Question on series/parallel strings for most output..

[mickhill]

Just a quick question... I have 8 - 100 watt Renogy panels, a Midnite Classic 150 and 4 - 125Ahr Vmax AGM batteries. Right now I have them hooked up in 2 strings - 5 panels in Series, and 3 panels in Series, joined in a combiner box. The most watts Im seeing on the Midnite is 400~ Watts. (Usually 430-450).  I had hooked them up that way because I plan to add a couple more later on, for a total of 10 -  2 strings of 5. Would it be beneficial right now to do 2 strings of 4 instead? Im just not sure why Im seeing 400 watts out of 800 watts in panels.

[Doug]

Hi Mickhill,

It would be good to start with the stringsizer at http://www.midnitesolar.com/sizingTool/index.php

It sounds like you have 3 panels in parallel with five. This is not good.
Combined strings should be of similar voltage so strings of the same number of series panels should work better.
Be sure to not overvoltage the Classic.
The stringsizer will help with cold temperature voltages as well.

Doug

[mickhill]

I have used the string sizer and Im well under max input voltage. The problem is the string sizer wont let you enter an odd amount of panels per string, so it really doesnt tell me anything. And I have the 2 separate strings in Series. 5 panels in series and 3 panels in series.

[Doug]

The string sizer will allow an odd number of strings but does require that all strings have the same number of panels.
The problem is once the voltage of the five panels goes above the voltage of the three panels they essentially stop contributing.
What is the VOC of your panels? Five in series will likely be above 150 Volts.

[mickhill]

Right, I have an odd number of panels on my strings. I'll probably just do 2 strings of 4 today after the sun goes down. Open circuit voltage is 22.5 x 5 = 112.5 @ 5.29 Amps Plus 3 panels 67.5 @ 5.29 Amps.  But I would have thought the wattage reading would still total ~700+watts instead of 400+. I'll re-wire them and see how they read tomorrow.

[Doug]

That should work better for you.
Let us know how it goes.

Doug

[mickhill]

I just went ahead and re-wired them into 2 strings of 4. Batteries are in absorb mode right now but it still wouldnt show over 490 watts when I first connected it. Now its back down to 200+ watts. I still dont understand why I dont see more watts. Does the wattage half in parallel like the Volts do? I understand I'll get the same amount of Volts and double the amps with 2 strings, but I would think the wattage would be true (700-800 watts). I guess I'll learn/figure this thing out one day. Thanks for your help.

[Doug]

The wattage will reduce when you are in absorb.
If you still have good sun and can put a load on it it should come up.

[Westbranch]

If you are not using your batteries, and drawing about 40% of their potential you will NOT see the full potential,of your panels.  The full potential at this time of year , June (summer) will be in the range of 70  - 75% of the rated wattage.... Why?  because the panels are 'rated' in a laboratory like factory at 25* C, etc etc... conditions that you seldom get in the normal outside conditions.....

[mickhill]

Right now there isnt a really big load on the batteries. I have a small chest freezer and that is all. Its averaging about 40 watts per hour. In the mornings my 500Ah battery bank is at about 80-85% or around 400Ah remaining.

[ClassicCrazy]

Are you using a Whizbang ? You must be otherwise you wouldn't have SOC percentage for batteries.
What battery voltage are you running ?
As others have said - depending on your settings and the batteries - once it is in absorb it will cut back the amount of current going into the batteries and hold the voltage at absorb voltage until it either gets to absorb time - or ending amps if  you have that set up -- which ever of those comes first . Then it will go to Float. 

[frodo2222]

I just went ahead and re-wired them into 2 strings of 4. Batteries are in absorb mode right now but it still wouldnt show over 490 watts when I first connected it. Now its back down to 200+ watts. I still dont understand why I dont see more watts. Does the wattage half in parallel like the Volts do? I understand I'll get the same amount of Volts and double the amps with 2 strings, but I would think the wattage would be true (700-800 watts). I guess I'll learn/figure this thing out one day. Thanks for your help.

I had the same issues when I started to be able to monitor my system when it was pretty full it would only show like 6 amps going in but then if I started a big draw ie AC then it would jump..the Bogart I use shows me what Unused power I have that is not going to batteries which helped me to understand why I was not getting the full amount my panels were able to produce.in Reality this is a good problem to have when the batteries are so full that they cant take ALL the power from the solar panels...well better then never getting to full of course Lol

[zoenen60]

The current is inversely proportional to the volt there for The string sizer will allow an odd number of strings but does require that all strings have the same number of panels  sea star hydraulic steering. The problem is once the voltage of the five panels goes above the voltage of the three panels they essentially stop contributing.