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Old 12-04-2011, 21:17   #1
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How large a panel, and what's best?

I looked through several threads but cant find exactly what I am looking for, so I am asking for advice. Our 31' is being moved to a dock w/out power. We do have a portable generator we use when needed but would feel better having a solar panel to keep batteries charged. Currently the batteries consist of 1 grp 29 deep cycle 115 ah and one grp 27 90 ah battery. We dont run a fridge or anything while docked unless the generator is on. We take many 2-4 day long trips a year, and also plan a 2 week trip but will have the generator for when needed. I would prefer enough solar juice to ensure the batteries stay charged for when we want to take her out, and also to ensure the bilge pumps will function. What size would be needed and what's best, also a charge controller. At our camp we have a small 10 amp panel on a deep cycle battery and I am much less then impressed with its performance.
Also wondering how much juice would be needed to run the auto helm, (st3000) and gps for an entire day while not draining the batteries down so much the engine would not start.

Thanks for any input, and reccomendations,
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Old 12-04-2011, 21:32   #2
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Re: How large a panel and whats best?

You need to start by calculating the daily power budget. Add up the specs on all the instruments and lights, and anticipated hours of user per day for each. Then when you have a total number of amp-hours per day you can run similar calcs on the solar needed. With solar you'll rarely if ever reach rated output, and any partial shadow cuts output significantly, and you need to allow for clouds and hours per day of high sunlight (don't even bother with the two hours after dawn or before dusk). So figure you need to over-estimate by a wide margin, maybe 2x your power budget plus.
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Old 13-04-2011, 05:02   #3
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Re: How large a panel and whats best?

How about just a simple system that would at least guarranty the batteries are fully charged everytime we go to the boat?
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Old 13-04-2011, 05:47   #4
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Re: How large a panel and whats best?

For a minimal size panel to keep up with self discharge and do a bit of charging over an idle week, A 35W like the smaller of these two would do the trick. These Starboard side rails with beveled ends keep them from snagging ropes and the extra ventilation maximizes V for a better charge. M.
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Old 13-04-2011, 05:55   #5
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Re: How large a panel and whats best?

Quote:
Originally Posted by Dulcesuenos View Post
I looked through several threads but cant find exactly what I am looking for, so I am asking for advice. Our 31' is being moved to a dock w/out power. We do have a portable generator we use when needed but would feel better having a solar panel to keep batteries charged. Currently the batteries consist of 1 grp 29 deep cycle 115 ah and one grp 27 90 ah battery. We dont run a fridge or anything while docked unless the generator is on. We take many 2-4 day long trips a year, and also plan a 2 week trip but will have the generator for when needed. I would prefer enough solar juice to ensure the batteries stay charged for when we want to take her out, and also to ensure the bilge pumps will function. What size would be needed and what's best, also a charge controller. At our camp we have a small 10 amp panel on a deep cycle battery and I am much less then impressed with its performance.
Also wondering how much juice would be needed to run the auto helm, (st3000) and gps for an entire day while not draining the batteries down so much the engine would not start.

Thanks for any input, and reccomendations,
If you just want to keep these batteries charged while you are away, to give you an idea, we are using three 7W flexible panels for just that purpose and has worked great for us for many years (on a 315Ah bank). To run an autohelm on batteries only will require more solar power.
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Old 13-04-2011, 06:16   #6
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Re: How large a panel and whats best?

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Originally Posted by Mark Johnson View Post
For a minimal size panel to keep up with self discharge and do a bit of charging over an idle week, A 35W like the smaller of these two would do the trick. These Starboard side rails with beveled ends keep them from snagging ropes and the extra ventilation maximizes V for a better charge. M.
Nice installation Mark.
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Old 14-04-2011, 03:31   #7
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Re: How large a panel, and what's best?

Quote:
Originally Posted by Dulcesuenos View Post
I looked through several threads but cant find exactly what I am looking for, so I am asking for advice. Our 31' is being moved to a dock w/out power. We do have a portable generator we use when needed but would feel better having a solar panel to keep batteries charged.
We are in a similar position and agreed with Marks suggestion. We have a 45w panel, but only because it came second hand which tops up our 2 x 110 AH batteries up during the week. During holiday cruises it provides 10 AH at (50 degrees North) so we had a daily deficient of 20AH a day which is topped up with the genny every couple of days.

More would be nice, but they are expensive so we get by okay at the moment. Our panel is on the coach roof so some shading from mast and boom during various hours of the day but the remaining time provides enough to keep the batteries topped up. Overall its a good cost effective solution for us.

Do consider some way of monitoring those amps, a NASA BM1 is probably the cheapest way although there are other makes. It means you don't spend hours guessing how long the genny needs to run thereby wasting time and petrol.

You might consider joining the batteries together next time one needs replacing. This would depending on space; double your capacity and then a third small one for engine starting. Doesn't need to be anything clever a small flooded lead acid one will do.

Raymarine manuals should give the max AH draw for the autohelm and GPS.

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Old 14-04-2011, 03:59   #8
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Re: How large a panel, and what's best?

The auto parts stores and RV centers sell portable panels in several sizes. Some of these are under $100. They don't have much power but if all you want to do is top off the batteries while you are away for the week then they will probably be fine. You just clip onto your battery so installation is almost instant and a no-brainer. BOB
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Old 14-04-2011, 06:44   #9
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VW Solar Panels

Dulcesuenos,

This is all you need to keep your batteries top off.
Go to eBay and type in VW Solar Panels. They are simple to use and work great.
Cost $30 to $40

Haul Out, On The Hard, Antifoul & Winter Storage

Mark
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Old 14-04-2011, 11:06   #10
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Re: How large a panel, and what's best?

The panels must be sized for the consumption, while it is nice to keep consumption low (which is not always possible though).

We have a 110 Ah battery and 150W of solar panels here and this set up works fine - we get 40Ah of solar energy on a nice day (we are in a sunny place though). BTW this set up will also keep our engine starter battery topped up.

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