How Much Solar Do I Need for an RV

Here’s the misconception that costs people: solar panels don’t power your appliances — they recharge your battery, and your battery is what actually runs things overnight, through clouds, and during the two hours you’re parked in the shade. Size your panels without sizing your battery first and you’ve solved the wrong problem. The second trap is quieter and almost nobody talks about it: your rig is draining its battery right now, even if you’ve touched nothing. Propane detectors, fridge control boards, switch panels — the whole RV bleeds 0.5–2A continuously, and if you’ve left the inverter switched on, add another roughly 25W of idle draw on top of that. Together, those invisible loads can pull 600Wh or more out of your bank in a day before you’ve made a single cup of coffee.

This guide works through both problems in sequence: what drives the real numbers, where the popular sizing rules come from and what they leave out, and how to build a system that actually covers your life in the rig — not just the appliances on your list.

Panels Don’t Power Things — Batteries Do

The mental model that causes most sizing mistakes is treating solar panels like a power source you plug into. They’re not. A panel is a battery charger. What keeps your lights on at midnight, what gets you through a cloudy afternoon, what determines whether your fridge survives a two-day storm — all of that is your battery bank. Panels refill it during daylight hours, and everything else flows from how much you can store.

This matters for sizing in a concrete way: your panel array needs to be matched to your battery capacity, not to a list of appliances. A rule of thumb that shows up across multiple sources is roughly 200W of solar for every 100Ah of usable battery capacity. If you’re running 200Ah of lithium, that points you toward 400W of panels. The math behind it assumes something like six sun-hours per day — which is itself a best-case assumption that erodes badly in winter, at higher latitudes, or with panels lying flat on the roof rather than tilted toward the sun.

These numbers all come from sellers and affiliate sites, and sellers who agree with each other are not a confirmation — they have a shared interest in making “200W minimum” sound like science. Treat it as a planning bracket, not a measurement. What the brackets actually look like in practice:

• ~200W: Maintenance-level. Enough to keep a parked bank topped off and run modest lighting. Fine if you’re mostly hooked up and solar is backup.
• 400–700W: The range most serious boondockers actually land in. Covers lighting, phone charging, a 12V fridge, small inverter loads.
• 800W+: Where you need to be if you’re running a residential 120V fridge, a microwave, or any attempt at air conditioning off-grid.

The fridge question deserves its own answer because the fridge is usually what forces a system upgrade. A well-designed 12V DC compressor fridge is the efficient choice — it draws roughly 30–55Ah per day under normal conditions. A residential 120V fridge is a different animal entirely: it pulls around 720W when the compressor is running, and depending on ambient temperature and duty cycle, it can consume several kWh per day. One worked example puts a residential fridge at roughly 1,000W of solar and on the order of 300Ah of lithium to run around the clock off-grid. That figure involves an assumed duty cycle that no nameplate tells you, and real consumption will swing with how hot it is and how often the door opens — so treat it as directional, not a spec to copy. The honest answer on fridge sizing is: measure your specific fridge, in your specific climate, with your door habits, before you commit to a system around it.

What Your Panels Actually Deliver (vs. What the Label Says)

Nameplate watts are measured under laboratory conditions — controlled temperature, optimal angle, idealized light. A panel sitting flat on an RV roof in real sun is not living in that lab. Field observation suggests a 100W panel lying flat on a roof realistically yields on the order of 300–400Wh per day (roughly 30Ah at 12V) under decent sun. That’s meaningfully below what you’d calculate by multiplying rated watts by sun-hours, and there are real reasons for the gap.

Heat is one. Panels running well above their test temperature give up a real chunk of output — hotter is always worse for yield. Flat mounting is another. A panel angled toward the sun captures more light than one lying horizontal, and the difference is largest when the sun is lowest: winter, early morning, late afternoon. One field test conducted in mid-January near Yuma, Arizona found that tilting and manually tracking a panel to follow the sun nearly doubled the daily output compared to the same panel lying flat. That’s a winter-solstice result in the Southwest — don’t generalize it to July in Minnesota — but it illustrates what flat mounting costs you exactly when you need the output most.

Then there’s the charge-stage problem. A battery doesn’t accept full current all day. In the bulk stage — when it’s depleted and hungry — it pulls hard, and your whole array can be working flat out. But once it climbs into the absorption stage, acceptance current drops sharply. A 220Ah bank in absorption might only take around 150W regardless of whether you have 400W or 800W of panels pointed at it. More panels speed up bulk charging and help on low-light days; they can’t force a near-full battery to accept energy faster than chemistry allows. This is why “just add more panels” hits diminishing returns once your bank is reasonably sized.

Sun-hours swing hard by season and location — field estimates put the range somewhere between five and nine hours per day depending on time of year and where you are. The same array that buries your bank all summer may barely keep up in January. If you’re winter camping or traveling in the Pacific Northwest, size for the bad days, not the good ones.

The Load You’re Not Counting

Here’s where most sizing plans fall apart: the appliance list. People add up the watts on their fridge, their lights, their phone charger — and stop there. That list is missing the loads that run whether you touch anything or not.

A modern RV has always-on draw from propane and CO detectors, control boards, antenna boosters, clocks, and various switch panels. Measured across actual rigs, this parasitic standby drain runs roughly 0.5–2A continuously. At the high end — newer trailers with sophisticated control systems have been measured at something like 48Ah per day just to keep the lights off. That’s real battery consumption for zero visible output.

The inverter compounds this if you leave it switched on. An inverter idling at no load burns approximately 25W — which works out to roughly 600Wh per day before you’ve plugged a single thing into it. And when you do run 120V appliances through it, add another 10–20% to whatever those appliances draw, because inverters are 80–90% efficient. Run a lot of AC loads and that tax accumulates. An oversized inverter running small loads actually performs worse on efficiency than the headline range suggests, because efficiency drops at very low load fractions.

The practical implication is that your sizing math needs two lines before the appliance list:

• Standby parasitic: Budget at least 12–48Ah per day depending on your rig’s electronics.
• Inverter idle: If you leave it on, budget roughly 600Wh per day for nothing. If you switch it off when not in use, that drain disappears — switch it off.

Neither of these shows up on any appliance spec sheet, which is exactly why they blindside people who’ve done otherwise careful planning.

How to Actually Size Your System

The sequence matters. Get this backwards and you’ll have the wrong everything.

1. Start with your daily load in amp-hours or watt-hours. List your actual appliances and their realistic run times, then add your standby parasitic estimate (12–48Ah/day) and your inverter idle if you leave it on. This is your real daily draw.
2. Size your battery bank first. For off-grid use, you want enough capacity to cover at least two days of your real daily draw without solar input — more if you camp in cloudy country. That buffer is what gets you through bad weather. Lithium lets you use a higher fraction of rated capacity than AGM or lead-acid, which affects how much rated capacity you actually need.
3. Size solar to refill that bank in reasonable sun. The 200W-per-100Ah rule gives you a starting point, but adjust upward if you’re in a cloudy region, if your panels mount flat, or if you camp in winter. Add panels until you can credibly replenish a worst-case day’s draw during a mediocre sun day — not the best sun day.
4. Check your charge controller’s capacity. Your solar array output has to fit within what your charge controller can handle. Panel wattage that exceeds your controller’s limit is wasted, and if you exceed the voltage limit you can damage the controller.

The one thing that cuts through all the vendor noise: know your own actual consumption before you buy anything. A battery monitor that measures real amp-hours in and out over a few days of your normal usage is worth more than any sizing calculator. Sellers can’t sell you that data — you have to collect it yourself.

Size the battery first. Then size the solar to fill it. And add the invisible loads — standby drain and inverter idle — before you finalize either number. That’s the whole framework, and it’s the one the spec sheets won’t give you.