Reducing Current Consumption Does Not Reduce Power Bills
Electric power savers for the home have in the recent past become quite popular (through some brute advertising). The companies who are busy promoting them claim that by just plugging one in to any mains socket or near your energy meter, you can reduce your home electric bill by as much as 40 to 50%.
That seems too good to be true, doesn't it? Let’s analyze their claims through a step-wise discussion.
Companies promoting and boasting their power saving equipment claim that their products are able to save domestic residential power consumption by employing an "active power factor correction" method on the supply line. The concept seems pretty impressive as the concept is true and legally accepted. But practically, you will find that it’s not feasible. A thorough technical discussion perhaps won’t be required as it can be proved through the following simple verifications:
There are basically two kinds of load that exists in every house: one that’s resistive like incandescent lamps, heaters etc.; and the other that’s capacitive or inductive like ACs, refrigerators, computers, etc.
PF, or power factor, may be defined as the ratio of the real power that’s being consumed by the load to the apparent power that’s being actually used by the load. It’s given by the formula:
PF = Real Power (Watts) /Apparent Power (VA),
Therefore, Real Power (Watts) = Apparent Power × PF = Voltage × Ampere × PF
Ideally a PF = 1, or unity, for an appliance defines a clean and a desired power consumption, because then the dissipated output power becomes equal to the applied input power.
In the above formula you can find that if PF is less than 1, the amperes (current consumption) of the appliances increases, and vice versa.
With AC resistive loads, the voltage is always in phase with the current and constitutes an ideal power factor equal to 1. However, with inductive or capacitive loads, the current waveform lags behind the voltage waveform and is not in tandem. This happens due to the inherent properties of these devices to store and release energy with the changing AC waveform, and this causes an overall distorted wave form, lowering the net PF of the appliance.
The above problem may be solved by installing a well-calculated inductor/capacitor network and switching it automatically and appropriately to correct these fluctuations. A power saver unit is designed exactly for this purpose, and to an extent may successfully do so. This correction is able to bring the level of PF very close to unity, thus improving the apparent power to a great extent. An improved apparent power would mean less CURRENT consumption by all the domestic appliances.
So far everything looks fine, but what’s the use of the above correction? The utility bill that we pay is never for the Apparent Power- it’s for the Real Power. The below given example will prove this statement:
Consider a refrigerator having a rated Real Power of 100 watts at 220 V AC has a PF = 0.6. The expression explained above becomes:
100 = 220 × A × 0.6
Therefore, A = 0.75 Ampere
Now suppose after appropriate power corrections, if the PF is brought to about 0.9, the above result will now show as:
100 = 220 × A × 0.9
And A = 0.5 Ampere
In the second expression we clearly witness a reduced current consumption by the refrigerator, but interestingly in both the above cases, the Real Power remains the same, i.e. the refrigerator continues to consume 100 watts, and therefore the utility bill remains the same. This simply proves that although the PF correction done by an energy saver unit may decrease the Amperage of the appliances, it can never bring down their power consumption and the electric bill amount.