Total newbie upgrading off-grid setup built in the 1990's

[ron_jeremy]

This off-grid solar setup was built many years before I moved to this home. The setup consists of:

- 24V Trace Engineering SW4024 inverter (120V only).
- 24V 23kW FLA battery bank (12 x 2V 960AH cells).
- 8 x 75W Siemens panels (hilarious, I know) in what looks like to me as two strings of four panels run in parallel.
- Xantrex 150V/60A SCC.
- Trace Engineering DC disconnect (the throw handle has “250” written on it).
- Trace Engineering AC disconnect (25A on L1 only)
- Yamaha EF4500iSE generator (battery charging).

Here's what the two strings look like:



Existing panel specs:



Lower string connects to upper string (combiner box?):



I have purchased the following from Santan Solar:

- Victron 150V/60A SCC.
- PV cable.
- Two x 20A MC4 inline fuses.
- Six x 350W panels.



The Plan:

- Disconnect the parallel connection (in combiner box thingy) between the two strings and remove old panels.
- Install three new panels on lower mount and run cable to the existing 150V/60A SCC plus install 20A fuse on positive cable close to panels.
- Install three new panels on upper mount and run cable to the new 150V/60A SCC plus install 20A fuse on positive cables close to panels.
- Configure each SCC for new panels (if required).
- One array to face SW for morning sun and the other W-ish for afternoon sun.

I can’t quite get behind the battery bank to confirm this, but it looks like the PV cable enters the garage (right beside the battery bank where I can’t see anything), goes up into the existing SCC, and then out to the battery bank main terminals.

Questions:

- What equipment needs to be disconnected or turned off before I do anything?
- Is there a proper order for disconnecting equipment (for example: SCC 1st, combiner box 2nd, arrays 3rd, etc.)?
- Can I still use the same DC disconnect for both strings or do I need to add a 2nd one?
- Am I missing anything or is anything ‘out of whack’ spec-wise?
- I see videos where a "shunt" is used at the positive terminal. What is this for?
- In the near future, I plan to add one more string of panels and a 3rd SCC (250V/70A). Any issues with this? Basically, can I add as many SCC’s and panels as I want or is there a limiting factor I’m not thinking of?

 

[rodrick]

You need to disconnect the pv first remember if the suns out there’s power when you start disconnecting everything before the combiner box be careful so start at the scc turning of power to it and work out to the panels

then with the inverter off disconnect The batteries there should be no power anywhere at this point once the capacitor in the inverter bleeds down flip the inverter on for a second and that should be good to make it safe at this point

the shunt goes from the main battery negative only thing hooked to the negative on the battery everything else gets hooked to the other end of the shunt everything must pass threw the shunt to get a accurate reading

 

[SamDeleted]

Any issues with this? Basically, can I add as many SCC’s and panels as I want or is there a limiting factor I’m not thinking of?

Hi Ron ,

The limit is the total maximum charge rate of your chosen batteries

It should all be available in the battery data sheet

 

[SamDeleted]

- 8 x 75W Siemens panels (hilarious, I know) in what looks like to me as two strings of four panels run in parallel.

Hey don't take the mick , siemans are a serious company lol

I bet that generator has to run a lot with only 600w of panels ?

 

[ron_jeremy]

- How do I size the shunt? For example, Victron sells shunts in 500A, 1000A, 2,000A, etc.
- Do the positive and negative cables from each charge controller all go directly to the battery or should they go to some other common bus before going to the battery? Also, do I need to fuse the positive cables between the battery and charge controller?

 

[ron_jeremy]

I bet that generator has to run a lot with only 600w of panels ?

Yep, over 6000 hours on one & about 1000 on the other. They get used for other things too but yeah 98% of the hours on the generators will be for battery charging duty.

 

[SamDeleted]

- How do I size the shunt? For example, Victron sells shunts in 500A, 1000A, 2,000A, etc.
- Do the positive and negative cables from each charge controller all go directly to the battery or should they go to some other common bus before going to the battery? Also, do I need to fuse the positive cables between the battery and charge controller?

For the victron shunt to work properly all current in and out should pass through it , shunt placed on the neg line

Generally easier to use a bus bar

Size shunt based on total amps you might draw, you take inverter & total DC loads in watts divided by lowest volts battery will see, eg for a 48v system:

5,000w ÷ 42v = 119amps


Yes to fuses , 125% of expected load in amps , also ensuring cable is of appropriate size to handle amps

 

[SamDeleted]

Yes to fuses , 125% of expected load in amps , also ensuring cable is of appropriate size to handle amps

In most cases, if you're running power through a cable , it needs fusing

There's a few exceptions like single solar strings not in parallel

 

[ron_jeremy]

There's a few exceptions like single solar strings not in parallel

I'll be running 3 panels in series to a charge controller, and the same to another charge controller. Are you saying I don't need to use the 20A MC4 fuses I bought?

 

[ron_jeremy]

Size shunt based on total amps you might draw, you take inverter & total DC loads in watts divided by lowest volts battery will see, eg for a 48v system:

5,000w ÷ 42v = 119amps

Thanks! I have a 4000W inverter so 4000/24 = 167A.
By the way, does it make sense to buy a smart shunt instead of a uhhh dumb shunt considering I have FLA batteries where I use a hydrometer and/or refractometer to measure the SoC?

 

[SamDeleted]

Thanks! I have a 4000W inverter so 4000/24 = 167A.
By the way, does it make sense to buy a smart shunt instead of a uhhh dumb shunt considering I have FLA batteries where I use a hydrometer and/or refractometer to measure the SoC?

Shunt measures SOC by amps and in amps out , minus efficiency. Victron shunts also account for Peukert's expondant which is important for accurate SOC

So for me it's worth the extra money to go blue

 

[ron_jeremy]

Any issues with connecting all four cables (positive and negative from each SCC) directly to the battery?