Confused about how much solar I can use

BroomJM

Solar Enthusiast
Joined
Apr 7, 2021
Messages
87
I bought a Renogy Rover Elite, 20 amp, MPPT solar charge controller.
The manual shows:
Max solar input voltage is 100VDC.
Max solar input power is 12v @ 260w - 24v @ 520w. (I am charging a 12v LiFePO4 battery)
Does this mean I can't use more than 260 watts worth of panels?
I recently purchase three (3) of the BougeRV, 180w, 9bb panels. I was planning to use two of them for charging this battery and the other panel for a different purpose. The BougeRV panels show the following specs:
Voc - 23V
Vmp - 19.2V
Short circuit current Isc - 10.23A
Max power current Imp - 9.38A
What I don't understand is if I put these panels in series I'll have Voc of 46V, which is less than half of what this controller is rated to handle, but is the max power input cutting it too close for a 20 amp model? Did I make a poor choice in charge controllers, limiting me to using only one of the panels at a time?
Sorry if this a really dumb question and thanks in advance for anyone who can help me understand my options.
 

Scixxor

Solar Novice
Joined
Nov 23, 2021
Messages
150
Okay so, all charge controllers have a maximum amount of solar they can use at a time. So for you're charge controller it can use 260 watts of solar power while using a 12-volt battery. With this being said you can probably still use 2 of those panels. Most people "over-panel" by 25% because your panels normally only produce 25% of their max capacity. On Will's website, he says the Renogy rover series can all handle over-paneling. I don't know if this is applied to the elite ones. Hell, I'm not even sure if it applies to the regular ones, after emailing the company about the same thing they said to not over-panel as it could damage the charge controller so I'm not sure. I hope someone can figure this one out for me.

Either way that charge controller is very small for the number of panels you had, you always want to get a bigger charge controller/inverter than you need so you don't need to upgrade them later. Oh, and you can also just add another charge controller to those batteries and hook up some of your panels to that. So not a complete waste of money if you can't get it returned.
 

BroomJM

Solar Enthusiast
Joined
Apr 7, 2021
Messages
87
Okay so, all charge controllers have a maximum amount of solar they can use at a time. So for you're charge controller it can use 260 watts of solar power while using a 12-volt battery. With this being said you can probably still use 2 of those panels. Most people "over-panel" by 25% because your panels normally only produce 25% of their max capacity. On Will's website, he says the Renogy rover series can all handle over-paneling. I don't know if this is applied to the elite ones. Hell, I'm not even sure if it applies to the regular ones, after emailing the company about the same thing they said to not over-panel as it could damage the charge controller so I'm not sure. I hope someone can figure this one out for me.

Either way that charge controller is very small for the number of panels you had, you always want to get a bigger charge controller/inverter than you need so you don't need to upgrade them later. Oh, and you can also just add another charge controller to those batteries and hook up some of your panels to that. So not a complete waste of money if you can't get it returned.

I'm glad to hear you mention buying a second charge controller. I was looking at some options and I think that's what I'm going to do. The portable power station I built has two Anderson connections available. One is connected to the Renogy Rover, through a 20-amp fuse, and the other goes directly to the battery (for use with an external power supply). If that external power is from a secondary charge controller, instead of a 110v charger, the battery will still be only seeing about 20a worth of input, total. This option is actually pretty appealing because having the external charge controller means I can connect and charge other batteries/power stations, when the main one is fully charged.

Thanks for your reply. :)
 

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
3,735
Location
USA
Most charge controllers can be "over paneled". If the panels can produce more power than the SCC can use at the moment, the extra potential is simply not made use of.

The 20A rating of your controller is the max battery charge current it will output. That current times the typical battery charge voltage is the maximum number of watts the controller can use. 20A x 13V = 260W. But if you are charging the battery at 14V then you can use 280W of solar.

If you put 360W of panels on that controller then at best the controller will make use of up to 280W. The advantage of having more solar on the controller is that you can get the max 280W for a longer period of time during the day. If you only put 280W of panels then you will almost never get 280W of power out of them. Is solar condition were to allow the panels to produce more than 280W then that extra potential simply won't be taken advantage of.

If you had purchased a 30A, 35A, or 40A controller then you could easily make most use of all 3 panels on one controller.

As mentioned, you can buy a 2nd controller. A 10A or 15A would be plenty for the 3rd panel. But if you can trade in the existing 20A for a slightly bigger one then you'll get better use of the 3 panels on one controller.

your panels normally only produce 25% of their max capacity
That must be a typo. If you only get 25% out of your panels then either it's mid-winter, really heavy overcast, or there's a problem with your system.
 

Scixxor

Solar Novice
Joined
Nov 23, 2021
Messages
150
That must be a typo. If you only get 25% out of your panels then either it's mid-winter, really heavy overcast, or there's a problem with your system.
THat's a really good explanation of over-paneling, thank you! That cleared a lot up for me. You're right I meant to say they normally produce 25% less than what they say, so a 100-watt panel might only produce 75 watts on average.
 

Yurtdweller

Solar Enthusiast
Joined
Nov 23, 2020
Messages
203
Location
USA
I over paneled a 40 amp Rover. It melted down. The main output to the battery, the clamp desoldered itself from the board. My array was producing 42 or 43 amps at the time. I complained to Renogy, and they sent me another. It melted, too. I increased my array to 1000 watts, and got an oversized victron 150v/100amp unit. Anyone want a slightly crispy 40 amp Rover? It still works, but I don't have the tools and skills to resolder the clamp, so I used it with a temporary home-made clamp/clip attached directly to the board until my new cc came in the mail.
 

Scixxor

Solar Novice
Joined
Nov 23, 2021
Messages
150
I over paneled a 40 amp Rover. It melted down. The main output to the battery, the clamp desoldered itself from the board. My array was producing 42 or 43 amps at the time. I complained to Renogy, and they sent me another. It melted, too. I increased my array to 1000 watts, and got an oversized victron 150v/100amp unit. Anyone want a slightly crispy 40 amp Rover? It still works, but I don't have the tools and skills to resolder the clamp, so I used it with a temporary home-made clamp/clip attached directly to the board until my new cc came in the mail.
Wow that's pretty scary, Will says they can all be over-paneled but between what the company has told me and this I'm not entirely sure what to think. I'm going to be buying a 40 amp Rover from them soon so I'll probably just size it so I don't need to over-panel.
 

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
3,735
Location
USA
You can over panel on Wattage but do not exceed Voltage or Amps input limits.
Clarified that.

Exceeding the wattage means you potentially exceed the charge current amps limit. The amp limit you must not exceed is the max PV short circuit current. Though not all SCC specs tell you what that limit is.
 

Yurtdweller

Solar Enthusiast
Joined
Nov 23, 2020
Messages
203
Location
USA
Fwiw, I had connected 8 panels of Renogy rng-100d-ss. I informed Renogy of this fact when I submitted my first case. They did not, at that time, inform me that this was contra-indicated. After the second meltdown, they DID recommend upgrading to the 60 amp unit. I had upgraded my battery bank to LiFePo4 at that time, however, and chose to purchase a cc with more programmability. I am certain that I didn't exceed input voltage. I had configured as 2 sets of four series panels. Note that the melting happened on the output to battery (cables were largest size possible for clamps) not on pv input. I'm not going to double-check all my math right now, but before raising my array to 8 panels, I did the math, and read other user cases, and I did contact Renogy support to verify my plans, and was told this size/configuration array was acceptable.
 
Last edited:

Ampster

Renewable Energy Hobbyist
Joined
May 3, 2020
Messages
6,305
Location
Kenwood, California
I am certain that I didn't exceed input voltage.
How about current? Component damage usually is caused by over voltage but meltdown of solder traces and connections is likely current related. That is consistent with the reason Renogy suggested a higher Amperage unit.
 

Yurtdweller

Solar Enthusiast
Joined
Nov 23, 2020
Messages
203
Location
USA
Renogy 100d-ss

Specifications

Maximum Power: 100W

Maximum System Voltage: 600V DC (UL)

Open-Circuit Voltage (Voc): 24.3V

Optimum Operating Voltage (Vmp): 20.4V

Optimum Operating Current (Imp): 4.91A

Short-Circuit Current (Isc): 5.21A

As I said, previously, I had two strings of 4 panels in series. While the output amperage did exceed 40 amps, I don't think the input amperage did? Idk. It is my understanding that we calculate the current based on IMP? Which would put my array below the cc limits, unless I am wrong.
 

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
3,735
Location
USA
Fwiw, I had connected 8 panels of Renogy rng-100d-ss
You had those 8 panels in 4S2P. That puts the Voc at 97.2V. What was the max PV input voltage of the 40A controller? If it was 100V then you would exceed that 100V if the temperature ever got below about 60ºF/16ºC. That probably explains why you fried the SCC. Your array's Isc would be under 11A. I doubt the controller has a max short current under 11A.

The 40A output is the max battery charge current that the SCC can produce. If you were charging at 14V then that's 560W max that the SCC could take advantage of. If your panels had the potential to produce more that that 540W in the current solar conditions then that extra potential would simply go unused.
 

Scixxor

Solar Novice
Joined
Nov 23, 2021
Messages
150
You had those 8 panels in 4S2P. That puts the Voc at 97.2V. What was the max PV input voltage of the 40A controller? If it was 100V then you would exceed that 100V if the temperature ever got below about 60ºF/16ºC. That probably explains why you fried the SCC.
Yep, the 40 amp rover has a max VOC of 100 volts. Also, how do you determine how temperature affects the VOC?
 

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
3,735
Location
USA
how do you determine how temperature affects the VOC?
Look at the spec sheet for the panels. Look for the temperature coefficients. There should be one for Voc. It will have a value somewhere around -0.3%/ºC. Being negative means the Voc goes up as the temperature goes down. The baseline is the 25ºC STC that the specs are based on.
 

Scixxor

Solar Novice
Joined
Nov 23, 2021
Messages
150
Look at the spec sheet for the panels. Look for the temperature coefficients. There should be one for Voc. It will have a value somewhere around -0.3%/ºC. Being negative means the Voc goes up as the temperature goes down. The baseline is the 25ºC STC that the specs are based on.
Thank you, that's very useful information.
 

BradCagle

Solar Addict
Joined
Aug 27, 2021
Messages
338
Anyone want a slightly crispy 40 amp Rover? It still works, but I don't have the tools and skills to resolder the clamp, so I used it with a temporary home-made clamp/clip attached directly to the board until my new cc came in the mail.

I'd take it off your hands, would be interested in doing a repair video on my youtube chan. I just reapaired this one

 
Top