Originally Posted by SaltyTanned
I plan to use solar only.
bank 6 x Trojan 105 or about 660 amp.hour.
For 24 hours I use around 125 amp.hour
Planning to install 750 watts of solar panels
and the boat is in the southern Caribbean with just about 12 hours a day of light year round.
On a grey day would this be enough solar?
No, but on the bright days before and after, you should be able to bank enough.
Keep in mind two factors: The usable band of battery power is about 30%: from 50% state of charge (SOG) to 80%. You need to have some extra bits to throw charge into a battery bank after 80% or so, and I would think it's worth it, if you have only solar as a charge source.
The second factor is draw-down. If you have a fixed draw, like a fridge, an investment in LED lights
, foot pumps for water
, extra insulation
for the fridge and maybe a nice big alternator
if you need to pump out 12 NM out and want to take the battery bank to 95%-100% or so have to be part of the plan. In the end run, you will save on NOT having a genset or burning more diesel
, and you will have a quiet life in a quiet boat. But you have to make it easier on your batteries by accepting that 750Ah means about 225 Ah of actually usable power
, and that you will be cycling often enough to want to clap on an equalization
charge (which may be possible with the solar, maybe not) and will want hydrocaps and temperature sensors and SG readings and other care and feeding aspects in order to get a good five or six years out of your T-105s.
So the question is not just "how much solar" but "how much use and how much capacity and how much monitoring determine how much solar?".
I have gone with four 135W panels
, a 400W wind
turbine, two 90 amp alternators and two Honda
2000s to keep about an 1,100 Ah bank happy and echo-charging a 12 V starter battery and an 12 V windlass
battery. Normally, I expect the wind
and sun to cover the estimated 125Ah/daily drawdown, but the alts are there to cover the spread, and if I am running a power tool, it's simple to keep the Honda
going at anchor
for two or three hours to pump in enough electrons to have a "movie night" or even to run the A/C or hot water