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Old 01-02-2016, 11:01 AM   #1
Mini-Skoolie
 
Join Date: Feb 2015
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Need help with my PV system!

Hi all! Hope this is the correct forum to post in. Over the last 6 months while I've been building my skoolie I've had my PV (solar) system up and running. My issue basically is regardless of season or panel orientation I cannot achieve a decent daily solar harvest.

Here's the problem:
--Maximum daily output is around 1.3Kwh. I feel that with 4 250w panels with an unobstructed view of the sun and with no shading I should be getting more.
--I switched from a xantrex c40 to the midnite 150 and maybe it's just me, but now my batteries never make it to float, and at the end of the harvest my OCV is only about 51v
--I'm running a POS inverter (described below) which keeps my chest freezer running all the time. Again, just been doing a long shakedown run. Can't afford a fancy DC freezer.

My system details:
--4x 250w Canadian solar, they're poly, 24v, and all 4 sit angled into the sun with no shading whatsoever
--they're all connected in series to my Midnite 150. I had 2 strings before, but I rewired to the current config to see if that would change my daily harvest. It did, raised by .3Kwh
--I do have a whizbang Jr. Attached, and if I only made 1Kwh a day, that's what I'm using for the inverter idle and the chest freezer.
--the maximum wattage the Midnite will ever read is 500 watts. This is almost 10amps because I have it setup for a 48v system.
--I have a 280Ah battery bank at 48v made of 8x 12v AGM C&D dynasty batteries in 2 strings.
--my battery connections are over engineered for sure, using only copper core wire and all is 0gauge, which is a little excessive for 48v.
--the inverter is a 3000 watt energy hog, MSW.

My goal:
--I want to make sure that I'm milking every single watt out of this array and that I'm not missing something here. I know solar outputs are never what's advertised, but 50%, really?. We're planning on full timing and this will be our juice!

I do have plans to obtain a different inverter. I'd like a smaller one with a search function that I can leave on indefinitely specifically for our chest freezer. Then I can use the bigger one for the a/c and the induction cooktop, and coffee, and tv....you get the picture.

Thanks In advance for any suggestions! Also please let me know if anyone needs additional details.
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Old 01-02-2016, 11:43 AM   #2
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Quote:
Originally Posted by Destroymix View Post
My system details:
--4x 250w Canadian solar, they're poly, 24v, and all 4 sit angled into the sun with no shading whatsoever
Well there's your problem! I see you're in Colorado. The Canadian solar panels aren't compatible with your US sunshine!

Problem solved.



How much were you monitoring power generation at the beginning (end of summer / beginning of fall)? With the clouds we've been getting and the tilt of the sun we've also been down to about 50% generation for the month.
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Old 01-02-2016, 11:47 AM   #3
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Also, do you have more specific information about the panels? Online reviews might provide additional insight into how well they operate in the real world.
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Old 01-02-2016, 07:20 PM   #4
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True, they most likely not compatible with US sunshine, let alone Colorado's "haze-filled" skies as of late!

I haven't looked into any online reviews, guess I could get the part number off the panels and Google it. I do know they're made in China.

I got the midnite 150 at the beginning of July, fearful that my PWM c40 was not giving me the full potential of my panels. Since then the only amount my harvest has changed was when I wired from 2 strings of 2 to all in series, went up .3Kwh/day.

Thanks again!
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Old 01-03-2016, 12:11 AM   #5
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Hey there! We're almost neighbors and I've got a very similiar setup to yours. I have been getting around 930 watts peak on a 1200w array when the sun is directly over the panels. I also use a midnite 150. Your numbers sound low--I would hope for more like 2/3 of the rated power at max sun. Keep in mind too that the angle of the sun and length of day is just about as bad as it gets right now.

FWIW, I bought 2 more panels and will be moving to a 1800W array. I also use a converted chest freezer and have it running all the time with no problems at all and my batteries do get equalized regularly. My bank is 8 6V Trojan T105s and my inverter is a TrippLite modified sine wave--not the most efficient!

When you set up the midnite, did you enter in the amp-hour capacity of your battery bank? Are you getting fully charged at the end of each day? If so, the controller will stop charging and thus, you'll collect no more sun but having the wrong AH on the 150 might make it shut down prematurely... Also, make sure that the float, bulk, equalize, and absorb voltages are programed correctly for that particular battery as per the manufacturer's specs. The default on the 150 was different than what the manufacturer specd for my batts.

Im shocked that changing your string configuration changed the energy output by so much--did it improve the max wattage output you were seeing, too? If it didn't, then Im doubtful that it changed the performance too much. I will say that charging a 48v battery bank with PV input voltage of around 48 is not advised. You always want to be coming in higher than your battery by a healthy margin. That might have something to do with it. Come by the bus yard sometime!
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Old 01-03-2016, 12:15 AM   #6
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I would seriously consider adding 2 more panels and running 2 strings of 3 each. At this point, $500 more in panels is not much for what you've already got in it for 50% more generation.
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Old 01-03-2016, 12:32 AM   #7
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First off, I'd LOVE to come by. Sometimes I feel like such a closet skoolist, it'd be nice to hang out with someone whom shares my interests, although my neighbors....intrigued, it'd be nice to bounce ideas back and forth LIVE.

Thanks for the reply. I was thinking about 2 more panels then making 2 strings of 3.

I do think that one of my early issues was my input (PV) voltage was commonly lower than my battery bank, this is my theory as to why I developed a better solar harvest after going all in series. My AM cold OCV on the array is near 140v!

Because my batteries are old backup batteries, I can't find much on specific bulk and absorb specs, let alone bulk/absorb times, etc. I did program the whizbang side to 280Ah, with a 96% efficiency.

As far as adding additional panels I sure have the room, we were planning on having a large roof rack bolted on near the back, Im afraid it may have to be one or the other. Or maybe I could design 2 long roof racks to sit on the left and right of my panels, uh oh, pencil and paper now!

Thanks for the reply! Also, FYI the panels are squeaky clean

I did setup the midnite input from "tested" other similar applications to my own. I do keep my bulk low, around 58v because my POS inverter trips the high voltage shutoff at 59v, this was my major reason for leaving the C40 charge controller, it could not keep the voltages exactly where you preset them.
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Old 01-03-2016, 12:37 AM   #8
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Roof space is a consideration, that's why, if you ever do it again, 300W panels fit nicely sideways and you can fit about 10 on a midsize skoolie. I think you need more power.

Shoot me a text or call me sometime 303 9311904
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Old 01-03-2016, 11:43 AM   #9
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Will do, thanks! My cell phone is broke and a new one won't come until Thursday because I'm cheap and wouldn't pay $30 for shipping. I'll give you a jingle then!

I did spend a lot of time brainstorming how I would mount the panels. I have 2 before and 2 after the first emergency hatch at the front. I wanted to be able to tilt them any way needed. With the rack system I designed I can tilt each individual panel ANY direction up to 30 degrees without shading other panels. If I were to redesign my rack, it would have to begin with the mounts for the old one, since my ceiling is nearing completion.

I know we have a pair of great second hand PV suppliers here in town, Scott and Marion, anyone else you'd suggest charles_m?

Thanks again!
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Old 01-03-2016, 01:14 PM   #10
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I have a guy named Joel who I get my stuff from. Most of it is extras off pallets or other leftovers. The commercial solar world is full of surplus panels! I sometimes find 305 Watt panels for $200. Love that price.

Looking forward to meeting up!
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