Suppose I have a DC power source (a solar array) that can output up to 110V & 40A, and I want to log the voltage produce by the panel throughout the day. Since feeding 110V directly into the analog input pin of my data-logger will damage it, I am going to scale down the voltage to a maximum of 4.5V. Also, I want to minimize power dissipation by the two resistor, so I am going to use 2 high resistance resistor (maybe 1MegaOhm and 40kOhm) // with the panel, so that a tiny amount of current can flow through the resistors.
But, I heard that high resistance voltage divider is not going to give high precision voltage output.
That depends entirely on the resistance of the load it is driving - which in this case is the input resistance of the data logger. If the data logger is one of the analog inputs of an Arduino, then its input resistance of about 100Mohms, and you have nothing to worry about if you use 1M and 40K. I have used 2 x 4.7Mohms in the past.
My question is - is it possible to use a lower resistance values resistors with an op amp in voltage follower configuration to yield high precision and low power dissipation voltage divider, considering an OpAmp has Infinite input impedance?
What I think you mean is: can you use high value resistors in the voltage divider, feeding an op amp in voltage follower configuration, to mitigate the effect of the datalogger input resistance on the voltage divider. Yes you can - but if the datalogger has a high input resistance compared with 40Kohms then there is no need to.
I guess using an OpAmp also has another advantage - in order to measure the voltage from the voltage divider, I am going to have to connect the ground of the 110V solar panel with the ground pin of my tiny microcontroller. If my voltage divider has infinite impedance, it can effectively eliminate ground loop effect. Can anyone confirm this? Thanks!
No, you still need a common ground connection. If you were to use an instrumentation amplifier, then you could tolerate the solar panel ground and the datalogger ground being at slightly different potentials, but only by a few volts. If you really need to isolate the datalogger from the solar panels, you could use a digital isolator chip such as ADUM6401 with an ADC chip on the isolated side.