Am I thinking this wrong?
a panel 24v 255w open circiut voltage is 37.4 v dc
a panel 24v 240w open circiut voltage is 37 v dc
4 x 37.4 = 149.6 v
4 x 37 = 148 v
The max voltage for a Flexmax 80 is 150v so it would be at the top of the safty margin. I have a Flexmax 60 now.
I would need a mppt controler that would be able to handle the high voltage. 175/200 v max.
This is based on the open circiut high voltage on the upper end of the panels.
Their operating voltage is around 30v. the operating curent is 8.03 for the 240w and 8.3 for the 255w
Where can I find out a voltage loss chart for 525 ft of power line from panels to control room? I might be within working range of my panels I wish to install with the power loss. I'll have to study the power curve for the best usage.
I would only have to find a single 24v 240w panel.
13
Thirteen, yes you are actually thinking this wrong...
Unless you live in Hawaii there's a good chance you will kill an otherwise fine FlexMax80 by hooking up four regular 60-cell panels in series.
As you noted, your panels have an open circuit Voltage of around 37 Volt. Very typical for 60-cell modules intended for grid-tie use (these days all in the 250 - 285 Watt range).
That Voltage is measured when the cells are at 25 Centigrade (about 78F)!! When silicon solar cells get colder that Voltage goes up, when they get warmer it goes down. By quite a bit.
For example:
Here in the Ottawa area we can see winter temperatures as low as -35C (about the same in F). That is the temperature commonly used over here to calculate the maximum panel Voltage (to get more of a safety margin it would not be a bad idea to add another 5C though). The temperature coefficient of (nearly) all regular silicon solar cells is -0.34% per degree Centigrade.
So we have a temperature difference of 35 + 25 = 60 Centigrade vs. that standard 25C temperature.
That means a difference in Voltage of 60 * 0.34 = 20.4%
That means the open Voltage of that panel at -35C will be Voc = 1.204 * 37 = 44.5 Volt (!!)That means a string of 4 panels, as you proposed, will generate 4 * 44.5 = 178 Volt! Well above the 150 Volt absolute limit for a FlexMax80!
Maybe your lowest temperature (n)ever measured is not quite as low as -35C for where you live. Just plug it in and follow the same calculation as above. For almost all locations in the US you will still go well above the 150 Volt limit of the charge controller. This is something to keep in mind for any MPPT charge controller one plans on using.
-RoB-