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Old 05-07-2018, 11:19 PM   #1
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Solar Panel Review Request - Solarworld SWA 295

Hi All,

Having recently acquired our new bus, I'm in the planning stages for the mechanical/electrical side in getting it prepped for our family's use.

Regarding power, I'm thinking during daytime and particularly while traveling from one spot to the next, I'm wanting to deploy some solar. I plan to backstop the solar with a diesel generator mounted midships in one of the storage compartments.

In trying to size up solar size/runtime, here's what I'm trying to reconcile :

-- 2x Dometic 13.5k BTU airconditioners
-- Small residential refer

I realize I'm not going to have enough to run the above items full-time, but am calculating defraying some diesel costs to keep a battery bank charged.

In terms of batteries, was thinking 4 deep cycle cells, but am open there as well.

I've studied some of the setups here, but am still on the fence as to how to best architect the correct solution.

So - to kick it off, I'm thinking I can use SolarWorld SWA 295w panels based on their size, output, etc. I was curious if any members might have thoughts on if this type of panel makes sense, or if there are suggestions as to other vendors or types that I'm not thinking of.

Here's the link for reference to the cells I'm looking at:

https://www.wholesalesolar.com/19223...no-solar-panel

Any feedback appreciated - thank you in advance !

/Matt
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Old 05-07-2018, 11:44 PM   #2
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I bought 100 watt Grape Solar panels from Home Depot for $89 per panel delivered (not including tax). That would be 89 cents per watt. More panels to hook up, but I hope they will blend in with the form of the roof better than wide panels.
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Old 05-08-2018, 12:20 AM   #3
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Quote:
Originally Posted by bus-bro View Post
I bought 100 watt Grape Solar panels from Home Depot for $89 per panel delivered (not including tax). That would be 89 cents per watt. More panels to hook up, but I hope they will blend in with the form of the roof better than wide panels.
I'm going to look that up and compare it. One thing I'm learning real quick is cost versus space versus efficiency. The panels I posted are $350 for 295W, so I can see the cost savings versus what you posted. I need to look at the size. The Solarworld panels are 65.95 × 39.4 × 1.3 inches by comparison.

Good stuff, keep it coming and thanks !

/Matt
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Old 05-08-2018, 03:34 AM   #4
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Quote:
Originally Posted by atl_oldskool View Post
Hi All,

So - to kick it off, I'm thinking I can use SolarWorld SWA 295w panels based on their size, output, etc. I was curious if any members might have thoughts on if this type of panel makes sense, or if there are suggestions as to other vendors or types that I'm not thinking of.

Here's the link for reference to the cells I'm looking at:

https://www.wholesalesolar.com/19223...no-solar-panel

Any feedback appreciated - thank you in advance !

/Matt
Matt, I got my panels here. Even with freight they were 50-ish cents per watt.
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Old 05-08-2018, 04:06 AM   #5
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Originally Posted by ComfortEagle View Post
Matt, I got my panels here. Even with freight they were 50-ish cents per watt.
Whoa - those are some seriously good prices. Thanks ! Looks like I have some google-fu'ing (is that even a word ?!?!?!) to do on some of these models on their spreadsheet. Good stuff.

/Matt
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Old 05-08-2018, 04:48 PM   #6
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Matt,

Are you putting in any insulation? Even with a full 40-ft bus with only decent insulation, I think 2 x 13.5k BTU/h is much more than you need.

Assuming a 40ft bus with 1.5" foam insulation on walls/floor/ceiling, 110 F outside and 60 F inside, I calculated a total cooling load of 8k BTU/h.
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Old 05-08-2018, 05:16 PM   #7
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Quote:
Originally Posted by ThunderstruckStudios View Post

Assuming a 40ft bus with 1.5" foam insulation on walls/floor/ceiling, 110 F outside and 60 F inside, I calculated a total cooling load of 8k BTU/h.
Only if the sun has died!

You know that when the bus manufacturers fit AC, they fit at least 80k btu.

Even with a good number of windows deleted, and good insulation, 20k btu is not unusual to cool down the interior when camping.

Those fitting mini-splits are often fitting 8k units in the back and 12k in the front.
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Old 05-08-2018, 05:38 PM   #8
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I assume the 8kbtu/h is as it says ,...running all the time. Most ac have a duty cycle so I could see that 8k becomes 24 K with a 30% duty cycle. The other issue is that most people want almost instant gratification so it needs to cool of quickly for us to be satisfied.

Was the 8 kbtu/h calculated with any wind speed of the 110F air on the outside? An how large was the window area?

Thanks, later J
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Old 05-08-2018, 06:03 PM   #9
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Quote:
Originally Posted by ThunderstruckStudios View Post
Matt,

Are you putting in any insulation? Even with a full 40-ft bus with only decent insulation, I think 2 x 13.5k BTU/h is much more than you need.

Assuming a 40ft bus with 1.5" foam insulation on walls/floor/ceiling, 110 F outside and 60 F inside, I calculated a total cooling load of 8k BTU/h.
I put 1-1/2" of spray foam insulation, RV windows, and 2x 12k BTU roof a/c's in my last bus. I spent quite a bit of time in AZ, NV and TX in the summer.

A number of times I wished for a third a/c.

I am suspect that 8k BTU would be plenty in a 40' bus if you don't ever need a/c while driving and spend your summers in Seattle.
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Old 05-08-2018, 07:34 PM   #10
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Right, the 8k BTU/h is exactly what it would take if running constantly to hold the inside at 60 F with the outside air at 110 F. That's not to say that a single 8k Btu/h AC unit would be sufficient; you usually want to oversize the AC unit(s) so you have some margin. Another way to look it at is if it was 110 out and 80 inside, it would cool off very slowly (but it would lower the interior temp).

PNW_Steve, did you have adequate thermal breaks on your walls and ceiling? All the spray foam in the world doesn't help much if you have metal studs conducting heat into your space.

joeblack, the calculations were done using Chapter 25 of the ASHRAE manual for HVAC design. I assumed outside air is 110 F, average 10 mph wind speed, and vertical walls and horizontal roof/floor. I assumed 28 windows (14 row full size bus) each of 1.5 x 2 ft, plus a window in the back and windshield in the front.
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Old 05-08-2018, 07:45 PM   #11
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thanks, i will look that chapter up.. pretty nice stuff at your website .

my gut feeling would say that the row of windows would outdo the thermal breaks because of the studs.
thanks for forcing me to think about it.

later J
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Old 05-09-2018, 09:54 AM   #12
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Wow - these are some thought provoking responses. Life happened, so I'm just responding myself.

I'm trying to balance need versus want. I've been thinking in talking with my co-pilot (wife) that since we're planning to spend a good amount of time in our bus, but still have a home base to recoup, that we could do some amount of weather chasing. I've been talking to every RV and Skoolie owner I come across recently, and it seems this is somewhat the school of thought. I like that, since it forces us to move and see as much as possible. We're doing this Skoolie adventure not only for us, but to get our kids out now while they are young to see what our country is really like - so it seems like that jives together.

On topic then, I've been trying to speed learn power and cooling as relates to RVs. I do have a long background in Data Center building, running, management, so some of this comes naturally (the conversion of watts to amps, BTU calculations, etc). Obviously, I haven't really had much concern in my past for R factors, since most data centers I worked in or helped build had a solid foundation shell.

Here's where my head is currently:

Air Conditioning

2x Dometic Rooftop units, 12k or 13.5k. During normal operations, since we plan to have essentially 3 "sections" to the bus, the rear unit would not be running while traveling or doing daylight activity. The middle unit (as I visualize it) would be running in the day-room/bunk/living room area. I was then thinking about the driving quarters. Do I really need something there, or is the midships Dometic going to be enough. Or is it worth getting a small window unit and figuring out a top mount. I really want to try and keep the lines on this BlueBird clean, but I'm not a glutton for pain.... LOL.

Power Generation

Solar - I don't want to go overboard on it, but since we don't plan to have shore power most of the time when away from home base, and where we can do some chasing of weather, it would be nice to NOT have to run a generator every time batteries are needed. My goal would be to have enough solar to offset the refer and 1 of the Dometic units - during travel time or daytime. Beyond that, I'm comfortable and resigned to the idea of using a generator to actually charge back up.

Generators - I'm on the fence. My background tugs me towards diesel, but the cost for gas gens is pretty compelling. I've been looking at some 9k nominal/12k burst generators that are under $1000 that are gas and apparently rated highly from reviews and otherwise (people reviews, not manufacturer accolade junk). I'm not keen on having to maintain 2 fuel sources, however, if I can find a way to engineer a larger tank to support a gas gen, maybe that works. One of my hotshot friends has an external fuel tank for his rig (think, RAM 3500) that was reasonable, built tough to withstand being placed in a pickup bed, and holds 60 gallons. I was thinking maybe if I paired that with a gas generator, and put the tank in the storage bay, secured, that perhaps that makes sense. Burn rate seems to be 3/4 gallon/hour at full load on the unit I'm looking at, delivering 9k. Unit has 50a outlet and can do 50a or 30a.

Batteries - https://www.batteriesplus.com/batter...p-31m/sli31mdc

Thinking minimum of 4, but could see going to 8 to get some long run time. I haven't figured out how long these would take to charge on either generator or solar, but amp wise 8 seems like it would more than carry us at a full power load for a day. If we're not in the blazing sun, maybe 2-3 days. I'm not sure yet, so that statement makes me a little nervous. I need more advice and need to do more research to establish - but it's not worth essentially $500 to NOT buy enough battery.

Ugh, I need more coffee, but wanted to respond. This subject is critical I feel to a proper build on this bus - aside from the mechanical which I'm going to have reviewed in the coming weeks to make sure that mechanically there aren't surprises that we will be unable to overcome before tearing into the unit.

Good Morning !

/Matt
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