Series *and* Parallel hybrid for solar

[vincode]

I'm using Odyssey Extreme Series batteries for my electrical storage.  I would have preferred another option, but because of my van configuration, I had to do the best with the space and fitment I had.  I have 225 amp hours total in 3 batteries.  These batteries like a lot of amps when charging.  I have a 225 amp alternator and 30 amp onboard charger I can use, but I still want my solar to push as many amps as possible to avoid using those.

Because these batteries want lots of amps to charge, I am looking at the 400 watt Renogy kit with the MPPT.  That is the most solar I can fit on my roof.  My understanding is that MPPT controllers like lots of volts and that the Renogy Rover 40a MPPT controller included with the kit works with 12 or 24 volts.

Are there any downsides to wiring two pairs of the 4 panels in series and then combining them in parallel to have a 24v solar system?  Is this even necessary or am I over thinking this?

 

[B and C]

I have a series parallel setup. I have 200 watts on the roof in series and the 200 watts portable that are also in series. All panels are 100 watt. When I connect the second portable set, they are in parallel with the first set. Works well for me. BTW, all panel are identical.

Edit to add: the 12v-24v is talking about your batteries, not the panels. The charge controller manual will tell you how much input voltage (from the panels) that it will accept.

 

[highdesertranger]

one downside to the series wiring is partial shading. a little shading can knock both panels out of the charge circuit. highdesertranger

 

[vincode]

one downside to the series wiring is partial shading.  a little shading can knock both panels out of the charge circuit.  highdesertranger

So if I do series-parallel then I would lose use of 2 panels if 1 of the 4 is shaded?  I should still have 2 panels working right?

 

[B and C]

Correct

 

[frater secessus]

Yes. 

If the renogy panels are mono (Vmp == 18.9v) the mppt will be fine with all four in parallel.  There is enough excess voltage available with the mono panels up to ambient temps of 125F+.  [For onlookers, this is important because cell voltage and therefore Vmp decreases with heat.  It's why panel output is measured in lab/ambient conditions of just about freezing.]

If the Renogy panels are poly (Vmp == 17.8v) [in parallel configuration] there may not be enough excess voltage in hot areas (~100F) for MPPT to do its thang and PWM would be mucho cheaper.

 

[B and C]

^^^This is why I do the series parallel thing. Even with lower light because of cloud cover/light rain, I still get solar gain with my MPPT controller. Also if I am parked under trees, I can put the portable panels in the sun. My controller (MidNight Kid with WhizBang Jr. + shunt) handles the higher voltage of two panels in series well with headroom left.

 

[John61CT]

You don't lose all a pair's power from a little shadow, but a higher percentage than you'd think.

Get a flexible enough controller and you can A/B test charging output with an ammeter yourself, it's just a change in wiring layout.

 

[Canine]

If you hook them all up in parallel, you are pushing a lot of amps (25 amps) through the wire which would make for a higher voltage drop. If you went series/parallel, then you would be pushing only 12.5 amps which is closer to what the wire can handle comfortably. Neither way is wrong, just what you prefer.

This is a bit off topic, but I'm curious: I looked at the size of that Renogy 100 watt panel- pretty sweet size. Have you checked out the slightly larger 160 watt, though? 3 of those would be 480 watts for $522 compared to 4, 100 watt panels at 400 watts for $520. I'm not figuring in package prices and you would also need a different charge controller. That would give you more wattage for your cottage. The overall square footage would be less, but am wondering if the larger size panel may be a deal breaker.

 

[frater secessus]

> you are pushing a lot of amps (25 amps) through the wire which would make for a higher voltage drop.

One assumes the OP would size the wiring between the combo box and controller accordingly.

Panels larger than 100W generally require $$$ freight-style shipping but they can be a great value if picked up locally. I found 190w panels for $120 each locally without too much effort.

 

[wayne49]

"One assumes the OP would size the wiring between the combo box and controller accordingly."

"One" could make an assumption.

The "OP" may not do their due diligence.

One might use the standard solar cable for all connections and not think about it until reading that comment.

 

[B and C]

My panels came with 10 Ga wire and that is the same Ga I used to extend to my SCC. My charge controller is about 8 cable feet away one way (16 round trip) on the attached panels. I have a 50 Ft 10 Ga electrical extension cord that I connect my portable array to. I also have a 25Ft one for when I hang the panels off the awning for that early morning sun. I don't think I am leaving much on the table as I have a MPPT controller. I know I have bigger losses in the long extension cord but it really does help with charging. With the panels in series parallel I have a higher starting voltage than if the panels were all in parallel so the voltage drop does not affect me as much because the voltage is still above battery voltage.

 

[frater secessus]

"One" could make an assumption.

The assumption was already made that the OP would not do due diligence, and since specific amps were mentioned we know a further assumption was made that OP would err in using a particular gauge of wire.

We don't start from a priori every time.

 

[frater secessus]

Feel free to interpret the sentence in question as "OP will, of course, have to size the wiring between the combo box and controller accordingly in order to keep voltage drop in an acceptable range."

 

[Canine]

frater, I did assume using standard 10 gauge solar wire.  :-/  This is a good example of the value of using a good forum.  

 

[vincode]

This is a bit off topic, but I'm curious: I looked at the size of that Renogy 100 watt panel- pretty sweet size. Have you checked out the slightly larger 160 watt, though? 3 of those would be 480 watts for $522 compared to 4, 100 watt panels at 400 watts for $520. I'm not figuring in package prices and you would also need a different charge controller. That would give you more wattage for your cottage. The overall square footage would be less, but am wondering if the larger size panel may be a deal breaker.

The longer panels don't fit with the rest of the stuff on my roof.

 

[Canine]

vincode, I kinda figured that, but wanted to know for sure. 400 watts is still pretty good. I'm like Tim 'The Tool Man' Taylor- when I see 600 watts+ on an RV/van, I started hooting like a gorilla.