Expanding my solar power system

[justananimal]

Hey!

Currently I have 2x100watt panels wired in parallel and connected to a 20amp renogy mppt on my RV. I am looking to do a total overhaul by adding 3 more 100 watt solar panels, so total of 5 x 100 watt panels.

From my understanding, I will be needing a 60amp MPPT controller and I'm planning on getting a renogy one which seems to only be able to take max 48 volts. 5 panels in series would bring it to a 60 volt system, which I guess would eliminate the plan of wiring all in series. Plus, I'm planning to cluster 3 solar panels together and a few feet later cluster the last 2 panels. See my diagram in the image attached. I feel like I want to kind of have 2 "independent" clusters since they're a few feet apart so that if one cluster is shaded, the other one is not affected. Is it possible to do what I'm showing on the diagram with a single charge controller, or am I displaying a total lack of knowledge ? or should I simply connect them all in parallel?

I also want to keep the output at 12v as I'll be hooking up 3x100ah batteries in parallel. From my understanding, the charge controller can convert 48 volt input to a 12v output going into the batteries.

 

[MisterSandals]

From my understanding, I will be needing a 60amp MPPT controller and I'm planning on getting a renogy one which seems to only be able to take max 48 volts. 5 panels in series would bring it to a 60 volt system, which I guess would eliminate the plan of wiring all in series.

The MPPT takes higher array voltage and converts it to the charging voltage of your battery (12V, 24V or 48V depending on voltage range of the SCC)..

The trick is getting an MPPT SCC that accepts the array voltage (max input voltage). The max input voltage is the temp adjusted Voc of your panels (not 12V as your post suggests).

What is the Voc of your panels?
What is the max array input voltage of the SCC you are considering?

 

[justinm001]

Get a victron mppt

 

[justananimal]

The MPPT takes higher array voltage and converts it to the charging voltage of your battery (12V, 24V or 48V depending on voltage range of the SCC)..

The trick is getting an MPPT SCC that accepts the array voltage (max input voltage). The max input voltage is the temp adjusted Voc of your panels (not 12V as your post suggests).

What is the Voc of your panels?
What is the max array input voltage of the SCC you are considering?

I'm getting the 100 watt 12 volt renogy panels (VOC 24.3v).

Ahh okay, I'm getting a better hang of it. The description for the mppt controller said it's for "12V/24V/36V/48V". I thought this meant that my max solar voltage input to MPPT was 48v, but that's the compatible battery system that is max 48v. The renogy 60amp MPPT has a max input voltage of 140, so technically I can hook all of them up in series 24.3x5=121.5.

So hypothetically, if a 20 amp mppt controller had a 140v max input (it doesn't), I would be able to connect 5 100 watt 24.3 VOC solar panels in series? But the 12v output would be limited to 20 amps at 12v (12v battery system) regardless? Currently with 2 100watt panels, I max out like 14 amp on the best summer day to my 12v battery system. 5 panels would bring in around 35 amps.

I guess technically the higher input voltage into the SCC the better as I can use smaller wire, but in reality I don't mind doing lower voltage and higher amperage. Going back to my diagram, would it be possible to connect the 3 panels in series as shown, and then in the second group connect the remaining 2 panels in series and then combine the two with y connectors? Would the two "groups" of panels work independently, ie: if the 1st series group of 3 panels is totally shaded, will the 2nd group of 2 panels still generate power? See attached image.

 

[justananimal]

Get a victron mppt

Everything on my setup is renogy so I figured I might as well go with a renogy MPPT with hopes that it all works better. But if I get a better understanding of what I want to do and if it's possible, I guess I can explore other brands as well.

 

[justinm001]

Everything on my setup is renogy so I figured I might as well go with a renogy MPPT with hopes that it all works better. But if I get a better understanding of what I want to do and if it's possible, I guess I can explore other brands as well.

Renogy is trash, victron is king and they just dropped their prices.

 

[justananimal]

Renogy is trash, victron is king and they just dropped their prices.

How dare you?

I mean if I can dial in the proper size of the MPPT needed and victron turns out to be cheaper, then why not. But I have not had any issues with the Renogy 20amp MPPT for 2 solid years of use. I'm already planning on sinking close to $1500 on the upgrades (2 additional batteries, 3 solar panels, charge controller and misc), so I don't want to sink even more cash.

 

[justinm001]

How dare you?

I mean if I can dial in the proper size of the MPPT needed and victron turns out to be cheaper, then why not. But I have not had any issues with the Renogy 20amp MPPT for 2 solid years of use. I'm already planning on sinking close to $1500 on the upgrades (2 additional batteries, 3 solar panels, charge controller and misc), so I don't want to sink even more cash.

You get what you pay for. It's well worth the extra cash.

 

[MisterSandals]

The renogy 60amp MPPT has a max input voltage of 140, so technically I can hook all of them up in series 24.3x5=121.5.

The 140V max needs to use the temp adjusted Voc.
Do your panels list the temp coefficient?

Temp coefficient is usually around .35%. For every deg C below 25C (77F), the voltage increases .35%

What are the record lows in your area or what low temp do you want your setup to survive (if not unplugged during a deep chill)?

And FWIW, Victron stuff is terrific. The bluetooth setup and monitoring is super easy and the 5 yr warranty is mighty nice for peace of mind.

 

[MisterSandals]

Going back to my diagram, would it be possible to connect the 3 panels in series as shown, and then in the second group connect the remaining 2 panels in series and then combine the two with y connectors?

(Simplifying your panels for easy math as 25V 4A to explain how array configs work)

No, you would negate 1 entire panel. When you combine a 75V string in parallel with a 50V string in parallel, the 75V gets clipped to 50A. The amps of the 2 strings are added.

Resulting string would essentially be 2S2P:
50V x 8A = 400W

5S array:
125V x 4A = 500W

6 panels as 3S2P would work nicely if you could fit 1 more panel.

 

[justananimal]

(Simplifying your panels for easy math as 25V 4A to explain how array configs work)

No, you would negate 1 entire panel. When you combine a 75V string in parallel with a 50V string in parallel, the 75V gets clipped to 50A. The amps of the 2 strings are added.

Resulting string would essentially be 2S2P:
50V x 8A = 400W

5S array:
125V x 4A = 500W

6 panels as 3S2P would work nicely if you could fit 1 more panel.

I've had my current setup plugged in at temps -25f, so I want the updated setup to survive the extremes worry-free.

6 x 100 watt panels will not fit, 5 is pushing it based on my free roof area.

I've reached a good and simple solution this morning. Initially I was going to give away the existing 20a MPPT and get the expensive 60a MPPT for the whole updated setup. I might as well keep the 20a MPPT for the 2 x100 watt panels and get an additional 40a MPPT (which is half the price of the 60a one), buy 2 x 200 watt panels (which barely fit in the provided area), and recreate the current setup, just with twice the solar panel wattage on the 40a MPPT side. Easier, I get 100 more watts than planned, I utilize all the existing equipment, the 2x200w panels run independently of 2x100w panels as I wanted, and I only pay $20 more for the updated setup than previously estimated.

600 watts of solar total.

 

[MisterSandals]

I might as well keep the 20a MPPT for the 2 x100 watt panels and get an additional 40a MPPT

You should also consider 2S2P array with the 40A and a single panel to the 20A. Especially if 3S voltage is inconveniently too high.

And with the big Victron sale, this top tier SCC is 47% off. Dang hard to beat. This 100/50 is $184 with the incredible bluetooth capability (you will never settle for less after using it just once). 5 yr warranty does not suck either.

Amazon.com

 

[justananimal]

You should also consider 2S2P array with the 40A and a single panel to the 20A. Especially is 3S voltage is inconveniently too high.

And with the big Victron sale, this top tier SCC is 47% off. Dang hard to beat. This 100/50 is $184 with the incredible bluetooth capability (you will never settle for less after using it just once). 5 yr warranty does not suck either.

Amazon.com

But with the current strategy I only have 4 panels total(2x100w and 2x200w), so I don't think 2s2p (requires 4 panels?) on the 40a mppt and 1 panel on the 20a is possible.

That 50a Victron controller you've linked is only $20 more than the 40a renogy I was looking at, so I might bite it, although in my mind I already had a vision of the setup looking pretty in my cabinet with 2 same design charge controllers back to back ?

 

[MisterSandals]

I only have 4 panels total(2x100w and 2x200w),

Ah, i missed the switch from 5x 100W.

So yea, 2x 100W into your current 20A. And 2S 200W into your new best friend a Victron 100/50 (or 100/35 since mounting flat won't get you 100%).

Depending on the panels specs, you might be able to put the 100W in 2S and put that in parallel with the 2P 200W with a Victron 100/50 for simplicity. Though i am not so thrilled about this much paralleling.

 

[justananimal]

Ah, i missed the switch from 5x 100W.

So yea, 2x 100W into your current 20A. And 2S 200W into your new best friend a Victron 100/50 (or 100/35 since mounting flat won't get you 100%).

Depending on the panels specs, you might be able to put the 100W in 2S and put that in parallel with the 2P 200W with a Victron 100/50 for simplicity. Though i am not so thrilled about this much paralleling.

I'm going all out. My plan is to bolt the 2x200w panels together and make a tilting bracket for them, repeat same for the 2x100w, so I think I want a min 40a new controller on top of the 20a one.

 

[MisterSandals]

so I think I want a min 40a new controller on top of the 20a one.

I am a big fan of redundancy!

I'm going all out.

Then I'd seriously consider getting a MUCH better SCC for just a little more.

Here are some posts from someone who made the switch from Renogy to Victron:

Search results for query: victron

diysolarforum.com