I'm weighing the benefits and losses with adding two more array's to a 48V 1KW array already in operation.
Am considering adding one 1KW array to the east and another to the SW to get closer to a C/10 rate throughout the day for a 370AH battery bank.
I am thinking that if I use schottkey diodes on the outputs of the array's to enable the use of a single Classic will they reverse bias when another array has output voltage exceeding another array. In effect this would allow only one array to work at a time.
Is that what I can expect in practice?
Tnx
Why do that ? If you are worried about too much current charging the batteries with the newest Classic firmware you can limit the current going to the batteries but still have all available power for loads.
Wouldn't that be a better alternative ?
You should also use the Midnite string calculator and see the results of adding extra panels in different configurations.
Larry
Re-reading my original post I can see how it presents the idea you got from it. I'm looking at options other than running three separate lines and controllers.
I am not looking to block other array's I want the additional current. I'm concerned that by using diodes they will reverse bias and only allow one array at a time to produce.
I see no reason to use anything as "blocking" diodes.
I doubt you will have issues with multiple arrays into one controller through a combiner of some sort. I doubt one array will blow power back through a shaded / low light array.
I have done this in the past (arrays pointing different directions to same controller) and saw no issues.
Use the String Sizer to sort out the proper amount of panels to feed the controller.
Its not really clear what you are specifically asking advice about.
Tom
Quote from: EW Zuber on March 09, 2017, 02:28:59 AM
Re-reading my original post I can see how it presents the idea you got from it. I'm looking at options other than running three separate lines and controllers.
I am not looking to block other array's I want the additional current. I'm concerned that by using diodes they will reverse bias and only allow one array at a time to produce.
Use the Midnite string sizing tool and see what the maximum amount of PV you can use on one controller. For example if not exceeding the limit you can put one string east , one string south, and one string west , it won't matter if one string is not in direct sun - those just won't add any power.
Each string is connected to a combiner box by their own wires, and then there is just one feed into the controller from the combiner box.
The only time you need additional controllers is if you exceed the limits for one controller and the Midnite string sizing tool will tell you that.
http://www.midnitesolar.com/sizingTool/index.php
Larry
Won't an array in the shade act as a load for the array in the sun?
These arrays will also be made from different panels with quite different voltage characteristics.
The array that has been up and running for about 10 years is made up of Solarworld mono 175's. There are two strings with 3 panels each wired in series which brings the voltage up near the limit of the controller (typically about 135VDC and sometimes higher) and works very well. It produces 920 watts in full sun on a regular basis with about 130 feet of distance using #4 copper down lead.
The new additional arrays will consist of strings of 3 REC 250's wired in series which will produce about 112VDC. I can't see any way these won't act to load the Solarworld array without blocking diodes.
Hi EW Z,
The other reason that multiple CCs would need to be used, is when the Vmp of differing strings of PVs exceed about 10% between them.
The REC 250s that I find, have a Vmp of 30.2 V.
The SW-175s have a Vmp of about 38.8 V.
This represents a difference of about 18 % -- notta good match, IMO.
Simplistically, the SW-175s are 72 Cell modules, and the RECs are almost certainly 60 Cells .... not a happy match!
FWIW, Vic
Vic, exactly what I was thinking. I'm thinking maybe use blocking diodes to run the East array and SW array (both REC 250) on a single CC. But, I don't want to lose the cloudy day performance I would get from having both array's operational at the same time and I suspect that the diodes will reverse bias and only allow one array to operate at a time.
I don't mind having only one array operational in direct sun but wold like the additional cloudy day performance.
Cheapest solution sounds like a KID CC... :) no hookup problems etc...
EWZ,
What TomW says above and...
Get the MPV of each array as close as possible.
So the 190W PVs are in strings of three to give 3*38.8 = near 120volts
And a string four of the 250 watt PVs will be 4*30.2 = near 120 volts
Then just wire all of the arrays via combiner/breakers to the one Classic and it will sort out the maximum power point at any time of the day even if one array is shaded or partially shaded.
Forget additional diodes and backfeeding any array from another array, it won't happen.
I have configured many systems with arrays with close but not exact MPVs and the Classics cope with absolutely no issues.
dgd
Quote from: Westbranch on March 09, 2017, 04:33:19 PM
Cheapest solution sounds like a KID CC... :) no hookup problems etc...
Probably true. I used this idea in a system with an established array and a pile of REC 250's added on a roof that had potential shading problems. Used 3 kids on the roof array in conjunction with a Classic. Works well.