Interesting results (for me, at least) using a kilowatt meter

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Rybren
Rybren Solar Expert Posts: 351 ✭✭
in Solar Beginners Corner #1
Well, you guys have been stressing how important it is to define the loads as the first step in planning an off-grid system, so I picked up a kilowatt meter from the library to see what it would tell me.

The first thing I tested was my laptop. The battery was pretty much dead at the start of the test. 5 hours of charging brought the batteries to full and used a whopping 0.04 KWH

Next up was my tablet - a Playbook. The battery was showing about a 50% SOC at the start of the test and I left it to run overnight. According to the meter, it used 0.00 KWH during the eight hours. I assume that this means that it used between 0.00 and 0.01 KWH. At the begining of the charge cycle, it showed that it was using 5W.

Charging my BlackBerry and my wife's cell phone showed similar results to the Playbook - 5W initial use and 0.00 KWH used by the time that a full charge was achieved.

I am really suprised at how little energy these items used. I was expecting to see much higher numbers.

Tonight I'll test the charger for my 18V drill. I think that this and a yet-to-be-purchased ShurFlo pump (likely an AC version) will be the biggest energy users for my system.

Anyway, just thought I'd share my results.

Jerry
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #2
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    Re: Interesting results (for me, at leat) using a kilowatt meter
    Rybren wrote: »
    The first thing I tested was my laptop. The battery was pretty much dead at the start of the test. 5 hours of charging brought the batteries to full and used a whopping 0.04 KWH

    Yep, smaller devices (tablets, rechargeable radios, cell phones, etc.) are going to be on the order of 5 WH (0.005 kWH) to recharge overnight.

    The laptop sounds a bit on the low side though...

    The run of the mill smaller (cheaper) PC Laptops I use are around 20-30 Watts when being used, and will consume 30-60 watts while recharging... Or, a laptop used on and off during the day will use ~0.4 kWH (400 WH) a day.

    A really low power laptop may use down towards 8 watts--So it is possible if yours is really low power (and/or has a failing battery pack), you might see numbers that low.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #3
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    Re: Interesting results (for me, at leat) using a kilowatt meter
    BB. wrote: »
    Yep, smaller devices (tablets, rechargeable radios, cell phones, etc.) are going to be on the order of 5 WH (0.05 kWH) to recharge overnight.

    I'm a tad confused. Wouldn't 5WH be 0.005 kWH and 50WH be 0.05 kWH?

    I figured that my laptop, at 0.04 kWH, used 40 WH and my tablet/phones used <10 WH
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #4
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    Re: Interesting results (for me, at leat) using a kilowatt meter

    Sorry--You are correct... I will fix.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #5
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    Re: Interesting results (for me, at leat) using a kilowatt meter
    Rybren wrote: »
    I figured that my laptop, at 0.04 kWH, used 40 WH

    I'd look at that number skeptically unless 1) it was sleeping most of that time and 2) your battery is very old. A typical 6 cell laptop battery alone is around 48 watt-hours all alone, and a low power laptop takes about 16 watts to operate.
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #6
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    Re: Interesting results (for me, at leat) using a kilowatt meter

    Sorry, I should have specified. The laptop was off while charging and the batteries are old.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #7
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    Re: Interesting results (for me, at leat) using a kilowatt meter

    OK, that makes more sense.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Skippy
    Skippy Solar Expert Posts: 310 ✭✭
    #8
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    Re: Interesting results (for me, at leat) using a kilowatt meter

    I have 3 - 110 watt solar panels, and a 300 watt generic grid intertie inveter from china, and just for the heck of it, I plugged the inverter into the killowatt meter with a small cf light for a load and a small fan running - meter read something like 25 watts being used. . then I connected the panels to the inverter and it went from 25 to 10 to 3 then up to 150 watts- after turning the fan and the light off, it read about 190 watts . . . so assuming that the killowatt meter reads backwards - does that number sound about right for 330 watts / 12 volts of pv feeding into a 120 V grid ? Switching to amps, it was reading only 1 amp. . . so 190 watts at 1 amp. . does that sound right ?
    2 - 255W + 4 - 285W PV - Tristar 60 amp MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
    Google "undergroundandlovinit" no spaces.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
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    Re: Interesting results (for me, at leat) using a kilowatt meter
    Skippy wrote: »
    I have 3 - 110 watt solar panels, and a 300 watt generic grid intertie inveter from china, and just for the heck of it, I plugged the inverter into the killowatt meter with a small cf light for a load and a small fan running - meter read something like 25 watts being used. . then I connected the panels to the inverter and it went from 25 to 10 to 3 then up to 150 watts- after turning the fan and the light off, it read about 190 watts . . . so assuming that the killowatt meter reads backwards - does that number sound about right for 330 watts / 12 volts of pv feeding into a 120 V grid ? Switching to amps, it was reading only 1 amp. . . so 190 watts at 1 amp. . does that sound right ?

    You cannot get accurate readings this way. GT inverters do not output steady Voltage against varying current. It also shows the danger of such inverters, for the output should be zero if it is not connected to utility power.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #10
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    Re: Interesting results (for me, at leat) using a kilowatt meter
    Cariboocoot wrote: »
    You cannot get accurate readings this way. GT inverters do not output steady Voltage against varying current. It also shows the danger of such inverters, for the output should be zero if it is not connected to utility power.

    The OP is not too clear on what is connected to what. I think the OP has plugged his kill-a-watt meter into a wall outlet and then (using a powerstrip?) has plugged both his inverter and some loads into the kill-a-watt. At that time the kill-a-watt read that the inverter and loads were consuming 25 watts. When he connected the panels to the inverter and turned off the loads, the kill-a-watt read 190 watts. The OP is asking: Is the kill-a-watt reading backwards? I know from another recent thread that it is difficult to detect which way AC power is flowing, so I imagine (but don't know) that the kill-a-watt does read backwards.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Skippy
    Skippy Solar Expert Posts: 310 ✭✭
    #11
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    Re: Interesting results (for me, at leat) using a kilowatt meter
    vtmaps wrote: »
    The OP is not too clear on what is connected to what.

    --vtMaps

    Sorry about that, and yes, you are correct, using a power strip, that is still connected to the grid, I shut off all the other loads, and I believe it did read backwards. Once I pulled the plug on the grid, everything shut down, with no power coming or going out of anything, so the GT inverter is doing what its supposed to.

    Just curious, what does OP mean ?
    2 - 255W + 4 - 285W PV - Tristar 60 amp MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
    Google "undergroundandlovinit" no spaces.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #12
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    Re: Interesting results (for me, at leat) using a kilowatt meter
    Skippy wrote: »
    Just curious, what does OP mean ?

    Original Post or Original Poster --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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