Solar current/voltage question. Using an MPPT controller

[TT_Vert]

Short circuit voltage is 21V and current is 4.95A and i have verified such.   I'm just running one 100W panel for my shed right now to the EPEVER 40A MPPT.  I know it's overkill, just learning the setup for now).  I have an app i can use to monitor output of the panel to the MPPT.   When the sun is in the same position sometimes I will see 15V/1A then a bit later 19V/1A, and then a few minutes later w/ no real changes  I may see 20V/.75A or similar.  I'm just curious how the output voltage/current is regulated or if the panel puts out what it puts out.  I know the solar energy dictates this but does the MPPT have anything to do w/ this based on battery SOC?    Just curious why the voltage can move so significantly from minute to minute as well as current. 

Thanks
Dave

[mikerj]

Short circuit voltage is 21V

Open circuit voltage may be 21v, short circuit voltage is 0v!  You will see the panel voltage moving around a bit with an MPPT controller as it changes it's impedance to find the maximum power point.

[TT_Vert]

Short circuit voltage is 21V

Open circuit voltage may be 21v, short circuit voltage is 0v!  You will see the panel voltage moving around a bit with an MPPT controller as it changes it's impedance to find the maximum power point.

Wow, what an amazing explanation.  I appreciate you taking the time to write all of this!!