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Old 09-25-2022, 11:54 PM   #1
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Solar Panels, Flat Deck VS Roof Contour?

So I'm planning to put 18 24v 200w panels on top of my bus. Some would probably consider this excessive, but I don't like being hot so air conditioning is a requirement for me.

The thing I keep going back on forth on is how to mount them. My initial and still somewhat preferred idea is arrange them in 3 rows along the contour of the roof, that is to say directly bolted through the roof sheet metal and reinforced on the backside with thick strips of aluminum. The largest downside appears to be the system would have a lower maximum output as the panels will be in 3 different planes.

Or I could build a deck so all the panels are on the same plane relative to each other. I feel this option requires more complex engineering to mount to the roof, wouldn't look as nice or clean, and raises the overall roof clearance more, especially at the edges of the bus. But the performance of all the panels would be the same.

Any thoughts? Perhaps I'm overlooking something critical?

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Old 09-26-2022, 12:22 AM   #2
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A thought or two:

Consider what you will do with your bus. Will you travel a lot or very little. Will you live in it full time?
If you travel only once in a while, mount them in a single fixed plane. Consider the things that already stick up through your roof line. Can you build around them with your array. If you travel a lot mount them to match roof contour. You appear to have large power requirements (3,300 watts). Where will you be using the bus? Even with 3,600 watts of solar, that won't really run an air conditioner with other things like a fridge.
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Old 09-26-2022, 03:29 PM   #3
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With that much PV power you'll be needing more than one charge controller, so you could have three rows of six panels, each row with its own CC. One row could be along the roof's centerline, and one row on each side. This way it doesn't matter how much power each row is producing: each CC will produce as much power for the batteries as the panels can make, and the batteries will all end up being charged OK.

This is essentially what I did: I have a central roof walkway between my two roof hatches, and hinged from the walkway I have a row of four Sharp 255W panels on each side. Each row of panels (an array) feeds its own CC which in turn powers its own bank of batteries; in other words, I have two entirely separate PV systems in parallel. If one system should crap out on me I will still have half my PV power: redundancy is always good!

Because the panels can be raised, I can always harvest as much power as possible, even in winter or in northern areas when the sun is much lower. When the panels are stowed for travel they are against the roof at 21 degrees down, or they can be raised to level (but why do that?) or to 21 or 33 or 45 degrees up. If parked pointing east or west, I can raise the panels on the opposite side to the sun; in summer the ideal angle for fixed arrays in SoCal is about 21 degrees anyway! In winter it's much better to have half the panels at only 21 degrees and the other half higher than to have all of them flat. Each panel sits inside a support frame made from 1.75" x 1/8" 6063 angle, with sliding/pivoting/hinged/telescoping stainless-steel struts to raise the panels to whatever angle I want. If a panel ever needed to be replaced, it would be a simple 5-minute job to remove the old one and put a new one into the frame. There's plenty of cooling air circulating under the panels, and there's no wind noise from them while driving. So far, so good.

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Old 09-26-2022, 04:45 PM   #4
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I dont have off-grid air, but I'm pretty proud of my panel and deck mount system.

I mounted 2 2/6 boards running the length of the bus, bolted to each rib using lag bolts and steel L brackets. Its strong enough to build a room addition on it.

4 320 watt panels fit in the front, and I have a large deck from the middle of the bus back. If I ever want to scrap the deck, I can thrown on 4 more panels for 4 are enough to do my power needs including 5 gal hot water heat.

Under the panels I have insulation to prevent heat transfer to the bus, as panels get pretty hot. Side benefit, the height of the 2x6's allows the panels to tilt, using standard garage door hinges.

Hope that gives you some ideas.
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Old 09-26-2022, 06:49 PM   #5
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A thought or two:

Consider what you will do with your bus. Will you travel a lot or very little. Will you live in it full time?
Let's say "extended stay" and quite possibly frequent mobility, with the bus functioning as a base of operations but not full time occupancy (like commuting to a regular job).

I'm investing so heavily into solar to hopefully offset as much fuel burn as possible. I don't expect diesel to dramatically fall off in price in the next couple years so I figure if I can avoid running a large generator for most of the day (especially while I'm not there), then the high up front cost in panels and batteries (probably at least 20kwh) is worth the fuel savings later.

A fridge and minisplit (or possibly a couple of removable window units) are the primary loads, but I would like other stuff (i.e. washing machine and microwave) but that will be largely running on generator power.

Quote:
Originally Posted by Iceni John View Post
With that much PV power you'll be needing more than one charge controller, so you could have three rows of six panels, each row with its own CC. One row could be along the roof's centerline, and one row on each side. This way it doesn't matter how much power each row is producing: each CC will produce as much power for the batteries as the panels can make, and the batteries will all end up being charged OK.
A good idea, I was planning on doing every bit of roof that'll fit a panel including the center. Even then, I'm within the specs of the hybrid solar invertor I plan to get, which can put out a continuous 6,500 watts, supports two separate 4,000 watt arrays, and support for a generator.

Quote:
Originally Posted by Peterjk View Post
I dont have off-grid air, but I'm pretty proud of my panel and deck mount system.

I mounted 2 2/6 boards running the length of the bus, bolted to each rib using lag bolts and steel L brackets. Its strong enough to build a room addition on it.

4 320 watt panels fit in the front, and I have a large deck from the middle of the bus back. If I ever want to scrap the deck, I can thrown on 4 more panels for 4 are enough to do my power needs including 5 gal hot water heat.

Under the panels I have insulation to prevent heat transfer to the bus, as panels get pretty hot. Side benefit, the height of the 2x6's allows the panels to tilt, using standard garage door hinges.

Hope that gives you some ideas.
I considered buying a set of panels like this, unfortunately I decided at the time that I hated the overhang I was going to end up with and have already bought the first 8 panels. Now I'm back on the fence for what I want.
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Old 09-27-2022, 02:35 PM   #6
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I don't really don't have any overhang with these panels. Model is here.
Its important to exactly match the panels with the BMS your using. At least it was in my case.
Mine are 60 cell panels, 2 each in parallel. Its more then enough power. I suppose if I had air-conditioning, I would use 8. But A/C in all reality requires shore power. Ive never tried it. There's always one guy w a roof full of panels in AZ that will prove me wrong. But I'm in the Midwest. You're lucky to go two days at full sunshine, real lucky.
Take a look at Electrodacus.com. It only requires one BMS with up to 60 panels max across 30 DSSR20's, 2 per dssr20, which is what I use. A dssr20 is a switch which turns 2 panels on or off, just like a mppt controller, except faster, and cheaper. Once the batteries are fully charged according you for SOC, the solar power is diverted, in my case to heat water in a 5 gal tank. I have 120 deg water by noon. Once the sun goes down, water gradually starts to cool and by next morning its still warm enough to bathe or whatever.
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Old 09-27-2022, 04:41 PM   #7
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Its important to exactly match the panels with the BMS your using. At least it was in my case.
Can you explain this further please?

I'm opting for batteries from BigBattery.com. They make a bunch of self-contained lithium batteries that are plug and play with only a single connection. The BMS is built in and according to them, only Renogy brand chargers don't play nice with them. My panels and hybrid invertor are all from Rich Solar and available through shopsolarkits.com which offers Big Batteries in many of their kits.

So as far as I am aware so long as my input into the hybrid inverter is with it's specs, the inverter will manage supply and demand of the system while the battery built in BMS babysits itself.

From my understanding it greatly simplifies the system.
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Old 09-27-2022, 04:55 PM   #8
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Ok, Ill cope/paste what I learned from Dacian, who designed and built the electrodacus BMS. I had to read it about 10 times before it sunk in.
A DSSR20 is the mppt, its just a switch which flips the panels on/off.
The SBMS0 is the BMS.

By match for my 24v system means 60 cell panels. With these specs:


Here we go....



PANELS
https://electrodacus.com/SBMS0/SBMS0v03d.pdf
For DSSR20 ideal and most cost effective is 6mm2 (AWG #10) PV cable for groups of two parallel panels. The two panels can be 60 cell panels for 24V battery so 250 to 320W depending on panel efficiency and if panels are very far like more than 20m (60ft) then you may consider going with 72 cell panels as then you can accept higher voltage drop and can sue this same cable up to 60m (200ft).With 32 cell panels for 12V batter keep the distance below 20m (60ft) with same 6mm2 (AWG #10) for two parallel panels if made with 156mmx156mm (6x6”) cells usually rated 160 to 180W depending on cell efficiency or you can use up to 3 panels in parallel if panels are made with 32 or 36 cells in series that are 125mmx125mm (5x5”).


You can see the DSSR20 as an ideal diode plus a solid state switch in series so there will be almost no voltage drop on the DSSR20 (just a few mV) The important part is your battery that is 25.6V nominal but most of the time it will be around 26.5 to 27V and so the panel when hot needs to have at least this 27V + depending on cables 2 or 3V drop on those so around 29 to 30V max power point voltage with a 60 to +70C panel. The max power point for 60 cell panels is around 32 to 33V at STC meaning panel at +25C but for panel to be at +25C ambient needs to be around -10C.
But PV panels are constant current sources so voltage of the panel if connected to battery will be the same as battery voltage plus the voltage drops on the wires. So in most cases (mostly dependent of PV panel temperature) the 60 cell panels + DSSR20 + 8s LiFePO4 battery will result in a 90 to 100% efficiency so an average around 95% and thus it is an ideal match. <<<This is what I meant by matching my panels to my BMS.
If you go for a panel with exact same cells but 72 of them then those extra 12 cells will not contribute with anything but the open circuit voltage of 72 cell panels is below 51V so it is not a problem for the DSSR20 is just that a 72 cell panel has 20% more cells and so 20% higher power rating than a 60 cell panel and also a 20% higher cost but charge current will be the same so will be the charge power thus there is no advantage other than aesthetics (in your case) to pay 20% extra.
So DSSR20 can handle 60 cell and 72 cell panels with no problem is just that there will be no difference in power provided to battery.
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Old 09-27-2022, 05:08 PM   #9
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Quote:
Originally Posted by Peterjk View Post
Ok, Ill cope/paste what I learned from Dacian, who designed and built the electrodacus BMS. I had to read it about 10 times before it sunk in.
A DSSR20 is the mppt, its just a switch which flips the panels on/off.
The SBMS0 is the BMS.

By match for my 24v system means 60 cell panels. With these specs:


Here we go....



PANELS
https://electrodacus.com/SBMS0/SBMS0v03d.pdf

If you go for a panel with exact same cells but 72 of them then those extra 12 cells will not contribute with anything but the open circuit voltage of 72 cell panels is below 51V so it is not a problem for the DSSR20 is just that a 72 cell panel has 20% more cells and so 20% higher power rating than a 60 cell panel and also a 20% higher cost but charge current will be the same so will be the charge power thus there is no advantage other than aesthetics (in your case) to pay 20% extra.
So DSSR20 can handle 60 cell and 72 cell panels with no problem is just that there will be no difference in power provided to battery.
Really? He earlier mentions MPPT charge controllers, but the paragraph above would only be true with PWM charge controllers. The whole essence of a MPPT charge controller is that it converts a high voltage and low current from the panels into a lower voltage and higher currant for the batteries, thus keeping the input power and output power about the same (except for its own internal losses). PWM charge controllers cannot do this: their current to the batteries can never exceed the current from the panels, and excess voltage greater than what the batteries need is just wasted. In other words, a PWM charge controller is "just a switch which flips the panels on/off", to quote Electrodacus's supposed description of a MPPT charge controller. Or am I completely wrong here?

John
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Old 09-27-2022, 10:52 PM   #10
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I honestly would recommend you hit up Dacian on his forum with your specific question. He will answer you. I don't want to hyjack this thread with our discussion. The comparison comment between a mppt and a dssr20 was mine not his Btw. It was probably misinterpreted. Not many know what a dssr20 is.
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Old 09-27-2022, 11:58 PM   #11
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For what its worth, I did 4 24v 295w panels.



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Old 09-28-2022, 12:00 AM   #12
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For what its worth, I did 4 24v 295w panels.



If I may ask how did you compensate for the curve of the roof using the unistrut?
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Old 09-28-2022, 09:53 AM   #13
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I used 1" square tubing cut the same length as the panels for the frame. the center is bolted to the middle strut directly. For the outside brackets, i cut 2" angle iron into 2" pieces then drilled a hole and attached 2 pieces together and tightened them to account for the angle. There is enough width in between the tubing that the panels actually rest between the tubing on that angle iron. then there are bolts through the tubing on each end holding them to the frame.
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Old 09-28-2022, 10:10 AM   #14
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Old 09-28-2022, 09:17 PM   #15
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Thank you, that's actually really helpful if I wanna go for the deck route.
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Old 09-29-2022, 06:34 PM   #16
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I was lucky, my bus came with a luggage rack. It was too tall so I cut the top part off, shortened it and used it for the front rack. Added the center rails for mounting the panels. Basically everything is 1" square tubing.





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Old 10-01-2022, 05:36 PM   #17
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Quote:
Originally Posted by Truthseeker4449 View Post
So I'm planning to put 18 24v 200w panels on top of my bus. Some would probably consider this excessive, but I don't like being hot so air conditioning is a requirement for me.

The thing I keep going back on forth on is how to mount them. My initial and still somewhat preferred idea is arrange them in 3 rows along the contour of the roof, that is to say directly bolted through the roof sheet metal and reinforced on the backside with thick strips of aluminum. The largest downside appears to be the system would have a lower maximum output as the panels will be in 3 different planes.

Or I could build a deck so all the panels are on the same plane relative to each other. I feel this option requires more complex engineering to mount to the roof, wouldn't look as nice or clean, and raises the overall roof clearance more, especially at the edges of the bus. But the performance of all the panels would be the same.

Any thoughts? Perhaps I'm overlooking something critical?
Why 18 200W panels? We have 12 327w panels on the roof and 4 more on a trailer. We went with the 327w panels because they were as much wattage as we could afford per square foot.
What are the dimensions of these 18 panels? Can you really fit them on your bus? Why not fewer more energy dense panels?
Perhaps you haven't considered how big the panels are. A listing on Santansolar.com gives the specs for Thier blemished 250w panels at 69.7"x39.5". If you run them two wide side by side and end to end you can fit 14 on the roof of a forty foot bus with some overhang.

At the same time
New Canadian bifacial 405w panels can be had for less than two hundred bucks apiece. Take it from someone who chased the comfort zone, adding to my system till I reached autonomy, go as big as you can afford from the getgo.
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Old 10-01-2022, 09:00 PM   #18
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Why 18 200W panels? We have 12 327w panels on the roof and 4 more on a trailer. We went with the 327w panels because they were as much wattage as we could afford per square foot.
What are the dimensions of these 18 panels? Can you really fit them on your bus? Why not fewer more energy dense panels?
Perhaps you haven't considered how big the panels are. A listing on Santansolar.com gives the specs for Thier blemished 250w panels at 69.7"x39.5". If you run them two wide side by side and end to end you can fit 14 on the roof of a forty foot bus with some overhang.

At the same time
New Canadian bifacial 405w panels can be had for less than two hundred bucks apiece. Take it from someone who chased the comfort zone, adding to my system till I reached autonomy, go as big as you can afford from the getgo.
Because those were the panels I determined I could fit without overhang, which I very much did not want. And having already purchased 8, I'm not exactly inclined to revamp the entire plan with new larger panels. A major part of my plan is to retain the original roof hatches (which I've already replaced) for emergency escape and ventilation. This naturally limits putting giant solar panels on the roof.

Before I purchased panels I did some calculations and found most solar panels offer the same bang for the buck for each square foot and each watt produced. So I came to the conclusion the main thing that mattered was space considerations. Now it's entirely possible I never came across a panel that offered more than what you can normally find.
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Old 10-05-2022, 05:02 PM   #19
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Have you thought about an auxiliary, mobile plug in array? Maybe mount some permanent fixed to the roof, then build another two sets of two to a substrate and keep them in the bus until you park, then pull them out and jack them in facing the sun? Just a though...
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Old 10-05-2022, 07:21 PM   #20
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Have you thought about an auxiliary, mobile plug in array? Maybe mount some permanent fixed to the roof, then build another two sets of two to a substrate and keep them in the bus until you park, then pull them out and jack them in facing the sun? Just a though...
I have thought about using the second PV plug on the invertor for such a purpose, though after doing some more measuring the other day I found I do not have enough space to put 18 panels on, only 17 so if I stick to my original plan then I'll be forced to used that port for the center row of panels. It would also be a significant amount of panels I would have to store, and based on my layout mapping, I don't really have that much space.

However if I can get someone to build me a trailer hitch then I would eventually build an array over a car hauler.
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