∫∫ Voltage Optimization

Voltage optimization is all the rage these days. Children and retirees alike cannot stop raving. Grocery stores, pizzerias, and major retailers can’t keep the shelves stocked.

Or maybe not. Since it is, in fact, a relatively obscure energy modulating solution. And though it has recently begun being marketed as an energy efficiency panacea, odds are you have probably not heard of it—yet.

Voltage optimization is the process by which the voltage entering a piece of equipment is fine-tuned (usually reduced). A number of technologies of varying degrees of sophistication deliver voltage optimization: many are simply adjustable transformers that step down the voltage, just as your utility reduces your voltage on your nearby poles. In theory, voltage optimization lowers energy use, because of the equation:

  • P = I * V   where
  • P = Real power used by a device measured in Watts
  • I = Current used by a device measured in Amps
  • V = Voltage used by a device measured in Volts

If we make V lower, P decreases as well. Saving Watts. Saving Power.

Sounds great. Of course, so do the best synthesized bird calls. That doesn’t make them real.

While voltage optimization solutions can deliver energy savings, principally for certain kinds of motors, in many cases their value has been grossly inflated by marketing efforts. Voltage optimization advertisements saying you’ll reduce carbon emissions in your home by 10% are in most cases simply greenwashing.

What is greenwashing? It is the practice of marketing processes or technologies as environmentally-beneficial when in fact their benefits are negligible or non-existent. The Greenwashing Index through the University of Oregon tracks some corporate products and advertising that are suspected of greenwashing.

But general consumer goods companies are not the only ones that greenwash their products. Much greenwashing relates to energy efficiency. How to properly verify energy efficiency efficacy is well-established but that doesn’t mean consumers can do it or that they know to ask for it.

Some products that claim to deliver energy efficiency are actually just energy reductions without the efficiency. Doing the same thing more efficiently does not sacrifice an end product (light levels stay the same, the amount of cooling your AC provides remains the same, etc.), energy reductions not gained through energy efficiency might sacrifice operations or comfort. Energy reductions are fine where appropriate – many commercial office spaces in the U.S. have lighting levels well in excess of modern recommended amounts and are therefore excellent candidates for removing 10-40% of the lamps – but if light levels are already appropriate, reducing the number of lightbulbs may not be a good idea.

If I reduce the voltage going to your light bulb, it receives less power. But if it receives less power, it produces less light. If you do not mind lower levels of light, no problem. But then you could have just bought a lower wattage light bulb instead. Voltage optimization is usually no more than a simple energy reduction. By contrast, you could buy a 20-Watt incandescent light, but it would produce about 25% of the light as a 20-Watt compact fluorescent light. Same power, greater usefulness: that is energy efficiency.

In many cases, voltage optimization delivers temporary power reductions. But in many of these cases, these power reductions do not actually provide overall energy savings because of the nature of the energy consumption. Some specific cases will help illustrate this point:

  • If you reduce the voltage to a 2000 W space heater by 10%, so that it now only uses 1800 W, it will also produce less heat. You will need to run it longer to give you the desired effect though, so there are no real energy savings.
  • If you reduce the voltage to your hot water kettle, it will take longer to boil. There are no shortcuts to the specific heat of water: it needs 1 BTU of energy to increase its temperature by 1 degree Fahrenheit. Reducing the voltage just means the kettle will need to draw less current for a longer time.
  • If you reduce the voltage to your refrigerator, it will run the compressor for longer. You will not save energy, because your refrigerator has to produce a set point temperature. There are no shortcuts to thermodynamics.
  • If you reduce the voltage to a motor outside its recommended 10% tolerance you will degrade the motor’s operation. The U.S. Department of Energy has helpful papers on this topic. If the motor is fully loaded, then even on a small voltage drop the motor will draw more current to meet the load. This will cause it to run hotter, shortening its life. A voltage drop will also reduce torque and motor efficiency (see p. 385 in this IEEE article for a more thorough treaterment). Not good at all. If you reduce voltage for a motor serving a variable load, there will be some energy savings (this happens because of the relationships between slip, load, efficiency, and voltage and the fact that magnetizing losses are lower at decreased voltage; the short explanation here is the slip at a lower load is less, which actually is more efficiently served by a lower voltage, so in this regime a lower voltage will still meet the load requirements while reducing magnetization losses. Therefore, the optimal voltage decreases as load decreases). Nonetheless, a Variable Speed Drive is still widely considered a more robust and more cost-effective solution for variable loads.

As you can see, the devil haunts the details of each application. The above is only a summary. The United Kingdom’s Ministry of Defense (MoD) conducted a wide-scale review of the energy savings opportunities resulting from Voltage Optimization. Their conclusions broadly match with those of our team.

Voltage optimization has been a major topic in the United Kingdom in particular because of reports of systemic overvoltage. This results partially from 1995 EU regulations that required voltages to come down to 230 Volts. In many areas of the UK, this did not occur. As a result, reducing the voltage that enters homes and offices offers some savings opportunities for consumers. But because transformer losses in voltage optimization equipment are still a few percent, a better solution would be to reduce voltage levels fed into the grid and, especially, to adjust the step-down equipment along the grid so that it produces the targeted 230 Volts. Skeptics of voltage optimization in the UK abound.

In a normal grid, proponents of voltage optimization argue it can reduce energy consumption by as much as 10%. It can. In select circumstances: mostly in industrial concerns, sometimes in commercial concerns, and almost never in homes. The main advantage of voltage reductions on the grid are temporary power reductions when the grid is stressed, not overall energy savings.

At Carbon Lighthouse, our excitement for technologies like voltage optimization is muted partly because too often voltage reducers are simply a greenwashed product. More importantly, voltage optimization, while it has its limited place, does not bring us closer to a more sustainable planet. Compact fluorescent lights cut the lighting energy needed in a home by 75% but still deliver the light we need. High efficiency washing machines use less energy and less water while providing the same clean clothes. Variable speed drives cut motor energy by 20-80% and deliver the power we need to pump chilled water and ventilate our buildings. Drawing window blinds on a hot day reduces heat load on our buildings. These are the kinds of changes that bring us closer to where our planet needs to be.

Not all that glistens is green.


End Note

Voltage imbalance in a motor can be a serious problem, causing substantive reductions in energy performance. For such motors it would be beneficial to undertake voltage correction (which frequently can only be solved not with a silver bullet “voltage optimizer” but rather with a comprehensive analysis of the building’s electrical one-line diagram, ground faults, 120 Hz vibration issues, and faulty power factor correction equipment).

6 Responses to ∫∫ Voltage Optimization

  1. Variable speed drives says:

    Sure is fascinating to take a look and see how far technology has come over the past 100 years. Is the downside to those fluorescent bulbs the fact that they take a lot longer before they illuminate the room?

    • Depending upon the ballast (a device that controls the current going to a fluorescent lamp), some fluorescents require a minute or two to “warm up” to full power. There are several critiques of fluorescents: the quality of the light, their (quite small) mercury content, their operating temperature limitations. Most of these issues can be addressed by choosing the latest technology with the desired light color type and the appropriate ballast (rapid start, instant start, dimmable, etc.).

    • Hi Jackie,

      There are both downsides and upsides to fluorescents. They take longer to warm up and provide light than an incandescent, but are much faster than a metal halide or other high intensity discharge bulb. The older fluorescents have that horrible flicker (a function of their magnetic ballasts), and are relatively inefficient. Newer fluorescents that have electronic ballasts have no noticeable flicker and provide nice light very efficiently.


  2. In addition, as an organisation implements more and more energy efficiency measures, and reduce consumption as a result, the savings from VO are also reduced proportionally. These are interactive effects over the long term.

  3. For residential use, I think there are several alternatives that should come first prior to voltage optimization; more efficient lighting, more liberal thermostat settings, smarter power strips. However, I like the direction of voltage optimization. Visibility into power use, and the ability to optimize energy use for equipment, would be exciting steps to reduce wasted electrons.

  4. One of the areas not covered in the article is the impact of over-voltage on motors. The impact of reducing voltage too low is clear.
    However, if the optimal voltage for a motor to run most efficiently is 220 volts and the supply is the average of 242 volts in the UK, what is the formula to calculate the impact of the additional voltage (22 volts) on the life cycle of the motor?

    We are doing tests with the University of Southampton and the Technology Strategy Board in an NHS hospital, to determine the impact of lowering voltage incrementally to the lower range of motor tolerance levels (6% below 220 volts) to determine if there is any substantial reduction in performance. Same for lighting. The Unbalance of Voltage is resolved, as we are using voltage regulators which control each phase to within less than a 1% variance from the fixed voltage.

    Regular Voltage Optimizers usually only control to within 2.5% on an average of the three phases (11 -15 volt spread) and that’s why there are mixed opinions on their effectiveness. Individual phase control Voltage Regulators solve the voltage unbalance problem and generate more savings due to tighter voltage control.


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