Mixing solar panels

[Newfiejeff]

Hey, here is my predicamen!
I have 4 Longi 350 watt panels 2S2P and wanting to add another 2 panels but I can’t get a supplier locally for the same size panels. The supplier has Longi 405 watt panels.
What will the outcome be if I purchased two more of the newer ones hooked in series and then parallel with the existing 350’.
My charge controller and wires can handle the extra panels.
My system is a 24 volt system.

see attached of the two types.

 

[zanydroid]

Terrible match on voltage and current.

54 cell are higher current than older panels. In series they will output LESS power than your 350s due to the lower voltage.

Parallel setup will typically operate at the Vmpp of the lower voltage string, take the expected current on higher voltage string and scale down by the ratio between lower and higher voltage strings.

Can you find 60,66,72 cell with same current as your existing 60s. Is the resulting 3s voltage acceptable for your MPPT?

And don’t limit search to Longi.

 

[Newfiejeff]

Thank you for your reply!
The MPPT will accept the extra, Victron 150/85.
I was hoping to match the same look but also be acceptable enough to work.

 

[chrisski]

There’s some math you can do in my signature block for mixed panels to see the exact loss.

Me personally, I’d want to add these on-a separate SCC. I have three different sets of panels on three different SCCs on my build.

 

[Newfiejeff]

There’s some math you can do in my signature block for mixed panels to see the exact loss.

Me personally, I’d want to add these on-a separate SCC. I have three different sets of panels on three different SCCs on my build.

I was hoping to get away with the extra wire, charge controller , etc

 

[zanydroid]

Thank you for your reply!
The MPPT will accept the extra, Victron 150/85.
I was hoping to match the same look but also be acceptable enough to work.

Ah matching the exact same look is good but you have to balance that with the cost efficiency. Unfortunately as you’ve learned, if you want to match it exactly best to buy it all at once…

If you can get a smoking deal on cost and don’t mind the inefficiency it might be OK.

Another hack I’ve learned of recently is to buy optimizers hacked to a fixed DC output to match unmatched strings, either in parallel or series. There are $45 hacked SolarEdge optimizers you can buy off AliExpress and have them do the programming before shipping. These are hacked to not need a SE string inverter

Or just buy standard optimizers and make them do the matching. TIGO is probably able to match these panels OK (TIGO has less capability to overcome mismatch than SE but requires less arcane hacking)

 

[zanydroid]

On my house I would probably only consider adding MLPE to compensate if I really needed the style match (which is totally valid)

 

[Newfiejeff]

How about this one mixed with the Longi

 

[zanydroid]

This is also 54 cell (or rather half cut 108, which from a current and voltage angle is the same as single cut 54). It’s identically bad basically

Look for one with matching current or voltage. And review my guidance on shopping by cell count.

 

[zanydroid]

You may need to ask supplier in your area what the supply chain situation is. 72s were super sparse while 54s were common back a few months ago where I am, and it’s possible there’s just not that many factory assembly lines for 72s in a cost efficient place close enough to your location.

 

[Newfiejeff]

Ok, I found some to ship but pricey.
IF I went with a second charge controller what size would I get? Stupid question I know. I have 1400 watts of panels now and a Victron 150/85. If I got another 810 watts of panels I know will need a charge controller of at least 100 volts but what amperag.

Batteries hooked as a 24 volt system and can accept a max charge of 85 amps.
If I was to use a different charge controller will there be an issue with both putting in a charge beyond max of the battery when in bulk? I know Victron would be hooked together and can all Victron controllers that are smart be wire togethe?

 

[chrisski]

What are the VOC of the panels and the record cold temps?

The panel spec sheet has a temp compensation and a base temperature.

A warmer area may get by with a 100 volt SCC and a victron 100/30 could be good, but a colder area would need a 150 VDC SCC.

 

[Newfiejeff]

What are the VOC of the panels and the record cold temps?

The panel spec sheet has a temp compensation and a base temperature.

A warmer area may get by with a 100 volt SCC and a victron 100/30 could be good, but a colder area would need a 150 VDC SCC.

 

[Newfiejeff]

Temps here at the cabin may get to -25 celcius

 

[chrisski]

Ought to be record cold temp at the cabin, not what it normally reaches

Check my math of this link, but appears to be around 84 volts with two panels in series. If my math is right, A Victron 100/20 is right for -25C, but this needs to be adjusted to the record cold of when the SCC will be hooked to the panels.

–25C-25C=-50C

-50*-.265%= PERCENTAGE INCREASE IN POWER

OR %13.25 INCREASE