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Old 05-27-2015, 02:49 PM   #1
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How many watts/panels/batteries do we need?

Hello, we have a 31' Excella on some acreage near Owen Sound, Ontario. I have a Sunforce 4 panel , 80 watt solar package that I bought from Costco, hooked up to (2) 12 volt deep cell batteries ( parallel wired) . We would like to be able to run lights as required @ night and the Propane fridge electronics for 2-3 days max. We always run out of juice into day 2 @ best. How much more do we need & of what ? Thanks for any help.
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Old 05-27-2015, 02:55 PM   #2
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Depends on your solar exposure. Here in the Deep South I can get away with ~200 watts and live pretty large unless we have a run of cloudy weather. Typically I can recharge in 4-5 hours in the winter what I use overnight running the furnace and lights. That is with a 100 watt portable panel, that I can move for optimum gain.

Given how far north you are and the probability of cloud cover you may need more battery and a whole lot more solar. Eighty watts is obviously not enough. I would expect you are going to need in the 240 watt range just to break even.

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Old 05-27-2015, 03:11 PM   #3
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Originally Posted by RJB54 View Post
Hello, we have a 31' Excella on some acreage near Owen Sound, Ontario. I have a Sunforce 4 panel , 80 watt solar package that I bought from Costco, hooked up to (2) 12 volt deep cell batteries ( parallel wired) . We would like to be able to run lights as required @ night and the Propane fridge electronics for 2-3 days max. We always run out of juice into day 2 @ best. How much more do we need & of what ? Thanks for any help.
Don't know if you've done this or not, but you can reduce the amount of power you use for lighting by about 75-80% by switching to all LED bulbs.
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Old 05-27-2015, 03:31 PM   #4
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Don't know if you've done this or not, but you can reduce the amount of power you use for lighting by about 75-80% by switching to all LED bulbs.
I forgot about LED... I have switched my house, RV's and barns over. I don't even think about non-LED stuff anymore.

LED's will definitely help reduce current draw if you use the lights much at all. On my RV's I have found the furnace, fridge control board and the smoke/CO and LP detectors to be the biggest draws. We use lights pretty sparingly and seldom watch television. I much prefer a good book.

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Old 05-27-2015, 05:15 PM   #5
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Is your solar package 80 Watts total? 80 watts into the batteries is going to give you on the order of 26 amp-hours a day - or roughly 4 hours of running your furnace.

I'm saying you need more than 80 watts of panels, but Lewster would be The Man to pitch in here.
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Old 05-28-2015, 01:25 PM   #6
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Have you considered using tow six volt batteries and running them in series? That is what I have and can do pretty well. I guess running the batteries in series gives you more amp hours.
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Old 05-28-2015, 01:56 PM   #7
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Have you considered using tow six volt batteries and running them in series? That is what I have and can do pretty well. I guess running the batteries in series gives you more amp hours.

You have to connect 6 VDC batteries in series to get to the required 12 VDC. The amp/hour rating stays the same. Series connections increase voltage. Parallel connections increase amperage.


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Old 05-28-2015, 03:31 PM   #8
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Looks to like it would be easier to start the 2000 watt honda generator......
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Old 05-28-2015, 04:43 PM   #9
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nice little calculator here:
Solar Sizing Calculator
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Old 05-28-2015, 05:22 PM   #10
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We would like to be able to run lights as required @ night and the Propane fridge electronics for 2-3 days max. We always run out of juice into day 2 @ best.
You must be using incandescent lights. First, get LED replacements. If I run every light in my AS except inside cabinets I use 29.2 watts. Your fridge electronics should not be too much a draw. Two nights would be 10 hours as I run the lights for about 5 hours each night. One of those OEM light bulbs is I believe 14-28 watts depending on type, I had two types in mine - a 1141 and another one. That is a huge difference. My 48 hour light use at max would be 292 watt-hours DC. Your 80 watt panel should be able to add around 64 watts per hour avg. into the system for around five hours, then less as daylight weakens. That is 320+ watts DC. This example is how they figure it and tell you how much you need. They told me that I would need a 300 watt system to boon dock indefinitely as I used 226 watt-hours each day and needed the other wattage to charge the battery plus the low draw times, etc. I plan more off and on use like you so I am looking at 150-200 watts. I use two group 24 batts with a total of 184 amp hours or 1764 watts that needs charged to keep topped. The simplified calculation is 1 watt for every amp hour.
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Old 05-29-2015, 12:32 AM   #11
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Originally Posted by RJB54 View Post
Hello, we have a 31' Excella on some acreage near Owen Sound, Ontario. I have a Sunforce 4 panel , 80 watt solar package that I bought from Costco, hooked up to (2) 12 volt deep cell batteries ( parallel wired) . We would like to be able to run lights as required @ night and the Propane fridge electronics for 2-3 days max. We always run out of juice into day 2 @ best. How much more do we need & of what ? Thanks for any help.
To start, you should have LED lighting as mentioned above as incandescent lights are real power hogs. Next, you have to determine your approx. amperage use for each day you wish to be off grid. This is done by listing every appliance you desire to operate, the estimated amount of time for each and their amp draw. The total will give you the amount of amperage (or wattage, depending on which measure you use) you can reasonable expect to draw from your batteries each day.

Next, multiply this amount by a factor of 4. Say you calculate a 38 amp draw each day. This would be a total of 152 amps per day. I would then suggest a battery bank with a capacity of 300 amp/hours minimum which would allow your batteries to be discharged to the 50% level each day.

Next, depending on your latitude, the type of batteries you have and seasons that you will be using the trailer off-grid, you then plan the size of your solar array. Liquid cell batteries take more amperage and more time to re-charge due to their higher rate of internal resistance. AGM batteries are far better and quicker to re-charge, and lithiums are lightning fast for recharging.

Based on where you are and starting with liquid cells, I would use a 600 watt array, AGMs; 400-500 watt array and lithiums; 300-400 watt array, all with an MPPT charge controller of sufficient capacity to handle the array.

Over capacity will allow you to have full batteries each day, even in overcast conditions and as I have been told by clients, battery charging from their solar array even in the rain!

Any of these configurations will allow you to stay off-grid far beyond the 2-3 days you are experiencing now.....but be forwarned! You don't get systems like these for Costco prices!!!
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Old 05-29-2015, 10:59 AM   #12
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Don't know if you've done this or not, but you can reduce the amount of power you use for lighting by about 75-80% by switching to all LED bulbs.

Thanks, we are already switching our house over, makes good sense to do the same with the trailer.
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Old 05-29-2015, 11:24 AM   #13
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Thanks, we are already switching our house over, makes good sense to do the same with the trailer.
And you can even consider using 120 volt LED bulbs powered by a small inverter in your Airstream as an inexpensive way to do the conversion.

See my post on the subject:

http://www.airforums.com/forums/f447...am-126542.html
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Old 05-29-2015, 11:52 AM   #14
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We have a basic system installed by Can-Am when we picked up our trailer two years ago. We have a 160 watt GO Power panel mounted on the roof (with no inverter) used to the power the lights, fridge electronics, furnace, etc. We upgraded the batteries to Lifeline AGM Group 24 six months later. We have no problem in the U.S. south west running lights, furnace (at night), etc. when we have a reliable source of sunlight. With cloudy, cold weather (i.e. Grand Canyon this past April), we can last at most two days being careful. During a one month period (April to May) from Grand Canyon to Moab, we dry camped about 15 days with no problems keeping the batteries at full charge. In Newfoundland last summer, we were OK after two days of cloudy weather in Terra Nova National Park; then again we didn't require the furnace in summer.

That said, we are considering a generator for periods of cool, cloudy weather which we may encounter on Vancouver Island this fall.
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