12 or 24 volt?

[tx2sturgis]

Again, let's help the OP.

Further personal attacks or insults will be deleted without notice.

 

[rruff]

I'd put the portables on their own controller since they will be seeing different conditions.

Is that really important? I looked into this awhile back and decided it wasn't (providing that the panels have similar I-V characteristics), but maybe I goofed.

For instance, the mppt will adjust voltage to maximize the power. In the figure below you can see that the optimal voltage changes depending on irradiance (the angled line) but that the difference in power output at the optimal voltage is tiny compared to the power output at the optimal point for full irradiance (the vertical line). Based on variations in irradiance, there is very little potential loss associated with using the same controller for multiple panels....



.... But... now I have to consider the effect of temperature! The optimal voltage can vary quite a bit more in that case. Generally you expect the panel getting the most sun to be the hottest one, though a remote panel will probably have better air circulation than one on the roof. I'll be camping in moderate temperatures, so the +50C and +75C curves would be more relevant. The ambient temperature may be 25C, but a panel would only be that cool if no sun was shining on it at all... in which case it's not providing any power anyway. So say I have 2 100W panels, one panel is in full sun and 75C, and the other angled to receive half the irradiance, and is 50C. The mppt will favor the hot panel since it is providing more power. Eyeballing the chart below, the 50C panel would be about -5% of it's optimal power output at the hot panel's optimal voltage, which would reduce my total power production by ~2%.




Is a 2% loss part of the time (kinda worst case), worth getting another mppt?

 

[USNvet]

Here is one of the quality sellers, WAY better deals than most, ahem. https://www.amazon.com/Ampere-Time-...330-a548-74a658715741&pd_rd_i=B08P6LP1J9&th=1
also these folks https://www.amazon.com/dp/B091YCZV2...pY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1
I will add a video of a well trusted guy in the community for MANY years, where the battery is broke down, and he gives the test results, as I IMPLIED in my other post. Here is a short about him, https://shopsolarkits.com/blogs/learning-center/who-is-will-prowse-diy-solar

That Chins battery looks like a good option, however I like the newer model linked by Amazon to their 24V 200amp battery.

It will be a while until I do a full solar conversion, but just for the short camping trips I now do, I have one 200 watt panel I just lay on the ground, and hook it up to an Epever 40amp 12/24V MPPT charge controller to keep a 110 AH lead acid topped off. It keeps the frig running and phone charged! If 110VAC needed, I have a 2200W generator.

I'll look at the big picture when I'm ready to do the full conversion, as there is a constant turnover of new goodies coming to market all the time. If done today, I'd go with 4 200w panels on the roof wired with 2 in series X 2 banks in parallel for a 24V system. The Epever will handle up to 1040 watts at 24V, so that is good to go, and I'll add a 3000W inverter. I like the new rack mounted 24V/200W lithium batteries now, and they are about the same price and built with the same guts as the Chins battery, but easier to open and work on:

 

[frater secessus]

Interesting input, thanks. {Mods: note that this digression is directly related to OP's mention of adding portables to the system later. Rruf and I are discussing ways to do that.}

In theory all other things being equal best-to-worst harvest would be:

1. separate MPPT for each panel
2. separate MPPT for each similar array (spec, area, orientation)
3. single MPPT for disparate arrays (or conditions)

In practice #1 usually only happens in Very Serious setups like round-the-world sailboats. The rest of us compromise with #2 or #3 to reduce complexity and/or cost. So the question then isn't so much "do we compromise?" but "where do we draw that compromise line?".

I am confident making a general recommendation of #2 to non-technical users, and in using it for my own setup. Having said that, it is entirely possible that a single MPPT running disparate arrays (#3) may be able to find a compromise power point that is acceptably close to the combined output of separate controllers. I encourage OP to A/B test this if they are interested and report back. I am for whatever works.

Anecdote: right now my flat-mounted array is running Vmp = 30.3v and the tilted portables at 18.03v (actual under local conditions, not rated spec). Is there a Vmp where a single MPPT could run the combined panels and get nearly-as-good results as the separate controllers? Maybe.

{Anecdote update: I just went out and separated my series-connected portables, turned one to get differrent insolation, and attempted to get both individual and aggregate readings. The sun is coming in/out of clouds so I could not get useful readings. I bailed on the experiment. I will repeat it when I get stable sunlight. }

There is a lot of academic interest in the problem of finding the true MPP when a lumpy aggregated power curve is presented to the algorithm, as in #3. The challenge is getting the controller to find the actual MPP under given conditions while recognizing and avoiding quasi-MPP peaks (the lumps) that individual panel{s} and combinatinos introduce to the curve. This can be done reliably with frequent full sweeps but that's relatively slow and expensive in terms of lost harvest while sweeping. I look forward to the day when retail controllers can have our own custom MPPT algos loaded into them.

worth getting another mppt?

Maybe not, but I wasn't necessarily suggesting that. The presence of one MPPT in the system is useful since it addresses PWM's low voltage Achilles' Heel. Once bank voltage is up into PWM's comfort range the advantage of a 2nd MPPT may be minimal and may not pass a cost-benefit analysis.

I do use a 2nd mppt for the portables because I already owned it. If I didn't already own it I'd likely throw a configurable PWM in there. I'd lose the ability to run the portables in series but that's not a dealbreaker for me.

 

[Cajunwolf]

@USNvet,
I went with the Chin's back in November last year. I picked up four 12 Volt 200Ah for $600 each (free shipping to my door) through a factory rep I met on Will's forum; I'm a member there too. I've had no problems so far. I have them in a 2s2p configuration for 25.6 Volts behind a Giandel 4kW PSW inverter. I know several of the guys over there who bought them too and are happy as well.

 

[Cajunwolf]

@Daiki Jin,
Check out Santan solar if you're interested in some 250w to 300w plus used solar panels that work great. I bought some 250w panels for $65 each and have no complaints. Some folks have got to have new, but some of us are on a limited budget, and this is an option for more bang for your buck. One can always upgrade panels later; they're usually the cheaper component.

 

[Daiki Jin]

Since there is a trailer involved I would skip DC-DC and spend that money on more panel for the trailer, enough to support your loads offgrid. If you are married to the idea of DC-DC charging the trailer battery see this approach to injecting higher voltages into the 7pin.

I have it, doesn't mean I would use it plus the fact that it only has 4plug for trailer. But when I used to live in my SUV I did run 2AWG wires with an anderson plug to my back tailgate area so in theory if I really want to I have a nice heavy wired plug to the hitch and just run another anderson plug into trailer to charger...If I felt I need it

 

[Daiki Jin]

Check out Santan solar if you're interested in some 250w to 300w plus used solar panels that work great.

HA.. Thank you I will check them out especially since they have a warehouse 30 miles from me!

 

[Cajunwolf]

... since they have a warehouse 30 miles from me!

That's a lucky break; shipping to Houston is costly nowadays. Are you in Az or Ga? I'm looking at some Canadian Solar 250w panels they have in Az. I need to upgrade/repair and have two that have tree damage, and the three-panel array that rides on top of my WJ Grand Cherokee I use for ground deployment when not on the road shows wear from my hastily built rack that attaches them to the cargo rack on the Jeep. I'm trying to get one of the sales folks to get me some better pictures. I want to use two four-panel arrays set up 2s2p to better utilize my 40 amp 150v MPPT charge controllers. If you're in Az and pass by, get some pictures.

 

[Daiki Jin]

I would love too but I'm outside of Savannah. But when I was browsing the site I wished I had funds for the pack they have listed https://store.santansolar.com/product/santan-solar-t-series-240w-cracked-vinyl-solar-panel-lot20/

 

[Cajunwolf]

I would love too but I'm outside of Savannah. But when I was browsing the site I wished I had funds for the pack they have listed https://store.santansolar.com/product/santan-solar-t-series-240w-cracked-vinyl-solar-panel-lot20/

Yeah! That's a good deal for a lot of power for the buck. All one has to do is paint the bottom with a little flexible epoxy sealant, and you're good to go.

 

[Zerpersande]

Here is one of the quality sellers, WAY better deals than most, ahem. https://www.amazon.com/Ampere-Time-...330-a548-74a658715741&pd_rd_i=B08P6LP1J9&th=1

- I went with the Ampere-Time 24V 100Ahr battery. Smaller wire sizes, one battery rather than two.
- Have talked with Ampere-Time a couple of times. Service is great. Even though I bought my battery back in early December, they were willing to take it back if I wanted to upgrade to a 200Ahr battery. Of course I hadn’t open the battery yet and I pay shipping.
- The battery I bought isn’t self-heating so you’ll need to be careful of charging in low temps. I bought some terrarium heating pads and a controller really cheap though it probably won’t be needed in my area.

 

[CampingOdyssey]

Hi,

I'm looking to build a system this week, but I'm torn between a 400ah 12v or 200ah 24v battery.

Because of the holiday, a few companies have a sale ending tonight, so I feel like I need to purchase today.

I did a small 12v lead acid build a few years ago (batteries dead) so I should have most of the wires I'll need (at least I think). A fair amount of 2ga wire and some 10 and 14awg. I also have a fuse block and kill switch from that build I'd like to use. I have an older 12v, 750 inverter but it's not pure sine wave so I'll upgrade that this week anyways (a 2000w invertor should be plenty for me at time).

I have a 100w Renogy foldable solar panel and plan on adding about 400w of additional panels (those will likely be foldable as well). Because all the panels are foldable, they won't be permanently attached to the outside of the van, instead I'll take them out when parked and I'm able to.

In addition to the 100-500w of solar I'd like to use a dc-dc charger to get power from the car while driving.

The best dc-dc charger I found for a 12v system was the Renogy 60a. For 24v the best I saw was a 15a with Bluetooth. I like that the 12v, 60a will charge twice as fast as a 24v, 15a and I don't really want Bluetooth, so because of all that I like the 12v option.

If I can get on average of 6 hours of good sun with 500w of solar that should give me enough to power all of my needs. On days when I can't get solar, the 12v, 60a dc-dc charger driving for 6 hours would be enough. The 24v, 15a dc-dc charger would be ok but about half my needs.

I keep hearing that 24v is better. However, in my situation since it's a relatively smaller system and I'd like to charge via dc-dc, I'm wondering if the benefits of a 24v system still make it worth wile? For example, I hear 24v is more efficient, does that mean the 500w of solar I have will charge the bank faster? Does it also mean that I'll use less power overall on my daily loads on a 24v system? I also hear with a 24v system you save money on wires, since I already have large 2ga wire, should I just go with the 12v?

The largest energy using appliance will be a 120v air fryer that I'm hoping I'll be able to use maybe 2-3 times a week for 45minutes at a time using1200-1500w. Maybe at some point in the future some sort of smaller AC unit but no plans for that at the moment. Any help would be appreciated!

 

[RvNaut]

What one chooses for voltage depends on the capacity of battery and the quantity of solar.. less than 800 watts solar is good for 12v.. 800-1500 is 24v territory and above that is best served by 48 volt.. HOWEVER... battery size also matters... you need enough battery to hold the amount of charge you intend to pump into it.... and that of course depends on how much you intend to use for power and how long you want to be able to operate without sun.
.
So.. calculate max load... put batts in place to handle that load for your chosen time frame and then figure what solar you need to support that demand.

 

[rruff]

Hi,
I'm looking to build a system this week, but I'm torn between a 400ah 12v or 200ah 24v battery.
Because of the holiday, a few companies have a sale ending tonight, so I feel like I need to purchase today.

I'd like to know who is having a sale!

The efficiency difference between 12v and 24v is just wire losses I think, with 24v being 1/4 the loss for the same power and wire. In my case it seems like 24v panels and 12v battery are probably best, as 12v lights and things are more popular in the US, and for 120v it won't matter. With 24v panels you can use longer cables to place them further from your rig. This is assuming that you use a MPPT charge controller of course, and you will probably need to wire your panels so they output 24v, but this is easy.

For your dc-dc make sure your alternator is big enough to handle it. Renogy is probably conservative, but they recommend a 200a alternator for a 60a charger.

Also, I'm a little grumpy after looking at a dozen sites to try to find out how much energy an air fryer uses, and they were all absolutely worthless... probably AI generated. It may draw a max of 1500w, but once it warms up it will surely have a set temperature and much lower power consumption. So, find a site where someone has actually measured it, or if you have one, measure it yourself. It's probably a lot less than you think.

 

[CampingOdyssey]

Hi,

I wasn't aware that it's possible to wire the solar panels at 24v and use those to charge the 12v battery bank! If that's the case, then going with a 12v system seems like a good bet in my case. If I do expand it to have more solar (say for example I want to add 2000watts someday), I could wire them as 24v to save on wire cost and loss? I'll definitely do that if it's possible.

The air fryer I'm referring to is the Ninja DT251 here: https://www.amazon.com/gp/product/B08BXXQ37X/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 It's a pretty big one but it's really helped me to eat better so being able to use it a few times a week is, now that I think about it, pretty important to me! I was under the impression that it was 1500w but on the link it says 1800w. Not sue the actual usage because I've never used it on full power. Now I'm worried that I I'll need an inverter that is too big for a 12v battery to handle.

I'm considering a 12v, 410ah battery and was originall thinking this inverter: https://www.amazon.com/dp/B01COA0UT...ng-20&linkId=6101f02ee602a4335f2b813bbea68f82 but that may not be big enough to handle the Ninja Air Fryer I have. Do you think this inverter would be better? https://www.amazon.com/Power-Invert...ng-20&linkId=096f1217257e6940fd25c818f44f65b3 I was originally going to use

 

[CampingOdyssey]

I forgot to mention the companies having a battery sale are: https://ipowerqueen.com/, https://www.litime.com/, https://www.weizeus.com/, and https://www.redodopower.com/

 

[Zerpersande]

Hi,

I'm looking to build a system this week, but I'm torn between a 400ah 12v or 200ah 24v battery.

One thing to consider…
I went with 24V to be able to use smaller wires. This means setting up my panels in series to get a high enough voltage to charge my battery. Series need full sunlight. You probably get the picture.

 

[CampingOdyssey]

One thing to consider…
I went with 24V to be able to use smaller wires. This means setting up my panels in series to get a high enough voltage to charge my battery. Series need full sunlight. You probably get the picture.

I only have one 100w foldable solar panel at the moment but plan on getting more solar to add to the system. I saw a 400w foldable panel at an affordable price that I may buy. If I do end up going 24v, I was planning on wiring them together so the 100w has the necessary voltage to charge a 24v battery. Will I be able to do that or am I misunderstanding how it works? When you say they need full sunlight, do you mean that, during non-peak sun or in partial shade, panels in series are not as effective at charging as the same number of panels in parallel? Thanks for the help.

 

[Zerpersande]

I only have one 100w foldable solar panel at the moment but plan on getting more solar to add to the system. I saw a 400w foldable panel at an affordable price that I may buy. If I do end up going 24v, I was planning on wiring them together so the 100w has the necessary voltage to charge a 24v battery. Will I be able to do that or am I misunderstanding how it works? When you say they need full sunlight, do you mean that, during non-peak sun or in partial shade, panels in series are not as effective at charging as the same number of panels in parallel? Thanks for the help.

I’ll explain what I learned, but fact check, okay?

Series are additive for voltage. If you want to charge a 24V battery you have to up the voltage to above that. I have 3 x 175W Renogy panels, 21.6V/10.3A. Wired in series the amperage is still 10.3A but the voltage goes up to 65V. So it will charge the battery.

For your situation you need to look at the rated voltage and amperage for each panel. If it’s a folding panel it’s pre-wired, right? Which may lock you in the whatever the overall V/A rating is.

And I just thought of something…maybe I can wire 2 of my panels in series and then the other one in parallel to those. Put the parallel unit on either the front or back of the array on top of the van so maybe I can position the van so the single panel can be in the shade if I have limited area of sunlight.