Digital electronic instruments measure many parameters and can be used where a wattmeter is needed : volts, current, in amperes, apparent instantaneous power, actual power, power factor, energy in [ k ] W�h over a period of time, and cost of electricity consumed.
22.
A complication is the necessity for a " drive regulator ", which implementation is quite simple at 10 kW or lower levels, but is more complicated at higher levels . " Drive regulation " is most effective when the instantaneous power output approaches zero.
23.
If one were to create a physical voltage source which followed x ( t ) and applied it to the terminals of a 1 ohm resistor, then indeed the instantaneous power dissipated in that resistor would be given by " x 2 " watts.
24.
For systems large enough to justify the extra expense, a maximum power point tracker tracks the instantaneous power by continually measuring the voltage and current ( and hence, power transfer ), and uses this information to dynamically adjust the load so the maximum power is " always " transferred, regardless of the variation in lighting.
