Solar System Advice/Feedback for new Truck Camper

Mike@Asheville wrote:
Also, I'm giving up on the future expansion idea as I only have room for 2 batteries. ...

I'm attaching a picture of my roof. ... I'm thinking two 120w or 140w panels instead of my original plan of three 100w.

...

I'm going with the Morningstar SureSine 300 Inverter.

...
So I need to decide on the controller. There seems to be some difference of opinion here. For this system should I go with PWM or MPPT knowing I may want to use a portable panel with the same controller in the future?

Also, what is a good source for the roof mounts that allow you to tilt them?

1) Expansion:
The rule 1W of solar per 1 AH of battery bank is not a dogma. You can have 300 or 400W solar for 225 AH bank, and with small solar you should.

2) Roof photo and panels wattage:
From the picture it looks like it's easier to install few small panels (100-140W) rather than one or two big 24V panels. 120 and 140W panels are often of the same size (or very little difference). Fit as much solar as you can, as long as you can walk around them. Don't know why I would want to walk on the roof though.

3) 300W inverter:
If you are OK with running a generator 3, 4, or 5 times a day, for making coffee and running microwave - then yes, 300W inverter should suffice for your other needs. I wouldn't be happy with such an arrangement, but this is your lifestyle. Also, check Cpap machine wattage if it's less than 200W.

4) Ignore the difference of opinions on PWM-MPPT. It's feasibility decision. If your roof has no room for big 24V panels, then you install few 12V panels, and then you go for PWM. There is no benefit in using MPPT with 12V panels. I still think that $100 MPPT Eco is better for 2*140W 12V panels than $30 PWM, because of metal case, but this isn't awfully important.

5) What controller:
When you will know better how many 12V panels and of what wattage you will install, then you will ask what PWM controller to buy. At 280W it's a toss a coin on Eco MPPT 20 and - whatever it name was - $30 PWM gizmo. Either one has display and on-board temp compensation.

6) Portable in future - instead or in addition to existing roof solar?
If controller is capable of handling 280W roof array, it will handle 100W or 200W portable instead. BUT, if you are adding, say, 200W portable to existing 280W roof solar, then you need to buy controller that allows 280W+200=480W total.

You don't know your roof wattage yet, you don't know your planned portable wattage. There is no exact answer then.

7) Good source for panel mounts that allow tilting:
There are some, bu there are no good ones. Everybody that have it tilt-able, had to make their own mounts. I don't think you should be concerned with tilt, considering planned daily generator run on one hand, and pains of daily roof climbing for tilting, on the other hand. Here is what I did to make it tiltable to the side. Nothing new, many other had done the same before me:


Click For Full-Size Image.

If you look close, it is tilted now. There are 2ft legs attached to the North side of panel - and to the same L-brackets. When lowered, hind legs are removed and panel rests on the same side screws. Anchor screws #10 into the roof, one machine screw into the panel side. A piece of aluminum angle, $3 each, including cutting. But you don't have to have a tilt. You also don't need 6 anchor screws into the roof. Even with my 40 lbs panel I don't think that I needed 6 screws. My roof is rubber over plywood, your MH roof is different, so the anchors will be different.

There were L-brackets in solar stores, I forgot where. Ask installer. If they know anything at all, they would know where to get L-brackets.

Also, there are 2-piece Z-brackets, it utilizes the existing holes in panel frame and don't require drilling the panel frame. Adjustable height. Look a bit flimsy to me, but so do most off-the-shelf brackets.

I wouldn't go for one-piece Z-brackets offered with 12V kits in places like Solar Blvd - once attached, panels will be difficult to remove without ripping the brackets off the roof.

Temp comp just adjusts controller set points. Your batteries aren't going to be much warmer than ambient anyways so the EcoW's internal temp comp is fine.

I think the temp adjustment feature, whether remoted to the battery or not, just adjusts the controller's set points for temp. Has no effect on panel voltage or MPPT bucking AFAIK

With high temps the battery voltage set points would be adjusted lower so the spread between battery voltage and the lower panel voltage might be maintained? Is that what you mean?

FWIW my controller is right beside the batteries so its non-remoted temp comp should be about the same comp as a remoted one. I am still getting the MPPT heat loss effect as described.

Shows the Eco-W (internal temp comp) near the batts (two T-1275s and four 6s--two of the sixes off to the right of this photo) Now have the Solar30 disconnected and the whole six batts as one bank off the Eco-W since the 130w panel was sold that the Solar30 did. Am getting to Float mid afternoon and full SG by dark most days on the 230w tracking in the contraption.

Hi,

Perhaps if there is a temperature compensated charger probe on the battery bank the loss of amps may be different? worse? better?

I'm sure others know more than I do, and probably explain it better. But from what I have read going parallel will make your two panels less likely to have shading effect the total output of the array.

If you go serial it might be more subject to shading issues, it doubles the voltage and allows for less loss on the longer run of cabling.

This is subject to debate as well as PWM or MPPT controllers.

I kept things simple with parallel wiring and a PWM controller. But there are plenty of ways to do this.

Yet another example of Mono vs Poly where you lose amps with Mono (with 12v and PWM)

You get Isc with 12v and PWM so you want the highest Isc per watt of panel or dollar per amp. dollar per watt is no good if the amps are lower, so you should do dollar per amp with 12v and PWM.

Mono spec quoted above vs 150w Poly panel (Sun brand)

Voc 22.5/21.0
Isc 9.05/9.58

So you lose half an amp with the Mono because its Voc is jacked up higher. So two 150s with the Mono will cost you an amp.

At 300w its 18.10/19.16

But now you have to do it in dollars per amp to see which is the better buy.
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In series you add the voltage and the amps are the same.
In parallel you add the amps and the voltage is the same/

MPPT wants high voltage to work with so series is optimum for that.
If in series you must have MPPT to get back to 12v for the batts,

PWM is already at 12v, so it just takes the total Isc rating amps and that's what you can get to the battery.

Whether the MPPT will do more amps to the battery than the PWM would depends on the temperature. If cool out, it will do a little better, but if hot out, it will not do as many amps as the PWM.

You have to know what it will be like when you are camping when and where before you can decide that. Money comes into it somewhere too. 24v panels cost less than 12v panels usually. But the MPPT controller costs way more than the PWM controller. there is a break even point depending on prices. Prices vary wildly all over the map, so it is impossible to say what would work best for you without knowing what YOU know. So it is up to YOU! :)

Thanks Heap64. I confess, I don't know how you determine to wire parallel or in series. For my needs what would be best?

The 150w panels Renogy is selling have only been available a few months now. They didn't have them when I bought my 100w panels. I would expect them to be made to the same quality level.

Here are the links to the specifications for their new 150w panel.

http://renogy.com/wp-content/uploads/2014/05/RNG-150D-Datasheet-01.jpg

http://renogy.com/wp-content/uploads/2014/05/RNG-150D-Datasheet-02.jpg

These panels already have MC4 connectors on them which makes cabling easy.

If you are going parallel you can buy a pair of MC4 Branch Y Connectors (MMF and FFM) and that will let you easily go from two panels to your extension cable. You shouldn't need too long of extension cable. Buy one cable twice as long as you need and cut it in half to make your extension cables.

If you want to go serial and your panels are next to each other you won't need the Branch Connectors.

westend wrote:

BFL13 wrote:
Logic has nothing to do with it

Yeah, sometimes it ends up like that. I'm surprised that temperature should cause you to lose any power from the MPPT controller, compared to the PWM. It is what it is, I guess.

You are surprised because you keep confusing yourself by talking about "power" Think amps! MPPT makes its amps from power which drops with heat along with voltage, but the panel's Isc goes up a bit.

PWM gets you Isc---that's the beauty of it. No loss of amps with the heat. Power shmower. Don't need no steenkin' power, just amps. :)

BFL13 wrote:
Logic has nothing to do with it

Yeah, sometimes it ends up like that. I'm surprised that temperature should cause you to lose any power from the MPPT controller, compared to the PWM. It is what it is, I guess.