Off grid upgrade checking parameters

Normally we use the 20 hour rate for our rules of thumb... Assuming 24 volt battery bank:

• S605 bank, 4x series => 468 AH bank
• S550 bank, 4x series x 2 parallel => 428 AH * 2 parallel => 856 AH bank

Typically, for a battery system.. Suggest minimum 5% rate of charge (weekend cabin, emergency backup) to 10%-13% for full time off grid... 

• 856 AH * 5% rate of charge = 42.8 Amps minimum
• 856 AH * 10% rate of charge = 85.6 Amps nominal
• 856 AH * 13% rate of charge = 111 Amps typical "cost effective" maximum

I suggest that 13% and over rate of charge you should have the remote battery temperature sensors setup so that the banks don't over heat from too much charging (Lead Acid battery bank charging voltage drops as the batteries get hotter).

And something like 20-25% maximum rate of charge.

• 856 AH * 20% = 171 Amps "starting to worry about too much charging current for "daily charging"

Your solar array, I would expect:

• 16*220 Watt panels = 3,520 Watt array
• 3,520 Watt array * 0.77 panel+controller deratings * 1/29.0 volts charging = 93.5 Amps approximate cool/clear/noontime maximum charging current

So at this point, I would not "current limit" your Outback charge controllers... Set them for full rated output current and you should be fine for solar.

The wind turbine is a wild card here... Guessing:

• 1,500 Watt / 29.0 volts charging = 51 Amps from turbine rated output

How much current do you typically see?

The max (math wise) output from solar + wind:

• 93.5 Amps solar + 51 Amps wind = 144.1 Amps max Wind+Solar (best case)

Depending on your weather conditions--You probably rarely see full 25+ MPH wind and Noon Time sun (cool/clear day)--And even so, you probably would never exceed the 171 Amps (assuming 20% rate of charge) into the battery bank anyway.

And remember that FLA batteries tend to start "throttling back" on accepted charging current at >80% state of charge--So that you have more charging current available will not accept more than "safe" charging current for batteries.

And FLA batteries when charging below 80% SoC tend to be more efficient, so they should not overheat when charging at high currents at low SoC conditions. Assuming you have the correct charging voltages programmed...

Rolls has their recommended charging voltages (and detailed charging recommendations):

https://support.rollsbattery.com/en/support/solutions/articles/237882-calculating-proper-charge-settings-for-rolls-flooded-lead-acid-batteries

And, as always, read the whole manual:

https://rollsbattery.com/wp-content/uploads/2019/11/Rolls-Battery-User-Manual.pdf

My guess/suggestions. I am certainly no battery expert....

-Bill