Two cases here Sri:
Case 1:
Implications of variations in radiation level or low sunlight on a motor that has started and already running:
In this case the MPPT logic takes care of any sudden drop in power and still runs the motor with available power. Meaning less discharge proportionate to available power.
Case 2:
Implications of variations in radiation level or low sunlight on a motor that is stopped and not running:
When there is no enough sunlight to generate the starting torque the system shuts down and waits till power available to start. So no discharge till power enough to start.
Not every system is the same Sri,
Performance of the solar water pumping unit would depend on
A)Quality of solar panels (The problems you have highlighted happens when improper cell configuration is selected)
B)Quality and size of cables and connectors (Voltage drops, cable heating due to amperage, low gauge conductors etc)
C)Quality of the control unit (The problems you have highlighted happens when one uses a industrial grade VFD as against VFD with Solar MPPT program)
D)Quality of motor
And of course quality of water source i.e yield.
I can give all my references and confidently assure you that none of my clients has reported the above issues till date. BTW our oldest installation is 2 1/2 years and never we have received such complaints or needed any service. I am sure I need someone to guide me to reach the place as well, its been long!
Few of my clients who use it with drip systems dont have any issues as well. We advise them how effectively they can make use of the valves. Like example, we ask them to irrigate the nearest piece of land when sunlight is less typically during morning or evening and farthest points during peak hrs. They listen and they follow and are happy!
Couple of our customers from cold areas are happy that they even placed repeat orders with us for various solutions and happily using our systems.
Regards,
Saravana
P.S: " Solar cannot your full time energy source."
“Full time” cannot be quantified to a universal constant, can we?
Let me give you an example;
One of my customers using a 5hp motor to irrigate 10 acres field, also pumps and sells tankers because he has surplus!!