Warning, wall of text! But I'm too hungry to add emoticons. Must. Make. Supper!
Here are some thoughts/opinions:
danesk wrote: July 23rd, 2020, 6:51 am
Here are a few details about my installation:
Okay, this is great. Now we have some info to go on. Putting the panels on the driver's side is a good idea (if you are only going to put them on one side) because it's a straight shot to the batteries. IIRC, you have about 108" to the bathroom skylight, so if they are typical 100 watt panels, you should have no problem.
Which Renogy 100 watt are you getting? (Since they have about ten different ones...)
danesk wrote: July 23rd, 2020, 6:51 am I will be using the supplied Renogy mounting hardware with added 3M 4950 tape and plenty of dicor.
Here are some opinions from me:
I wouldn't be too committed to using all of Renogy's parts and pieces. I mean, if they are your choice, then great. But if it's just because "it's a kit!" then I'd say do some thinking about whether each part is what you want. For example, if you use something like Z brackets (not saying you are), then you have one time you can put the panels on the roof with VHB, and you can never lift them again without breaking the VHB bond. What if you want to check a wire or something? For that reason, I prefer two-part brackets. You can buy or make them. With that type, the bottom part gets VHB'ed to the roof, and the top part is bolted to the panel, and then another fastener joins the two bracket parts. Now you can lift the panel if you need to without breaking the VHB bond. This is also a bit easier during install, IMO (securing the wires and etc.).
Another example would be controllers. If theirs has the right specs, then great. But if they are not both user customizable, and with remote temperature compensation (this means the probe is on the batteries, not on the solar controller, and is going to be VERY important for your AGM's in the battery compartment), then I would look elsewhere. I have some familiarity with most of the major brands so if you are shopping we could talk over the pros and cons. I don not know the details on the Renogy but they could be researched.
I would not use any dicor if it were me. I researched this and found papers where 3M basically tortured the VHB and nothing "seeped" under the edges. So those Dicor blobs on top of the brackets, IMO, are not doing much but maybe trapping dirt. I know they say it's to protect the VHB, but from the studies I don't see that it needs protecting.
danesk wrote: July 23rd, 2020, 6:51 amOn the inside, a monitor had been installed where the original TV was...when traveling/camping, the last thing we need is a movie, so that can come out to provide room for the new controller and perhaps a small bookshelf.
It would be better if you could get the controller a bit closer to the batteries, but that's still better than on the other side where the original one was. Here's why I say this: you are pretty much never going to have zero voltage drop (but that's what you would like, unless your controller has a voltage sense wire, which not many do these days). Now, any voltage drop between the panels and the controller, is "lost" power, but it doesn't affect your charging voltages. It just means your solar controller has a bit less power to work with. BUT, voltage drop after the controller means that your charging voltages are not what they should be (by X amount). So it's always better to have the controller basically right next to the batteries if you can. So could you get it closer? Perhaps you could put it between the water heater and the driver's seat down by the LVD, as long as you don't stuff that area full of blankets or something (heat dissipation). My controller is under the couch (as are my batteries) and with space around it does not get hot.
danesk wrote: July 23rd, 2020, 6:51 amSince a parallel connection would provide more amperage, I believe that is the best way to go...?
It's a little different than that. I'll elaborate. You don't get "more" power either way, except maybe a tad more morning and evening in series; but I mean the "doubles the amps" in parallel is not any different than same amps at double the voltage in series. Once it comes out of the controller, it will be about the same - no free lunch.
So, you can put the two panels in series or parallel (presuming you use an MPPT controller). In parallel, the amperage adds up, and the voltage stays the same. So let's say you have panels that are 6 amps at 18 volts. Two in parallel will output 12 amps at 18 volts. This means you have to have larger electrical cables because more amperage will equal more voltage drop. That's a downside. On the other hand, if one panel is shaded it won't affect the other one quite as much (it will still have some effect which is why now many people recommend one smaller controller for each parallel panel). Another slight downside is that early in the morning and late in the evening you might not get quite as much power that the controller can pick up. So what about series?
In series, the voltage adds up and the amperage stays the same. So now you have 6 amps at 36 volts. With the higher voltage you can have smaller cables for the same voltage drop, so that's a plus. You may also get a bit more power morning and evening because the controller has "more to work with" in a sense. The downside? There is more effect on both panels if one is shaded. I wanted to put my two panels in series, so I did some experiments....
I set up two panels, at around noon in July, flat on the ground in full sun. I monitored them with my battery monitors. They were two 135 watt panels of about 17.5 volts each. I set them up in series, and in full sun the controller was putting out 15 amps. That's the max my controller can put out and fairly close to the max of the panels. Okay, time for some shade! I did a bunch of different shade simulations, and took notes of my meters. I did things like put a few branches about six feet up, kind of sparsely across the panels, then bigger ones closer, then some actual leafy trees made some distant "real" shade on one of them, and lastly, I took a piece of cardboard and totally covered one cell on one panel.
In a nutshell, what I found was that the thin branches, far away leaf blobs, and etc. really only "took out" the one shaded panel. The sheet of cardboard completely covering one cell, took out both. Since I don't have any blocks of shade (no roof air or anything else tall on the roof), I will probably put my roof panels in series. I do have my ground panels in series and would not go any other way because I have a 35' wire lead on them and it would have to be HUGE if they were in parallel.
So, I don't know that there is one best way. Although if you do have something that could make a "block" of shade, then parallel is probably a better choice, and you will just have to run larger wire.
I like to shoot for less than 2% voltage drop, and less than that is even better. So let's say you run your two panels in parallel, because you have the air conditioner up there and that could be the "block" type of shade. So you will have around 12 amps coming down in full sun. I don't know if you are going to combine your wires up top or inside, but let's say you do it right around the roof entry point for the sake of discussion. Here is the voltage drop breakdown:
--The two panels on the roof. So each one has a ~2' 12 AWG lead you need to count. 6 amps going through that is .3%. Now you will have some, let's say 10AWG wire connected to those leads. Maybe another foot on the forward panel, and and 2.5 feet on the rear panel. So let's just say 2'. That adds another .2% Now for your main lead to the controller (now they are joined so you have 12 amps at 18 volts). To come into the roof, over to the cabover, down the pillar to the controller (I'm going to say it's at the bottom of the pillar by the LVD) is about 10'. Let's make that 8AWG and see what we get. That adds 1% (10AWG adds 1.6%). Now from the controller (presuming MPPT) we'll say 15 amps at 14 volts (I can only input round voltage numbers), and we'll say it's 4' long (you'll need some loop shapes). With 8AWG that adds .7%, with 10 AWG it's 1%, and with 6AWG it's .4%.
So if you do the following selections: 12 AWG panel leads, 10 AWG on roof, 8AWG down to controller (if at bottom of pillar), and 6AWG to battery area, you will end up with 1.9% voltage drop. The critical point is after the controller though, and there you only have .4% . That means that your supposed 14.4 volts in absorb, will be degraded to 14.34 volts. That to me is acceptable, but I wouldn't want any more. I like that combo, but if you want or need to reduce wire size anywhere, I would do it on the leg from panels to controller, and not from controller to battery bank. You can also see why it is advantageous to have the controller really close to the batteries (because if it's up by the TV, you'll have more voltage drop (or heavier wire), where it counts more. Some really top of the line controllers have a voltage sense wire. That doesn't magically make power, but what it does is sense the voltage (drop) and up the output of the controller to make up for it. But not many (and not many 15 amp if any) have that.
Some people may (rightly) point out that these figures are for max panel output and so with lesser output you could use smaller wire for same voltage drop. That's true, but solar is such a relatively weak power source, and we only have room for so many panels on the roof -- so my feeling is I don't want to lose any of the potential. I've wired up for under 2% voltage drop at max output and have never been sorry I did.
danesk wrote: July 23rd, 2020, 6:51 amI think my main question and likely most difficult task will be to run the new wire from battery up. I had read in a similar thread on this forum about the difficulty removing the pillar...was that your project?
I have removed the pillars (thanks to A Rooney's tips no-one is still trapped in there
). I can't see running wire in there without removing the one pillar. I mean, it's possible, but then how would you secure it, how would you get loom or other chafe protection on it? That said, the wire I ran down for my panels on that side, doesn't actually go in the pillar, BUT, I don't think I could have run and secured it without the pillar off. I'll explain. My panel wires will come in at the old TV antenna "crank" hole. Then, on the forward/inside edge of the over couch cabinets, I have a breaker (which can be used as a switch but is a bit more compact), and a negative power post. This is where I transitioned to 8AWG wire (my panels will be at 35 volts in series, so smaller wire is ok). Since my controller is under the couch, the wire actually runs down between the side wall and the shell - kind of over the water heater, then to the forward side of it. But because I had the pillar off, I was able to easily access that area, get loom on the wire, and secure the wire in a few spots so it can't flap around in between the walls.
Also, you are going to want to drill new hole(s) to get the wire to your outside batteries, and a good spot for that is behind the pillar (stock wires do that from the LVD). So I'd just remove the pillar. BTW, my sofa frame has never been removed. I did remove that little side sofa "wallette" and LVD cover, and I can remove the cushions (I re-did my sofa). But since they are easily removed I didn't even try to remove the pillar with them in place. But the sofa frame was in place. That's not to say you can't figure something out - or run it on the interior in loom - but it would certainly be easier with the pillar removed, if you can do that.
I think you'd want to drill new hole(s) into the battery compartment wall vs. cramming the wires in an existing hole. Take care to provide chafe protection. Another consideration is not to put too many wires right on the battery terminals. If you can work out some bus bars that would be preferable (and you could unload a few wires even). Kind of depends on what you have now.
Note that a good option can be "duplex" wire. I tend to use Ancor, and they have duplex in gauges up to and including 6AWG. This gives you an automatic extra outer layer of chafe protection (it does make the wire more of an oblong shape vs. a circle, but then you only have one vs. two).
Another thing is you want to make high quality crimps, with good tools. Heat shrink is a friend here. With 8AWG and 6AWG, they are past the usual small crimper size. A good option if you don't want to buy a huge (expensive) crimper and lugs is to buy pre-made wires from Genuine Dealz. They have a nice web interface where you can "build" your cable, with wire size, termination eye size, shrink color, the works. I did this with a friend when we re-wired his camper out on a trip and we did not have the big crimper and lugs. I'd say they were good quality and a good deal if you only need a few. For wire termination in general, Compass Marine (Marine How To) has some excellent photo tutorials with tool recommendations. Also, labels are good.
BG