Help Designing an upgradable rv solar system...go big or go home, right?

[CleanEnergyGuy]

Hi, My wife and I just bought a 2002 Fleetwood Terra Class A motor home that we plan on going boon docking for extended periods of time. Sometimes it will be in hot, muggy environments. So, I want to build a system that could eventually run the AC off of the batteries.

After watching Will's videos, I'm thinking that I would like to build a 48 Volt system starting with (8) 200 watt rigid solar panels and (4),100ah Battle Born lithium phosphate batteries wired in series. I'm planning on adding additional panels and batteries at a later time as I can afford them.

The AC unit that is currently up there is a Carrier and I believe that it is a 13.500 btu unit which should take 2750 watts to start up and 1250 watts to run. I plan on installing a soft start so if anybody has any opinions on that, your input would be greatly appreciated.

Anyway, what do you guys think? Your help is appreciated!

Bob

 

[snoobler]

Hi Bob.

Powering RV A/C is very challenging.

You should really use link #1 in my signature to conduct an energy audit of what you want to power, how much power it uses and how long you want to run it.

Then keep link #5 handy for when you want to find out how much sun is available for a particular location. Link #6 is useful if you want to use lat/long coords or see what an existing system can produce.

I have a same size Dometic, and mine uses 1400-1500W. You also have to figure in the DC-AC conversion losses... 1250 *1.15 = 1437W. 2750W surge is if you're lucky. You can get that with a soft start, but it's well above that regardless of what specs and the interwebz says.

Soft starts are a very good idea and worth the $300.

You'll need a 3-4kW inverter - preferably a low frequency type that can handle power surges.

Not also that your 900-1000W microwave will actually use 1500-1600W - they're horribly inefficient.

4 * 12.8 * 100 = 5120Wh - about enough to run your AC and ONLY your A/C for 3 hours.

Our off-grid compound is 2X RVs and a 40' shipping container with 3kW of panels and 10kWh of lead acid providing off-grid "shore power". In AZ summer sun, we can run ONE A/C unit off solar for about 8-10 hours with only about a 10% dip into the batteries in the afternoon.

1600W of solar + batteries might get you about 6 hours of A/C run time, but you'll be out of juice.

Consider completely ditching your existing converter/12V system and feeding your DC bus with a 48-12V converter. The conversion from 48VDC to 120VAC to 12VDC is only about 75% efficient.

If you have a propane fridge, you MUST run it on propane. It will consume massive amounts of AC power - almost your entire battery bank in a 24 hour period.

Consider leaning heavily on the genny, and try to utilize it at 50% or greater consumption - they're more efficient there.

Consider a smaller deployable array you could setup externally while you have the RV parked in the shade - 8X200W on the roof in the shade and 4X 200W 50' away sitting in the sun. 800W is quite a bit when you don't need A/C. If you're going to be there awhile, 30 minutes of setup and tear-down isn't a big deal.

 

[Bob B]

Instead of spending money on making your existing A/C easier to start I would look into replacing it with a much more efficient mini split. Those are getting better and better. This is on the dream sheet for my RV.

 

[snoobler]

I almost went there too. A typical 1 ton unit goes for about $1000 and uses 500W peak with a lower run power once set temp is reached.

 

[Dzl]

As others have mentioned an efficient minisplit would be a good investment, 12,000 BTU units can touch 30 SEER nowadays, though most are not quite so efficient. However, one issue with this is you need to get a bit more creative with the install, since to my knowledge, none use the rooftop form factor popular with RV's.

 

[CleanEnergyGuy]

Hi Bob.

Powering RV A/C is very challenging.

You should really use link #1 in my signature to conduct an energy audit of what you want to power, how much power it uses and how long you want to run it.

Then keep link #5 handy for when you want to find out how much sun is available for a particular location. Link #6 is useful if you want to use lat/long coords or see what an existing system can produce.

I have a same size Dometic, and mine uses 1400-1500W. You also have to figure in the DC-AC conversion losses... 1250 *1.15 = 1437W. 2750W surge is if you're lucky. You can get that with a soft start, but it's well above that regardless of what specs and the interwebz says.

Soft starts are a very good idea and worth the $300.

You'll need a 3-4kW inverter - preferably a low frequency type that can handle power surges.

Not also that your 900-1000W microwave will actually use 1500-1600W - they're horribly inefficient.

4 * 12.8 * 100 = 5120Wh - about enough to run your AC and ONLY your A/C for 3 hours.

Our off-grid compound is 2X RVs and a 40' shipping container with 3kW of panels and 10kWh of lead acid providing off-grid "shore power". In AZ summer sun, we can run ONE A/C unit off solar for about 8-10 hours with only about a 10% dip into the batteries in the afternoon.

1600W of solar + batteries might get you about 6 hours of A/C run time, but you'll be out of juice.

Consider completely ditching your existing converter/12V system and feeding your DC bus with a 48-12V converter. The conversion from 48VDC to 120VAC to 12VDC is only about 75% efficient.

If you have a propane fridge, you MUST run it on propane. It will consume massive amounts of AC power - almost your entire battery bank in a 24 hour period.

Consider leaning heavily on the genny, and try to utilize it at 50% or greater consumption - they're more efficient there.

Consider a smaller deployable array you could setup externally while you have the RV parked in the shade - 8X200W on the roof in the shade and 4X 200W 50' away sitting in the sun. 800W is quite a bit when you don't need A/C. If you're going to be there awhile, 30 minutes of setup and tear-down isn't a big deal.

Wow! Thank you very much for your reply! Unfortunately, we had a family celebration and I had a couple, so I'll have to revisit your ideas in the morning! I was particularly appreciative of your point about removing the converter...I just replaced it because the old one was bad and I just wanted to get the thing going...but, I was curious if it could be replaced.

Anyway, I'll continue tomorrow and thanks again....

 

[CleanEnergyGuy]

Instead of spending money on making your existing A/C easier to start I would look into replacing it with a much more efficient mini split. Those are getting better and better. This is on the dream sheet for my RV.

Now, that's an idea to look into! Thanks!

 

[chrisski]

After watching Will's videos, I'm thinking that I would like to build a 48 Volt system starting with (8) 200 watt rigid solar panels and (4),100ah Battle Born lithium phosphate batteries wired in series. I'm planning on adding additional panels and batteries at a later time as I can afford them.

I am planning on getting 6 BattleBorn 100 AH batteries if I upgrade to 24 VDC. With this, I would expect to be able to run the microwave a little, which I say will be warming up some meals, not cooking. I plan on having 1350 watts of panels if I do this. Although this may be able to start my AC, I doubt amps into the battery from solar would come anywhere near amps out from the AC.

I really had to temper my expectations when I started this solar thing.

 

[CleanEnergyGuy]

Hi Guys! I got distracted and posted the following post to a different thread, but I didn't want to leave you guys hanging...so, here is that post. Please let me know what you think!

Hi, I hope that you guys don't mind me jumping in on your conversation, but it looks like I'm in a very similar position to Carl in that I'm wanting to put a solar system with lithium battery backup for my 31' Class A motor home.

My goal is to be able to boon dock in a hot environment and to not have to use my generator too much (or as close to not at all as possible) for multiple days. I realize that this is difficult, but I want to come as close to accomplishing it as I and my budget can get.

So, here's my battle plan. Please let me know what you guys think.

Step One: Replace 13,500 BTU Carrier AC Unit with a Senville Senl-12cd mini split ac/heat pump. It pulls 1260 watts per hour when cooling, slightly less when heating. I plan on leaving the propane furnace in place as heating back up.

Step Two: Install 8, 250 watt Santan used solar panels for a max total of 2000 watts

Step Three: Install a Growatt 48 V SPF 3000 TL LVM - 3Kw 120 Solar Charge controller

Step Four: Install 4 100Ah Battle born Lithium batteries wired in series

Step Five: As time goes on and I can afford it, I'll add another bank of 4 100 Ah Battle Born Batteries

I also have purchased a Bluetti AC200 solar power station that I will be able to use to power my freezer chest, computers, etc. if I'm pushing things.

So, what do you guys think? Does this sound like this system will allow me to run my ac at least most of the night?

Also, when I talked with the rep at Battle Born, he suggested that I consider going with a 24 volt system, so I would greatly appreciate your input on if 24 is better than 48 vice versa or something else.

Thanks!

Bob

 

[CleanEnergyGuy]

I am planning on getting 6 BattleBorn 100 AH batteries if I upgrade to 24 VDC. With this, I would expect to be able to run the microwave a little, which I say will be warming up some meals, not cooking. I plan on having 1350 watts of panels if I do this. Although this may be able to start my AC, I doubt amps into the battery from solar would come anywhere near amps out from the AC.

I really had to temper my expectations when I started this solar thing.

Hi Chris, thanks for replying to my post! I just posted the specifics on the system that I'm thinking about. With the mini-split (which won't be pulling the 1260 watts continuously, but rather something less) I'm shooting for being able to run my ac for 8 hours without firing up the generator.

Let me know what you think?

Bob

 

[chrisski]

Before you listen to anything I have to say, I am hoping to flip the switch on my first real build within a week for my RV. I also think solar A/C for a large RV that you will be driving around is not practical. If you're to attempt it, a mini split would be the way to go, but by dropping down to the split you mentioned, how many BTUs is it putting out?

I'm in ideal conditions in sunny AZ, and I will get 4 sun hours a day. I get a lot more sunshine than 4 hours, its just the geometry of that adds up to 4 full hours of 100% sun, when the sun is actually shining 13 or more hours a day. With the few tests I have done so far, I would say 4 sun hours is correct, because the panels were always less than the 6 amps they are rated for, and that's because the tests were early morning and mid morning. I did not believe the 4 sun hours until I did those tests; I thought I'd get a lot more than that.

With that you'd make around 8000 watts of power a day, which probably would put you in the hole for what you really needed to run the A/C.

Also, 4 battleborn batteries store in the range of 4800 watt hours of energy.

With what I've seen with wiring to run my microwave for microwave popcorn and deciding on 4/0 for the inverter, 48 volts would reduce the wires needed considerably over 24 volts, and attempting A/C sustained on 12 volts is a terrible idea.

When I watch this video, I think solar AC is a bad idea, always less amps in than out.

That is a small RV that only has one A/C, and most would require 2. So yes he did it, but more amps out than in. If you read the comments, people are using A/C, but they are not picking up there 2 Axle fifth wheel and driving to a different park every weekend. So can it be done for a two axle fifth wheel, I would say yes: if you have enough ground mounted panels, or perhaps stay in a place overnight and come with fully charged batteries, and leave before they're depleted, but not for true Boondocking with the comforts of AC set to 74°.

There's a video posted on the forum of someone who owns a large tactical vehicle and has made AC practical for him with an 800 watt split, but the space inside makes this like a putting a cab on the back of a pick up.

 

[CleanEnergyGuy]

Congrats on getting ready to pull the trigger on your new system! It's amazing how far into the weeds that you can get with this stuff! ;-)

Our situation is that my wife is retired and I'm going to be working part time from the road. We plan on taking several extended RV trips per year lasting up to 4 or 5 months. Our first trip will start in January and take us from North Carolina (where we live) to Dallas. While in Dallas, we'll probably stay at a RV park due to convenience in spending time with our son.

After we leave Dallas, we plan on easing our way to San Diego. We haven't mapped it out let (and maybe won't), but we plan on bouncing between points of interest (Death Valley, The Grand Canyon, etc) where we plan on boon docking as much as possible and might stay in one place for several days. All that said, with the time of year that we're planning on doing this, I'm assuming that AC won't be much of an issue...at least not as much as it would be during the heat of the summer.

Once we leave San Diego, we plan on going to Las Vegas and then up the eastern side of California and eventually on to Portland, Oregon (where our daughter lives). Again, due to the time of the year, AC shouldn't be an issue.

We then plan on easing our way back to NC and be back here by April (in time for the pollen). Our trips over the summer will be for shorter duration's of a week to ten days with us finding a spot, then staying put for 90% of the time.

I guess that I should admit that part of what I'm attempting to accomplish is to make our RV a demonstration project that I can use to sell these upgraded solar/battery systems off of. At this point, I'm not 100% sure how it's going to turn out or even if this is something that I will actually pursue, but I figure that the worst case scenario is that I'll end up using my generator more than I hoped to and that I will have pissed some money away on building as nice a system as I can for when we do use the RV.

Thanks again for your input. As Donald Rumsfeld once said, "We don't know what we don't know", so I truly appreciate your help!

Bob

 

[CleanEnergyGuy]

Before you listen to anything I have to say, I am hoping to flip the switch on my first real build within a week for my RV. I also think solar A/C for a large RV that you will be driving around is not practical. If you're to attempt it, a mini split would be the way to go, but by dropping down to the split you mentioned, how many BTUs is it putting out?

I'm in ideal conditions in sunny AZ, and I will get 4 sun hours a day. I get a lot more sunshine than 4 hours, its just the geometry of that adds up to 4 full hours of 100% sun, when the sun is actually shining 13 or more hours a day. With the few tests I have done so far, I would say 4 sun hours is correct, because the panels were always less than the 6 amps they are rated for, and that's because the tests were early morning and mid morning. I did not believe the 4 sun hours until I did those tests; I thought I'd get a lot more than that.

With that you'd make around 8000 watts of power a day, which probably would put you in the hole for what you really needed to run the A/C.

Also, 4 battleborn batteries store in the range of 4800 watt hours of energy.

With what I've seen with wiring to run my microwave for microwave popcorn and deciding on 4/0 for the inverter, 48 volts would reduce the wires needed considerably over 24 volts, and attempting A/C sustained on 12 volts is a terrible idea.

When I watch this video, I think solar AC is a bad idea, always less amps in than out.

That is a small RV that only has one A/C, and most would require 2. So yes he did it, but more amps out than in. If you read the comments, people are using A/C, but they are not picking up there 2 Axle fifth wheel and driving to a different park every weekend. So can it be done for a two axle fifth wheel, I would say yes: if you have enough ground mounted panels, or perhaps stay in a place overnight and come with fully charged batteries, and leave before they're depleted, but not for true Boondocking with the comforts of AC set to 74°.

There's a video posted on the forum of someone who owns a large tactical vehicle and has made AC practical for him with an 800 watt split, but the space inside makes this like a putting a cab on the back of a pick up.

Hey Chris: I watched the video and came away with a few observations. The first of which is that we're going to be running 2000 watts of solar. So, a bit over 3 times as much as this guy had. We're starting with the same 4 100 Ah batteries, but when we add the second back of 4 100 Ah batteries, I would think that we'll be okay.

The second thing is that we've already decided to make the switch to the mini split. Which I assume will come in at about the 800 watts per hour consumption whereas this guy's ac was pulling something like 1700 (I think that I remember him saying). That should extend our battery usage.

Lastly, while I was surprised by how loud the generator was, we're not totally opposed to using it if we have to....

So, we'll see how this works out...

Bob

 

[chrisski]

You know, I think you will work through the problems I mentioned and come up with something. I live in the Desert Southwest, and its often comfortable from October to April, so little need for it, and certainly nothing like the summer!!

I hope you do a build thread for this as it progresses.

I also hope your demonstration goes well. THere’s got to be a market for RV solar builds by professional installers with some decent off the shelf packages at least with as many RVs as there is. I Think that market is very undersized.