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Old 07-14-2015, 02:37 PM   #1
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thinking about solar?

I don't plan on doing a lot of boondocking but am sure I will be doing some. I have two 12 volt batteries I can use and am plannjng o addig a pair of 6 volt golf cart ones to the trailer.

I have a generator I can use but would rather leave it home and go solar when the weather is not too hot. I will only take it if I am going to need to run air conditioner.

I don't want to mount anything on the roof. I often park under trees so want something I can move around to get in the sun. This is what I am looking at:

Solar Panel Kit - Save on this 45 Watt Solar Panel Kit

I know many of you are using solar so my question to you is this a big enough system? Is 45 watts enough? Or can I go smaller?

13 Watt Briefcase Solar Charger

15 Watt, 12 Volt Solar Panel

I understand that if I go to the smaller panels I will need a regulator such as:

7 Amp Solar Charge Regulator

One comes with the 45 watt system.

So give me your thoughts.

Jim
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Old 07-14-2015, 03:07 PM   #2
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The math is fairly straight forward.
Solar will never replace your generator with panels so small.
Here is why:

A single size 24 "Marine" battery contains about 80 AH of capacity.

80 AH times 12 volts = 960 watt hours or 960 watts for 1 hour.

if you have a 10 watt solar panel it will provide 10 watts of charging power in full sun with 90 degree incidence to the panel.

Assume you have disconnected your (dead) battery from the camper so that all panel output is directed to charge the battery.

Assume also that your panel is mounted on a computer controlled motor driven pedestal so it follows the sun across the sky at the proper angle for the latitude you are camping at.

Assume next that the sun shines for 12 hours and sets for 12 hours.

a 10 watt panel will need 960/10 or 96 hours to charge the battery.
96 hours/12 hours = 8 DAYS to recharge the battery.

If you use only 1/2 of the capacity before you remove the battery for charging, it is still 4 days to recharge it.

If you have a fixed installation the panels are only 15% (industry standard) efficient your 10 watt panel will only produce 1.5 watts and need 640 hours / 12 hours per day = 53 days to charge your dead battery.

Getting a 100 watt panel is not enough as it will still take 5.3 days to recharge your battery.

About 500 watts (2 - 250 watt panels) is about when solar starts to make sense as a generator replacement for short 3-5 day trips.
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Old 07-14-2015, 04:14 PM   #3
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I have 520 watts of solar making 35 amps to keep my 435ah battery bank charged. I use an inverter and run everything except the 2 A/C units. I've never ran out of battery while boondocking in the cooler months. I did design my system so I can add more solar if needed though.
At least put as many watts of solar as you have AH of battery so If you have 200ah of battery then use at least 200 watts of solar as a minimum. Yes you'll need fusing and disconnects and a good charge controller. You get what you pay for in charge controllers and a MPPT controller is a lot better than a PWM controller. I have a 60 amp Morningstar MPPT controller. You can see pics of my system on my profile albums.
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Old 07-14-2015, 04:40 PM   #4
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Mud Yapster,

The examples were to recharge a dead battery.

Obviously if you are a smart husband of battery power you can get away with a few hundred watts of solar. Once the battery is dead, you still need to haul out the generator and use a dedicated battery charger.

And not everyone has the payload for 435 AH of battery stack...
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Old 07-14-2015, 05:05 PM   #5
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Herk7769,
Sorry my bad, and yes an extra 300#s of battery can be a problem for some.
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Old 07-14-2015, 05:11 PM   #6
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Quote:
Originally Posted by mud yapster View Post
Herk7769,
Sorry my bad, and yes an extra 300#s of battery can be a problem for some.
My TOTAL payload is 920 pounds. Since I now need to carry 300 pounds of dialysate solution for the DW's nightly dialysis for a week trip, I have even been thinking about removing the second battery so I can pack an extra pair of shorts or two.
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Old 07-14-2015, 05:52 PM   #7
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Quote:
Originally Posted by mud yapster View Post
I have 520 watts of solar making 35 amps to keep my 435ah battery bank charged. I use an inverter and run everything except the 2 A/C units. I've never ran out of battery while boondocking in the cooler months. I did design my system so I can add more solar if needed though.
At least put as many watts of solar as you have AH of battery so If you have 200ah of battery then use at least 200 watts of solar as a minimum. Yes you'll need fusing and disconnects and a good charge controller. You get what you pay for in charge controllers and a MPPT controller is a lot better than a PWM controller. I have a 60 amp Morningstar MPPT controller. You can see pics of my system on my profile albums.
Very nice system and I don't imagine very inexpensive. Each panel is about 5 feet long right? I would have a hard time fitting them on my 5th wheel, LOL!

From what I am reading I don't think solar is going to work for me.

Jim
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Old 07-14-2015, 05:58 PM   #8
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Yes I do have some cash in my system over $4500 with the AGM batteries and Inverter. It sure makes it convenient to only need to fill the fresh water tank and leave then camp where you want no need for shore power. If it rains a lot we have a 5500 watt Onan with 30 gallons fuel tank. Boondocker set up for sure.
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Old 07-14-2015, 06:02 PM   #9
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Quote:
Originally Posted by Herk7769 View Post
My TOTAL payload is 920 pounds. Since I now need to carry 300 pounds of dialysate solution for the DW's nightly dialysis for a week trip, I have even been thinking about removing the second battery so I can pack an extra pair of shorts or two.
Sorry to hear about your DW! Take good care of her, trust me, you would miss her! Lost mine 8 years ago come August and still miss her! Thank God for my dog!

Get a couple of those vacuum bags for the shorts. You can tuck them under the hood.

Jim
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