Recently I have seen multiple references to the "proper" voltage to run into a Classic as a function of battery voltage. Oversimplified it says "Closer is better" for less power loss as heat in controller.
My thoughts take a bit of a different course here.
I think that maybe a higher input voltage will get me more power on cloudy days and we see some clouds here regularly? In my case the panels are not very far from the controller.
I consider power production to be a marathon not a sprint.
If I lose a little on heavy production days I think it is offset by the increased production on cloudy days and when the sun is less than perpendicular to the panels.
Any thoughts?
Tom
It will depend on the PV panel chemistry too. Amorphous has better low light production, but shorter panel lifetimes.
And now you have me thinking about the different MPPT modes the classic can use, I may try some preset voltages or % instead of the internal setpoints. I'm seeing a sister array to the classic, starting earlier and running later than the classic is.
Quote from: TomW on August 06, 2014, 10:11:50 AM
I think that maybe a higher input voltage will get me more power on cloudy days and we see some clouds here regularly? In my case the panels are not very far from the controller.
Voc is not very dependent on insolation. Isc certainly is. Voc is very dependent on temperature.
In the real world Voc actually increases with a decrease in insolation (clouds). This is because lower insolation means the panel is not as hot and therefore has higher Voc.
I do not know how insolation affects Vmp.
As far as string length (voltage) is concerned, the lower the better... as long as there is enough headroom for the Classic to find the Vmp. Optimum string length (for 60 cell panels) is one panel for a 12 volt system, two panels for a 24 volt system, and three panels for a 48 volt system.
I don't think the efficiency decrease of a Classic with higher than optimal voltages is a big deal... except when the Classic is near its power handling capacity.
--vtMaps
Its one of lifes ironys that while mppt controllers can run at higher input voltages, you kinda dont want to do it. In my anaylsis here (with really poor source data) some cable losses were a more manageable proposition than high controller losses. Given that i have 72 cell panels theres even a rebellious part of me that wants to see what the actual quantitive difference between mppt and a real nicely built pwm would be in our setup. Frankly i doubt there would be much in it. vt is right, Vmp varys on a given day almost nothing. Take a look at a your own Vpv curves and youll see this.
Folks;
All good info and I appreciate the responses. Some things I had not considered.
I probably will not rewire things now because we are selling the farm and moving south soon. I will let the new owners do that.
I guess my main thought was there is more than one way to look at this stuff.
Thanks again.
Tom