15w solar panel

JamesG161 · Aug 4, 2016

You might think about the Sun's light energy changes as Latitudes get smaller.
But I would suspect it would keep your battery topped off.
Jim...

Stu Jackson · Aug 4, 2016

I left my 390 ah bank on an 11W panel for a month. Returned to find the batteries healthy at 12.85V.

Do NOT hook it up without a controller.

Solar Systems: Selection, Installation & Controllers by Maine Sail SUPERB

http://www.pbase.com/mainecruising/solar_panel

BudGates · Aug 4, 2016

It all depends on your personal power usage. I used a 15W solar panel on my Venture 2-22 and it kept the batteries up for week long vacations with no problem. If I had switched to LED lights it would have done even better. Other people use a lot more power.

AaronD · Aug 4, 2016

BudGates said:
It all depends on your personal power usage. I used a 15W solar panel on my Venture 2-22 and it kept the batteries up for week long vacations with no problem. If I had switched to LED lights it would have done even better. Other people use a lot more power.

@fred1diver: Here's a quick summary of the power budget I did for our Catalina 22.
On 24 hours / day:
--Charge controller + display (mixture of standby + operating modes): ~50 mA (~14 w/h per day)
--Battery monitor (Xantrex LinkLite): 9 mA
--Fuel vapor alarm (Xintex): 200 mA (that's the spec'd max - I'm sure it doesn't actually use that much, so I need to measure it)
--CO Detector (Xintex): 16 mA
--Bilge pump float switches (Water Witch 230): 6 mA x 2

On when sailing:
--VHF: 650 mA (estimated as a mixture of the specs for standby, receive, transmit)
--Depth sounder: 40 mA
--Knotmeter: 60 mA (it's never accurate - I don't know why I waste the power...

Other (multiply by estimated hours used where appropriate):
--Navigation lights (LED): 2 watts / ~160 mA
--Steaming light (LED): 1 watt / ~80 mA
--Cabin lights (4 x 2m LED strips): 3.2 A (rated consumption - I should measure this too)
--Charging 2 iPhones: ~18 w/h (1.5 A/h)
--Charging 1 iPad (used as chart plotter or movies for the kids): ~65 w/h (~5 A/h)
--Charging handheld VHF: unknown

In total, I budget ~300 watt hours (~25 A/h) a day, although we rarely if ever use that much. I'm (obviously) not all that careful to be strict on power. Your usage is surely lower. But hopefully that list helps you think through your own power budget.

Also, you should read Maine Sail's recommendations about installing small solar systems (and getting your batteries back from partial discharge promptly). See his featured contributor forum here and his articles at pbase.com.

Brian D · Aug 4, 2016

My 50 watt will keep the battery topped even under sail. It will power mostly everything I am using; VHF receive, autopilot, two GPS (one for autopilot and one for DSC). Even when these are running I check the battery status and the controller says the batteries are topped.

I am sure 15 watts will keep your batteries topped, but probably not provide for much in the way of being out and about. If all you really want to do is get off shore power (if available) then 15 watts should be good. But if you are out and about and using your electronics, 15 watts might not be enough.

YMMV

joker460 · Aug 4, 2016

fred1diver said:
hey everyone, I was wondering if a 15w solar panel would be sufficient for my 23ft sailboat? I know bigger is better but I dont have much room to install one
so I'm looking at a 15w it gives off .76 amp, so on a good day I'd get 6 amps of power, it wouldn't cover all my needs but it would help extend the battery life.

Keep in mind your location. I loose 30% just because of location.

Benny17441 · Aug 5, 2016

It is hard to tell if it would add a significant boost to your batteries. It would depend on the sunlight energy at your latitude, the average weather conditions and the usage. It seems the best use would be as battery maintainer for a boat in a mooring but if you are thinking about extending battery power on an upcoming trip I concur that putting the money into an extra battery may yield the best results.

walt · Aug 5, 2016

My wife and I just spent a little over a week on a trailer sailor with a 20 watt panel/ mppt controller. Like you are thinking of doing, I have extra battery capacity with a two golf cart battery setup.

I was in a mostly sunny area (S. California) but get a little partial shading on the panel part of the day. Assuming a typical trailer boat (no electric fridge - this changes things dramatically), a panel size of 30 to 40 watts pretty much lets you just not at all worry about what you are using. If you want to keep the panel size small, you need to monitor things a little better and I like a battery monitor for this (one that tells you net amp hours in/out of the battery).

My largest drain is my laptop/cell phone hot spot powered from an inverter at about 6 amps and I have to limit myself somewhat on how much I use the laptop. I have all the normal stuff in the boat like LED lights, fans etc and this trip we also watched maybe an hour of TV per day (free off air - at less than one amp). On this trip we actually were at either a dock or mooring most of the time and usually not on the boat for a significant part of the day. When the boat was being used (motored or sailed), I had a Raymarine ST2000 autopilot plus GPS/fishfider plus VHF radio on all of the time and an Ipad/Navionics on part of the time.

At the end of the trip, I was down about 35 amp hours total. If I assume I was getting about 5 amp hours per day from the 20 watt panel (based on measurements I have done previously) and I ran the outboard for about 6 hours, I can estimate an average for my daily usage and this is about 11.3 amp hours per day. Like another poster above, if I do a power usage analysis, I come up with maybe 15 to 20 amp hours per day but actually never use that much.

I did one experiment while sailing with the Auto pilot, VHS radio and GPS/depthfinder. I noted the battery monitor before and after several hours of this and the 20 watt solar panel/mppt controller completely supplied all the charge needed. I used no net power from the battery during this time.

With about 200 amp hours capacity (golf cart batteries), being down 35 amp hours was no big deal. I could have gone several more weeks before having the batteries 50% down.

Last winter I kept the boat in a slip for four months with just a 10 watt panel/ PWM controller and this was not enough. My big use in the slip was probably the car stereo and it did get used a fair amount. Several times during the winter I had to supplement the battery charging with a temporary 40 watt panel. Temporary because I just dont care to have that large of panel on the boat all the time (just personal preference). So this year I changed to the 20 watt panel/MPPT controller and this should work for me for both the slip during the winter (low sun/short days) and also for taking a week or so sailing trip. Ive had a 40 watt panel in the past and noted that my batteries were fully charged about all the time.

Since you are also trying to get by with a small solar panel (15 watt), one other thing to consider is the charge controller. I went to the Genasun GV-5 this year and it has the MPPT boost for maybe an extra 15% on average but it also has very low night time discharge. With a larger panel, the night time discharge doesnt matter much but it makes at least a slightl difference with the smaller panel.

Anyhow.. that is my data point with a fairly small solar panel.

AaronD · Aug 5, 2016

walt said:
...
Since you are also trying to get by with a small solar panel (15 watt), one other thing to consider is the charge controller. I went to the Genasun GV-5 this year and it has the MPPT boost for maybe an extra 15% on average but it also have very low night time discharge. With a larger panel, the night time discharge doesnt matter much but it makes at least a slightly difference with the smaller panel.
...

Good comments and advice, @walt. I bought the Genasun GV-10 for the same reasons you listed - I really liked the low standby power drain and the compact size (and the price is good too). But then I found that it has very limited voltage configuration, and the target voltages were too high for my Lifeline AGM batteries. You can order a custom-programmed unit from Genasun, but I didn't know to do that up-front. I contacted them, and they offered me a discount on the custom one, but I ended up switching to a Rogue 20A unit (recommended by Maine Sail, and made here in Oregon). It's a lot more configurable, has a nice remote display, and enough capacity for another panel if I ever needed it

My understanding is that voltages for flooded batteries are somewhat more consistent from one manufacturer to another (and that flooded cells are less sensitive to charge voltage variance). So the default Genasun flooded cell setting is probably fine. So I'd definitely recommend the Genasun, but check your target voltages ahead of time, and buy the custom-voltage unit if needed. Hope someone finds that helpful.

Davidasailor26 · Aug 10, 2016

Unless you have some emergency load (like an engine starter) that you need to save power for, then don't use the batteries separately. They're more efficient used combined. Maine Sail has some good posts on the reasons like the peukert coefficient, but the bottom line is that the total can be greater than the sum of its parts.

Davidasailor26 · Aug 10, 2016

fred1diver said:
at the moment I don't have time to wire them

I see. At first I thought the switch was the only part you didn't have.

Davidasailor26 · Aug 10, 2016

Depends on how far the wire runs are, then check a wire gauge selection guide like https://www.bluesea.com/resources/1437

Brian D · Aug 10, 2016

Don't think in terms of "smallest gauge". I would think in terms of voltage drop. I would recommend at least 6AWG.