Are solar panels interchangeable between 24V & 48V systems?

[ron_jeremy]

This system I've inherited needs a total redo but I'm looking at a stop-gap measure until I scrap it entirely. It's a 24V system but is horribly unbalanced -- not enough PV and too much battery meaning lots of generator run-time. The system hasn't been touched since it was commissioned in the mid 1990's but we've rented our main residence and now we're going to be spending more time at this property .

My knee-jerk reaction would be to replace everything and move over to a 48V setup but that's a big pill to swallow so I'd like to delay that for a couple years. Right now all I want to do is replace the 8 x 75W panels with new panels in the 400W/ea range.

I have learned a lot since discovering this forum but I have enough self awareness to understand I only know enough to be dangersous. I will have many questions about panel sizing, layout/wiring schemas, inverter & charge controller compatibility, etc., but none of those questions are important at this point because the only question I want to ask is:

If I buy new 400W panels to upgrade my current 24V setup can I use these same panels when I move to 48V?

If the answer is 'no, then I have a big decision to make.

[foggysail]

I can guess, but remember, I am no expert. I say that you can mix them IF you wire a 24V pair ins series then place them in parallel with the 48 panels. But I believe the system will better married if you are using microinverters. Others with greater knowledge I think will share suggestions. Individual inverters I believe will provide better MPP performance.

[SunEagle]

It really depends on how you wired those 75W panels and what your CC can handle as max input voltage. Going to a 48V battery system usually requires a quality CC so what do you plan to purchase and how do you plan on using all of your panels?

[chrisski]

Yes you can,but… need to take a good look at the charge controller, all in one, or inverter you will use.

for a 150 volt SCC, that can be limiting with 400 watt panels. One 400 watt panel i looked up had 85 volts with 5.5 amps. That means you can’t place 2 in series, they all need to be added in parallel. With 100 watt panels, they are around 22 volts and 6 amps, so they can be placed 5 to 7 in series, depending on the cold temp rating.

Of course the solution is to buy something that can process more than 150 volts ,but that gets expensive for the SCC and circuit breakers.

So depending on what you will plug into, you may find putting this ‘puzzle’ together easier with 200 watt or 250 watt panels. A caveat to that is because i am located in the phoenix area,i have access to some inexpensive panels i can pick up from a distributor (SAN TAN SOLAR), but elsewhere, that is not the case and shipping becomes a factor.

[ron_jeremy]

We have a Trace Engineering SW4024 inverter, 24V 960AH battery bank (12 x 2V), and the below charge controller. I am open to wiring the new panels in whatever design is best & most effecient, and also buying whatever charge controller (or multiple controllers if they can be used) to make this work.

Note: when I eventually switch over to 48V I plan on using 8 x 6V Rolls 6CS17P 568AH batteries and most likely an inverter from Outback.

Xantrex solar charger id plate.jpg

[jflorey2]

If I buy new 400W panels to upgrade my current 24V setup can I use these same panels when I move to 48V?

Short answer is - probably.

Longer answer - any panel can be made to work with any system. In general each string of panels needs to sum to an MPPT voltage about 10% higher than the battery voltage. (10% to take care of MPPT overhead and temperature-related voltage reduction.) Each string also has to be of either identical or very close to identical panels. That puts a slight crimp in what panels you can use.

Example - let's say you build a 24 volt system, and each string is two panels in series. You get the panels a piece at a time. You have two 85 watt BP panels, two 400 watt Neon-2 bifacial panels, two 135 watt Sanyo panels and two 365 watt Sunpower panels. You series the similar panels and you put all strings with the same cell count in parallel. You'd probably need two charge controllers to handle the different cell counts of the various strings - but overall that would probably work pretty well.

But now let's say you want to switch that to a 48 volt system. Either you now have to use a boost converter (which is hard to find especially at high powers) or you have to go out and buy two new 85 watt BP panels, two 400 watt Neon-2 panels etc etc. since you can't put an 85 watt panel in series with a 400 watt panel. That could be hard.

However, let's say you were smart and initially bought 8 400 watt Neon-2 panels. Now you can reconfigure them however you want. You could do 4 strings of 2 and be OK, since those are fairly high voltage panels. You could also do 2 strings of 4 if you like. You could even do 1 string of 8 (if you can find an MPPT to handle the input voltage) - and doing that would be advisable if there's a long wire run from the panels to the charge controllers.

In your case, with 400 watt 72 cell panels, you could use exactly the same panel configuration for 24 volts as for 48 volts. A 2s4p configuration would give you about 80 volts at the controller, which would work with either 24 or 48 volt batteries. (And would work with your existing controller.)