Just so you know, placing just two of your entities will be more laggy than perfect ratio solar. Solar panels and accumulators are both O(1). You can't make something that is O(n) faster than that.

Solars have to calculate max power * percentage based on time and day, so add time for the if(time) statements, * by time, etc.

The Entity just does "add max power" - ignores time of date.

Basically:
Solars:every tick, if(time) add(power) else if(different time) add(0 power) else add(power based on what% of day and night)
The Entity: every tick, add(power)

Solar panel power production is 4 lines of code for an unlimited amount of solar panels. Electric energy interface power production is 11 lines of code executed for every electric energy interface that exists in the game.

No matter what you do, the Electric Energy Interface will take more CPU time to calculate than solar panels because 2 lines of the solar panel logic is executed regardless of even having solar panels in the electric network.