How best to solve air conditioning problem

[tedsc]

I converted my 23 foot travel trailer into a home office and it works fine for now with a heavy duty extension cord to the 15 amp connection at the house. That will all change in the summer when I will want to run the air conditioner. My initial thought was to install a 30 amp RV hookup. Doing so will cost me a few thousand between the trench work and the electrician. I then started to wonder how much I would have to invest in a solar setup that could handle that load? Additional considerations are that I live in a place with frequent cloud cover so I imagine I need a larger battery bank. The trailer does not move and I do not intend to roof mount the system. I would also prefer to keep the system at 12 or 24 volts. The "Mobile Solar Power" page Will put up is helpful, but it does not include running an air conditioner in even the most robust system he laid out. Are there any pre-packaged solutions for this kind of problem? If not, are there any guides like the "Mobile Solar Power" guide that include the power requirements of an air conditioner?

Thanks,

Ted

 

[Rednecktek]

Depending on how big an aircon unit you want to run and how long you need to run it, the trenching might be cheaper. Aircon, stoves, ovens, and well pumps are all destroyers of batteries because they have such high constant draw.

Just for some rough numbers, a 12k BTU inverter style mini-split, which are about as efficient and low power as they come, are about 1200w at full bore and drop to somewhere around 800w to just keep things cool. Assuming you go with a 24v system (which would probably fit your needs best) that's 800wh / 24v = 34a/hr or a little over 1/3 of a 24v 100Ah LFP battery each hour you want to run it. Just for arguments sake lets say you get one of the 200Ah 24v rack-mount batteries, that's 6hrs maybe per day of aircon, not including anything else you want to power like lights or laptop or TV or noodle maker. Rule of thumb is 3 days battery bank, so you're looking at $4500 just in batteries for the aircon.

Then you're going to need panels and SCC to refill that, and if you do some serious looking and go with used panels you'll pay about $0.50-ish per watt of panel, and to recharge hose panels with the average 4-sun hours per day, that's about 3Kw of panels to recharge your battery bank in 1 day, or about $1500-$2000 in panels.

Then you'll need the AIO you're thinking about which is about $700 for the Growatt 3Kw 24v model. That's not going to have enough amperage to fully charge your batteries in a day so you'll need at least another 60a MPPT controller to parallel up which is another $300 - $600 depending on how fancy you want to get.

You mention you're in a pretty cloudy area so you're probably going to need to significantly over panel your system, so double the size of the array to 6Kw for $4000 in panels and a LOT of space in the yard.

So, rough numbers here:
Panels - $4000
Batteries - $4500
SCC's & Inverters - $1000
Lots of yard space for racking
Storage space for batteries & parts

You can doodle the numbers to your needs to get a more accurate number, but you get the idea of what it's going to take. You'll want to do a full power audit of what you currently use then add in the Aircon system's numbers to get a more accurate estimate. I'm rounding high here a bit because it makes the napkin math easier. I'm sure once you start filling in the blanks on the power audit the numbers will be smaller.

 

[tedsc]

A full power audit is tricky. If I build an off grid system I would need to plan around worst case circumstances which would include running the AC. I cannot run the AC without sinking a few thousand into the RV hookup. If I am going to build an off grid system anyway, I would rather not sink a few thousand into infrastructure that I will not use int he long run. Frankly part of the motivation is that we get a 2 week stretch in the late summer of 100 degrees where the local power grid often cannot keep up. I feel like putting a few thousand into an RV hookup that won't really add any value when the AC is most needed is throwing money away. That 2 week stretch is the exemption from the frequent cloud cover we see here so panel production would be higher during that time.

 

[Rednecktek]

That makes sense.

Well, the nice thing about the power audit form is that you can doodle multiple different layouts and specs for free to see what you'd actually need. If you plan out your system right, you can use that 115v line you have now to supplement the power coming from the panels in winter and not need to rely on the grid in summer when you get ALL THE LUMENS from the daystar.

If you only really need the high demand when you have the most sun then that cuts your battery and panel costs significantly. Go ahead and run through the power audit and just see what the numbers come up with. Since you're using an extension cord already, you can save a lot of steps right now by throwing a Kill-A-Watt in at the cord and just getting a current overall usage to play with. Basically fill it out twice, 1 for what you currently use if you were to go off-grid and a second run with the Aircon in the mix and more sun hours.

 

[WindWizard]

A full power audit is tricky. If I build an off grid system I would need to plan around worst case circumstances which would include running the AC. I cannot run the AC without sinking a few thousand into the RV hookup. If I am going to build an off grid system anyway, I would rather not sink a few thousand into infrastructure that I will not use int he long run. Frankly part of the motivation is that we get a 2 week stretch in the late summer of 100 degrees where the local power grid often cannot keep up. I feel like putting a few thousand into an RV hookup that won't really add any value when the AC is most needed is throwing money away. That 2 week stretch is the exemption from the frequent cloud cover we see here so panel production would be higher during that time.

Or go super cheap-o and buy a fan and a squirt bottle of water.

 

[Supervstech]

Paint your roof with a quality IR reflective white coating.
Insulate everything to the max.
Add awnings to your windows, and doors.

Get an inverter ac setup. Be certain it is a true variable speed inverter drive system.

Use the heavy duty cord you currently have, and it will be fine.

Solar will cost quite a lot, but it is doable.

 

[rmaddy]

I converted my 23 foot travel trailer into a home office and it works fine for now with a heavy duty extension cord to the 15 amp connection at the house. That will all change in the summer when I will want to run the air conditioner. My initial thought was to install a 30 amp RV hookup. Doing so will cost me a few thousand between the trench work and the electrician. I then started to wonder how much I would have to invest in a solar setup that could handle that load?

I'm confused. If you add to your house such that you can get 30A service to your travel trailer, then why do you need to consider solar and more batteries? Everything in the trailer, including the A/C, will simply run from the 30A shore power. No extra effort or expense will be required beyond getting 30A power from the house to the trailer.

 

[Supervstech]

I'm confused. If you add to your house such that you can get 30A service to your travel trailer, then why do you need to consider solar and more batteries? Everything in the trailer, including the A/C, will simply run from the 30A shore power. No extra effort or expense will be required beyond getting 30A power from the house to the trailer.

He meant installing and running a 30A circuit would be a few thousand to implement, so putting that towards solar seems like a smarter idea, even if more expensive up front.

 

[rmaddy]

He meant installing and running a 30A circuit would be a few thousand to implement, so putting that towards solar seems like a smarter idea, even if more expensive up front.

OK, now that you say that, it seems obvious.

The solar route will likely be more expensive and take a lot more effort to implement (replacing stock A/C with mini split, for example).

It boils down to the OP's goal.

1) Pay an electrician to add the 30A service in a few days and then be able to use the trailer as-is with A/C.
2) Spend more money and many weeks modifying the trailer to run off of solar.

Option 2 is great if the OP has a desire to do all of that work and have a trailer that can be taken on the road and not be stuck in campgrounds.
Option 1 is quick and simple if the goal is to get back to work and not roast in the summer.

 

[Rednecktek]

Sadly the OP mentions that in summer the grid gets flakey so he can't trust it to run an AC when it starts getting hot out, hence running it from batteries and solar.

If he's got the money to spend and the space to place all the parts, doing a fully off-grid setup and supplementing it through the current extension cord seems like a great way to go for reliability.

The biggest concern I see is just the physics of where to stick it all.

 

[sparrowhawk]

Why not do both? Add your RV hook up and build your solar system large enough to supply your trailer and the excess gets sent to your house to power a critical loads panel. That way you will always have power to your refrigerator and whatever else your system can handle.
I originally decided to build my system for the occasional power outages we have here but I decided to expand on the idea. I put in 6 kilowatts of panels, 6 kilowatts of split phase inverters, 24 kilowatts of lifepo4 diy batteries.
I run my electric water heater, a large SxS refrigerator, a small chest freezer, all my lights and TVs and in the summer I run a standard 7000 BTU window A/C.
Weather here is a mix of cloudy and sunny days and I can usually go 3 days without sun. I never know when the grid goes down until I notice the clock on electric stove is either off or blinking. It's also nice to know that I will always have at least some power and it doesn't hurt that my electric bill has been reduced by at least $125 a month and could save even more if my rates go up. With my current electric rates my payback will be about 8 years but my peace of mind is priceless.

 

[tedsc]

Thanks for the feedback all.

 

[sunshine_eggo]

Missed this thread the first time 'round.

I had a 50A RV outlet installed by my panel - about $350.

I ran 3X 6awg RV extension cords back to the RV (other side of house) - about $300.

$650 total

Beat the $2100 it would have cost to put the RV box by the RV.