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Old 04-10-2017, 11:16 AM   #21
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Originally Posted by family wagon View Post
It'll probably take a combination of compromises, and this one is a good suggestion. If only a portion of the bus is A/C sanctuary that'll be easier in terms of equipment (dollars) than A/C cooling the whole bus. Good insulation, thermal mass, and air infiltration/exfiltration will be important too. Sunlight shining through windows = massive heat gain, glass has terrible insulating value, and school bus windows aren't going to have any significant sealing against air leakage, so think long and hard about keeping those. Maybe the remainder of the bus can be kept bearable with fans and shade.
All good thoughts

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Old 04-10-2017, 11:18 AM   #22
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Yep,
I have the cab of the bus closed off, the 5000 btu AC unit above the windshield, at 100 degrees outside it cools to about 85 with blacked out windows, at night with the help of a fan it cools the whole bus.
85 is very bearable inside when the AC is running.

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Old 04-10-2017, 01:04 PM   #23
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Ok... I'm the one that said $30k. I wasn't being literal and apologize for being negative. I was trying to say - "it is possible but it won't be cheap and it won't be compact." That is not the least bit helpful as everyone defines "cheap" and "compact" differently. Allow me to offer some academic numbers/thoughts - for the sake of discussion. I don't know if they will help the OP but I hope so.

Without knowing much of anything about this project. it is impossible for me to even guess what the OP needs. I have no idea what his bus is like, how well insulated it is, how hot it is outside, etc...

If we assume you have one typical RV 15,000 btu roof AC unit (like the Dometic Penguin II) and that unit is going to run 12 hours at 50% duty cycle and 12 hours at 85% duty cycle (I'm thinking hot and humid Houston) then you are going to consume something around 2200 Ah at 12.5 volts per day (1377 Ah + 810 Ah). This may not be realistic, I do not know. It doesn't even sound like you need an AC unit of this size. The duty cycle actually required (and thus the power consumed) will depend on the current operating conditions.

If we assume 8 hours of good sunlight each day (which is two more than the average solar insolation data), you will need to generate 315 amps of power each hour to replace what was has been used and operate the system during the day. That will require about 5000 watts of solar (assuming 85% efficiency).

I do know that quality solar panels can be had in the $1/watt range (some a little cheaper, some a little more expensive). There are certainly some deals to be had but this is a realistic budget number. I recently paid just a hair over $1/watt for my SunPower E20 435 watt panels.

A quality (IMHO) 60 amp-ish MPPT charge controller is in the $500-$600 range. You will likely need several for the size of array that we are likely talking about. Yes, cheaper ones are available. I've never worked with such a large array but can imagine you will need several controllers that are networked/talking to each other. Way out of my scope of knowledge.

Then the battery. You can do it with lead acid. You may even want to if you are in one place and have no need to move it. A 2000 Ah bank of 6 volt lead acid batteries is going be something around 20 batteries, each weighing 60 lbs. So, lots of physical space (in my opinion) and about 1300 pounds. That will give you 1000 Ah capacity (50% discharge) which appears to be enough to run for the 12 overnight hours (AC at 50% duty). They can be had from $70-$100 each so about $1,500. It is purely my opinion and preference but I like big power capacity and the ability to take it with me when I travel so lithium is the answer. The Chevy Volt battery is a great idea - probably more of these becoming available all the time (with all the Hybrid cars being manufactured). I've got to believe there is some engineering and parts involved to properly charge and care for this battery but no experience. Assuming purchasing a fully engineered lithium solution, I like the GBS package from Starlight Solar. Their 1000 Ah package is $8,500.

Obviously, scrounging is ALWAYS a great way to go. I would think you could save a lot of cash if you can scrounge the necessary components for a lithium battery bank. I have a hard time believing that scrounging solar is possible unless you are willing to put a whole mess of small 12 volt panels together.

Clearly the above numbers do not add up to $30k. However; there is a bit of coin involved.
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Old 04-17-2017, 12:09 PM   #24
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Quote:
Originally Posted by joeblack5 View Post
I am a little more positive about solar and AC. On my 5 window bus I have space for 900 watt. So a full size could be 2500 watt or more
I think the $ 30K mentioned is about someone else doing it for you.
In my last thread with Elfie we picked up a Chevy Volt battery that holds 16 Kwh, for long life 12 kwh. I paid $ 900. see images.
3000 watt solar can cost less then $1500. weight less then 400 LBS
4 mppt Charge controller at about $ 150 / each
Wire and frames / material can all be had from the scrapyard.
your labor free.
A cheap new split 9000 btu is about $ 400.
A used one $ 150

A nice new silent generator is also not cheap but a used harbor freight one is about $35

I think it depends where you are coming from and yes if you require to keep your bus in a 105 F environment and the inside on 65F with 6 cloudy days in a row then you will have a problem.
Everything has its limitation so very good insulation, get rid of windows etc. is all required.

If you believe you can do it then you can and solar is very cheap and very very pleasant.

Later J
Super insulate the roof and walls consider a solid canopy that slides out from under the roof solar panels with additional solar panels and a small canopy that folds up on drivers side with more solar panels and shade for those windows also. As a rule of thumb 15 watts per square foot of panel and when you need the ac the most the sun is making your solar work the best. Plus the solar shades your roof. Find a electrical engineer they will tell you this is possible with a battery bank. Watch out for bad electrical advice. One last note solar is something that you need to study good before jumping in as its changing daily and I see lots of questionable advice. However it can be done. See the post "I think I'll call it bus 52" IN NEW MEMBERS FORUM
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Old 04-17-2017, 12:58 PM   #25
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Originally Posted by mmoore6856 View Post
Super insulate the roof and walls consider a solid canopy that slides out from under the roof solar panels with additional solar panels and a small canopy that folds up on drivers side with more solar panels and shade for those windows also. As a rule of thumb 15 watts per square foot of panel and when you need the ac the most the sun is making your solar work the best. Plus the solar shades your roof. Find a electrical engineer they will tell you this is possible with a battery bank. Watch out for bad electrical advice. One last note solar is something that you need to study good before jumping in as its changing daily and I see lots of questionable advice. However it can be done. See the post "I think I'll call it bus 52" IN NEW MEMBERS FORUM
The hotter the panel gets the less efficient it gets. So you all want to park in the sun to make electric so you can run an ac unit to keep you cool because you parked in the sun. Ok
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Old 04-17-2017, 01:28 PM   #26
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Where are the trees in the southwest that provide this magical cooling you are suggesting??????
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Old 04-17-2017, 01:35 PM   #27
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The hotter the panel gets the less efficient it gets. So you all want to park in the sun to make electric so you can run an ac unit to keep you cool because you parked in the sun. Ok
What is the point of your stupid sarcasm ????
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Old 04-17-2017, 01:48 PM   #28
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the efficiency from mono and poly drops 0.48 to 0.50 per 1 degree celsius increase ABOVE 25 degree celsius.
So if you are 20 degrees higher you loose 10% production. For a 1000 watt array 100 watts. If required compensate with $50 more solar panels.

Later J
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Old 04-17-2017, 02:08 PM   #29
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The point of having a skoolie is it being mobile . move it so your not dealing with temperature extremes And save yourself alot of money and hassle . were doing more with less. This is a forum. Its my comment. My opinion.
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Old 04-17-2017, 02:10 PM   #30
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Quote:
Originally Posted by JDOnTheGo View Post
If we assume you have one typical RV 15,000 btu roof AC unit (like the Dometic Penguin II) and that unit is going to run 12 hours at 50% duty cycle and 12 hours at 85% duty cycle (I'm thinking hot and humid Houston) then you are going to consume something around 2200 Ah at 12.5 volts per day (1377 Ah + 810 Ah). This may not be realistic, I do not know. It doesn't even sound like you need an AC unit of this size. The duty cycle actually required (and thus the power consumed) will depend on the current operating conditions.

If we assume 8 hours of good sunlight each day (which is two more than the average solar insolation data), you will need to generate 315 amps of power each hour to replace what was has been used and operate the system during the day. That will require about 5000 watts of solar (assuming 85% efficiency).

I do know that quality solar panels can be had in the $1/watt range (some a little cheaper, some a little more expensive). There are certainly some deals to be had but this is a realistic budget number. I recently paid just a hair over $1/watt for my SunPower E20 435 watt panels.

A quality (IMHO) 60 amp-ish MPPT charge controller is in the $500-$600 range. You will likely need several for the size of array that we are likely talking about. Yes, cheaper ones are available. I've never worked with such a large array but can imagine you will need several controllers that are networked/talking to each other. Way out of my scope of knowledge.

Then the battery. You can do it with lead acid. You may even want to if you are in one place and have no need to move it. A 2000 Ah bank of 6 volt lead acid batteries is going be something around 20 batteries, each weighing 60 lbs. So, lots of physical space (in my opinion) and about 1300 pounds. That will give you 1000 Ah capacity (50% discharge) which appears to be enough to run for the 12 overnight hours (AC at 50% duty). They can be had from $70-$100 each so about $1,500. It is purely my opinion and preference but I like big power capacity and the ability to take it with me when I travel so lithium is the answer. The Chevy Volt battery is a great idea - probably more of these becoming available all the time (with all the Hybrid cars being manufactured). I've got to believe there is some engineering and parts involved to properly charge and care for this battery but no experience. Assuming purchasing a fully engineered lithium solution, I like the GBS package from Starlight Solar. Their 1000 Ah package is $8,500.
I have many newbish questions as well. Not singling you out, it just sounds like you know what you're talking about.

The HotSpot system ($7000 for their biggest) that StoneGuard linked is using 6V batteries or 12V batteries. If I'm reading the chart right you can use four 12V for nine hrs of operation or up to sixteen 6V batteries for 24 hrs of operation. Why use 6V batteries? Four of these guys arr putting out 100A for 4 hrs in series.
https://www.tractorsupply.com/tsc/pr...-f4dlt-0470742

I don't know what the 6V cost but I think I'd rather run 8 of the 12V batteries instead. Two banks of 4 in series. These are "only" 86 lbs each. Call it 100 with some wiring and it's lighter than sixteen 60lb batteries.

It seems they have 305W panels and 250W panels. Their biggest system uses the smaller panels which makes no sense to me either.

Anywho, I have a 40' bus. There is 18 feet x 7 feet between the emergency hatches of completely empty roof space. Another 15 feet in front of the the first hatch and room for at 2 more behind the rear hatch. With that kind of real estate, I can fit a lot of panels. One of the sites I saw listed their panels at 77" x 39". That's 6 panels just between the hatches. Another 6 up front plus the 2 in the rear. 14 panels at 305W...

Please check that I'm doing is right (not for realistic expections but just to see if I have the formula correct). That's 4270 W per hour? Times the 4.5 hours is 19,215 W. 80% of that is 15,372 W. That has to be almost as good as 1.21 jigawatts.

Yes I know this is ignoring the OP's $3000 budget by a LONG shot but I'm also seeing the same thing you said on other sites. AC just isn't viable on solar. With the figures above I don't see how you can't be 100% solar with AC included. No idea the cost or how long this would last. The guy with a 45' coach who has $300k+ to spend isn't going to whine about a $30k system.

This guy is 320W and 77" x39"
https://www.gogreensolar.com/product...ly-solar-panel
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