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I'm looking for a 25W panel and a controller.
That's roughly 2 amps per hour at maximum efficiency, which no solar nor windgen ever seem to deliver max. Are you sure that is sufficient? It would keep your bank topped, with little to no draw, while you are away. If you were discharged even 25%, at realistic output, it would take days of sunlight to fully charge.
 
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Another solar panel dealer ironically said that my 14 ah load was pretty low and that I may not need a solar charger.
Hang on a second - you are saying you only use 14 ah a day.

That's if you only use each of the items you listed for 1 hour. I think that is unlikely.
I made that comment (now multiply by number of hours used) back where you posted the items and their draw.
 

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So far this is what I have ... pretty low draw I think:

Endless Breeze 12v Fan 3.0
LED interior lights 0.5
Nav LED running lights forward 0.5
Stereo 1.0
Raymarine x-70 Autopilot 5.0
Garmin navigation GPSMAP 500series 1.0
Cockpit VHF Standby 1.0
Depthmeter 1.0
Speedometer 1.0

Total so far - 14.0 ah
David,

Let's now say you go for a 5 hours sail, spent 10 hours sailing on the Chess htis past saturday so not uncommon...

Your Ah draw is now each device X 5 (except nav lights which would be used less hours)..

So for a 5 hour sail...

Speed = 5Ah
Depth = 5Ah
VHF = 5Ah
GPSMAP =5Ah
AP = 25Ah
Stereo = 5Ah
Fan = 15Ah


Excluding nav lights you are somewhere around 65Ah / day for a short 5 hour sail....

You would be very well served by a battery monitor so you know the actual average daily consumption. Theoretical and real consumption are often quite far off... It will make sizing a solar panel easier. Either way you are likely below 80%SOC so sizing a solar panel to replace that 20% in a couple days is wise.... This will likely be bigger than 25W...
 

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For 5 hours, then anchoring over night -

So for a 5 hour sail...

Speed = 5Ah
Depth = 5Ah
VHF = 5Ah
GPSMAP =5Ah
AP = 25Ah
Stereo = 5Ah
Fan = 15Ah
Take out the AP, GPS Speed and Depth, then add in more lighting and fans plus a anchor light (some are 1amp per hour, some are less).
Add back in the AH you get WHILE you are sailing and sitting (I got 30-35 a day with my 80w panel).
For multi-day anchoring out figure 40-50 ah a day on the hook. If you have a standard 50amp alt you really need to know that 1 hour at idle is REALLY only 20-25 amp.

Now figure your panel(s) for that.
 

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For 5 hours, then anchoring over night -



Take out the AP, GPS Speed and Depth, then add in more lighting and fans plus a anchor light (some are 1amp per hour, some are less).
Add back in the AH you get WHILE you are sailing and sitting (I got 30-35 a day with my 80w panel).
For multi-day anchoring out figure 40-50 ah a day on the hook. If you have a standard 50amp alt you really need to know that 1 hour at idle is REALLY only 20-25 amp.

Now figure your panel(s) for that.
The op said he was on a mooring:

I'm usually on a mooring
Most alternators, with a bank like the OP described, can get the bank back to about 80% state of charge without too much trouble, if you run the engine long enough. If he can get back to 80% then a solar panel sized for a mooring top up will get him the charge in the bank he needs for longevity. Sizing for cruising loads will obviously require a larger panel.

This is why a good battery monitor should often be the first cash outlay in a system. The OP has no idea where his SOC will end up, or how to figure his loads, so he ideally needs to see it, touch it and feel it in order to size a solar panel for an intended purpose. A battery monitor for $144.00 can do this for him and allow him to "see" what is going on..

Any solar is better than none but if he was always getting back to 80% and only needed to replace 25 Ah's then a 140W array could be an over kill expense when a 50W panel would have him topped up by the time he came back to use the boat....

BTW when I got back from the Annapolis show the battery on my car was FLAT DEAD. I had left the dome light on at 3:00 am in the lit parking garage so never knew it.

It is a BCI Group 35 battery, pretty small. I threw it on my bench charger and it took over 12 hours to charge it to full. When full it was taking about 0.3A at 14.4V. The charger has double the capacity the battery will "accept" and yet to get to "full" it took over 12 hours..

No sailboat runs the motor that long unless doing the ICW so this is why solar can be sooooooo useful to mooring sailed boats because it has the time required to top the bank up, which an alternator just does not, due to acceptance and the bank limiting current once in absorption..


With two group 31's figuring 105Ah's each he has a 210 Ah bank. At 80% SOC he will have a deficit of 42Ah's.

42 Ah's X 1.15 (charge inefficiency) leaves him with a real world deficit of 48.3Ah's needing to be returned to the batteries.

If he wants to recharge in:

2 Days = 24 Ah's per day
3 Days = 16 Ah's per day
4 Days = 12 Ah's per day
5 Days = 9.5 Ah's per day
6 Days = 8 Ah's per day

If we figure 4.5 hours per day at "rated" (Imp) output he'd need..

2 Days = 5.3A rated panel (roughly a 100W panel)
3 Days = 3.5A rated panel (roughly a 65W panel)
4 Days = 2.6A rated panel (roughly a 45W panel)
5 Days = 2.1A rated panel (roughly a 40W panel)
6 Days = 1.3A rated panel (roughly a 25W panel)

The above is "best case" scenarios. I see the averages run between 3 hours per day to 4.5 hours and sometimes 5 hours per day at rated panel (Imp) where isolation numbers are high like Maine is in June.....
 

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MS,
being on a mooring doesn't preclude the occasional night anchored elsewhere.
 

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MS,
being on a mooring doesn't preclude the occasional night anchored elsewhere.
No not at all, but I am talking about just "recharging" the batts to get the most longevity from them while on the mooring. The OP specifically talked about charging on the mooring or coming dock side to do it, which can take 10+ hours. Solar is far easier.

Ideally you want them back to 100% in the shortest time frame possible, usually 1-2 days but 3-4 days is better than never getting above 80-85%... With AGM's as the OP has these would be the "minimum" sizes needed. I would advise trying to keep the time to 100% to less than 3 days for the best longevity.

Any panel in the 1-2 day from 80% SOC size range can and will help when off cruising too. Unless you are going for multiple weeks or more, a night or two is not going to make much difference as long as you are regularly getting back to 100% SOC on a regular basis.

If you want to have your solar array get you back to a reasonable charge level when cruising, and using loads at the same time, then it needs to get quite big. This is something I doubt the OP wants to do, based on what's been written thus far. Actually it does not sound like he really want to go much bigger than about 25-30W, which is not ideal for a mooring sailed boat with AGM's, but certainly better than nothing or a 5-10W panel...

I size and install lots of solar panels for mooring "recharges". This is a different goal than being self sufficient on solar when cruising, which I also install a lot of. For mooring charging the goal is to get the banks from the "avg" state the boat returns to the mooring at to full in the fewest days possible. Often times this is around 80% SOC but it can be lower.

The average in increased bank life on the mooring sailed boats I've done has gone from 2-3 years to 5-7 years on the batteries with AGM seeing the most increase in life.. Big differences with little expense especially if the owner has $$$$$ AGM or GEL batteries.

Mooring sailed boats have a whole different set of "charging" problems than do dock sailed boats and that is where I was coming from to help the OP in his questions.
 
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