Maximum safe wattage for Renogy Rover 40 amp

[ByeBye]

I'm wanting to add a portable panel, or two smaller ones, to my rig. Specs say Rover 40 amp is good to 520 watts. I currently have a 305 watt panel on top. Looking at Santan Solar they have lots of mid 200's watt panels pretty cheap. How stringent are those maximum specs?

I probably wouldn't use the portable unless the roof panel was shaded. At least not till I increase my battery bank capacity.

Anyone got an uber way to add a portable panel to an existing system? I have about 70 ft of 10 gauge solar cable but not sure a 35 ft extension would be enough. 

Thanks in advance,
Marcus

EDIT: I checked the specs and those are residential sized panels, 40+ lbs. Not what I intend, but I am interested in anyone with quality way to add to an existing system.

 

[highdesertranger]

according to Morning Star you can go over the wattage on their controllers but you can't go over the voltage, that is what kills them. remember also that your panels will hardly ever put out their ratted wattage.

also all the panels that feed a controller should be close to the same voltage. you can mix wattage but you can't mix voltage.

also for portable panels the higher the voltage the better. they are more efficient over long runs of cable.

highdesertranger

 

[sushidog]

Also you have to remember that when you overpanel a system (have more wattage in panel output than the controller can pass through to the batteries) the excess energy will be given off as heat. This is why controllers have cooling fins, fans, etc. The advantage of over-panelling is that even though your peak power output will be truncated by the controller, you will notice increased production during morning and evening hours when your panels are producing less than the controller's max capacity.

My owners manual on my 50 amp Epever MPPT controller limits the over-panelling to 50% of the controller's rated capacity. In other words, according to my controller's manual (other controllers will have different specs) my controller is rated to handle 625 watts of solar at 12v output but I could connect up to 937.5 watts of panels on this controller on a 12v system.

Remember, if you are mounting your panels flat, the current they will produce will usually be 60-80% of their rated power, depending on season and latitude. This is with new panels. With used panels, which typically lose about 1% power output per year of service, they will produce even less. For instance if the used panels had been in service for say 10 years before you purchased them you can expect them to produce about 90% of their rated power. Both panel age and mounting position must be taken into account to estimate their actual output to the controller.

Chip

 

[ByeBye]

Thanks guys.
My Opt Operating Voltage (Vmp) is 32.9
My open circuit voltage (Voc) is 39.7

How close do I need to stay to those?

 

[highdesertranger]

you have no control over those your controller takes care of all that. just make sure your controller can handle those voltages and you will be fine. highdesertranger

 

[ByeBye]

you have no control over those your controller takes care of all that.  just make sure your controller can handle those voltages and you will be fine.  highdesertranger

You said this earlier "also all the panels that feed a controller should be close to the same voltage."
That's what I'm referring to, how close?

 

[highdesertranger]

you really need Jim or one of the other experts to give you an exact answer. but I am under the impression that the panels must be within a couple of volts of each other. in other words 2v would be ok but 10v would not. I know that's a wishy washy answer, sorry. highdesertranger

 

[rayrey]

Actually you want matching panels. Mixing voltages in parallel will cause the MPPT to hunt. Mixing them in series will cause the lower power panel to create two lower powered panels. Since mono and poly panels react to varied light differently, I would highly suggest sticking to whatever you have.

 

[jimindenver]

Actually you want matching panels. Mixing voltages in parallel will cause the MPPT to hunt. Mixing them in series will cause the lower power panel to create two lower powered panels. Since mono and poly panels react to varied light differently, I would highly suggest sticking to whatever you have.

 

[ByeBye]

Thanks guys

 

[ByeBye]

I guess I could get another cheap controller just for the auxiliary, right?

 

[highdesertranger]

yes, you could go with another controller. that is what I do. highdesertranger

 

[tx2sturgis]

The OP mentions adding portable panels to help power production when the roof panels are shaded. Also mentioned is the addition of another battery bank.

Options mentioned above are good, but also consider a separated system, where the existing roof panels, controller, and battery bank remain as is, powering compatible loads, and then add another on-board battery, controller, and portable panel system. Rather than tying the two systems together, you end up with two independent systems.

Then the two systems can power different loads, and you can move heavier loads (by swapping connectors or flipping switches) to take advantage of whichever system has the surplus of energy to supply power to those loads.

This gives you redundancy and is not that much more effort to install.

 

[XERTYX]

yes,  you could go with another controller.  that is what I do.  highdesertranger

Can you connect 2 controllers to 1 bank? I didnt think that was kosher. I.E. roof mounted panel -> controller -> battery <-controller < - portable panel

 

[highdesertranger]

"Can you connect 2 controllers to 1 bank?"

yes you can, that is no problem.

highdesertranger

 

[jimindenver]

You can use two controllers on one bank as long as they are set to the same values in voltages

 

[Gypsy Freedom]

I have about 70 ft of 10 gauge solar cable


, but I am interested in anyone with quality way to add to an existing system.

when figuring wire gauge for distance run. i highly recommend using and online voltage drop calculator. like https://www.calculator.net/voltage-drop-calculator.html general solar specs suggest 3% or less i target 1% but settle for under 2% oftenhttps://www.calculator.net/

the quality way to expand is to only use identical panels on the same charge controller. better to use separate controllers when mixing panels. 

yes, you can mix panels, not like anything is going to break or burn down. but the closer you keep the panel volts and amps, the less power you will lose. 

you can run 2 controllers to the same battery bank. the controllers can be of different ratting or even different tech, ie 1 mppt and 1 pwm controller to the same bank is just fine. even if the voltage set points are slightly different they will work fine. if the volt settings are a little different the it just means the one with the lower set point will think the battery is full and go into float while the other is still charging. this is usually inconsequential as by that time both controller are well into absorb and tapered of the current and when the lower set point controller drops to float the other picks up the slack. you might lose a little charge capacity if you dont have enough solar to fully charge your bank by the time the sun start dwindling. but it wont be much

 

[ByeBye]

@Gypsy Freedom
Thanks very much for the detailed reply. It was helpful.
My 12v needs aren't great, so low I haven't even done an amp hr total calculation. Only significant draw is my fridge/freezer then it's 3 interior LED lights, 2 VERY low draw computer fans on heater and Nature's Head toilet and charging phone/laptop.

I am just wanting to have the option of a portable panel for those times I'm in tree cover or less than ideal weather conditions. (Looking at doing a lot of wilderness boondocking)
Addressing the tree cover/shaded parking issue I would assume using a separate controller would be better, do you agree?


EDIT: Wow, just used the calculation link you offered, 10 AWG @ 35 ft
Voltage drop: 0.70
Voltage drop percentage: 5.83%
Voltage at the end: 11.3

I don't want to invest in heavier cable at this point. What's the consequences of that much voltage drop?
Might just have to go with shorter run, which I DON'T like

 

[ByeBye]

Hmmm...I calculated that cable sizing @ 12v. Think I should have used the panel's operation voltage which is 32.

 

[highdesertranger]

yes use the 32v up to the controller. highdesertranger