Some VO units have been installed on high frequency lighting circuits, offering little or no commercial benefit, therefore one must be careful when the term is used.
Installing a VO unit to 'optimise' all supplies would give a longer return on investment, a higher capital outlay and makes little commercial sense.
A reduction in voltage does not affect the energy used by the domestic appliances which use resistive loads except in devices such as kettles and toasters which will take longer to do their job due to atmospheric losses.
The main commercial benefit when installing VO units, is on inductive loads, like motors which run pumps, fans and the like.
[4] It is a common misconception that fridges and freezers do not provide savings through voltage optimisation because they are fitted with a thermostat.
If a fridge or freezer is driven from a higher voltage the result is also heat however this is not helpful in its intended purpose (cooling).
It can cause a reduction in equipment lifetime and increases in energy consumed with no improvement in performance.
A commentary on the Wiring Regulations BS 7671 makes the following statements in relation to overvoltage: "A 230 V rated lamp used at 240 will achieve only 55% of its rated life" (referring to incandescent lamps) and "A 230 V linear appliance used on a 240 V supply will take 4.3% more current and will consume almost 9% more energy".
Reliability is also important, and there are potential problems inherent in running full incoming power through electro-mechanical devices such as servo-controlled variable autotransformers.
If the design of the VO does not take into consideration voltage drop over distance to remote power users, then this may lead to premature equipment failure, failure to start up, increased temperature in the case of motor windings and loss of service.
Harmonics are caused by non-linear loads, which include power supplies for computer equipment, variable speed drives, and discharge lighting.
[6] The efficiency of electrical loads can be improved by attenuating harmonics at the supply, or by preventing their generation.
Imbalance between the phases causes problems such as heating in motors and existing wiring, leading to wasteful energy consumption.
There are a number of low voltage ride through techniques including Uninterruptible Power Supplies, the use of capacitors on low voltage DC control circuits, the use of capacitors on the DC bus of Variable Speed Drives.
[7] Excessive overvoltage results in saturation of the iron core, wasting energy through eddy currents and increased hysteresis losses.
[10] However, other types of lighting can also benefit from improved power quality, including systems with resistive or reactive ballasts.
Fluorescent lamps on modern electronic ballasts will use approximately the same power and give the same light.
[3] To provide the same wattage at the reduced voltage will require a greater current and increase cable losses.
A northern European installation would not have the large number of small single phase motors for air conditioning.
Therefore, older commercial and office premises may save more than modern buildings or industrial sites.
However modern lighting systems (typically LED) will save significantly more energy due to higher efficiency than energy saved on older lighting systems following installation of a voltage optimiser.
Obtaining energy savings with a voltage optimiser used with modern lighting systems is very questionable.
Furthermore, since the light output is reduced by so much, higher savings could be made by changing to a 75 watt incandescent lamp without a voltage optimiser (1312.5 lumens assuming 17.5 L/W).