Solar and cooling?

Hakunamatata

Member
Joined
Apr 11, 2023
Posts
11
Set up:
20’ short skoolie
4 100w 12v Renogy panels in 2s2p
3 100ah 12v Renogy batteries in parallel
1500W unknown brand pure sine wave inverter

Panels used to be 4p but advice online said to try 2s2p but we haven’t noticed a change.

We’ve been living on this skoolie for a couple years and have never been able to rely on our solar power. We got an EcoFlow 1300 Delta Solar Generator with a 100w 12v portable Renogy panel not knowing that wouldn’t be enough power to charge it, so we’ve just been plugging it into the wall at the gym and places like that and using it as a really big portable battery and relying on that.

Last summer was really hard dealing with the heat as we don’t have enough power to charge anything like an AC. We had to just park in shade and open the windows, but that often wasn’t enough. Especially as we have pets that can’t survive when it gets really bad.

And we’re moving to Florida from NE US so we’re trying to prepare for that weather consistently and long term.

How does everyone else deal with heat in their skoolies?

We tried a little air cooling water evaporator thing from Walmart but it did nothing.

When I’ve posted on the solar forum everybody says we need like 20 panels to do anything we want to, including things the previous owner of the bus did with just 2.
 
Panels used to be 4p but advice online said to try 2s2p but we haven’t noticed a change.
That's just going to change your voltage and amperage, not the total power coming in. 400W of panels is not much. Your entire system is pretty small for trying to run any electric cooling.
We tried a little air cooling water evaporator thing from Walmart but it did nothing.
I'm guessing that's a little mini swamp cooler. We had those when I lived in Arizona. The idea is to lower the air temperature by adding humidity. Works great in the desert (except during Monsoon season), would never work in Florida as you experienced. Wouldn't work here in the midwest either.
 
A heat pump type AC should run <60% of the time. What size of bus and what insulation type does your bus have, please? And area that is window and single or double glazed?

As an example, a 12kW mini split could likely need 20A @ 120VAC when running, and if running 24 hours would need @ a duty cycle of 60% would be 38kWh. Sunlight is available in the summer (when you are more likely to need it like that, for roughly 12 good hours, so, with roughly 90% efficiency of solar to heat pump, you need 3500W of solar for that, and you have 400.

Not 20 times what you have, but easily 9x .

I can tell you I went into debt to avoid propane heat or running the generator all the time, and have 6400W of solar sunwards. I don't regret it.
 
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A heat pump type AC should run <60% of the time. What size of bus and what insulation type does your bus have, please? And area that is window and single or double glazed?

As an example, a 12kW mini split could likely need 20A @ 120VAC when running, and if running 24 hours would need @ a duty cycle of 60% would 38kWh. Sunlight is available in the summer (when you are more likely to need it like that, for roughly 12 good hours, so, with roughly 90% efficiency of solar to heat pump, you need 3500W of solar for that, and you have 400.

Not 20 times what you have, but easily 9x .

I can tell you I went into debt to avoid propane heat or running the generator all the time, and have 6400W of solar sunwards. I don't regret it.
It’s a 20’ short skoolie. We haven’t been able to do any insulation yet. We had reflectix on the windows that was given to us by the previous bus owner, but we’ve never noticed much of a difference. I don’t know what area the windows take up. They’re average school bus windows. Single glazed.

How do you fit 6400W of solar panels on your bus?
 
Does anyone know of an alternative cooling method to an AC? How is everyone else staying cool in their short skoolies?
 
It’s a 20’ short skoolie. We haven’t been able to do any insulation yet. We had reflectix on the windows that was given to us by the previous bus owner, but we’ve never noticed much of a difference. I don’t know what area the windows take up. They’re average school bus windows. Single glazed.

How do you fit 6400W of solar panels on your bus?
One column down the middle, crossways, on the roof raise portion, which is all windows but the last. The minisplit condenser is on top on the back unraised bit of roof. Another column is hinged at the top of the drivers' (utilities) side and is lifted away from the side and braced to an 40ish degree angle with covers per panel to remove first. It's ugly and not easy. The panels were from SanTan Solar and are 400W ea @ 80" x 40". The bus is a 13 window Thomas at about 35'6" rear engine. Probably 2.5" of spray foam overall.

The good bit is your bus is small, the bad bit is the no insulation to speak of. I suggest any 120vac window mount is worth while, and put a blanket across the bus so you are only strongly cooling some of it. Your animals will pile in the cool part and stay there whenever they are hot.

Thing is you have to have more solar panel wattage, about the smallest Walmart window AC I can search up will need ~5amps at ~115V. I have to believe with the insulation it will run no less than 66% of the time (and may ice up at that). With a 90% percent over all efficiency for the system, you need 900W not 400W, and to run at night you need some storage, like 8kWh (I'm presuming it won't run as much at night as in the day). With it being Florida, if your bus seals more or less ok (tape plastic over the widows?) then a dehumidifer may also help . . . and will itself need power. Like for the animals (dogs?) panting will work better if the air is drier.

Later EDIT

*I should add 8kwh is like 7 of 12V, 100AH deep cycle lead acids which at that usage will die early, or 7 of 12V, 200AH deep cycle lead acids which would probably then have good service lives (for lead/acid, which is still not as good as LiFePo4). 7 of 12V, 100AH LiFePo4 should get you at least whatever number of cycles the battery is rated for and maybe more. With 900W of panels you could (January/Feburary?) maybe get away without running your generator, the rest of the time you would need to run the generator for anywhere from 3 hours to it barely warms up all the way (I don't remember you mentioning any generator capacity) to top off the batteries for overnight, since the 900 probably can't both charge the batteries and run the A/C in all conditions. You more likely need 1500 watts of solar to get away without running the generator, and at that I can't swear you'll be doing all the LED lighting or charging phone/PC/etc. which you may want to. 1600W is a safer bet. I felt I needed 6400W since my goal was as all electric as I could manage, and I have been able to avoid propane as a house utility but still need diesel to heat water and as backup heat to the heat pump. At that (as long as the Canadian border is open) I hoped to get up to Alaska for a few years and overwinter, so heat above freezing at all times no matter what was my chief concern.
 
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You don't have enough solar to not burn fossil fuels and run the A/C in Florida. You have two options for two different budgets.

Option 1: Cheap upfront cost. Buy a 1500-1800w inverter generator (Gasoline) and use it to charge your batteries. It will be about $400. You will at least get some cycle time where your generator can rest and you don't have the noise 24/7. Not sure if you have an A/C, but below are the options ordered by cheapest to best. You'll also need a battery charger for about $100 to convert from A/C to your existing 12v System.
A: Window A/C in the back window
B: RV Rooftop A/C
C: RV inverter A/C
D. Mini Split Heat Pump

Option 2: Fix it all up and do it right. Throw away the existing system which was only meant to maybe run a fridge or live without climate control. This will be expensive and i still recommend a gas generator as a fallback for cloudy days or to supplement your system for days where extra batteries are solar aren't worth thousands to you.
A: Insulate your walls and build curtains or foam inserts for your windows.
B: Buy a few residential panels (whatever you can fit on the roof) My local greentech has 450w panels that have small discoloration on the frame for $100.
C: This is highly variable, and there are many options to use, but Victron is the gold standard and just works. A multiplus and one MPPT can run your whole system. For something using A/C i recommend 24v for most. Looking at about $2k for the blue stuff. Might be able to do something like an EG4 3kw for $1k or clone for $500.
D: Use the Ecoworthy server rack batteries or EG4 24v batteries. I think two would be sufficient and you have some redundancy.
E: Install A/C of your choice

If you went all Ecoworthy, you could be under $3k for a workable system, $5k for victron/EG4.
 
Does anyone know of an alternative cooling method to an AC?
#1 In the desert you can use evaporative cooling like we discussed earlier, that's not going to help in humid climates though.
#2 Your best bet is simply ventilation and air flow. A maxxair fan or two in the roof pushing hot air out and open vents/doors near floor level will draw in fresh outside air and create a breeze that will make the air feel cooler than it is. 92 degrees and 100% humidity is still going to be hot, but moving hot air is better than stagnant hot air.
 
lots of good info from these folks. like Talia does.... im a fan of going thru the math to figure out your needs. find an online heat loss calculator and start there.
i run twin rooftops for a total of 30k btu's and you're gonna need a sweater, but im well insulated. everyone's needs are different.


i just want to add unrelated, related info...
old rv parks were set up to the electric standards that tell you how much energy you need. a 30A hookup is 1 rooftop, a 50A hookup is for 2 or more rooftops.
 
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One column down the middle, crossways, on the roof raise portion, which is all windows but the last. The minisplit condenser is on top on the back unraised bit of roof. Another column is hinged at the top of the drivers' (utilities) side and is lifted away from the side and braced to an 40ish degree angle with covers per panel to remove first. It's ugly and not easy. The panels were from SanTan Solar and are 400W ea @ 80" x 40". The bus is a 13 window Thomas at about 35'6" rear engine. Probably 2.5" of spray foam overall.

The good bit is your bus is small, the bad bit is the no insulation to speak of. I suggest any 120vac window mount is worth while, and put a blanket across the bus so you are only strongly cooling some of it. Your animals will pile in the cool part and stay there whenever they are hot.

Thing is you have to have more solar panel wattage, about the smallest Walmart window AC I can search up will need ~5amps at ~115V. I have to believe with the insulation it will run no less than 66% of the time (and may ice up at that). With a 90% percent over all efficiency for the system, you need 900W not 400W, and to run at night you need some storage, like 8kWh (I'm presuming it won't run as much at night as in the day). With it being Florida, if your bus seals more or less ok (tape plastic over the widows?) then a dehumidifer may also help . . . and will itself need power. Like for the animals (dogs?) panting will work better if the air is drier.

Later EDIT

*I should add 8kwh is like 7 of 12V, 100AH deep cycle lead acids which at that usage will die early, or 7 of 12V, 200AH deep cycle lead acids which would probably then have good service lives (for lead/acid, which is still not as good as LiFePo4). 7 of 12V, 100AH LiFePo4 should get you at least whatever number of cycles the battery is rated for and maybe more. With 900W of panels you could (January/Feburary?) maybe get away without running your generator, the rest of the time you would need to run the generator for anywhere from 3 hours to it barely warms up all the way (I don't remember you mentioning any generator capacity) to top off the batteries for overnight, since the 900 probably can't both charge the batteries and run the A/C in all conditions. You more likely need 1500 watts of solar to get away without running the generator, and at that I can't swear you'll be doing all the LED lighting or charging phone/PC/etc. which you may want to. 1600W is a safer bet. I felt I needed 6400W since my goal was as all electric as I could manage, and I have been able to avoid propane as a house utility but still need diesel to heat water and as backup heat to the heat pump. At that (as long as the Canadian border is open) I hoped to get up to Alaska for a few years and overwinter, so heat above freezing at all times no matter what was my chief concern.
Our batteries are LiFePo4.
We’re still willing to use the generator, just would like to not have to rely on it.
In order to minimize the time needed to run the AC, what kind of insulation would you recommend that’s easy to set up and cost-effective?
 
I have two 12K minisplits with around 1500W of solar and 1000AH @12v.bus is spray foamed 3''. windows removed. and replaced with dual pane rv. on a sunny day and one minisplit on. for back bedroom... i get a draw of around -30A--60A off the bank. so around 10-12H w/o the gen needed. so solar and batts. in winter at night I get around 4h before the gen kicks in to keep the bank >60-70%
 
Hi,

You are concerned about your animals, I think, as a first thing.

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A) If money is supertight but you can swing it -- because it is a part of every other option I'm thinking of working well, get 4 more of your 12V 100AH LiDFePo4 batteries (or 1 more, more is better up to 8kWh ~ 10kWh storage) and two 400W 12V solar panels ( or just a handful more of 100W again until you are past 12kW you don't have "extra" panels), and get a dehumidifier. SanTan Solar I can recommend for panels, their batteries are not that great a deal. NoName 12V 100AH LiFePo4 can be seen on Amazon for $100~110ea., really good ones for $130~$160. Altogether this will be about $1.1k ~ $1.5k, and you need the power to run the A/C and humidifier at night -- you will make back what you put into solar collection and storage by not running the generator as much or at all for weeks at a time,

Even with only minimal insulation, if you put that together with blocking off half the bus during the day with a blanket, I really believe the cooled half will be tolerable in soggy sunny Florida.

B ) You aren't moving into a tent while you gut the bus, so you aren't gutting the bus. This will have minimal further cost. Mostly this is effort plastic sheeting and tape. < $500.00.

If you have reflectix on the windows, then you are already not worried about seeing out of the windows. Clean the windows to water clear if you can, as much as you can. Have the least crud/dust on the glass to intercept light and heat up. Wipe the reflectix dust free on the shiny side and then put it back in the windows. Tape plastic sheeting all around the borders of the windows to zero air infiltration from them.

Keep one unsealed.

Get a hair dryer (any small blower). I have no idea if a cigar is cheaper than a pack of cigarettes, but get whichever is cheaper. Take the unsealed window and rig the blower (on cool for hair dryer) through cardboard and plastic, pointing in and sealed up. You are trying to inflate the bus. Take the lit smoking product and pass it over all fittings, apertures, corners, seals, the dash, etc. You are looking for cracks to tape over. It might be so leaky you have trouble isolating any, I have no way to know. If you get to the point you can't secure the blower with tape because you are inflating the bus, then you might have tightened it up enough to worry about oxygen depletion -- then you might need to keep a vent open/window cracked. I can't believe you'll get there, too much deliberate ventilation and ports in the dash/firewall.

Seal up that last window like the others.

In addition to a regular window style A/C, get and run a dehumidifer. You will not get away I think without running the generator every evening as late as the neighbors can stand, because the battery storage to avoid it is not there. The point is low humidity air at 85deg can be stood by most people and animals with a fan, 75deg at 90% humidity is horrible.

Silica gel dehumidifiers are not the way to go unless you can use a lot and can safely ( for them ) heat the silica outside to dry it back out). Doing that would become a daily or near daily chore. If you don't reuse the silica, dry silica bead costs will eat you alive -- but you don't want to be drying them in the bus because that puts the moisture and heat from drying them back into the bus. The little solid state dehumidiers (or say they are Peltier) are quiet and cheap, but also low capacity and put a lot of heat into the bus for what they do. You are looking for a single room refrigeration cycle dehumidifier with compressor and fan.

C) You are going to move into a tent while you gut the bus.

Wow, do you have options, like hella lotta options.

$900 gets a 600 board ft spray foam kit from Amazon that will probably get R6 at least while zeroing air infiltration wherever it goes. With a wire wheel you can probably pare it back to where you can put the original interior metal back, and you need the wire wheel to clean up all rust and loose paint before spraying. Also before spraying, cover any rust with rust converter. You have a lot of area in the front windows you can not cover and it is and will be single glass sheets, there's not a lot you can do with that. With 20' you can't really spare the living area either. This will get you the best performance out of any given combo of A/C and dehumidifier. This plus incidentals (like a breather and tyvek suit, so you can install the foam safely) probably could be done for <$1,500. That is $1,500 in addition to more panels, batteries, and the dehumidifier.

This is a potentially suitable spray foam option (I have not used it) with less coverage and more variable reviews towards customer satisfaction -- but, less than half the cost for way more than half the coverage.

1743263816029.png


The chief advantage of any spray foam of closed cell type is the 100% sealing from air infiltration and no volume inside the metal to trap water vapor, which you get in addition to R6~7 per inch of depth.

Then you have all the other options.

Rigid foam boards, fiberglass, natural options like wool, and reflective materials.

I think none of the last three are good for your application because of the difficulty of keeping a vapor barrier of plastic intact while installing them. Any place there is a leak you will get water condensing and being trapped. There will be mold and rust. Frankly, "natural options" will be food for mold when wet.

Rigid foam with great stuff gap sealer is an option, probably comes to a middle of the other foam options for cost, and -- the foam board manufacturer has done the job of creating the foam correctly. For either other spray foam option it is on you to have the temperature right (still required for gap sealer but larger allowed range) and prepare the surface for foam adhesion and to mask off any areas where any overspray must not be allowed to land. If you do rigid foam and don't seal it up, then you are back to some degree of water condensation inside the metal envelope of the bus -- but the foam board itself will not absorb water and it's outer surface will not condense water much if at all.

I am predicating these suggestions on the idea your generator can not be run at night much or people will b***h and make you move, and, you aren't getting gas for free. Most of these will almost certainly save $1000plus in gas the first year, and then keep on doing that for years. As is (400W of solar) you will need to run the generator some of the time during the day, so . . . Adding a 400W panel and a few batteries while definitely getting a dehumidifier to go with the A/C and sealing up every air leak you can is a first step.

If the A/C you have is all the time running water then it may be doing a good job of dehumidifying air already, but, if it starts to ice up then it needs dedicated dehumidifying help.

I hope your future experience leaves you feeling I've covered options well.

TL/DR. You do not need 20 solar panels, but, you need more panels period, like 2X, 3X of what you have, and 2X storage. Probably you need a dehumidifier for Florida and to seal up every air leak you can. You have reflectix for all windows, right, and LED lighting? The expenditure I am thinking of will pay for itself beginning on completion and in 1.5 ~ 3 years, and likely means you may get away with not running the generator for weeks at a time.

For that 3X panels to work, I am counting on lowered humidity letting you get away with not running the A/C nearly as much. Having the A/C run at between 60% ~ 66% duty cycle 24/7 and you are back to always needing the generator, or, you need that 3500W of solar. Almost all 12V panels you can parallel without worrying much about differences in wattage, so you can always add panels a bit at a time -- key thing to that is keeping the Vmp as close as possible for all panels.

The present value of avoided future cost for gasoline, minus the cost of even the most expensive option, is more than twice the cost of the most expensive option. Any of it is a good use of your money.
 

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I have 2,000W of solar on my roof. I put a 12K minisplit on the back. I ran some tests over the past week. If I try to run it in the middle of the day it sucks 1200W of electricity. I tried running it late afternoon and evening. Once it cools down it takes about 200W to 300W to keep the inside cool.

You have to be careful when looking at units. I bought this one: Pioneer® Diamante Ultra 12,000 BTU 22 SEER2 Ductless Mini-Split Inverter++ Energy-Star Wi-Fi Air Conditioner Heat Pump Full Set 115V with 16 Ft. Kit

The documentation for that unit said it would only pull 920W. When I ran it I saw more watts pulled. I called them and they gave me some bs answer saying that's nominal and they didn't write it. It definitely pulled more than 920 at startup. What you want is an inverter type of minisplit so that once the place cools down the unit will use less.
 
I have 2,000W of solar on my roof. I put a 12K minisplit on the back. I ran some tests over the past week. If I try to run it in the middle of the day it sucks 1200W of electricity. I tried running it late afternoon and evening. Once it cools down it takes about 200W to 300W to keep the inside cool.

You have to be careful when looking at units. I bought this one: Pioneer® Diamante Ultra 12,000 BTU 22 SEER2 Ductless Mini-Split Inverter++ Energy-Star Wi-Fi Air Conditioner Heat Pump Full Set 115V with 16 Ft. Kit

The documentation for that unit said it would only pull 920W. When I ran it I saw more watts pulled. I called them and they gave me some bs answer saying that's nominal and they didn't write it. It definitely pulled more than 920 at startup. What you want is an inverter type of minisplit so that once the place cools down the unit will use less.
Please mention your bus size, window delegate, and insulation approach. I'm guessing 23' ?
 
I guess that would help.

28 foot. No insulation yet on the roof. All windows are in the bus. I should also say that I am only trying to cool down the back for sleeping.

Whom ever wrote that dog article needs to be reminded that AC is a recent invention of mankind.
 
Nothing yet. I have a room in the back and a hallway. I let the AC run at night and it was able to cool the backend of the bus. It also cooled the front end. The back end next to the AC was of course cooler.

It's not going to keep the bus cool during the day. During the day you will be fighting the sun.
 

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