Off-grid PV system upgrade- 12V or 24V?

[green_getaway]

I bought an off-grid home with an existing 1KW PV system (Siemens/Shell Sm-55's wired parallel, xantrex 2512 modified sine wave inverter, C60 charge controller, 8 L-16's- 4 series pairs for 12V). I need to upgrade to a pure sine wave inverter and increase battery and PV capacity. I bought eight additional SM55's and a third zomeworks tracker to mount them on, and 24 GNB Sprinter 12V 165ah batteries for my new battery bank. Here is where I need advice- the house has both 120V and 12V circuits. The current battery bank supplies the DC service panel directly as well as the 120V panel through the 12V input inverter. If I reconfigure the panels and batteries to 24V series pairs to supply a 24V pure sine inverter, will it be complicated/expensive to convert the 24V to 12V for my 12V circuits? Or would I be better off finding the most powerful 12V pure sine inverter I can get and leave everything wired for 12V? Thanks for your comments.

[greenHouse]

I'd look at the 12 volt loads and see if you can find a 24 to 12 volt DC-to-DC converter and use that to supply your 12 volt loads.

Another possibility that people have suggested to me is using a 12 volt PWM charge controller connected to a 24 volt bank (most of my off-grid clients are 24 volt systems ...) and then have a small-ish 12 volt bank. I'm not fond of the inefficiencies in a setup like that, but if there are high current 12 volt loads it would be cheaper than a large 24 to 12 volt converter.

You want to get to a 24 volt system. The DC currents are lower and the inverters have an easier time making AC power with the higher DC voltages.

[Mike90250]

Buy first, ask questions later.

24, 12V batteries ? yikes

Even wired for a 24V system, you still have 12 parallel banks. That will require matched cable lengths to prevent the lowest impedence loop, from sequentially killing your batteries.

The output of the charge controllers, and your inverter loads, should all go to the same set of terminals. Battery bank should be wired on "diagonal"

Diagonal wiring explained and illustrated: (for your battery banks)

http://www.smartgauge.co.uk/batt_con.html

[green_getaway]

24 12V batteries

I was following a plan for an AGM 24V battery bank consisting of 12V series pairs wired, with same-length (short) cables, to positive and negative busbars, rather than to each other. The charge controller and inverter connections are to the busbars.

[greenHouse]

I was following a plan for an AGM 24V battery bank consisting of 12V series pairs wired, with same-length (short) cables, to positive and negative busbars, rather than to each other. The charge controller and inverter connections are to the busbars.

A buss bar is just a big, fat, fancy wire-thingy. It still has resistance and differences in voltage drop from one end to the other can still create problems.