Capacitors are indeed sold to improve energy efficiency. Because there is a delay between voltage and current in a typical electrical system, a great deal of energy is wasted. This includes residential electricity and all other applications. The amount of power wasted is quite substantial, and saving this wasted power delays the construction of new power plants, and lowers electric bills overall by millions of dollars a month. (not to mention the CO2 gas that is withheld from our atmosphere)
The measurement of true power VS. apparent power is called a “power factor measurement”. Only this will determine the size of the capacitors to be installed, to correct the power factor error.
Measuring the power consumed by wall wort transformers does nothing to indicate power factor, and this method leading to the conclusion that residential power consumers do not need to correct power factor is far off track. Your measurement indicates absolutely nothing about power factor. It is a wholly inaccurate conclusion, and you are using the wrong method to measure it.
Further, power factor correction does not cause appliances or motors to “sip” electricity. It only causes the power that is being used to arrive at the appliance or motor with better efficiency; and in doing so saves a large factory, office building, or shopping mall tens of thousands of dollars a year in electric bills.
Next time you want to talk about electricity, find an electrical engineer, and get the real facts. Your recent article about capacitors, power factor correction is the most inaccurate that I have ever seen you publish.
N.T.- Certified California General Electrician
Greetings Nicola.
It is customary here to give the link of the article you are posting about, like this:
http://www.straightdope.com/columns/read/2851/am-i-really-wasting-money-leaving-appliances-plugged-in
I’m afraid I don’t understand your claim. It is in the nature of AC signals for amperage or voltage to be out of phase. How do capacitors address this? Do you use them to supply DC? And, why does the fact that they are out of phase matter to the “true power”?
The article never said wall warts, or measurements thereof, had anything to do with power factor. It answered two completely separate questions with two separate answers. You are confusing the two.
Hopefully one with better reading comprehension than you.
I doubt this (or at least you’re horribly misinformed and therefore not very good at it). Because this:
Is very nearly completely wrong. The ONLY time there is a phase lag between current and voltage is when you have a highly reactive load, either capacitive (rare) or inductive (motors, transformers and the like). While residential loads do include some motors and small transformers, the bulk of the load is resistive and the power factor of the typical residence averages pretty close to unity. Even in the rare cases where a residential load PF is significantly lower than unity not a dime would be saved by the customer by installing a power-factor-correction cap. Why? Because power utilities don’t bill residential customers for power factor. They get billed for usage strictly by kilowatt-hours consumed. It’s true that power-factor correction improves energy transfer efficiency, meaning less energy is wasted in transmission, which is why utility companies like power factor to be as close to unity as possible. But this only occurs for highly reactive loads like the large motors typical of heavy industry; hence, these types of customers ARE billed for power factor, which in turn encourages the customers to minimize their costs by installing caps.
Residential customers do NOT benefit from these caps and anyone selling them as such is con artist.
Note that there is a parallel thread involving power factor correction. See the Phantom Electricity thread.
If you want to see an independent test of a home cap system here’s a link.
Indeed, this is one of the few things I remember from my required intro to EE course for my CS major.
Capacitors when added in parallel cause the electrical length of the line to become shorter, balancing out the inductive component. When capacitive and inductive components are balanced, the power will arrive to the appliance with current and voltage in phase, resulting in less wasted power. (a very real savings).
And no, we are not using the caps for DC, we are speaking solely of AC transmission lines.
Of course the electric company really could care less since the more power you waste, the more money you pay. And the more power plants that are built, the richer they get. Electric utilities want you to use as much power as possible.
And considering electric washers, dryers, air conditioning and heating etc…the larger your house is, the more you could benefit…
Apparent power is the measurement of current times voltage- VA, the measurement of true wattage compared to VA will tell you your power factor, and this has nothing to do with power wasted by VCR’s and wall worts.
Then to accurately answer the original question, yes, capacitors do improve energy consumption and do save you money, when correctly applied. And these devices are being used widely to save a huge amount of money.
Whether you choose to apply this to saving money and energy in a residential application is I suppose, a matter of your budget and concern for our environment.
But the savings are very real!
ALL uses of electricity could stand power factor correction, and this becomes more of a concern as our planet becomes choked with CO2 emissions. The appliances labeled “energy star” are frequently the same appliances that continue to use energy when they are switched “off”, go figure.
Or perhaps some people would prefer building more and more nuclear power plants, to trade wide spread radioactive contamination for CO2 emissions…
Let me leave you with this thought: For all the electricity generated by commercial power plants, more than 60% is wasted before it even reaches your house.
Surprise! Commercial electricity is very inefficient and wastes huge amounts of fuel.
That’s why we try and recoup some of the losses with power factor correction. DO IT!
The bulk of the load in a residence is air conditioning, heating, dishwasher, dryer, washer, disposal- all inductive motor loads, all saving energy with correction.
The power industry taught you that a residence would not gain anything by correction and you believed it. Time to question authority.
If you measured the power in your own house properly, you will most certainly understand that power delivered to a house is not archiving unity, the error in power factor is driving your bill up.
The only con artists in this equation are the utility companies themselves.
Okay, listen to me. I’m going to say this one more time hoping it will sink in: Residential customers DO NOT PAY FOR POWER FACTOR. It doesn’t matter if your power factor is .1; it won’t cost you a cent. The losses are in generation, transmission and distribution, which the power company essentially eats for residential consumers. And they don’t care, because–once again–residential power factor averages pretty close to unity most of the time. It’s the industrial use, the large, powerful motors and the like which are the major problem, and they DO get billed for it.
First off your heating and dryer are not inductive loads they are almost entirely resistive. The other loads have some inductance but the power utility charges you in kilowatt-hours not kva or kvar. If you correct your power factor in the home you are helping them with their line losses not saving on your own power usage. You might get some surge protection from the capacitors but that’s about it. large companies pay a penalty when their PF goes below a set value, usually 85 - 90% so they need it. Also, they could run into issues with overheating neutrals and motors without power factor correction.
Nitpick: by “heating” loads being significantly inductive, our friend nicola may be thinking “heat pump.” He’s still incorrect about what the residential customer is charged for.
No, it is not. You are confusing thermodynamic systems conversion losses with T&D losses. T&D losses are relatively small.
See the portion marked “T&D losses” on the right-hand side: http://www.eia.doe.gov/emeu/aer/pdf/pages/sec8_3.pdf
I really hate having to keep re-posting this.
But the Evil Big Government Industrial Power Comany Utility Super Uber Bad Guy Conglomerate just want you to think that! Stop being Sheeple!
It seems a simple test of these capacitor devices, would be to run all the devices in the building that these capacitors are supposed to work with, before connecting the capacitor(s), while watching the speed of the meter on the building that the power company read when they determine what to bill, then connect the capacitors and read the meter again, and see if it’s running any slower, reflecting decreased power use. Naurally, the building’s meter is what the power company uses to determine how much to charge for electric power usage, and no other technical considerations mean anything except that single thing.
I also keep hearing that huge power loss figure for transmission and distribution–usually the figure is quoted as between 50% and 60%. The chart Una refers to, says it’s only 9%. I wonder why the larger figure is usually the one that gets quoted. In any case, it seems that with local power generation (solar panels on roof, etc.), at least 9% would still be a decent savings for the grid, though that would require most locations to generate their own power, which won’t happen for a while.
This would work if your meter read kVAH or kVARH, but for most residential buildings, it doesn’t. It reads kWH. Of course, your method will differentiate the two, so it’s not completely off-the-wall.
“The larger figure” is approximately equal to the overall losses in converting the energy stored in coal (and natural gas, etc.) into usable electricity. As you can see from the diagram Una posted, most of that loss is from the thermodynamic cycle losses (conversion losses).
I suspect that the ideas of “overall efficiency, including thermodynamic losses” and “efficiency of transmission and distribution” are conflated into “electrical efficiency” by people using unclear terminology. As to why the larger figure is often used in place of T&D efficiency, I would hazard that either a) people unfamiliar with the terminology and industry repeat the erroneous figure because they don’t know any better, or b) people with a product to sell repeat the erroneous figure because it sounds more impressive. (The same thing happens when talking about fuel efficiency of vehicles, FWIW.)
In any case, when anyone conflates thermodynamic efficiency with T&D efficiency, be sure to evaluate their other statements with the above in mind.
I think the point is that it doesn’t matter what the meter is reading or how it works, if the meter spins more slowly, you’re being charged less.
My concerns would be how large of a capacitor you’d need, and how are you planning on hooking it (or them) up. Also, you’d want to make sure you are running the same load both times. This wouldn’t be hard for lighting, but for large inductive loads like motors (which is what you’ be concerned with), you’d have to do some planning.
Sizing the capacitor, in my experience, requires you to know what power factor your system is running at or knowing the power factor of the load, depending on where you’re installing the caps. Where I work we correct the power at the service but it can be done at the load. For 3-Ø motors it’s listed on the nameplate, for 1-Ø it’s not usually on the nameplate but is available from most manufacturers.
Personally, I would just unplug intermittent loads like the fridge or freezer and make sure that other loads such as the dryer are either running with the same load for both tests or off for both. Run some fans, etc. The power factor of a motor is usually maximum at full-load and minimum at no-load. I don’t believe you would see any difference at the meter anyway but it would be interesting to try it and see for sure.