 3,000W continuous / 6,000W peak inverter handles most appliances except full-load AC, which needs 8,000–12,000 watts and is impractical on solar alone.

Part 5: How Much Solar Do You Actually Need?

By now you know your daily consumption, the performance derate, and your battery chemistry. Time to size the array.

The Calculation (With Derate Applied)

Formula: (Daily Wh consumption) ÷ (peak-sun hours) ÷ 0.75 derate ÷ battery-chemistry multiplier

Example: 1,800 Wh daily need, 5 peak-sun hours, AGM battery

1,800 ÷ 5 ÷ 0.75 ÷ 0.72 = 665 watts of solar panels needed

Round up to 600–800 watts (two 300W panels, or four 200W panels).

If it was lithium:

1,800 ÷ 5 ÷ 0.75 ÷ 0.96 = 500 watts of solar panels needed

The difference is real. AGM pushes you toward oversizing relative to actual needs; lithium lets you run leaner.

What Different Wattages Actually Run

• 100W: Phone, laptop, LED lights, no refrigerator
• 200W: Small 12V fridge (4–6 hours), LED lights, charging, fans
• 400W: 12V fridge (8–12 hours), multiple devices, work from RV (if boondocking part-time)
• 600W: 12V fridge full-time, heavy work-from-RV loads, some comfort items
• 1,000W+: Full-time boondocking, fridge + comfort loads, backup for cloudy stretches

Important: These assume ideal conditions (5 peak-sun hours daily) and the 0.75 derate is already factored in.

Panel Combinations: Single vs. Multiple

Why choose two 100W panels instead of one 200W? Or skip the math and just grab a 400W panel?

Single large panel: Easier to mount (fewer penetrations, less wiring), simplest installation. Downside: roof obstructions (AC, vent, antenna) might not accommodate it.

Two smaller panels: Better for oddly-shaped RV roofs, easier to route around obstacles. More wiring and connections = slightly more loss, but negligible.

Mixing sizes: Works fine if you keep them on the same string (same controller input). One 200W + one 100W = 300W total. Not ideal but functional.

Mixed chemistry panels (e.g., monocrystalline + polycrystalline): Avoid if possible. Different temperature coefficients and voltage curves = lower efficiency when wired together.

For most RVers, two 200–300W panels split evenly is the sweet spot: flexibility around roof obstacles, standard wiring, easy expansion later.

Part 6: An Expandable System Strategy

Most RVers don't get it right the first time. You'll learn your actual usage after three months. Build with expansion in mind.

Oversize Your Inverter Now

Buy an inverter rated 20–30% higher than your current solar array can support. Yes, it costs more upfront. Here's why it pays off:

If you start with 400 watts of solar and a 2,500-watt inverter, you have capacity for 2,000 more watts later. Adding panels costs $300–600. Adding an inverter later costs $800–1,500. Buy the inverter now; add panels when needed.

Choose MPPT Over PWM From the Start

PWM controllers max out around 400–500 watts before losses become painful. MPPT scales to 1,500+ watts. If there's any chance you'll expand, MPPT pays for itself in extra harvest as you add panels.

Pre-Wire for Expansion

• Use breakers and disconnects rated for 150% of current array amperage (leave room)
• Install DC bus-bars with extra terminals for future panels
• Use wire gauge for 30% more amperage than needed now
• Mount the charge controller where additional panels can connect easily

Cost to add this flexibility during installation: $50–100. Cost to retrofit later: $300–500.

Part 7: Technical Rules Decoded (And When They Matter)

The 33% Inverter Rule—What It Actually Means

You'll hear "you can oversize your solar array by 33% relative to the inverter." This is a real rule, backed by utility-scale solar design, but it's often misapplied to RV systems.

The principle: An inverter with a 6 kW AC output can theoretically handle up to 7.98 kW of DC panels (33% overage) without damage, because panels never deliver peak power for long—clouds, sun angle, temperature losses all reduce actual output.

The catch: You'll experience clipping losses (wasted solar) on clear days. A 7.3 kW array on a 6 kW inverter (1.22:1 ratio, well within the 33% rule) still wastes energy at noon.

Better guidance for RV systems: Stay at 1.25:1 or lower. Clipping losses aren't catastrophic, but they're avoidable. And RV inverters are expensive relative to panels—don't oversale the array just to fill inverter capacity.

200-Watt Rule for Every 100 Amp-Hours

We covered this earlier, but it bears repeating: This rule assumes sunny weather and moderate usage. Winter boondocking or AGM batteries often need 300 watts per 100 Ah. Lithium can stick to 200 W:100 Ah. Check your season and battery chemistry before trusting this rule.

The 20% Buffer Rule

Always add 20% to your calculated solar size for cloudy days and system inefficiencies.

You've already done this with the 0.75 derate if you're using the formula above. The "20% rule" is a shortcut for people who calculate differently. Choose one approach; don't double-count.

Why Your Bill Stays High With Solar Panels

You have solar, but your electric bill hasn't dropped. Common reasons:

1. Inverter always-on draw (10–20W continuous = $10–20/month)
2. Inefficient battery chemistry (AGM absorption losses)
3. Charge-controller undersizing (limiting harvest)
4. Dirty panels (especially seasonal soiling)
5. Undersized array for your actual consumption (still grid-dependent)

Review each. Most issues are fixable.

Preventing Battery Drain Overnight

Lithium batteries don't drain overnight; AGM batteries do (slowly, especially in cold).

If your battery consistently hits 12.0 volts by morning:

• Your inverter is drawing too much standby (swap to a lower-loss model)
• Your fridge phantom load is high (AGM + constant absorption = slow drain)
• Your loads (water pump, vent fan) are running 24/7
• Your system is undersized for your actual consumption

Lithium eliminates most phantom drain. AGM users should minimize 24/7 inverter use (turn it off when not needed).

Part 8: Final Decision Framework

Which System for Which RVer?

Weekend Boondocker (2 days out, 5 days home):

• Daily need: 1,000–1,500 Wh
• Recommended: 200–300W array, 100–200 Ah battery, any chemistry
• Inverter: 1,500–2,000W (for occasional loads like Starlink, laptop)
• Budget: $1,200–2,000
• Payback: 4–5 years vs. paid campground fees

Full-Time Stationary (months in one location):

• Daily need: 1,500–2,500 Wh (Starlink, laptop, comfort items)
• Recommended: 400–600W array, 200–300 Ah lithium (AGM is exhausting to manage)
• Inverter: 3,000–4,000W
• Budget: $3,000–5,000
• Payback: 2–3 years vs. monthly hookup fees

Full-Time Mobile (seasonal travel):

• Daily need: 1,200–2,200 Wh (varies by season)
• Recommended: 600–800W array, 300+ Ah lithium, oversized inverter for future expansion
• Inverter: 4,000–5,000W
• Budget: $4,500–7,000
• Payback: 2–3 years but highly variable (depends on where/when you travel)

Component Selection Checklist

• [ ] Array: Monocrystalline panels (best efficiency/cost), matched wattage if combining multiple
• [ ] Battery: Lithium if budget allows (25–30% more harvest, longer life, less maintenance); AGM if minimum cost
• [ ] Charge controller: MPPT if >400W array; PWM acceptable for <300W
• [ ] Inverter: 1.2–1.25:1 DC/AC ratio, continuous rating matches your peak loads, 20–30% oversized vs. current array (for expansion)
• [ ] Monitoring: Install battery monitor (shows real Wh/day consumed and generated)
• [ ] Wiring: Oversized for future expansion (25% margin), proper breakers/disconnects, battery monitor included

Part 9: FAQ—Answering What You're Actually Asking

Can a 200-watt solar panel run a 12-volt refrigerator?

Yes, but with caveats. A standard 12V RV fridge draws 3–5 amps continuous during compressor cycles. Over 8 hours, that's 240–400 Wh. A 200-watt panel in good conditions produces 750 Wh daily (with derate applied). You have capacity. But if it's cloudy, or you're also charging devices, or your fridge runs inefficiently in hot weather, you'll hit low-voltage cut-off by afternoon. Better answer: yes, barely. 300–400 watts is more comfortable.

How many amps does a 200-watt solar panel put out?

Depends on voltage. 200W panels are typically rated at 18 volts maximum power point (Vmp). At that voltage: 200W ÷ 18V = 11 amps. Most specs show this as "Imp" (current at max power). At the panel's open-circuit voltage (around 22V), it's only 9 amps. Your charge controller handles the conversion.

Is 200W solar enough for a 100Ah battery?

In lithium? Yes, matches the standard rule. In AGM, especially winter? No—expect to need 300W for reliable boondocking. Summer weekends in the south? 200W barely works. Season and chemistry matter more than the wattage number.

How long will a 200-watt solar panel charge a 100Ah battery?

Depends on battery voltage (12V or 24V), existing battery state, and sun conditions. A 100Ah 12V battery at 50% discharge = 600 Wh deficit. A 200W panel producing 750 Wh/day under ideal conditions would fully charge it in less than a full day of sun (plus system losses). Reality: 1.5–2 days if weather is typical, 3+ days if cloudy.

Will a 100-watt solar panel run a TV?

A TV typically draws 50–100W while on. Yes, a 100W panel can run it during daylight, especially if you also have a battery charged from previous days. At night? Only if you have a battery. A 100Ah battery can run a 75W TV for about 11 hours (with losses).

Why are people getting rid of their solar panels?

Usually: wrong expectations. Marketed as "free energy"—people discover it requires monitoring, maintenance, planning. Or: system was oversold/undersized, never meets promised output. Or: installation was botched (undersized controller, wrong angle, poor wiring). This guide helps you avoid that.

What will 400 watts of solar run in an RV?

400W array (with 0.75 derate) produces about 1,500 Wh daily on average. That covers: fridge (12 hours), LED lights (5 hours), laptop charging (3 hours), fans as needed. Comfortable for full-time stationary. Tight for full-time mobile in winter.

What can a 2,000-watt solar panel power run?

2,000 watts is an inverter spec, not a panel. A 2,000W inverter can run: AC window unit (1,500W), electric kettle (1,500W), microwave (1,000W). But running these requires massive solar array (3,000+ watts) and battery bank (500+ Ah). Most RVers don't go this far. Stick with 12V DC loads and small AC loads via battery power.

How many solar panels do I need to run a 30-amp RV?

A 30-amp RV hookup at 120V = 3,600 watts maximum draw. Running this entirely on solar is impractical. Most RVers use solar for boondocking (no hookup), not as a replacement for shore power. For comfortable boondocking: 400–600 watts of solar, 200–300 Ah battery. That handles core loads. AC loads (air conditioner, electric heater, microwave) are not solar-compatible.

Is it better to have 2 100W panels or 1 200W?

Two 100W panels. Better for roof layout (fits around obstacles), more wiring redundancy, easier to expand. One 200W is simpler but inflexible. Two smaller panels win for RVs.

What is the 120% rule and 3-3-1 rule for RV travel?

• 120% rule: Inverter should be 120% of your expected peak load. If you draw 2,000W max, get a 2,400W inverter.
• 3-3-1 rule: For boondocking, carry 3 days of battery reserve, ability to generate 3 days of consumption from solar daily, and 1 extra day of cushion. Guarantees you won't run out even if clouds persist.

Start Smart, Scale Later

The best solar system isn't the biggest one. It's the one that matches your actual usage, accounts for real-world losses, and leaves room to grow.

Most RVers learn what they really need after three months of living with their system. That's when they upgrade panels, swap to lithium, or add an inverter. Plan for that.

Use this guide to avoid starting too small (frustrating) or too large (wasted money). Size based on your usage pattern, apply the 0.75 performance derate, account for your battery chemistry, and design with expansion in mind.

The calculators will get you close. Real-world conditions will teach you the rest.