KID with LiFeO4 batteries? How to integrate mixed watt panels with KID?

[snickell]

Hi, I have a Midnite solar KID, with an existing 355 watt panel (VOC: 47.3, VMPP 38.9) and a small 48V bank.

I'm wanting to upgrade my system capacity roughly 3-4x, though squeezing out every drop isn't a priority. Keeping my existing panel, and adding some new ones is more important to me (cost sensitive). I found a good deal on up to 8x 200 watt panels (VOC 47.8, VMPP 40.0). I could use all 8, and I'd have my KID maxed out, but I'd rather not "throw away" the 355 watt panel since its already mounted, etc.

1) Is there a way I could set up the strings to mix 4-6 of the 200 watt panels along with the existing 355 watt panel? I'd have an electrician do the work, but the opportunity to buy the panels is open today, so I'd buy them in advance of talking to a solar installer.

2) I'd like to switch to a Simpliphi 3.5 kwH lithium battery, and give my existing (small) AGM bank to my neighbor. Is the KID compatible with Simpliphi lithiums?

Thank you so much, I know these are very basic questions, but I appreciate your patience :-)

[Vic]

Hi snickell,   Welcome to the Forum.

In general  a careful design of battery-based power systems will result in  good results.

Having clearly-defined picture of the loads that the system will supply,   the length of time and time-of-day  that the loads are present,   the peak power demand of the load,   etc  will be a great place to start.

You already have some equipment,   but,   would suggest that you stop buying hardware,   and focus on what your power system needs to do.

Regarding the PV compatibility,   those Vmps that you note for the 355 W PV  is within about 3% of the Vmp of the 200 W PV,   this would be close enough to run those two different PVs in parallel (for a 24 V battery,  for example).  But,  there appears to be only one of the 355s,   which would be an issue,  as,  you will need a string Vmp that is greater that that on that single 355.

We need some more info:

What brand are each of the different PVs,  the model number of each,   OR  what is the Imp of each of those PVs?

Regarding the requirements of the new battery,  verses the KID's capabilities,   will let others,  here comment on that.

Thanks for the added info,   Vic

[FNG]

The kid will charge the simpliphi just fine, Simpliphi has done a lot of work to make the battery charge more like an AGM so setup is a breeze.

As for the modules, I assume the 355 has a higher ISC than the 200 as the VOC is basically the same. Based on the comment that 8 would max the kid out I am assuming a 48v nominal battery. With that assumption, you need 2 of these modules in series to properly charge a 48v battery

That means groups of 2 modules. You can put the 355 and a 200 in series together to make a string, you will just lose the extra power the 355 could make, it essentially becomes a 200 watt module.

So choices that I see;

1- Buy all 8 200's and wire them in 4 strings of 2 and don't use the 355
2- Buy a second 355 and wire it in series with the first one, add say 4-6 of the 200s also in strings of 2
3- Buy 3,5,7 of the 200s and wire one in series with the 355 and the remaining 2,4 or 6 in strings of 2 as well.

If you go with number 3 I might suggest buying the extra 200 just to have an even number even if you don't use it right now