New member with a 30 foot sailboat powered by a 10 kw. brushless motor and a 48 volt fuel cell.

Welcome to the forum.

More or less, the best place to start is understanding your loads... How many Watt*Hours / Amp*Hours (@48 volts?) per day? What seasons will you be using the power? Where will the installation be made? Will the solar array be mounted "flat" or can it be tilted and facing south (i.e., fixed vs floating dock, etc.)?

Ignoring the loads for the moment--We can start with your battery bank. Typically, for a lead acid battery bank, we suggest 5% to 13% rate of charge--With 10% or more for full time off grid (>9 months a year of daily use).

With 8x 6 volt @ 220 AH batteries:

• 8 batts * 6 volts * 220 AH * 1/0.77 panel+controller deratings * 0.05 rate of charge = 686 Watt array minimum
  
• 8 batts * 6 volts * 220 AH * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,371 Watt array nominal
• 8 batts * 6 volts * 220 AH * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,783 Watt array "cost effective" maximum
  

Then there is "hours per day" of sun for your location... Say Fishers IN:

http://www.solarelectricityhandbook.com/solar-irradiance.html

Fishers
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 50° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
2.95	3.43	4.02	4.55	4.70	5.11
Jul	Aug	Sep	Oct	Nov	Dec
5.34	5.04	4.99	4.20	2.89	2.48

Toss the bottom three months (no boating, use genset for help, etc.), leaves us with Feb as the break even month. The amount of energy per day would be:

• 1,371 Watt array (using nominal array) * 0.61 DC off grid system eff * 3.43 Hours of Sun (February "break even") = 2,869 WH per day (Feb)
• 2,869 WH * 1/48 volt battery bank = 60 AH @ 48 volts (February typical day)

In general, it would be a good idea to only discharge the battery bank by ~25% per day if used every day... If you only do weekends or so, you can discharge 50% or more then use the rest of the week to recharge (it will take ~2 days of sun to recharge a lead acid battery bank from 50% to 100% State of Charge).

Note, for charging a 48 volt battery bank, you will need a solar array with a minimum Vmp-array~72 volts if you use standard PWM or MPPT type charge controllers. There are a few (at least one) "boost" capable solar charge controller--However it is a relatively small (low power) unit.

You will need to figure out what panel (wattage, Vmp rating), and the series/parallel connection to give you an acceptable array for charging your battery bank.

Smaller panels (140 Watts or less, Vmp~18 volts) would require a minimum of 4 panels in series and can use a PWM (cheaper) or MPPT (more expensive) solar charge controller. There are larger panels (200 watts and larger) with Vmp~30 to 36 volts (typical for Grid Tied power systems) that can be 2-3 minimum in series (and usually require a more expensive MPPT charage controller).

Generally, a few different "paper designs" will need to be penciled out and see what works best for you.

Anyway--A few guesses as a start.

-Bill