230w 29.8v (vmp) solar panel for 48v battery bank

You want this for a 48 volt nominal battery bank?

If so, then you need Vmp~72 volts (array) with a PWM solar charger (PWM being the "less expensive" type).

And for an MPPT type charger, they do spec. pretty much Vmp-array ~72 volts minimum, you really want Vmp-array>80 volts to get the "MPPT" advantages (taking high voltage/lower current to lower voltage/higher current for the battery bank). With Vmp-array~72 volts (standard test conditions), an MPPT controller really acts more like a PWM (cheaper) controller.

The other issue is the Vpanel-input-max voltage for the charge controller... This is very solar charge controller specific, and also depends on your climate (how cold in winter) it gets... For very cold regions, a Vpanel-max of ~150 Volts, the array Vmp-array-std voltage should not be much above ~100 Volts or so (very cold, is freezing and well below freezing).

You need to check the specifications of your controller, panels, temperature range, etc. and see what will work. Some companies, like Midnite, have a web based calculator to help you make these decisions:

http://www.midnitesolar.com/sizingTool/index.php

And even the sizing tool(s) for Midnite, and different depending on which product family you are using.

Your panels are neither 12 volt or 24 volt panels... A 12 volt panel is (typically around) Vmp~17.5-19.5 volts. A 24 volt panel is Vmp~35-39 volts.

Your panel is Vmp~30 volts or a "60 cell" panel that is typically used for Grid Tied power systems, and can be used with MPPT type solar charger/battery based systems.

When everything is taken into account, a Vmp~30 volt * 3 panels or Vmp-array~90 volts is fine with many MPPT controllers (details matter), but "inefficient" with PWM controllers on a 48 volt battery bank (can work, just will lose around 20% of the energy from the solar panels (again, need to check the PWM controllers specs to make sure input voltage, Voc-cold is OK).

-Bill

Can you post a link to the inverter/charger you want to use?

Guessing you might be around Milan Italy?

https://weather-and-climate.com/average-monthly-min-max-Temperature-fahrenheit,milan-lombardy-it,Italy

The marketing specifications are not really accurate for statement #2... It should be Vmp-hot>maximum battery charging voltage (not Voc).

Your batteries probably charge around 58 volts or so (nominal) and 60-62 volts when Equalize charging.

Vmp falls when panels get hot... Very hot panels (full sun, no wind, hot weather), your 90 volt Vmp-array-std can get down towards 74 volts or so... That gives you ~14 volts between 60 volts battery charging and 74 volt Vmp-array-hot (allows for wiring voltage drop, MPPT charge controller drop, etc.).

-Bill

Luqman,

I noticed that you have auto-fill for the FLA battery. I suggest that you use a valve and only use the auto fill when you are watching. It does not happen often, but on occasion the cell valves have been known to stick and overfill. Makes a mess, plus you are left trying to drain the mostly water electrolyte and adding "the correct amount" of acid to get the cell back into service.

Regarding fuses/breakers and wiring... The DC power systems for batteries tend to run at high current for hours at a time (charging the battery from 50% to 80%+ State of Charge, usually current limited by the battery charger). In North America, our fuses and breakers (at least the NEC used for most uses) tend to be rated as--Will eventually trip at 100% of rated current (could be minutes to hours), and will not trip at 80% or less current... So, I like to derate the solar power/battery wiring because of this (and even your AC wiring, to avoid false trips and make things a bit more reliable and more efficient--heavier wiring, less voltage drops and losses). NEC is conservative, but I use 1.25x (or 1/1.25 = 0.80) as a derating factor):

• 30 amp max continuous current * 1.25 NEC derating = 37.5 Amp ~ 40 amp rated Fuse/Breaker/Branch circuit wiring minimum
• 30 amp circuit * 0.80 NEC derating = 24 amp maximum continuous current suggested

Marine wiring specifications do allow smaller gauge wiring than NEC would... Also (at least in North America), we have NEC rated wiring with different types/temperature rated insulation (Outdoor, wet, under sun, oil resistant, number of wires in conduit, ambient temperatures) which can get fairly complex if you are trying for an NEC (US National Electric Code) based installation.

And, check the ratings for fuses/breakers. There is a maximum working voltage, and AC vs DC current ratings (AC current is "easier to stop" vs DC current--So DC ratings are typically lower for breakers/switches/fuses). Remember that battery banks can output 100s to 1,000s of Amperes of current--Fuses/Breaker have a maximum Ampere Interrupt Current rating too. Here is a nice discussion if you want the details:

http://forum.solar-electric.com/discussion/353232/oversized-wire-and-breaker

-Bill