Energy saving capacitor

What is it and does it really help cut your electricity bill?

If you’ve seen claims that an energy saving capacitor is going to slash your electricity bill by 10% to 25%, you may be in for a disappointment. The fact is, these devices, while they do reduce the measured electricity use for some older electrical motors, will do little or nothing to cut most household energy bills.

A capacitor is a device that stores energy in an electrical field between two conductors, such as two plates of metal. People referring to ‘energy saving capacitor’ are usually referring to a device containing one or more capacitors that averages out the irregular pattern of energy use by inductive loads such as electric motors, to cut down on the amount of electricity you get billed for.

One area where a capacitor really does save energy is in devices such as wind-up flashlights and radios.

These devices often use an energy saving capacitor to hold a charge you provide by winding a crank on the device, or by shaking the device to move a magnet up and down past copper coils; these actions charge the capacitor. The electricity can then be slowly drawn out of the capacitor to feed a low-power-consuming device such as an LED light or a radio.

Because the capacitor in these wind-up devices has low power loss (compared to a battery) and the device being powered has low power draw, a few shakes or turns of the crank gives you plenty of dim blue light or crackly music.

But what we’re typically referring to when we talk about an energy saving capacitor is a device touted to attach to your breaker panel and dramatically cut your electricity bills. That’s what I’ll focus on in this article.

You’ll read sales pages for an energy saving capacitor that claim to improve the power factor of inductive loads. The idea is that voltage on an alternating current line fluctuates in an rregular form between positive and negative, switching 60 times a second; an energy saving capacitor improves the power factor (the proportion of current in the wave form that actually powers the motor).

That, in turn, supposedly allows more of the energy you are buying to do useful work; less is wasted because the power wasn’t needed at that precise instant. (It can be saved in the capacitor and released some tiny increment of time later.)

The explanation is usually quite convincing, although the claims may sound too good to be true. And remember, if it sounds too good to be true, it usually is!

In my opinion, most of these devices (sold as a ‘Power Saver’ or energy saving capacitor) are working devices that can actually save electricity, but that make exaggerated claims for savings that will rarely be realized by consumers.

Sure, you might realize some savings. But the savings are likely to be so small – perhaps in the realm of 1-5% – that any savings will be hidden by seasonal or random variation in your power use and in the accuracy of monthly meter readings.

Questionable claims: what’s in a date?

I found one website that claimed that their energy saving capacitor would save you electricity on any induction motor made before January 23, 2006. Interesting claim.

First of all, why such a specific date? Did all manufacturers switch to some new motor design on exactly the same date, discarding all old motor stock when assembling their furnaces, fans, fridges, freezers, pumps, dehumidifiers, air conditioners and the like?

When you see an exact date without explanation, it ought to raise your eyebrows. How is anyone supposed to figure out, before deciding to invest in an energy saving capacitor, exactly when the motors in all their electrical appliances were made?

How much of your electrical load is inductive?

There are two main types of electrical loads: resistive (anything that provides resistance to the current flowing through it, such as a stove burner, blow dryer heating coils, or incandescent light bulb) and inductive (such as an electrical motor). Unfortunately, an energy saving capacitor only works on inductive loads.

One of the main reasons why an energy saving capacitor doesn’t live up to its name is that inductive loads whose power factor can be improved by a capacitor typically don’t make up that high a percentage of a typical household load.

For example, a capacitor might cut the energy use of the compressor by 20%, but you’ve still got those resistive loads such as lights, stove, electric heaters and so on, that simply cannot benefit from power factor correction.

Another reason is that an energy saving capacitor in and of itself is a very cheap, small device that is easy to include in any manufactured appliance with an induction load, so manufacturers have been adding them to anything with an electric motor for several years.

That’s what makes that date of January 23, 2006 so suspect – from what I can gather, manufacturers were probably putting capacitors into household appliances as far back as 2003, since one ‘power saver’ claim from 2008 promised to cut refrigerator losses only for fridges at least 5 years old (ie. from 2003 or before).

If you’ve got a fridge from 2003 or before, you should be replacing the fridge!

Why did manufacturers start adding capacitors to electric powered motors?

Well, with consumers always looking for more energy efficient appliances, and with capacitors being so cheap, it wasn’t hard for the designers to see the value of adding a capacitor to their device and reducing its power consumption. An extra dollar in manufacturing costs. An extra 3-5% efficiency on the appliance. That can be enough to push an appliance across the ENERGY STAR threshold.

If you own an ENERGY STAR appliance with an electric motor, it may already have a capacitor to deal with power factor. So there is no gain from buying a home energy saving capacitor for that appliance. No gain from already-efficient inductive loads, no gain from resistive loads – so where’s the benefit of an energy saving capacitor?

Claims of percentage gain

Another thing you will notice if you read the sales pages of people selling these ‘power savers’ is that they hint at potential savings but don’t actually guarantee a particular percentage.

Of course, they can’t, because they can’t predict how much of your household electrical load is inductive (and not already corrected by an energy saving capacitor inside the device itself).

We can’t fault companies for being vague on this given that they really can’t be specific – your results may vary. But the sales copy often makes things seem more cut and dry than they really are.

When you see claims of a range, like 10 to 25% off your electrical bills, read the fine print: are they guaranteeing that? Or just saying you ‘should see’ or ‘might see’ that kind of savings?

In other words their claims are based on an unrealistic blend of inductive versus resistive loads, and on an assumption that your motorized appliances are all older vintage models. They are counting on your not noticing the lack of real savings, or being too embarrased to ask for a refund when the savings don’t materialize.

And even assuming you did see a gain of 10 or 25%, how would you know whether the gain came from that or from something else?

Look for the testimonials provided for an energy saving capacitor. Do customers claim to have cut power use month after month while using these devices? Or is there just a claim that power use dropped by X% after the first month?

Who provides the testimonials?

Suppose 100 people buy such a device and install it in their home. Since everyone’s power use fluctuates month by month, even if the energy saving capacitor does no good at all, some people are bound to see a drop in power use from one month to the next, while others will see an increase.

Those who see an increase might ask for a refund for their energy saving capacitor. Those who see a small gain will be content, while the small number who, for reasons unrelated to their energy saving capacitor, see major gains, will write a glowing testimonial.

The testimonial gets published, and the person who asked for the refund gets their money back (one hopes). How likely is the seller to publish negative testimonials?

Another point in favor of this scenario is the fact that often people create the result they want to see.

For example, one of the best ways to get people to cut their electricity usage is to get them to measure their electricity usage. As I explain in How to save electricity, that’s exactly what helped my family cut our electricity usage by 50% or more.

If you install an energy saving capacitor expecting it will save you energy, chances are, you’ll start measuring your electricity use on a more regular basis. And chances are reasonably good that the mere act of measuring electricity use will cause you or your cohabitants to be more careful about turning off lights and avoiding other big energy using activities.

So you could wind up cutting your electric bill with one of these devices, not because it saved you anything, but because you changed your habits. Why not just pay more attention to your house electricity meter – take daily readings and chart them? You’ll accomplish the same goal, with no gimmicks and no expense.

But if there’s a guarantee, it must be for real, right?

Some power saving devices even come with a money back guarantee. That’s great, but again, think of the hundred-customer scenario. If the money back guarantee is good only for three months, there’s still a chance that some customers will see an improvement because of random variability, while others will see no change or an increase in power use.

Those who see no benefit or an insignificant one may decide it’s not worth fussing with a refund request, and keep the device, assuming that savings will materialize later. (They may also be so embarrased by having been duped by a scam that they don’t bother asking for a refund.)

Those who see even a small an improvement will keep using the energy saving capacitor, with one or two of them even writing a glowing testimonial, even though it may be pure chance that their power usage dropped.

Finally, some of those who see an increase in usage will probably ask for a refund. But my understanding is that these devices are simple enough to manufacture that the $300 to $700 price tag still gives the seller a healthy profit even if 80% of those who buy the device return it for a refund (and of course the seller can still turn around and sell the used device to the next prospect).

Another thing to watch is the content of the testimonials.

First of all, how do you know the testimonial wasn’t fabricated? Second, what environment does the testimonial relate to?

For example, I found one site had a testimonial from a company that ran several large water pumps. Unless you run several large water pumps in your own house, you’re unlikely to see much gain with a residential energy saving capacitor.

Factory benefits

Of course, there’s a reason a company using many large water pumps sees a drop in their power usage when using an energy saving capacitor system.

For large electrical motors there really is a savings. Factories use larger versions of these devices all the time because there is a real benefit. That’s one of the arguments some sites selling these devices will use: if giant factories use them, and save millions on their utility bills, why aren’t you using them too?

Well, because your house isn’t a factory. You don’t have 300-horsepower pumps or printing presses or stamping machines. You’ve got a half-horsepower compressor on your fridge, that probably already has an energy saving capacitor. So there just isn’t much benefit for household-level use.

Conspiracy theory

The last argument I’d like to touch on – one you’ll see on many of the websites that are trying to sell you an energy saving capacitor – is that the utilities don’t want you to know about these devices.

The argument is that utilities exist to make money, so the more power they can make you consume, the more money they’ll make; and your using a power saving device like this to cut your energy use will somehow deprive the utility of profits.

This is an interesting argument, and there may be a few places on earth where utilities are trying to get people to use more energy, but in the vast majority of places, electrical utilities are regulated and are either strongly motivated, or legally required, to do everything possible to reduce demand among their customers.

In some cases utilities aggressively promote conservation, because from the utility’s perspective it’s cheaper to convince someone to cut their electrical use than to build extra generating capacity. Why do you think utilities and governments have all these programs to give away compact fluorescent light bulbs or to give people rebates on the purchase of an ENERGY STAR appliance in exchange for trading in an old, inefficient one?

Certainly not because they’re trying to get you to burn more electricity. They want you to cut back! If these things really did work, utilities would be banging at your door begging you to install one!

The best way to save electricity is not to use it

If you still think an energy saving capacitor is going to cut your electricity bill, go ahead and buy one.

Just make sure you buy it from someone who offers an iron-clad guarantee. Because as far as I can tell, the chance is pretty good you’ll be wanting a refund within a few months.

A few people – particularly those with several 300 horsepower pumps in their basements, pumps that, of course, were built before January 23 2006 – will see a drop in their utility bill. Most will see no change at all, or one so small that the $300 to $700 they paid for the energy saving capacitor will have a payback period measured in decades.

But the best way to cut electricity costs is to control your consumption. As I explain in How to save electricity, there are lots of ways to cut electricity use, and by measuring, deciding where you’re using the most energy, and cutting use accordingly,you can achieve dramatic savings. Maybe not the 50% we achieved, but certainly by at least the 10% to 25% the sellers of these devices promise.

And the best thing about cutting your power use yourself is, you don’t have to buy these overpriced devices. For a mere $20 or so you can buy a device like a Kill A Watt meter, start measuring the electrical consumption of household devices and appliances, and see real savings start to pile up in no time.