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Old 03-24-2014, 07:56 PM   #1
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100 watt solar panel?

I'm getting ready to set up my solar charging system. I have two 6 volt 225 amp hour batteries. I plan on a small inverter, just enough to run the TV, laptop, charge batteries for camera, etc. I want a single, portable panel. It's a small TT and I have converted all the lights to LED. When boondocking we rarely leave the furnace on at night, if it's really cold we find a plug in spot.

I have been looking at a 100 watt panel, but have had a couple of folks say that's not enough to keep up. Don't mind going to a 150 watt if that's what it takes.

If there is anyone using a 100 watt with similar demand I would appreciate your input. Would rather have the smaller, less expensive panel, but don't mind the extra bucks/effort if the 150 is the smarter option.
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Old 03-24-2014, 09:15 PM   #2
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Bigger is better with solar. Keep in mind that you won't get all 100 watts unless conditions are perfect, ie 90' to the sun & no clouds & cool temperature. Get the biggest (wattage) panel(s) you can. Remember that you can parallel two smaller, similar panels. To maximize output, get an mppt charge controller. Try solarblvd.com for panels.

2000 Cherokee 31BH, "flipped axles and raised",LEDs, solar, inverter, etc..aka "boondock ready". '07 Tundra 5.7L DC-LB, modded as well.
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Old 03-24-2014, 09:35 PM   #3
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When I looked into solar last year, I took everyone's various formulas for efficency and whatnot, solved them together to get:

40W of panel = 1 amp/hour

Between the fridge, LP/CO2 detectors and radio, I've got about 4 amp/hour parasitic load. Just to offset I'd have needed 160W of panel.

My findings are here

You'll have to figure out your load, multiple by 40 to get an approximate panel size as a start. From there you might be able to go up or down depending on variations in efficiency. Mine was based on the 42nd parallel.
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Old 03-24-2014, 09:48 PM   #4
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Quote:
Originally Posted by Kaadk View Post
When I looked into solar last year, I took everyone's various formulas for efficency and whatnot, solved them together to get:

40W of panel = 1 amp/hour

Between the fridge, LP/CO2 detectors and radio, I've got about 4 amp/hour parasitic load. Just to offset I'd have needed 160W of panel.

My findings are here

You'll have to figure out your load, multiple by 40 to get an approximate panel size as a start. From there you might be able to go up or down depending on variations in efficiency. Mine was based on the 42nd parallel.
I think your estimated output is low. I have 400 watts of solar and can easily get 18-20 amps out of my MPPT controller and if conditions are right nearly 23 amps. Using your math, I should only get about 10 amps.

2000 Cherokee 31BH, "flipped axles and raised",LEDs, solar, inverter, etc..aka "boondock ready". '07 Tundra 5.7L DC-LB, modded as well.
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Old 03-24-2014, 09:56 PM   #5
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Quote:
Originally Posted by RPAspey View Post
I think your estimated output is low. I have 400 watts of solar and can easily get 18-20 amps out of my MPPT controller and if conditions are right nearly 23 amps. Using your math, I should only get about 10 amps.

2000 Cherokee 31BH, "flipped axles and raised",LEDs, solar, inverter, etc..aka "boondock ready". '07 Tundra 5.7L DC-LB, modded as well.

My calculations are based on an average over 24 hours, not point in time. Point in time values are going to higher to lower as the sun arcs.
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Old 03-24-2014, 10:13 PM   #6
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I agree that the instantaneous output varies. A properly set up system should be able to hold the minimum charge current that the batteries need to charge. In my case I need 13 amps (c/20). Your math works for your installation, but I'm not sure it'll work for all scenarios.

The system needs to be sized as to replenish what is used over a 24 hour period. But, you need enough output to recharge the batteries in the best hours of the day...as in brightest hours. Use this calculator to determine how many hours of light for a given day.

http://rredc.nrel.gov/solar/old_data...redbook/atlas/


2000 Cherokee 31BH, "flipped axles and raised",LEDs, solar, inverter, etc..aka "boondock ready". '07 Tundra 5.7L DC-LB, modded as well.
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Old 03-24-2014, 10:17 PM   #7
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Ok, I don't know why the link isn't working.

2000 Cherokee 31BH, "flipped axles and raised",LEDs, solar, inverter, etc..aka "boondock ready". '07 Tundra 5.7L DC-LB, modded as well.
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Old 03-24-2014, 10:41 PM   #8
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Ok, so first off, the link worked for me in the app.

Secondly, you're right, 40W was based on my location, etc. Unfortunately, that was almost a year ago, so I don't remember the formulas used, I'd have to look them again but I remember some of my inputs were:

Fixed panel, not tracking, since it was for use in a storage lot I wouldn't be able to maintain an angle.
Flat orientation, since it would be roof mounted.
Meant to replace parasitic loads, so a constant draw over 24 h
Based on the 42nd parallel, since that's about where I'm at.

Like I said, he'd have to adjust based on his needs since things like TV watching aren't constant and would need to be averaged out over 24 hours, but it does demonstrate that 100W wouldn't have been sufficient to handle the parasitic loads in my trailer.
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Old 03-25-2014, 12:29 AM   #9
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In the Caribbean sunshine...divide the wattage by 4 to get your AVERAGE amp hours per day...100 watts = 25 amp hours of charge to the batts.
You can get 30 amp hours if you have an MPPT controller installed.

OldCat...it seems to me that the place to start is HOW MUCH DO YOU DRAW from your batteries each day when boondocking. That means you either need a real battery monitor installed that will give you amp hours....OR a clamp meter where you can take a bunch of current readings over the course of a day/night and estimate your daily use of amphours. Once you know how much you use daily...multiply by 4 and THAT is the size panel you need.
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Old 03-25-2014, 06:06 AM   #10
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Kaadk...I have to apologize..

after reading what I wrote last night, I think I sound like a pr#ck. Sorry.

To the OP, since you are using the solar as a mean to replenish what you are using while boondocking, versus just to maintain a charge, 100 watts isn't enough. You really should determine what you are using as camaraderie says then use the insolation chart to determine how much wattage you need.

A little research now will save you money later.You will be better satisfied with your system and that'll make for a better camping experience.
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