You've decided you're done with generator noise and campground hookups. You want to pull off a forest road near Tarryall Reservoir, park for four days, and run your rig entirely on solar. The only question standing between you and that trip is figuring out how much solar you actually need, and that question has a real answer that isn't "as much as possible."
- Bigger is not always better: Oversized solar arrays paired with undersized batteries waste money and still leave you short on cloudy afternoons.
- Start with your loads: Calculating daily watt-hours consumed is the only reliable starting point for any solar system design.
- Battery and panel wattage must match: A large panel array drains quickly into a small battery bank, and a massive battery bank barely charges from a tiny panel array.
- Chemistry changes the math: Lithium batteries discharge deeper and charge faster, which meaningfully shrinks how many panels you actually need compared to AGM.
- Colorado adds real variables: High altitude, shorter winter sun hours, and afternoon cloud buildup all affect how much usable solar energy your panels produce on a real trip.
- Custom sizing beats online calculators: Generic calculators miss your specific loads, battery chemistry, and the actual conditions where you camp.
1. Why "Bigger Is Better" Is the Wrong Way to Think About Solar Sizing
Walk into any RV forum and you'll find the same advice repeated as gospel: just add more panels. It feels logical. More solar means more power, and more power means you'll never run out. But that instinct leads a lot of RV owners to spend two or three times what they should, or to end up with a system that still doesn't perform the way they expected.
The problem is that solar panels only do half the job. They generate power when the sun is out, but your rig runs on power stored in batteries. If your battery bank can't hold what your panels can produce, the extra wattage is wasted. Conversely, if your battery bank is massive and your panel array is small, you'll drain the bank faster than the sun can refill it. Solar sizing is really a balancing act between three things: how much power you use, how much you can store, and how fast you can replenish what you spend.
The real cost of over-building
An oversized system isn't just expensive upfront. It's heavier, it puts more stress on your roof structure and mounting hardware, and it can actually overload a charge controller that wasn't sized to handle the input. Some RV owners add a second 400-watt panel array to a system built around a 30-amp MPPT controller, then wonder why their batteries still aren't charged by noon. The controller was never rated to handle that much input, so most of the potential energy was simply clipped and lost. Victron Energy's MPPT charge controllers are sized by both panel wattage and battery voltage for exactly this reason.
Why under-building is just as common
On the other side, plenty of RV owners buy a small "starter" kit because they just want to keep the lights on and charge their phones. Then they add a residential fridge, then a CPAP machine, then a second battery. Suddenly the 200-watt panel on the roof can't keep up, and they're running the generator every afternoon anyway. The fix at that point is usually replacing the charge controller and rewiring, which costs more than sizing correctly from the start would have.
2. How to Calculate Your Actual Daily Power Draw
Before you pick a single panel or battery, you need a number: your daily watt-hour consumption. Everything else in the system design flows from that number.
The process is straightforward. Make a list of every 12-volt and 120-volt device you run during a typical camping day. For each device, note its wattage (usually on a label or in the manual) and how many hours per day you run it. Multiply those two numbers together to get watt-hours for that device, then add up all the devices. That total is your daily load.
Building your load list
The loads that catch people off guard are the ones that run continuously or cycle frequently. A residential refrigerator might draw 150 watts when the compressor kicks on, but if it cycles for roughly eight hours per day, it's consuming around 1,200 watt-hours on its own. A CPAP machine with a heated humidifier can add another 400 to 600 watt-hours overnight. Lighting, device charging, and a water pump are relatively minor by comparison. Add in a rooftop air conditioner and you're in a completely different category, because running AC on solar requires serious battery capacity and often isn't practical without a generator assist.
Adding a realistic buffer
Once you have your raw daily load number, add 20 to 25 percent. That buffer accounts for inverter efficiency losses, wiring resistance, partial cloud cover that reduces panel output during peak hours, and the honest reality that camping days don't always go the way you planned. If your calculated load is 2,000 watt-hours per day, design your system to deliver at least 2,400.
3. Battery Capacity vs. Solar Panel Wattage: Matching the Two Correctly
Once you know your daily load, you need to work out two related numbers: how much battery capacity you need to store a day's worth of energy (with some reserve), and how much panel wattage you need to reliably recharge that battery bank each day. These two numbers have to be in balance, and that balance depends on your camping style and how many days of autonomy you want.
Sizing the battery bank first
Your daily load and your autonomy target together determine your minimum battery capacity. If you consume 2,400 watt-hours per day and want two days of autonomy, you need at least 4,800 watt-hours of usable battery storage. Note the word "usable" - this is not the same as total capacity, because no battery chemistry should be fully discharged.
Sizing the panel array to match
With your battery capacity established, your panel array needs to be large enough to recharge the bank within the available solar hours of a typical day. Colorado's Front Range averages roughly five to six peak sun hours per day in summer. If you need to put 2,400 watt-hours back into your batteries each day and you have five usable sun hours, you need a panel array capable of generating at least 480 watts under real-world conditions. Real-world output is typically 80 to 85 percent of rated wattage due to heat, angle, and wiring losses, so you'd want a rated array of 600 watts or more to reliably meet that target.
Charge controller sizing
The charge controller bridges your panels and your battery bank. An MPPT controller needs to be rated for both the panel array's maximum input voltage and the total watt output you're feeding it. Installing a controller that's undersized for the array clips your charging capacity, which defeats the purpose of having a larger panel array.
4. Lithium vs. AGM and How Battery Chemistry Changes Your Sizing Math
Battery chemistry is one of the most consequential decisions in a solar build, and it directly changes how you size every other component. The two most common choices for RV solar systems today are AGM and LiFePO4 lithium iron phosphate.
The core difference comes down to depth of discharge and charge acceptance rate. AGM batteries should typically not be discharged below 50 percent of their rated capacity without shortening their lifespan significantly. LiFePO4 batteries can be safely discharged to 80 percent or deeper. That single difference means a 200-amp-hour lithium battery delivers roughly 160 usable amp-hours, while a 200-amp-hour AGM delivers only around 100.
How lithium changes your panel math
Lithium batteries also accept charge faster. An AGM battery's charge acceptance rate slows significantly as it approaches full, which means your panels spend time producing power the battery can't absorb efficiently. A lithium bank charges at a consistent high rate until it's nearly full, then tapers off quickly. In practical terms, a lithium bank gets to 100 percent faster from the same panel array.
AGM still makes sense in some builds
AGM isn't obsolete. It costs considerably less upfront, handles cold temperatures reasonably well, and doesn't require a lithium-compatible charge controller profile. For an RV owner who camps primarily at established campgrounds with shore power and only occasionally goes off-grid, AGM may deliver a better return on investment. For serious boondockers or full-timers, lithium's cycle life and usable capacity advantages typically justify the higher initial cost over the life of the system.
| Attribute | LiFePO4 Lithium | AGM Lead-Acid |
|---|---|---|
| Usable depth of discharge | ~80% | ~50% |
| Cycle life (typical) | 2,000+ cycles | 300-500 cycles |
| Weight per usable kWh | Lighter | Heavier |
| Charge acceptance rate | Fast, consistent | Slows as charge rises |
| Cold temperature performance | Needs low-temp protection | Handles cold well |
| Upfront cost | Higher | Lower |
5. Colorado-Specific Factors: Altitude, Sun Hours, and Seasonal Variation
Generic solar sizing calculators use national average sun-hour data and flat-terrain assumptions. If you're camping in Colorado, those averages don't tell the whole story.
The good news is that Colorado is genuinely one of the better states for solar production. The National Renewable Energy Laboratory ranks Colorado among the top states for solar irradiance, and higher altitude means thinner atmosphere and more intense solar radiation reaching your panels on clear days. On a bluebird morning at 9,000 feet, your panels will often outperform their rated wattage under standard test conditions.
The afternoon cloud problem
The caveat is Colorado's afternoon weather pattern. From late spring through early fall, moisture builds over the mountains and often produces afternoon thunderstorms or heavy cloud cover by 2 to 4 p.m. If your peak solar window runs roughly 9 a.m. to 4 p.m., you may only get reliable full-output hours in the morning. Systems sized on a full five- or six-hour peak sun assumption can come up short when cloud buildup cuts that to three or four hours on most days.
Winter sun hours drop significantly
If you camp year-round in Colorado, seasonal variation matters a lot. Summer peak sun hours on the Front Range can reach six or more. Winter drops that to three to four hours, and lower sun angles mean panels mounted flat on an RV roof capture less energy per hour. A system sized for summer boondocking may leave you short in a November trip to Pueblo Reservoir.
Elevation and temperature effects on batteries
At higher elevations, temperatures swing more dramatically between day and night. LiFePO4 batteries with built-in low-temperature protection circuits will cut off charging when the cells are too cold to safely accept current, which matters on cold September mornings above 10,000 feet.
6. Common Sizing Mistakes That Lead to Underpowered Systems
The most common mistake is treating solar panel wattage as the only number that matters. Owners compare systems by panel count and wattage while ignoring battery capacity, charge controller rating, and wiring gauge.
Forgetting inverter losses
Running 120-volt AC loads through an inverter introduces conversion losses, typically in the range of 10 to 15 percent. If your daily load calculation was built around AC wattage numbers, you need to account for what the inverter draws to produce that AC power. Skipping this step means your solar system is always working harder than your math said it would.
Using peak wattage instead of average wattage
A blender or coffee maker might draw 1,000 watts for two minutes. A residential fridge compressor might draw 150 watts but run intermittently. Using peak draw numbers for everything overstates your system requirements. Using average or duty-cycle-corrected numbers gets you to a more accurate daily load total.
Ignoring wire gauge and voltage drop
Solar energy lost to resistance in undersized wire between the panels and the charge controller is wasted before it ever reaches your batteries. Long wire runs between roof-mounted panels and an interior controller need to be sized for the current they carry. For most RV solar builds, a certified installer will calculate voltage drop as part of the design.
7. Getting a Custom Sizing Assessment from The RV Smith
Running through this math yourself is genuinely useful. It teaches you what your rig actually needs and helps you have a better conversation with whoever builds your system. But the math has variables that a general article can't account for: your specific appliances, your actual camping patterns, how your existing electrical system is wired, and what your roof can physically support in terms of weight and mounting footprint.
The RV Smith is the only Victron-certified RV solar installer in Colorado Springs, and the shop designs systems based on your real load profile, not a generic template. Every build uses Victron Energy components because of their reliability, their depth of configuration options, and the quality of the data they provide through the VictronConnect app.
What a sizing consultation covers
A proper sizing conversation starts with your load list. From there, the assessment covers battery chemistry options, charge controller selection, inverter sizing if you run AC loads, and roof layout for panels. The goal is a system that runs your specific adventure, not a spec sheet that looks impressive at the RV show.
Systems The RV Smith builds and installs
Current builds range from 200-watt weekend systems with a compact lithium bank for light boondocking to 1,800-watt builds with large LiFePO4 battery banks designed to run residential fridges, air conditioning support, and full workstation setups for remote workers. Customers have driven from Albuquerque for this work because there isn't a comparable Victron-certified RV solar installation shop in the region.
FAQs
How many solar panels do I need for a travel trailer or fifth wheel?
It depends entirely on your daily load. A weekend camper running basic lights, a fan, and device charging might be well-served by 200 to 400 watts. A boondocker running a residential fridge, CPAP, and a laptop setup typically needs 600 to 1,000 watts or more. Calculate your daily watt-hour consumption first, then size panels to recharge your battery bank within your available daily sun hours.
Can I add solar to my RV without replacing my existing batteries?
Yes, but your existing battery capacity sets the ceiling for how much solar actually helps you. If you have two 100-amp-hour AGM batteries with 50 percent usable capacity, adding 600 watts of panels won't give you more storage. It'll just charge what you have faster. For most boondocking goals, a solar upgrade works best when paired with a battery bank sized to match.
Is lithium worth the extra cost for RV solar in Colorado?
For serious boondockers or full-timers, usually yes. Lithium's deeper usable discharge, faster charge acceptance, and longer cycle life translate to a smaller, lighter system that performs better over time. For occasional campers who mostly use shore power, AGM may offer a better return on the upfront investment.
How does Colorado altitude affect RV solar panel output?
Higher altitude means less atmospheric filtering and more intense solar radiation, so panels often produce at or above their rated output on clear days. The trade-off is Colorado's afternoon cloud and storm pattern, which can cut effective peak sun hours shorter than national averages suggest. Sizing in a buffer of 20 to 25 percent over your calculated minimum accounts for this variability.
What is the difference between an MPPT and PWM solar charge controller?
MPPT (Maximum Power Point Tracking) controllers extract more energy from your panels across a wider range of conditions and are significantly more efficient, especially in the partial-shade or cooler-temperature conditions common at Colorado elevations. PWM controllers are simpler and less expensive but waste a meaningful percentage of available panel output. For any serious off-grid build, MPPT is the right choice.
Conclusion
Sizing an RV solar system well comes down to one discipline: starting with what you actually use, not with what looks impressive on a spec sheet. Calculate your real daily load, match your battery capacity to your autonomy needs, select your chemistry based on how you camp, size your panel array to reliably refill that bank within Colorado's real sun-hour window, and account for the altitude and afternoon weather variables that make Front Range camping different from the national average.
The RV Smith serves RV owners across Colorado Springs and El Paso County with custom Victron-based solar installation designed around these exact variables. Whether you're planning your first off-grid build or retrofitting a system that's leaving you short, the shop has the certifications and the hands-on Colorado camping experience to get the sizing right.
Schedule Service with The RV Smith to start with a real load assessment and get a solar system sized for the actual trips you take, the specific rig you own, and the Colorado conditions where you camp.
