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Old 05-18-2011, 06:48 AM   #1
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2010 19' Flying Cloud
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How much solar do I really need

I'm new to the forum and I hope I posted this correctly. I purchased a 19ft Bambi last fall and took it out for the first time last weekend. I used to own a pop up and love going to the sate parks in Wisconsin. I found that the non electric sites are usually the best sites at the State parks, but since I wanted to try the Bambi out fully, I picked an electrical site.
Unfortunatley we were between 2 big 5th wheels where when sitting outside under the awning we were looking into the living room of the massive 5th wheel camper. There were many sites with out hookups available wich were much more senic than the hookup sites.
I really would like to be able to charge the batteries using solar to extend our stay more than a couple of days. I think I have read evey link on solar but am still confused on how much solar do I really need to just recharge the batteries. I would like to have a portable solar panel that I can connect to the batteries. I'm perfectly ok with not using the TV or the airconditiong but since we live in wisconsin, heat is really needed at night.
any sugeestions on how much solar I need to recharge the batteries.
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Old 05-18-2011, 07:09 AM   #2
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Welcome to Pandora's Box!

Search solar threads and especially read posts by Lewster. Visit AM Solar's website. FWIW, I've had a 40w panel for 7 years now ... it keeps my batteries charged, LEDs on, and propane heater running ... but nothing more.
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Old 05-18-2011, 10:33 AM   #3
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Some folks say a good rule of thumb is 1 watt per amp of battery capacity. For example, if you have a 100amp battery, then you might want to look at a 100w panel, 200 amps (like me) 200 watts etc. Again that is just a rule of thumb that I have read. Many get by with less such as UAP in the response above.

Best to take a look at what you want to use while on battery power, lights? water pump? furnace? etc. Do you want to run an inverter so you can use AC appliance such as a microwave (you would want to look at more battery power in that case).

Also look at how you can save energy. Have you converted your lights to LEDs, that really helps to reduce the battery load.

As mentioned above, lots and lots of threads on solar installations here on the form. You can search or browse the sub forum on electrical threads.

BTW many of use have installed systems by AM Solar. I just installed one myself, you may wish to visit their web site or give them a call, they specialize in RV Solar installations and kits. The have an "education' page that is worth reading.

BTW SGoetz, like you we find the non-electric sites in state parks more to our liking. About the only time we use electric sites is in the late fall (Nov.), when it starts to get cold and we want to run the furnace.
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Old 05-18-2011, 10:48 AM   #4
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I think you're on the right track. Those "more scenic" sites often have no electricity. But do read all the threads on here on solar. There are a lot of them, and they are informative.

I have a 23' Safari, with two 130 watt panels and three Lifeline batteries (AM Solar / Lewster install). Since the installation last January, I have NEVER had to start my generator, and have boondocked for 4-5 days at a time in below freezing temps, where the furnace has run much of the nights. No problem, even in largely cloudy Wisconsin sites ... though obviously this won't work so well if you're in a shady, treed site. I'm heading out tomorrow for a trip where we'll boondock for four nights, and I'm not even gonna' take the generator along. (But it IS a nice security blanket, and if I wanna' run the microwave or electric toaster, etc. could be useful ... though it seems to be rusting more than being used!)

For your somewhat smaller trailer, you could use a second battery, in case you're out in cloudy, cold weather and need/want to run your furnace hard. Obviously, limiting current/time draw is the key ,,, so LED lights help a lot, and as you say, no microwave or TV use also helps. Outside of the furnace fan and lights, the fans for stovetop and shower are big draws, so keeping them off as much as possible helps also.

If you are o.k. with practicing water conservation while boondocking and consider your batteries to be much like your fresh water tank, you'll do fine.
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Old 05-18-2011, 01:22 PM   #5
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The watt per amp hour is a good rule of thumb but I prefer to use different units to avoid confusion. Make that at least 1 watt of solar per pound of battery.

Another source of confusion is whether you want to charge the battery or just maintain the charge on the battery.

The idea of charging a battery gets into the problem of the usage of battery energy. As AirsDream notes, that becomes an issue of conservation more than anything else as there just isn't that much available energy in batteries.

General rules of thumb:

- determine energy need for 2 nights and three days to size your battery bank

- figure about 12 watt hours per pound of battery to determine how much battery you need to meet energy requirements

- plan on at least one watt of solar per pound of battery to be able to keep batteries charged in nominal conditions pretty much. This will not likely often provide the vigor of charging needed for optimum battery life, though.

Note that typical household electrical use is about 30 kWh/day so you'd need nearly 100 kWh for a typical reserve (2n/3d) energy capacity. A typical battery for an RV might have as much as 1 kWh usable energy. That means an RV energy lifestyle is quite constrained and also that it doesn't take much to totally blow the energy budget in an RV.

Also note that the energy availability in an RV battery may vary by more than 10% due to temperature, age, cycle to cycle variance or use profile. Each of these can cause differences of up to 20% or so.
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Old 05-18-2011, 04:58 PM   #6
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The received wisdom on the forums is that you need 300 watts of panels to get enough electricity to help out much with boondocking. AM Solar is presently selling panels for a little more than $4 a watt so that's $1200 worth of panels, and in most cases, is the largest array that will fit conveniently on the roof of an Airstream. Total system prices are higher even if you do the work yourself.

This advice comes from people in southern latitudes, where there is more sun and fewer clouds. In Wisconsin and Minnesota and places like that, where the late fall days are short and we often have clouds, such a system may prove disappointing.

You may want to consider heat sources that require no electricity or less electricity as a more cost effective alternative.
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Old 05-18-2011, 07:17 PM   #7
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I have one solar panel that outputs 130W. It keeps the 2 batteries charged. That's all I need. However, you may want to consider a Honda 1000W generator as a quick way to keep the battery charged. And if you get 2 you should be able to run the air, too.
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Old 05-18-2011, 09:10 PM   #8
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Originally Posted by nswhite View Post
I have one solar panel that outputs 130W. It keeps the 2 batteries charged. That's all I need. However, you may want to consider a Honda 1000W generator as a quick way to keep the battery charged. And if you get 2 you should be able to run the air, too.
2000 watts AC from a pair of Honda 1000's won't run a roof A/C unit. Some get by with a Yamaha 2400 or step up to the 3000 watt unit, but most use a pair of 2000's for a combined output of 4000 watts.
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Old 05-19-2011, 06:27 AM   #9
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Thank you for all the replies. I'm really looking to keep it simple by just having a solar panel that I can attach directly to the batteries to recharge them after running them down. Maybe down the road I'll have some professionally installed to be able to do more. What's the minimum amount of watts needed to just recharge the batteries on a sunny day.
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Old 05-19-2011, 06:53 AM   #10
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30w works for us...
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Old 05-19-2011, 09:18 AM   #11
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We see solar as a way of keeping the lights running, running the water pump, igniters on fridge and water heater, ventilation fans, and my CPAP machine at night, charging batteries for laptops, cameras. etc. I removed the original furnace as it was non-functional (and dangerous); I've not yet replaced it with an alternate source of heat. We may choose to use a catalytic heater since those can work w/o large amount of electricity; if I have to plug in to stay warm I might as well use an electric heater. We tend not to camp in the middle of winter when freezing temps are a possibility here. Air conditioning isn't an option of course w/ solar power; we've never used ours anyway.

We have been remodeling the inside of the trailer extensively, and using LED lighting strips, spots, etc. to remove the need for running incandescents lights. This has reduced power consumption by a factor of 10 for lighting, and with the indirect lights is much more pleasant; the 70's model of a central light fixture in the middle of the room - gack.

For this usage model, the 200W AM solar setup I installed appears to be quite adequate; we'll see this year as we plan to spend time at Juplaya, Crater Lake and Burning Man w/o hookups.


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Old 05-19-2011, 09:26 AM   #12
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Amen on the LEDs. We had a Trimetric in our SOB and when I started switching out bulbs for LEDs it was amazing how much power we saved. I agree on the factor of 10 amount.

We generally use a catalytic for heating during the "awake" hours. I'll run the furnace for a quick warm up first. At night we generally don't run heat unless it is very cold, if it is, I turn it down low (50's) just to keep the pipes/tanks from freezing. If we are plugged in we also use an electric heater. One small one keeps the trailer pretty comfortable.
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Old 05-19-2011, 09:28 AM   #13
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2000 watts AC from a pair of Honda 1000's won't run a roof A/C unit. Some get by with a Yamaha 2400 or step up to the 3000 watt unit, but most use a pair of 2000's for a combined output of 4000 watts.
You're right. Got my models mixed up.
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