Powering AC unit built into travel trailer with solar?

All the calculations seem to be expecting to cool the whole RV, my plan is to use an inverter based 48V unit just for the bedroom, if it's above 80 when I'm going to go to bed start the AC 2 hours before and cool down the bedroom. With 2-3kW of solar panels and 10-15kWh of batteries this should be easy. It'll be about $12-15k with solar charge controller, Victron inverter, smart shunt, and misc parts.

pianotuna wrote:

Gdetrailer wrote:
No matter what "batteries" you use, they all need to be recharged as soon as possible, Lithiums are not immune to this and are not an exception if you want to get the most life for the money you spend.

I thought this was there main claim to fame???

Lithiums do a much better job than FLA, AGM or gel, but they are not 100% immune to some degradation if you continually allow them to sit in a partial discharge.

Some of the claim to fame is the not to charge to 100% in order to store them. Reality is you don't really control the charge, the BMS does that. Allow them to store at too low of a charge and you take a chance the BMS will disconnect (BMS has low voltage disconnect built in and most BMS once that is tripped are not able to be reconnected) and now you have an expensive door stop. The Lithium battery pack will have a bit more capacity built in, often about 10% more capacity, but you typically cannot use that capacity due to BMS. The BMS stops you from charging or discharging more than 90% of the battery, good quality BMS will prevent you from using more that extra capacity. Basically that extra capacity is reserved for the BMS and also not allow battery to fall out of normal and stable state of charge range.

I have had some small Lithium batteries swell after being stored in a partial discharge state (inactive for 6 months or more and were not charged until the BMS stopped charging before storing).

Gdetrailer wrote:
No matter what "batteries" you use, they all need to be recharged as soon as possible, Lithiums are not immune to this and are not an exception if you want to get the most life for the money you spend.

I thought this was their main claim to fame???

spoon059 wrote:
Couple of thoughts... I suggested a mini-split which would draw significantly less than 21 amps or 1000 watts. From what I am reading a 12K mini-split pulls about 4 amps at maximum draw and throttles down substantially from there. I've seen plenty of Youtube videos of people running mini-splits off 8 panel solar systems with larger battery banks. Its doable, likely for about the cost of a typical onboard generator.

I simply don't want to pay those prices to make it silent, so I'm leaning back towards a $1200 Honda 2200 for the occasional dispersed camping.

But, it is absolutely possible with a reasonable solar array and not nearly as expensive as your model.

The difference with inverter based mini-split units is they can adjust the draw to the output desired.

So if for a given rig at a given temp, it takes an average of 7500btu to achieve the desired temp:
- A 15k btu mini-split will draw power enough to put out 7500btu but run continuously.
- A 15k old style roof mount will draw power enough to put out 15k btu but run around 50% of the time.

Net effect is you need roughly the same amount of stored energy. Mini-split units might be a slightly more efficient but not a chance it's going to put out the same cooling btu at a 1/3 the power consumption.

spoon059 wrote:
Couple of thoughts... I suggested a mini-split which would draw significantly less than 21 amps or 1000 watts. From what I am reading a 12K mini-split pulls about 4 amps at maximum draw and throttles down substantially from there. I've seen plenty of Youtube videos of people running mini-splits off 8 panel solar systems with larger battery banks. Its doable, likely for about the cost of a typical onboard generator.

I simply don't want to pay those prices to make it silent, so I'm leaning back towards a $1200 Honda 2200 for the occasional dispersed camping.

But, it is absolutely possible with a reasonable solar array and not nearly as expensive as your model.

Doubtful.

Looked at a MR Cool 12K BTU mini split which uses inverter technology compressor, calls for minimum 14 ga wire which would be a "15A" circuit..

They are claiming 7.8-10 BTU/watt for efficiency in their brochure HERE

4A at 120V is 480W and at the max of 10 BTU per watt that gets you 4800 BTUs worth of cooling.

You would need to find a mini split well under 9K BTU that might get you closer to that magical "4A" at 120V range.

4A at 120V is most likely a very small window air like 5K BTU if it was using inverter technology compressor and low fan speed.. But unless you have a small TC or sub 17ft TT, 5K BTU isn't going to cut it in 90F+ temps with high humidity.

Lets face it, in most RVs even a 13.5K BTU A/C barely gets it done.

On edit..

Found a Bosch 5K mini split that runs on 120V HERE (out of stock of course).

So, there is some very small 5K BTU mini splits out there, but in most RVs 5K BTU isn't going to be of much help.

You almost need to check on sizing the system, found a guide on sizing a mini split (or any A/C for that matter)HERE

"To determine the size of a mini split, calculate the square footage of the room and multiply it by 25 to obtain the cooling capacity needed in BTU. Then, select the nearest mini split size based on the calculated BTU.

For instance, a 500 sqft room requires a 12000 BTU mini split because 500 sqft multiplied by 25 is 12500 BTU and the nearest mini split size is 12000 BTU.

As a rule of thumb, we use about 25 BTU per square foot to calculate the cooling capacity needed for a room. Because mini splits have several fixed capacities, we have to select the one that matches our needs.

But, we don't always need to use a rule of thumb of 25 BTU per square foot. Generally, anywhere between 20-30 BTU per square foot is acceptable to be used to calculate the capacity needed for room air conditioners such as a mini split.

However, the rule of thumb of 20-30 BTU per square foot is meant for insulated rooms or houses.

So, if your room or house is not insulated or, the insulation is known to be in poor condition, you need to double the rule of thumb figure or use 40-60 BTU per square foot to calculate the capacity needed thereby choosing the right mini split size."

RVs are very poorly insulated (R3 or less in walls and roof and R2 or less in the floor) and have single pane windows so landing on the oversized system typically is your better choice.

In my case, I have a 26ft TT, using 60 BTU per square ft gets me 12,480 BTU.. The 13.5K BTU roof air barely got the job done.. Now I have two Window units placed in cabinets.. 10K BTU for the main area and 6.5K BTU for our master bedroom.. Now we no longer lack for cooling.

Couple of thoughts... I suggested a mini-split which would draw significantly less than 21 amps or 1000 watts. From what I am reading a 12K mini-split pulls about 4 amps at maximum draw and throttles down substantially from there. I've seen plenty of Youtube videos of people running mini-splits off 8 panel solar systems with larger battery banks. Its doable, likely for about the cost of a typical onboard generator.

I simply don't want to pay those prices to make it silent, so I'm leaning back towards a $1200 Honda 2200 for the occasional dispersed camping.

But, it is absolutely possible with a reasonable solar array and not nearly as expensive as your model.

Lantley wrote:


We are not talking an industrial setting or 15K active devices.
What does that have to do with RV's? And you think I'm on some stuff...LOL
You are correct you would have to cover the roof in panels.
But believe or not solar enthusiast are covering their roof in panels.
The roof space is available. The genset compartment of my RV could hold 10-12 batteries easily..
I'm not trying to run A/C 24/7 on batteries. I don't need to.
I don't run my A/C with my Onan 24/7.
Running it overnight would be my goal and recharge during the day.
Worst case one would have a 2000 watt genset available for cloudy days...LOL.
I undesrstand solar A/C is not perfected, but its not a pipe dream either.
Back in 2012 when I factory ordered my genset solar A/C was a pipe dream. However in 2022 it is a viable option.
Give it 10 more years and it will likely be a OEM factory available option.
The one thing I can be sure of is the technology won't stand still.
I've seen enough game changing technology in my lifetime, especilally the last 20 years. That solar powered RV A/C is not that mind boggling at this point.

OK, so, lets do some "back of the napkin math" for real world right now.

No matter what "batteries" you use, they all need to be recharged as soon as possible, Lithiums are not immune to this and are not an exception if you want to get the most life for the money you spend.

Solar only charges when there is sufficient sunlight strength, just because you have daylight, does not mean you are getting a full charge or even a charge at all. The further you are away from the Equater, the less Insolation you get. In the USA that means about 5 peak charging hrs provided you have no clouds and no grey overcast weather.

Please, follow along very closely.

Running RV A/C from solar/battery

From a 24DC RV A/C manufacturer I found, their A/C is 12,000 BTUs, draws 21A max or 1,008W
They recommend 2,500W in panels for 24 hr operation. That is 2.5x the max running watts.

13,500 BTU RV A/C draws 13A at 120V or 1560W.
1560W x 2.5=3,900W, to make things easier we will round this to 4,000W or 40 100W panels
13A at 120V is roughly 130A at 12V, run that for 1 hr is 130Ahr for each hr run.
24hrs=3120Ahr,
But with solar, 3 days worth of battery capacity is used to cover bad weather days.
3 x 3120 = 9360 Ahr or 93.6 100Ahr batteries (we will round that to 94 100Ahr batteries)

100W solar panels 40 x 20 (we will round this to 4’ x 2’ or 8 square feet each panel for easy math), weigh about 15 lbs each, $1 per watt cost= 100W panel cost at $100.
40 x 8 = 320 square feet of roof or equivalent to a RV roof of 8ft wide and 40ft in length.
40 x $100 = $4,000
40 x 15 = 600 lbs

Best lithium battery price I can find is $269 for 100Ahr, needs roughly .5 square ft per battery, life cycles rated 3,000 to 7,000, weight is 26 lbs each
We need 94 100Ahr batteries, roughly 47 square ft of storage space.
94 x $269 = $25,286
94 x 26 lbs = 2,444 lbs
3,000 cycles/365 = 8.2 yrs life (I have found through experience that most lithium battery manufacturers way overstate the life cycles)

System cost for panels and batteries
$4,000 + $25,286 = $29,286
System added weight
600 lbs + 2,444 lbs = 3,044 lbs

But, wait, that does not include solar panel controllers, wiring or inverter costs, not to mention will not fit on sub 40ft RV roof without some exotic hinge/drawer system and a 40ft RV will need more than one 13.5K BTU A/C to keep it in some sort of comfortable range putting you into a solar and battery capacity deficit.

I can buy a lot of gas for a $250 generator even at $5 per gallon..

Most RVrs are not going to recoup or break even on that kind of cost.

So, unless you are 100% full timer the math doesn't add up to make good financial sense.

Lantley wrote:
While we can certainly debate the size of a typical RV.
Once installed the system is no more massive than my built in Onan 5500 lp.
While most bumper pull RV's do not have built in gensets. There are plenty of RV's that do have built in gensets that have the space to accomodate solar capable A/C.

If you are talking about an hour or two for a lunch stop, sure.

If you are talking about finding a nice boondocking spot for a week and the weather is hot for multiple days...not a chance.

One overnight run should be doable with a large battery. Most likely need to plug in the second night or will be limited run time based on installed solar and limited alternator charging.

Either way the OP is long gone.

All that is needed is some "wings" or awnings that are nested above the roof.