How Much Solar Power Do You Need for an RV? 200W to 1,200W
Divide daily watt-hours by peak sun hours, then by 0.7. The RV solar calculator sizes array, battery and controller: 200W weekends, 1,200W for AC.
Most RVs need 200 to 600 watts of solar. Size it with one equation: daily watt-hours divided by the peak sun hours where you camp, divided by 0.7 for losses. A 1,400 Wh day at 4.5 sun hours calls for a 445 watt array. Weekenders land near 200 watts, a full-time couple at 400 to 600, and running an air conditioner starts at 1,200.
RV solar calculator: panels, battery and controller size
Tick the loads that run in your rig, pick the region and the season you camp in, and the calculator returns the hardware: array watts, how many panels that is at 100, 200 or 400 W, the roof area they cover, the battery bank in amp-hours, and the MPPT controller rating. It opens on the worked example below, a 1,500 Wh day at 4.5 peak sun hours with 30% losses, which comes out at 476 watts of panel, five 100 W panels on 31 square feet of roof, a 195 Ah lithium bank and a 50 A controller.
RV solar calculator
Turn a day of watt-hours into array watts, panel count, roof square feet, battery amp-hours and controller size.
The array is daily watt-hours divided by peak sun hours, divided again by one minus the loss figure. The bank is daily watt-hours times days of autonomy, divided by usable depth of discharge (0.9 for LiFePO4, 0.5 for AGM and flooded), then converted to amp-hours at 12.8 V per 12 V block for lithium and 12.6 V for lead. Controller amps are array watts divided by the charging voltage (14.4 V on a 12 V bank, 28.8 V on 24 V) times 1.25, the continuous-current margin in NEC 690.8, rounded up to a rating that is sold.
Peak sun hours come from the regional table on this page, which assumes clean panels lying flat on the roof: the desert Southwest holds 6.5 in June and about 3.2 in December, while west of the Cascades December runs near 1.0. Tilting panels roughly doubles a December harvest and moves the winter rows. Roof area counts panel footprint only (100 W = 6.1 sq ft, 200 W = 11.2 sq ft, 400 W = 21.0 sq ft) and adds nothing for mounting feet or the walking space between rows, so treat it as the floor of what the job takes.
The tool sizes a flat, unshaded, clear-sky day. It does not model shade from the air conditioner, snow cover, series string voltage at cold temperatures, or an alternator or generator topping the bank up. Measure your own consumption with a shunt monitor for two nights before spending money on panels.
Three controls move the answer more than everything else combined. Peak sun hours is the first: switch the season list from spring to December in the Midwest and the same 1,500 Wh day goes from 476 watts to 1,261. The chemistry pills are the second, because that 1,500 Wh day needs 195 Ah of lithium or 357 Ah of AGM, which is one battery under a dinette seat against four and 230 lb of lead in a compartment. Days of autonomy is the third and the one people set too low: 1.5 days rides out a single overcast day, while 3 days rides out a rainy weekend and doubles the price of the bank.
Two flags fire on the failures that show up most often: an array needing more roof than a 25 ft trailer has left after the air conditioner and vents, and a load one 100 Ah battery cannot carry for even a day. When either lights up, the cheaper fix is on the consumption side. The controller figure carries the 25% continuous-current margin from NEC 690.8, so it can land one size above the divide-by-12 shorthand further down this page.
How do you calculate how much solar an RV needs?
Work backwards from consumption, never forwards from panel wattage. Three numbers decide the array: what you use in a day measured in watt-hours, the peak sun hours your camping season and latitude deliver, and a 0.7 derate that accounts for everything between the cell and the battery.
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Add up a day of watt-hours
List every load, multiply watts by hours, and total it. Use the table below rather than guessing. Expected: one number between 400 Wh for a weekend trailer and 6,000 Wh for a coach running air conditioning.
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Divide by peak sun hours for your worst month on the road
Peak sun hours is not daylight. It is the number of hours of 1,000 W/m2 sun your flat roof effectively sees, which is 5 to 6 in a Utah June and under 2 in a Michigan December. Expected: the watts of panel you would need if panels were 100% efficient at delivering.
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Divide that by 0.7
Controller conversion, wiring drop, heat, dust and a roof that never points at the sun each take a cut. Expected: the array you actually buy. Round up to the panel sizes that fit your roof.
Worked example, a couple in a 27 ft trailer with a 12V compressor fridge: lights 150 Wh, fridge 550 Wh, water pump 25 Wh, roof fan 200 Wh, laptop and phones 300 Wh, TV 120 Wh, inverter idling 8 hours 150 Wh. That is 1,495 Wh, call it 1,500. At 4.5 peak sun hours in September that is 333 watts, and after the 0.7 derate it is 476 watts. They buy 500 W and stop thinking about it.
Run the same rig through December at 40° north, where the flat roof gets 1.8 peak sun hours: 1,500 ÷ 1.8 ÷ 0.7 is 1,190 watts. That is not a rounding error, it is the reason snowbirds move south instead of adding panels. Decide which months you intend to camp before you decide the array, because the season moves the answer by a factor of three.
Step 1: what does your RV actually use in a day?
Total your loads in watt-hours, not amps, so a 12V fan and a 120V coffee maker land in the same column. Most trailers without a 12V fridge sit between 400 and 900 Wh a day. Add a compressor fridge and you are at 1,200 to 2,000. Add Starlink and an inverter left switched on and 2,500 is normal.
| Load | Draw | Typical use | Watt-hours per day |
|---|---|---|---|
| LED interior lights, 6 fixtures | 30 W total | 5 h | 150 |
| Water pump | 60 W | 15-20 min | 15-25 |
| Absorption fridge on propane (board, igniter) | 2-3 W | 24 h | 50-70 |
| 12V compressor fridge, 8-10 cu ft | 45-60 W running, 40% duty in heat | 24 h | 400-800 |
| Residential fridge through an inverter | 100-150 W running | 24 h | 1,200-2,000 |
| Maxxair or Fan-Tastic roof vent | 20-36 W | 8 h | 160-290 |
| Propane furnace blower, 30 °F night | 90-110 W | 3-4 h of run time | 270-440 |
| Starlink Standard | 45-75 W | 8 h | 400-600 |
| Starlink Mini | 20-40 W | 8 h | 160-320 |
| Laptop plus two phones | 60 W | 4 h | 250-300 |
| CPAP, humidifier off | 30-40 W | 8 h | 240-320 |
| 24 in 12V television | 40 W | 3 h | 120 |
| Inverter idling with nothing plugged in | 15-25 W | as long as it is on | 360-600 per 24 h |
| Coffee maker or Instant Pot | 900-1,200 W | 15-30 min | 250-450 |
| Induction burner | 1,500-1,800 W | 20 min | 500-600 |
| 13,500 BTU air conditioner | 1,300-1,600 W | per hour of cooling | 1,300-1,600 each hour |
Two lines on that table catch people out. The inverter’s idle draw is one: a 2,000 W pure sine inverter left on around the clock burns more watt-hours than the television, the lights and the water pump combined, and it does it while you are out hiking. The furnace blower is the other, because owners count propane and forget that the fan behind it is a 100 watt motor running on the battery.
If you want the number instead of the estimate, a battery monitor with a 500 A shunt in the battery negative reads consumed watt-hours directly. Camp two normal nights, read the total, and size from that.
Step 2: how many peak sun hours does your region give you?
Peak sun hours ranges from 6.5 in a Quartzsite January to under 1 in a Seattle December, and it is the term in the equation with the widest swing. A peak sun hour equals 1,000 watts per square metre for one hour, so a 400 W array in 5 peak sun hours generates 2,000 Wh before losses, regardless of whether the sun was up for 9 hours or 15.
| Where you camp | June, flat roof | December, flat roof | What that means for the array |
|---|---|---|---|
| Desert Southwest (Quartzsite, Phoenix, Las Vegas) | 6.5-7.0 | 3.0-3.5 | Winter works on the summer array |
| Rockies and high desert, 5,000-8,000 ft | 6.5-7.0 | 2.5-3.0 | Thin air and cold panels help output |
| Gulf Coast and Florida | 5.5-6.0 | 2.5-3.0 | Afternoon cloud, not latitude, is the limit |
| Midwest and Northeast, 40-43° N | 5.0-5.5 | 1.5-2.0 | Anything past October needs double the panel |
| Pacific Northwest | 5.0-5.5 | 0.8-1.2 | A summer-only tool west of the Cascades |
| Northern tier and southern Canada, 48° N | 5.0-5.5 | 1.0-1.5 | Plan on a generator November to February |
Those figures assume a clean panel lying flat on the roof, which is how 90% of RV arrays are mounted. A clear day is also the assumption: heavy overcast drops output to 10 to 25% of the clear-sky figure, and a full day of rain gives you almost nothing. Sizing on your worst month means sizing on the month you will actually be parked somewhere, not on the worst month the map contains.
Step 3: why you divide by 0.7
Between the panel label and the battery you lose roughly 30%, and the losses are additive rather than dramatic. An MPPT controller converts at 94 to 97%, and a PWM controller at 65 to 80%. Wiring drop over a 20 ft run of 10 AWG costs 2 to 3%. Heat costs the most: panel output falls about 0.35% per °C above 25 °C cell temperature, and a black panel bolted flat to a roof on a 100 °F day sits near 65 °C, which is a 14% haircut before dust or a fingerprint of shade.
Add the geometry. A flat panel is aimed at the sun for perhaps two hours around solar noon and meets it at an angle for the rest of the day, which is already inside the peak-sun-hour figure but leaves nothing spare. Use 0.75 if you run MPPT, short wire runs and a clean roof. Use 0.65 if the array is flexible panels adhered to the roof with no air gap under them, because those run 15 to 25 °F hotter than framed panels on brackets.
Three RV solar builds, and who each one fits
Pick the row that matches how you camp, then adjust with the equation above. Each build is balanced: array, battery and controller are sized to each other, and undersizing one of the three wastes the other two.
| Build | Daily budget | Array | Battery bank | MPPT | Inverter | Where it runs out |
|---|---|---|---|---|---|---|
| Weekend and shoulder-season | 400-800 Wh | 200 W | 100Ah lithium (1,280 Wh) | 20A | 300-600 W or none | Two cloudy days in a row, or a compressor fridge |
| Full-time couple, 12V fridge | 1,200-2,000 Wh | 400-600 W | 200-300Ah lithium | 40-60A | 2,000 W | December north of 38°, and induction cooking |
| Air conditioning capable | 3,000-6,000 Wh | 1,200 W plus | 600Ah lithium (7.7 kWh) | 100A or two controllers | 3,000 W with a 200A BMS bank | Cooling past mid-afternoon, and cloudy heat waves |
The weekend build is the one most people should buy first. A 200 W array with a 100Ah lithium battery covers lights, the pump, phones, a vent fan, a propane fridge and a couple of furnace cycles, which is a Friday-to-Sunday dry camping trip with no generator. It costs roughly $500 to $700 in parts and takes an afternoon to mount. Kits at that size are compared on the best RV solar panels page, and the roof work is on the RV solar panel installation guide.
The middle build is where full-timers land after a season. The step from 200 W to 400 W is not about doubling comfort, it is about the compressor fridge, which alone eats more than everything in the weekend build combined and does it 24 hours a day whether the sun is out or not.
How many panels is that, and will they fit on your roof?
Budget about 6 square feet per 100 watts for a standard monocrystalline panel and about 5 for a current N-type panel, then discount your roof by 40 to 50% for what is already up there. A 100 W panel measures roughly 42 x 21 in, a 200 W panel roughly 63 x 27 in.
| Rig | Usable roof after obstructions | Realistic array |
|---|---|---|
| Camper van, 144-170 in wheelbase | 45-70 sq ft | 300-600 W |
| 20-25 ft travel trailer | 60-90 sq ft | 400-600 W |
| 30-35 ft trailer or short fifth wheel | 100-140 sq ft | 600-1,000 W |
| 40 ft fifth wheel or Class A | 150-220 sq ft | 1,200-2,000 W |
The obstructions are the real constraint, not the length. An air conditioner shroud takes about 29 x 40 in, each roof vent 14 x 14 in, and then there are the plumbing vents, the antenna, the skylight and the refrigerator vent. Panels also need clearance from anything tall enough to cast a shadow on them, so the usable area is a set of rectangles rather than a single field. Two 200 W panels in a straight run behind the AC beat four 100 W panels squeezed around it, because fewer mounting feet means fewer holes in a sealed roof.
Rigid framed panels on brackets sit about 1.5 in above the roof, and that air gap is worth 5 to 8% of output on a hot day. Flexible laminates glued flat give it away and typically last 3 to 5 years against 20 to 25 for glass panels. Monocrystalline PERC is the default at 19 to 21% cell efficiency, N-type TOPCon panels reach 22 to 23% with a gentler temperature coefficient near -0.30%/°C, and polycrystalline has largely disappeared from RV kits because the price gap that once justified it is gone.
What size battery bank matches the array?
Match the bank to a day and a half to two days of your budget, so one overcast day does not end the trip. Take daily watt-hours, multiply by the days of autonomy you want, divide by usable depth of discharge (0.9 for LiFePO4, 0.5 for AGM), then divide by 12.8 to get amp-hours.
For the 1,500 Wh couple above: 1,500 x 1.5 = 2,250 Wh, divided by 0.9 is 2,500 Wh, divided by 12.8 V is 195Ah. A single 200Ah LiFePO4 battery. The same job in AGM needs 357Ah and about 230 lb of lead. Array and bank have to grow together: 200 W of panel per 100Ah of lithium for three-season use, and 300 W per 100Ah if you camp in trees or in winter. The full worksheet, including how many nights each bank size really delivers, is on the RV batteries for boondocking page.
What size MPPT charge controller do you need?
Divide array watts by 12 and round up to the next controller size: 400 W needs 40A, 600 W needs 50A, and 800 W needs 60 to 80A. A controller sized by wattage alone gets this wrong, because the same 600 W array produces 50 amps into a 12V bank and 25 amps into a 24V bank.
The specification that strands people is input voltage, not current. Panel open-circuit voltage rises about 0.3% for every °C below 25 °C, so a panel rated at 24.5 Voc reads roughly 27 V at -10 °C on a clear February morning. Four of those in series is 108 V, which permanently damages a 100 V controller in the first minute of sun. Count the series string at cold Voc, not at the label, and pick a 150 V unit if the string is four panels deep. PWM controllers throw away 20 to 30% of what the panels make in cool weather, which is exactly the derate you just paid for panels to overcome.
Can solar run an RV air conditioner?
Not from the panels directly, and not on a normal roof for a full day. A 13,500 BTU rooftop unit draws 1,300 to 1,600 running watts and surges to 2,800 to 3,000 for half a second at compressor start. What runs it is the battery and inverter; the array only replaces what the battery spent.
The arithmetic is unforgiving. Six hours of cooling at 1,400 W is 8,400 Wh. Replacing that at 5 peak sun hours with a 0.7 derate takes 2,400 watts of panel, which is more than fits on most fifth wheels and roughly four times what a travel trailer roof holds. What 1,200 W and a 600Ah lithium bank genuinely buy is three to four hours of one air conditioner through the worst of an afternoon, with the array covering the base load at the same time and the bank recovering the next morning. Two air conditioners on solar is a generator conversation, and what size generator an RV needs covers that side.
Three hardware conditions have to be met before any of it works: a pure sine inverter of 3,000 W (or 2,000 W with a soft start such as a Micro-Air EasyStart, which cuts the surge to roughly 1,000 to 1,300 W), a battery bank whose BMS passes 200 continuous amps, and 4/0 cable on a short run from bank to inverter. A 200Ah battery with a 100A BMS shuts down the moment the compressor kicks in, no matter how many panels are on the roof.
How much solar do you need to run an RV fridge?
It depends entirely on which of the three fridge types you have, and the spread is 20 to 1. A propane absorption fridge needs 50 to 70 Wh a day for its board and igniter, so 100 W of panel keeps it running indefinitely. A 12V compressor fridge in the 8 to 10 cu ft range uses 400 to 800 Wh a day in summer heat, which is 200 to 300 W of panel in June and 400 to 600 W by October. A residential fridge on an inverter uses 1,200 to 2,000 Wh a day and needs 600 to 800 W of panel plus a 300Ah bank to survive the night.
Running an absorption fridge on its 120V electric element instead of propane is the trap: that element pulls 300 to 350 watts continuously, or roughly 7,500 Wh a day. No RV roof supports it. Keep absorption fridges on propane whenever you are off grid.
What winter, shade and a dirty roof take off the top
Every number on this page assumes clean panels in full sun. Four things break that assumption, and three of them cost more than most owners expect.
- Winter sun angle. At 40° north in late December the sun peaks about 26° above the horizon, so a flat roof panel meets it at a glancing angle all day. Tilting panels to 45-60° roughly doubles December harvest, which is why tilt brackets are worth their cost on a rig that camps north in winter and worthless on one that does not.
- Partial shade. One air conditioner shadow across the bottom cells of a panel can cut that panel’s output by more than half, because the shaded cells throttle the whole string through it. Panels wired in parallel limit the damage to the shaded panel; a series string takes the hit across all of them. Parking so the roof stays clear from 10 a.m. to 3 p.m. is worth more than another 100 W.
- Snow and dust. An inch of snow means zero output until you clear it. Desert dust and pollen film build up to a 5 to 10% loss over a few weeks, and a rinse with a hose recovers it.
- Heat. Output drops roughly 0.35% per °C of cell temperature above 25 °C, so the 100 °F afternoon when you most want power is the afternoon the array is down 12 to 15%.
Sizing for the worst realistic day rather than the average day is the difference between a system you never think about and one you argue with. The rest of the power system, from converters to inverters to shore power, is mapped out in the power and electrical guides.
FAQ
Frequently asked questions
How many solar panels do I need for a 50 amp RV?
Service rating and solar size are unrelated. A 50 amp connection describes two 120V legs at the pedestal, not consumption. Size the array from watt-hours: a 50 amp coach with residential appliances typically runs 3,000 to 6,000 Wh a day, which is 1,200 to 2,000 watts of panel and a 600Ah lithium bank, but the same coach camped without air conditioning may only need 600 watts.
Will 400 watts of solar run an RV?
Yes for a rig using 1,200 to 1,600 Wh a day in summer: a 12V compressor fridge, lights, water pump, vent fan, laptops and phones. At 4.5 peak sun hours and a 0.7 derate, 400 W returns about 1,260 Wh a day. It will not cover a residential fridge, induction cooking or any air conditioning, and it will fall short from November to February above 40° north.
How long does 200 watts of solar take to charge a 100Ah battery?
From 50% to full, roughly one clear summer day. A 100Ah lithium battery at 50% needs about 640 Wh; 200 W of panel at 5 peak sun hours with an MPPT controller delivers about 700 Wh. In December at 2 peak sun hours the same charge takes two and a half to three days, which is why winter camping sizes the array.
Is it better to add panels or add battery?
Add battery if you run out overnight and the array reaches full absorption by early afternoon. Add panels if the controller is still in bulk charge at 4 p.m. and the bank never reaches 100%. A charge controller app answers this in two days of camping, and one of the two upgrades is usually wasted money.
Do RV solar panels work on cloudy days?
They produce 10 to 25% of their clear-sky output under heavy overcast and 40 to 60% under thin high cloud. A 400 W array that makes 1,400 Wh on a clear day makes 150 to 350 Wh in steady rain, which covers lights and phones and nothing else. Two overcast days back to back is what battery capacity exists for.
How accurate is an RV solar calculator?
The equation is exact; the inputs are where the error lives. Peak sun hours is a monthly average, so a wet week inside a 5.2 hour month delivers nothing like 5.2 hours a day. Daily watt-hours is the larger error, and it runs one way: owners underestimate their own use by 20 to 40% because a compressor fridge's duty cycle and an inverter's idle draw are invisible until a shunt monitor counts them. Type a measured number in and the array figure becomes a purchase decision instead of a guess.
Does the calculator include charge controller and wiring losses?
Yes, inside the 30% loss figure: MPPT conversion at 3 to 6%, voltage drop over the wire run at 2 to 3%, hot panels on a black roof at 10 to 15%, dust, and battery charge acceptance. It does not include shade, snow or a panel you never rinse. The coffee maker and microwave rows carry their own 12% inverter conversion loss inside the watts shown, because that current leaves the battery too. Drop the slider to 25% only for MPPT on framed panels with short 10 AWG runs and an air gap underneath.
Can I add more solar panels to an existing array later?
Yes, if the charge controller has the headroom and the new panels match the electrical characteristics of the old ones. Mismatched panels in series pull the string down to the weakest one; mismatched panels in parallel behave independently and cost less output. The cheapest expansion path is a controller sized for the array you will end with, not the one you start with.
RV owner since childhood trips in a Class C. Mr RV Expert is where I write down what actually works after fixing, replacing and testing the gear myself.
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