Kill-a-Watt meter vs electric bill

sofasurfer
sofasurfer Registered Users Posts: 9
I've seen the Kill-a-Watt meters but never got around to getting one. Don't you have to use a Kill-a-Watt meter seperately on each differant appliance or energy user? For instance, don't you plug your lamp into it for a time to get its usage and then plug your toaster into it for a time to get its usage? Thats a lot of individual testing. Is this really more important than just getting the usage off your electric bill?

Thanks

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Kill-a-Watt meter vs electric bill

    Yes, you need typically want to run the kill-a-watt meter for ~24 hours on each load to get a good average. The idea is you will now have a spread sheet of each load (average watts and Watt*Hours per day) for each appliance. And you can decide which ones you will support with your solar PV system--And which one may be a canidate for replacement with a more efficient model (i.e., desktop computer replaced with a laptop computer).

    This level of testing/measurement is usually worth doing. Conservation is critical to designing a cost effective off grid power system... Your utility power probably costs on the order of $0.10 to $0.20 per kWH--Off Grid power, more on the order of $1.00 to $2.00+ per kWH (based on cost of system and replacement over ~20 year life of system).

    It is almost always more cost effective to spend money on conservation (onetime cost) because of the long term avoiding of need to supply that extra energy 24x7 12 months a year... year in and year out.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Kill-a-Watt meter vs electric bill

    who is to say one will power everything in a household too? many just look to power or backup a few circuits and need to determine power usage to derive their battery bank, inverter, and if applicable their controller and pvs. sometimes this can show a faulty appliance as well if it's drawing too much power or even expose somebody in the house not conserving too well.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Kill-a-Watt meter vs electric bill

    Looking at your electric bill will indeed show you how much energy you have used, but that's of very limited value if you want to reduce consumption, as you have little or no solid information on where within your home that energy is being used. The Kill-A-Watt, if used properly, will show you where your consumption is taking place. For instance the toaster you mentioned. Yes, the toaster consumes a lot while it's on, but unless you're busy making toast for a large part of every day, it's overall monthly consumption will be very tiny compared to for example, your fridge which seldom sleeps. And don't forget your satellite receiver, most of them consume the same power even when "turned off", because they only give the illusion of being turned off. It's output signal and the little red light go off, but the rest of it keeps on consuming so you won't have to wait a few seconds for it to reboot when you want to watch "As The Stomach Turns".
  • plongson
    plongson Solar Expert Posts: 115 ✭✭
    Re: Kill-a-Watt meter vs electric bill

    The biggest issue I have with a K-O-W meter is it's for the "plug-in's" only. I really wanted to log usage on a forced air furnace, can't do. I had a few other items as well so i ended up using an amprobe and just winged it.
    3500w solar, 800AH with Rolls Surrette, Magnum inverter, Midnite charge controller, Kubota 21kW diesel genset...private well...and just recently connected to city power for additional options...nice to have options 
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: Kill-a-Watt meter vs electric bill

    If you have a little skill with a screwdriver and a lot of common sense you can use a KOW on non-plug ins. I've done this for my 120v submersible well pump. First... Cut power to the circuit at the panel (unless you like to live dangerously). Wire an extension cord replacement receptacle in the circuit, wire a plug on the last wire (the power wire to the furnace, well pump, whatever) and put the KOW between the two. Only works for 120v of course.

    This is only for the truly dedicated watt miser to do:p. Because we just have to know!

    Ralph
  • plongson
    plongson Solar Expert Posts: 115 ✭✭
    Re: Kill-a-Watt meter vs electric bill

    I didn't mean it was impossible just a PITA...LOL
    3500w solar, 800AH with Rolls Surrette, Magnum inverter, Midnite charge controller, Kubota 21kW diesel genset...private well...and just recently connected to city power for additional options...nice to have options 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Kill-a-Watt meter vs electric bill

    You can also purchase other Whole Home monitoring systems--some that have options to support additional circuits (put one on your AC system and another on the electric water heater, etc...

    The "TED" will support upwards of 4 measuring current clamps (don't have one, don't know the details, just a suggestion for further research).

    You can use a current clamp meter--But that can lead to some difficulties--If you have something that cycles over time--You need to know if it is running for 30 minutes every hour (example). Also, electric motors and some electronics have very poor power factor (on the order of 0.50 to 0.67) which can lead to overestimating how much power you are really using...

    Energy = Voltage * Current * Time * Power Factor

    Power factor consists of several elements... The "phase" angle between voltage and current, and the current wave form (sine wave, pulse train, etc.). An Amp meter, by itself, does not take Time (hours) and Phase Angle into account for power/energy measurements.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Kill-a-Watt meter vs electric bill
    BB. wrote: »
    You can also purchase other Whole Home monitoring systems--some that have options to support additional circuits (put one on your AC system and another on the electric water heater, etc...

    The "TED" will support upwards of 4 measuring current clamps (don't have one, don't know the details, just a suggestion for further research).

    You can use a current clamp meter--But that can lead to some difficulties--If you have something that cycles over time--You need to know if it is running for 30 minutes every hour (example). Also, electric motors and some electronics have very poor power factor (on the order of 0.50 to 0.67) which can lead to overestimating how much power you are really using...

    Energy = Voltage * Current * Time * Power Factor

    Power factor consists of several elements... The "phase" angle between voltage and current, and the current wave form (sine wave, pulse train, etc.). An Amp meter, by itself, does not take Time (hours) and Phase Angle into account for power/energy measurements.

    -Bill

    TED will graph the data and show if it ramps up and down, total kWh per day, history by hour, day or month. It will show Power factor as well on the live display along with system voltage if so desired.

    Edit you can see the attachments the light blue line is the Volt chargers

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