Inattrusive Metering of Inverter Grid Feed

[LowGear]

I'm currently clicking in a litttle above 40 KWH a day.  At 43 cents a KWH - You can do the math it's all becoming too painful for me.  I'd like to keep our local untility honest with a secondary meter what I supply and own.  I don't want to hack into the current wires between the inverter and the sub-panel so is there a modest method / meter I can install that will give me reliable information?

Casey

[Thob]

Casey,

I'm not sure what you're looking for here.  I see meter bases advertised at Lowes, but the only place I've ever gotten a meter was from the utility company.  I don't think they give them away for DIY projects, however it occurs to me that there *should* be a bunch of old mechanical meters available cheap since they are replacing them nationwide with "smart" meters.  Would a standard utility meter fit the bill for you?  Is this more than what a kill-a-watt (or two) could handle?  Are you looking for a DIY solution or off-the-shelf?

Another tactic might be to see if the utility meter is accurate.  You could try turning off just about everything, then plugging in a substantial load into a kill-a-watt (something like a 1500 watt space heater).  Let it run a few minutes add see if the utility power meter and the kill-a-watt agree as to the power used.

40 KWH per day?  Not only do you live in paradise, you must live in a mansion!  I use half that much, and I don't think I'm all that conservative with power usage.  I do have gas heat, hot water, and dryer; that could account for a big difference.  I got a kill-a-watt for Christmas and I'm going around finding out what various appliances are costing me per month.

[Carlb]

Casey,


You can get meter sockets at  home depot and pickup a revenue grade electric meter on ebay for less than 25 dollars.  Just wire it in line between your inverter and the sub-panel.  It is very easy to do just remember the feed is from the inverter side not the panel side or the meter will be going the wrong way.

[carbon-rod]

I like your idea Carlb, getting a second hand mechanical meter would be the best solution as these are usually pretty damm accurate as they are so simple, if they are within a small enough % of each other then It's all good.

What kind of stuff do you run? 40KW/h is quite a lot of power! I thought paying 20c per KW/h was getting expensive, I feel extremely lucky when comparing it to what you have to pay...

[LowGear]

Hi carbon-rod,

We are a BnB.  So we have three refrigerators, two water heaters, two water features and a pool pump.  The other stuff just catches up with you.

I was kind of hoping not to cut wire but that may not be an option.

Casey

[carbon-rod]

ahhh that makes more sense!

There are lots of other controllers that use CT's to measure current flow, you would still have to disconnect the cable to put the CT inline, although there are few which just open up and snap over the line however I don't know what you would be paying for a system like that, you would also need a voltage sensing wire unless the meter itself was running off AC.

for a simple method, you could use a tong meter which just clips over the power cable, this should give you a rough estimate of current in use, measure your AC voltage using a multimeter and then compare that with what the utility meter is saying. This would only be a very rough method as it doesn't take power factor into consideration (it would only give you a higher reading if you have a less than 1 power factor) and I doubt the uility meter would be out by that much any way as these things are usually built to certain specifications and go through pretty rigorous testing to become trade certified.

[Horsepoor]

Where do you live that the power company gets 43 cents per KWH? I'm paying 11.2 cents in Florida for residential service and not happy, perhaps I should be thrilled.

[BioHazard]

Surely you could use a diesel engine and some waste oil to heat all that water!  

If you go with a standard "spinny" meter I would suggest purchasing from these guys:
http://www.hialeahmeter.com/siphwame.html

[Carlb]

I use one of these on my solar array,  nice meter easy to read and digital. they have them here for 29.00 with free shipping.


http://www.ebay.com/itm/SCHLUMBERGER-C1SR-RADIO-READ-WATTHOUR-ELECTRIC-METER-240V-FREE-SHIPPING-/270879428651?pt=LH_DefaultDomain_0&hash=item3f11ac102b

[LowGear]

Thanks BioHazard and Carlb,

I didn't know they were that inexpensive.  I'm also looking at a WebBox by SMA.

http://www.sma-america.com/en_US/products/monitoring-systems/sunny-webbox.html

They're more than $30 plus base.

Casey

[Carlb]

You do know that you can get the info right from the inverter just by looking at the display.  it will give you kwh per day and cumulative.  You can take a reading on the first of every month and that will tell you exactly how much you made that month.  You would have to do that anyway using a meter that is inline.   If you only have one inverter its easy to keep track of.

that webbox will a lot more than 30 dollars.

[LowGear]

Hi Carlb,

I love tapping the lower rightish front of the SunnyBoy to step through the readings.  I love German engineering.  I'll be out at MEL Sunday morning.  I feel like the cosmonaut using a pencil to write stuff down in space.  No stinking ball points here.

Casey

If you think the Webbox is expensive just price out the rectifier they offer for the WindyBoy - WindyGirl (I believe).  YIKE$$$!

[LowGear]

Aloha,

I just returned from the MEL (Menehune Energy Lab) where the 15 Solar World Panels are feeding the SunnyBoy 6000 grid tie inverter.

3800 KWH and change.  At 42 cents a KWH that's $1596.

Total cost             $25,000
     Grant               -10,000
     Tax Credits        -8,000

Net Cost                 7,000

1596/7000=22.8%  Not bad.

This next 15 panel - 3675 watt addition will probably be about the same after Tax Credits.

Casey

[Carlb]

casey,

are you running the 6000 inverter on only 15 panels?   How large are the panels?

[LowGear]

Hi Carlb,

We're running 15 SolarWorld 245 watt panels currently.  In a week It'll be up to 30 panels and the 6000 will start paying its way. 

I've been looking at a WindyBoy 7000 and I'm starting to suspect all of these units are the same hardware only with different programming.  That's starting with the SunnyBoy 5000 right up through the WindyBoy 8000.

I checked output via your recommendation and the system produced 405 Kilowatts in January.  That's $174 worth here in the Islands.

Casey