24v solar panels

[clev]

Have any of you wired your solar panels in series producing 24 volts? I have Renogy panels and the tech informed me that 24 volt series would be more efficient that 12v. My controller is also maxed out at 800 watts for 12v and I'm considering adding 2 more panels, taking my total to 900; 24 volts, according to him, would cut those watts in half. I'm out of my element here and doing research. Any advice/information is appreciated......except from the 2 that I don't want to hear from.

[Long & Winding road]

I have "read" about the 24v systems. I dont know a lot but I think if I had like 6 to 10 panels (600 to 1000 + watts) like you have I would split them that way the if the front half of RV was in shade that back half will still work and charge the system. But run 24 volts which they say is more efficient. Plus you should be able to still use your current solar controler and wiring.

Tons of tread and website on this subject..... do your research first but it sounds like it would work for you.

Hopefully someone can chime in that is currently running 24 v.

[mtntrek]

Generally, yes as you increase Voltage, you decrease Amperage. Other things being equal the Wattage would remain the same. Some go to 48V or more.
Series panels can have other issues though, such as shading of any small portion of the said string "could" result in a large reduction of output to all panels in a series string.
Unsure of your controllers capacity and you battery bank type and capacity it would be difficult to determine what actual output might be.
You can only shove so much at your batteries at a given rate and temp to avoid overheating damage etc. If your tech thought it should work, go for it.

[scrubjaysnest]

Series panels will work best in none shade conditions like out west. You need to make sure that Voc of the series combination doesn't exceed the controller max voltage input. It also requires using MPPT controllers. The reduction in wire size may not offset the increase in cost of an MPPT controller.

[clev]

At this point, I have four 150 watt panels producing a max of ~33 amps into a 60 amp Renogy MPPT controller that feeds six Life Line 6-volt batteries wired in series for a total of 660 ah,

[wingnut60]

clev,
You mean 6 batteries seriesed in pairs, then paralleled? Otherwise, you have 36 volts output.
Joe

[clev]

Good morning, Joe. Your correct, but with our trailer system bring 12v, I thought that part would be understood. My oversight.

[wingnut60]

Sorry, clev, should have known...

[heiser252]

I am running three parallel strings of two panels in series on my fiver. My panels are 36 volt panels, so each series string can potentially produce 72 volts. I have a Magnum PT-100 charge controller that needs high voltage like this to work properly. Each panel is 235 Watts for a total potential wattage of 1410. This set up works very well for me.

As stated above, as long as your charge controller can handle the higher panel voltage and still output 12 volts to your batteries (which is what MPPT controllers are meant to do) the biggest problem to watch for is potential shading issues.

[juicesqueezer]

Originally Posted by heiser252

I am running three parallel strings of two panels in series on my fiver. My panels are 36 volt panels, so each series string can potentially produce 72 volts. I have a Magnum PT-100 charge controller that needs high voltage like this to work properly. Each panel is 235 Watts for a total potential wattage of 1410. This set up works very well for me.

As stated above, as long as your charge controller can handle the higher panel voltage and still output 12 volts to your batteries (which is what MPPT controllers are meant to do) the biggest problem to watch for is potential shading issues.

Question; with that wattage, can you run at least one air? We are considering 1200 watts with the Magnum controller and I believe it still won't run an air.

[wingnut60]

Joe,
Even IF you could run the air off the solar, you could not replace the power as fast as it is used. We have 1260 in panels, but the ACs and fireplace are not powered by them--the microwave is and works well for 2-5 min draws.
Still learning about the use and replacement time needed in full sun...

[clev]

I think that I am finally beginning to understand more of this. 1. Panels can be wired
in series, but must terminate in some multiple of 12 volts; 12, 24, 48. If that is correct, must the panels be paired so as to double the voltage each time, or can the string have an odd panel? Ex.- three 12 volt panels wired in series to parallel, to produce 36 volts? 2. Regardless of the voltage coming into the MPPT controller, it will step it down to 12 volts. Is that correct?

[ewacowboy]

Originally Posted by juicesqueezer

Question; with that wattage, can you run at least one air? We are considering 1200 watts with the Magnum controller and I believe it still won't run an air.

Joe,

I agree....it all depends on your battery bank capacity. Chad is running a 1040 amp hour capacity battery bank. If you want to look at his system he has a thread on Escapees here: My Solar Installs - Now with Solar Output Data - Technical Tips and Tricks - Escapees Discussion Forum

I'm currently installing a system with 1200 watts of panels but my battery bank isn't enough to run the a/c. Maybe when the new lithium technology becomes more affordable I'll change out to a bigger/better battery bank.

[wingnut60]

Keep in mind Chad's batteries are Lithium, not lead acid--he can utilize almost all of his AH capacity; I have 1200AH capacity, but mine are AGMs and are 6volt in series, giving me only 600AH and should not go below 300/50%.
Chad is one heck of a designer/installer...

[clev]

Yes, wing, Chad is really great with these systems, and I have nothing nearly as elaborate as what he has designed/installed. If he is monitoring, hopefully he or you can clear up my questions in the other post.

[heiser252]

Originally Posted by wingnut60

Keep in mind Chad's batteries are Lithium, not lead acid--he can utilize almost all of his AH capacity; I have 1200AH capacity, but mine are AGMs and are 6volt in series, giving me only 600AH and should not go below 300/50%.
Chad is one heck of a designer/installer...

Thanks for the compliment. I appreciate it. As to my battery bank, unfortunately I am running AGM batteries. I wish I had 1040 amp hours of Lithium instead of just AGM. It would give me more useable amp hours at a lot less weight. (My AGM bank weighs about 700 lbs).

[heiser252]

To the question about running an AC from solar/batteries, it can be done and one of these days I will probably do it as a proof of concept. There are however some limiting factors. First you need an inverter capable of putting out enough power to handle the initial surge of the AC compressor kicking on. Not a lot of inverters are capable of this. If I go this route, I intend to add a micro air easy start module to my AC unit before I try to wire it to my inverter sub panel.

Lithium batteries are also better than other types of batteries for trying to run an AC. This is because they produce a consistent, linear power output all the way from full charge to almost completely discharged. AGM and Lead Acid batteries output power more on a curve, with higher output at full charge and then ever decreasing output as the charge diminishes. Additionally, Lithium batteries can be discharged more deeply and don’t have to be fully recharged regularly like AGM and Lead Acid. This is more conducive to trying to run high draw items like an AC. This doesn’t mean you can’t run an AC from an AGM or Lead Acid battery bank because you can. It is just that a Lithium bank is better suited to do it, but I am digressing from the original topic. Of course you still need to replace the power drawn by the AC back in whatever bank you use, which is where solar comes in and why this topic was started.

[heiser252]

Clev asked me his original question from this topic (with a little more detail included) in a pm on another forum. I haven’t been monitoring this forum as closely recently, but with the pm, I came here and decided to add some additional information. I also wanted to post my response to Clev’s pm here so that others might benefit from the information. (Clev, hopefully I am not overstepping my boundaries here.)

Basically, Clev has an existing system with four 150 watt panels installed for a total of 600 watts. His existing MPPT charge controller is limited to a maximum wattage input of 800 watts and he wants to add two additional 150 watt panels to his system. This would give him a total of 900 watts. He wants to know if there is any way to wire the six total panels to keep them within the specifications of his existing controller. Here is my basic response to that general question:

“Sorry, I haven’t been keeping up with the Thor forum that much lately. To start with, here is a basic equation that should help:

Watts = Volts x Amps

For example, my panels are Canadian Solar 235 watt panels. I have six panels for a total of 1410 watts (235 x 6 = 1410). The Vmp rating of my panels is 29.8 and the Imp rating of my panels is 7.9 (29.8 x 7.9 = 235.42). This is why my panels are rated at 235 watts.

I run my panels in three parallel strings of two panels in series (six total panels). When you run in parallel, the voltage stays the same and the amperage is cumulative. When you run in series, the voltage is cumulative and the amperage stays the same. So in my case, I have two panels in series. This gives me 29.8 + 29.8 which is 59.6 volts at the same 7.9 amps. I then have three of these series strings. This gives me 7.9 + 7.9 + 7.9 which is a total of 23.7 amps at the same 59.6 volts. Again, Amps x Volts = Watts, so 23.7 x 59.6 = 1412.52 total watts, or basically the same 1410 watts (when you account for rounding). In other words, series or parallel makes no difference in my total watts. Hopefully this example helps you with your calculations.

If you go to six of your 150 watt panels, no matter how you wire them you still have a potential of 900 watts. In other words, you can overpower your existing charge controller. You can re-wire your system (with six total panels) into any combination of series/parallel and it will always come out to 900 watts, which is more than your particular controller is rated for.

MPPT controllers in general can take high voltage input and convert it to lower voltage at higher amperage output. Your controller could take the higher voltages of various series/parallel combinations of your six total panels (assuming they were within the maximum wattage rating of your controller) and still put out the appropriate voltage to your 12 volt battery system. This is what MPPT controllers are designed to do. They take the additional voltage input from high voltage panels and convert that extra voltage to additional amperage going into your batteries at the proper voltage.

You also do not want to mix one series string into your existing parallel set of panels. You will be mixing different voltages, which will pull down the voltage to the lower of the two. When you mix panels of different voltage (your two additional panels in series essentially become one panel with a higher voltage), the maximum output will be the lower of the two voltages. This is based on electrical theory that is too difficult to explain here, but it is what happens. This, in essence means you would not be getting any benefit from this new string any more than just adding one single additional panel (of the same ratings) to your existing array.

Hopefully this helps. Let me know if you have any more questions. I am happy to help.

Chad”

The Renogy tech that Clev mentioned in his original post did not give Clev completely correct information. He was correct in that running panels in series can be more efficient. This is because you can use smaller wire and components related to the wiring than the same wattage array run in parallel. Higher voltage can use smaller wire than lower voltage (this can be seen by plugging numbers into any wire size calculator). However, when the tech said running in series would lower the wattage of the array, he was incorrect (as I explained above).

Hopefully this information is useful. Again, Clev, I apologize if I overstepped by mentioning our PM conversation.

[clev]

Good morning, Chad. Thank you very much for this lesson and you have not overstepped anything. This grasshopper is extremely grateful.

[wingnut60]

Chad,
I apologize for spreading misinformation on your battery type--I remember your original posts on your system and thought it was lithium.
Thank you for the time you put in trying to explain solar to us guys.
Joe