Help with Mixing Panels

[DooverDixon]

So I need a bit of help. I built out my RV solar setup with some "room to grow" My current setup is as follows:

MPP Solar LV 2424 Hybrid
SOK 100ah 24v Battery
2x Newpowa 210 watt 24v panels

Most of this was purchased from suggestions i found by reading this forum and watching Will's vids (great site dude).

With that said, I need more solar to keep up with consumption, but......these panels are no longer available from newpowa!!! they make the 12 v version and now they make a new 200w 24 v version. But it looks like the 210w 24v's may be dead.

Im hoping ya'll can help me sort out the best options for adding to this setup (and appropriate wiring) and minimizing ugly losses from mixed panels. Ill post some stats:

My current panels:

Maximum power (Pmax)	210W
Voltage at Pmax (Vmp)	33.54V
Current at Pmax (Imp)	6.24A
Open-circuit voltage (Voc)	39.66V
Short-circuit current (Isc)	6.55A

New 200watt 24v option

Maximum power (Pmax)	200W
Voltage at Pmax (Vmp)	37.2V
Current at Pmax (Imp)	5.38A
Open-circuit voltage (Voc)	46.6V
Short-circuit current (Isc)	5.74A

210 watt 12v option

Maximum power (Pmax)	210W
Voltage at Pmax (Vmp)	16.77V
Current at Pmax (Imp)	12.48A
Open-circuit voltage (Voc)	19.83V
Short-circuit current (Isc)	13.09A

 

[sunshine_eggo]

For parallel strings, series Vmp-Voc range should be very similar - within about 5-10%. They will tend to operate at the lower Vmp, but the MPPT can find a happy place in between them if that's where the MPP is.

For panels in series, Isc, Imp - should be identical if possible. Panels in series will all operate at the LOWEST Imp value.

Current: 33.54Vmp, 6.24A Imp
200W: 372Vmp, 5.38 Imp
210W: 16.77V, 12.48 Imp

2X of the 210W in series would put you at 33.54 Vmp... need I say more?

So, for every 1S "current" 210W panel in series, you would have a parallel string of 2S "new" 210W panels. This is what I would choose.

If you have 3S "current", you could parallel 6S "new" 210W panels.

Never mix any of those in series. Big performance hit.

 

[DooverDixon]

I need to digest this a bit more, But it sounds like i need 4 more panels? There might be an issue with roof real estate. I think i have room for 2 more panels, but I doubt i can pull off 4.

I should have mentioned before. My current setup has the 2 panels wired in series to maximize voltage to the MPPT.

 

[sunshine_eggo]

Vmp 33.54 is still suitable for 24V system provided it's in the MPPT range of the controller.

You could parallel your two panels
2S the "new" 210 and parallel that string with your 2P panels.

Or

2P 210W old in parallel with 2S 210W new.

Vmp = 33.54
Imp = 24.96A

You'll lose a very small amount of power in early morning and late evening production... like probably 1% of your total daily consumption at a SWAG.

 

[Rocketman]

One other option (cause it is an RV and roof space it difficult…). If you cannot find panels that play well with your current panels. You can always get a stand alone solar charge controller and connect it to the DC side instead of into your MPP All-in-one. Something like a Victron Mppt 100/30. Then you can focus on getting panels that fit your space very well.

Also, look up different manufacturers panels- someone else may have panels that match your current ones electrical specs. (Hopefully they will fit).

Good Luck!

 

[DooverDixon]

I was under the impression that you want to push the voltage pretty high with mppt controllers. That why inwas aiming for ~60 volts with my current setup. The controller is rated for 30 to 115 volts. Do you lose much efficiency reducing voltage from 60 to 30?

 

[sunshine_eggo]

I was under the impression that you want to push the voltage pretty high with mppt controllers. That why inwas aiming for ~60 volts with my current setup. The controller is rated for 30 to 115 volts. Do you lose much efficiency reducing voltage from 60 to 30?

No. You actually gain efficiency. The larger the voltage change from PV to battery, the less efficient. It's probably a very small amount - maybe 0.5-1.0%. The losses with higher string voltage are typically offset by the reduced losses in wiring. higher voltage + less current = less losses in the wiring. This can be very significant when dealing with very long wiring runs.

MPPT are not magical. Their primary benefit is that they allow the panels to operate at or near their Vmp to produce the maximum possible power for the conditions. There is a belief that you will get vastly better low light performance. You won't. Might you get a 1-2% boost to your daily harvest? Maybe.

Configuring panels to operate within the Vmp range is what matters. My only concern with parallel in your case is heat causes voltage to drop, so in extreme heat, your Vmp could conceivebly drop below 30V.

Your options are very limited. It may make more sense to get a second controller as recommended above.

 

[DurkaDurka]

If you can't get the NewPowa panels you have, you aren't tethered to that company. See if you can find panels with similar Voc specs?