Solar for a travel trailer

A lot of travel trailers now ship an 8–10 cu ft 12 V compressor fridge, not a propane fridge. That single appliance uses 660 Wh a day in the RVWatt library — more than a small van fridge — so a trailer’s solar needs are closer to a modest motorhome than to a 50–65 L cooler. The example below is built from that library, not a hidden preset, and you can open it in the calculator with the loads already filled in.

A warm-season weekend trailer, 1,029 Wh a day

This example is an 8–10 cu ft 12 V fridge (660 Wh), interior lights at 40 W for 4 hours (160 Wh, the same lighting figure as the Class C preset), a water pump (18 Wh), a 32-inch TV for 2 hours (111 Wh from the battery, including inverter loss), two phones (60 Wh), and 20 Wh of inverter idle while the TV is on. Total: 1,029 Wh a day.

Place and season	Design month	Solar needed	Array	Battery, 2 days LiFePO4 at 12 V	Controller / inverter
Moab, UT, May–October	October, 4.34 sun hours	313 W	2 × 200 W (400 W)	214 Ah (2,573 Wh)	50 A MPPT, 150 W inverter
Denver, CO, May–October	October, 3.98 sun hours	342 W	2 × 200 W (400 W)	214 Ah (2,573 Wh)	50 A MPPT, 150 W inverter
Seattle, WA, May–October	October, 2.28 sun hours	596 W	3 × 200 W (600 W)	214 Ah (2,573 Wh)	70 A MPPT, 150 W inverter

The 150 W inverter is the calculator’s minimum for a 50 W TV with 25% headroom, rounded up to the next standard size. It is tight. If you might add a laptop or a phone charger on AC, a 300 W or 500 W pure sine inverter is a more practical buy; the calculator will follow whatever loads you add.

A 400 W solar kit with a 200 Ah lithium battery is a common factory or aftermarket starting point (for example, some Grand Design and Jayco packages land in this neighborhood). In Moab or Denver from May to October it covers this example’s solar (313–342 W needed) and is just shy of the 214 Ah two-day battery number — fine for a sunny weekend, short if you want two full cloudy days. In Seattle that season you want closer to 600 W of panels.

Open this trailer example in Denver, May–October Same trailer in Seattle

If you add a CPAP or the furnace

A CPAP at the library’s conservative 40 W for 8 hours adds 320 Wh. In Denver from May to October the daily total becomes 1,349 Wh, solar needed rises to 448 W (three 200 W panels), and the two-day battery becomes 281 Ah. A propane furnace blower at 80 W and 50% duty for 8 hours is another 320 Wh; in shoulder season that same trailer is 1,669 Wh a day, 554 W of solar and 348 Ah of lithium in Denver (April–October still designs to October’s 3.98 sun hours).

Add a CPAP to the Denver example

What this is not

This is not the Class C motorhome preset. That preset also uses the 8–10 cu ft 12 V fridge (660 Wh), but it adds a furnace, TV, CPAP, laptop, microwave and coffee maker, for 2,542 Wh a day. In Denver from April to October that needs 844 W of solar and 530 Ah of lithium — a much larger system. If your trailer has those loads, start from the Class C preset and remove anything you do not run, or add them to the example above.

It is also not a fifth wheel with a 120 V residential fridge. That fridge alone is about 1,400 Wh from the battery plus inverter idle, before lights and internet. Use the fifth-wheel preset in the calculator if that is your rig.

If your trailer still has a propane absorption fridge, you can remove the 12 V fridge from the list and your daily energy will drop by 660 Wh. Do not leave it in “just in case” or you will oversize the system.

Frequently asked questions

How much solar does a travel trailer need?

For a common warm-season setup with an 8–10 cu ft 12 V fridge, lights, a pump, a TV and phones (1,029 Wh a day), the calculator needs 342 W of solar in Denver from May to October, or 313 W in Moab — two 200 W panels — and about 214 Ah of lithium for two days. In Seattle that season it needs 596 W. A CPAP or a furnace adds about 320 Wh each and pushes the array up.

Is a factory 200 W or 400 W kit enough?

A 200 W standard roof kit is usually battery maintenance, not multi-day boondocking, once you have a large 12 V fridge. A 400 W kit covers this warm-season Denver or Moab example on solar, with a 200 Ah battery a little short of two full cloudy days. It is light for Seattle in October, and light if you also run a CPAP or the furnace.

What if my trailer still has a propane fridge?

Then you can leave the 8–10 cu ft 12 V fridge off the list and drop 660 Wh a day. Many newer trailers and Class C motorhomes have switched to 12 V compressor fridges, which is why the Class C preset now includes that load. Remove it in the calculator if yours still runs on propane.

Related guides

Safety: high-current DC is dangerous. A 12 V battery bank can deliver thousands of amps into a short circuit, enough to melt tools, weld rings and watches to terminals, ignite insulation and start a vehicle fire in seconds. Lithium and lead-acid batteries can also vent, burn or explode if overcharged, damaged or charged outside their temperature limits. Remove jewelry, use insulated tools, disconnect the battery before working, fuse every positive conductor as close to the battery as practical with a fuse rated for the battery's short-circuit current (often a Class T for lithium banks), use properly crimped lugs and pure copper cable, and secure batteries against movement. If you are not confident, hire a qualified RV or marine electrician. RVWatt provides estimates only; see our Terms of Use.

These figures are planning estimates from typical appliance ratings and NASA monthly sun averages for a flat, horizontal panel. Your real use will differ with heat, shade, dirty panels and how you actually live in the rig. Follow your equipment manuals and have a qualified installer check high-current wiring.