Power used by house inaccurate

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withoutatrace
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Power used by house inaccurate

Post by withoutatrace » Wed Oct 16, 2013 11:55 am

I am running a PowerFlex One GVFX3648 with 1600W of panels and a 48V battery bank in grid interactive mode. I can elaborate on my setup if more information is needed.

My MATE3 shows that it's producing 1.2kw, my house is using 0.4kw and it's selling back 0.8kw. If I go look at the meter, it's staying steady, sometimes forward, sometimes back, sometimes still. So I know my house is using approximately 1.2kw right now.

I want to set system up where it uses the maximum amount of energy from the panels, but does NOT sell back to the grid. If I set the sell-back voltage to 60V (eliminating sell-back), it shows the panels only generating 0.1kw for use by the house (and sell-back at 0.0kw).

I currently have the PowerFlex One hooked up to a breaker in the breaker box of my shed. There's a line running back to my house to the main breaker box on a double breaker (220V). Is this the reason the PowerFlex One only shows the house using 0.1kw when grid sell-back is disabled? Do I need to connect it to a breaker in my main breaker box?

Thanks.
Last edited by withoutatrace on Wed Oct 16, 2013 2:47 pm, edited 1 time in total.

withoutatrace
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Re: Power used by house inaccurate

Post by withoutatrace » Wed Oct 16, 2013 2:47 pm

A little more information...

The 0.1kw when grid sell-back is turned off appears to be the two 110V outlets directly on the inverter.

dhamilton
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My RE system: 2x VFXR3524A, FLEXmax80, 6x EnergyCell 106NC, Mate3

Re: Power used by house inaccurate

Post by dhamilton » Fri Oct 18, 2013 4:22 pm

To accomplish this you would need to have all your loads on the output of the inverters, and the utility connected to the input of the inverter. Set your sell to no sell and just invert power until your battery voltage drops.
In this scenario you will be using the utility like a back up generator.

I hope this helps.

jnh
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My RE system: GVFX-3524, FM-80+FM-60, ~4.9kW PV in mixed panels on movable platforms, 300 Ah AGMs @ 24V, 80Ah @ 12V, Hub4, Mate, FNDC, Brultech GEM 32-ch AC datalogger, Midnite E-Panel, homebrew DC-DC crossfeed to 12V system, Honda EU-1000i, Iota DLS-27-25
Location: St. Augustine, FL, US

Re: Power used by house inaccurate

Post by jnh » Sat Oct 19, 2013 8:33 am

A few points,

1. the AC ammeters built into all Outback FX inverters are notoriously inaccurate, and can be off by as much as 1.5A or so, usually reading lower than they should since fractional amps are truncated rather than rounded. I don't know why they were designed this way, but it's a definite weak point in an otherwise excellent product.

To get reliable numbers you have to add extra metering equipment. I use a Brultech ECM-1240 multi-channel/bidrectional power logger on the AC side, and an Outback Flexnet-DC on the DC. The FNDC can display its readings on the Mate, but the Brultech, not being an Outback product creates its own independent data stream.

2. Whenever a GVFX is operating in grid-tie mode, its AC-In and AC-Out terminals are always tied together. The inverter will supply as much AC power as it can while still maintaining a target battery voltage, and any not taken up on the AC-Out side will automatically flow to AC-In. In particular, it has no way of knowing how much AC-In current is going to loads back at your main panel, as opposed to flowing out to the utility. If you don't want to "sell" any power back, the only way to guarantee that won't happen is to turn 'grid-tie authority' to OFF (no sell).

(I think there were early plans to offer something like what you want, where the GFX's unused "XCT" terminals could receive sense inputs from an eXternal Current Transformer placed across incoming bus bars at the service-entrance panel, and a control loop would seek to drive this current to zero, but not to a negative value. The necessary software support was never completed, though).

3. If you really want to avoid grid-tie, read up on "HBX" (High Battery Transfer) mode, where the inverter can be programmed to take itself, and all AC-Out loads off-grid during times when you're getting adequate sun to operate independently. This can take a lot of careful adjustment to get good results, though, will wear out your batteries a bit faster, and will yield lower overall efficiency than running grid-tie. The combination of cycling losses, plus not having an "infinite load sink" available means some PV energy will end up wasted every day-- especially if, as in many households everyone is away at work, school etc. during the sunniest hours.

I'd suggest just setting up net metering if you can. I was leery at first of the inspection and paperwork requirements, but as it turned out that wasn't so bad. Having most components already integrated in the Flexpower enclosure should reduce the amount of work you need to bring things up to code.

withoutatrace
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Re: Power used by house inaccurate

Post by withoutatrace » Sat Oct 19, 2013 11:07 am

dhamilton wrote:To accomplish this you would need to have all your loads on the output of the inverters, and the utility connected to the input of the inverter. Set your sell to no sell and just invert power until your battery voltage drops.
In this scenario you will be using the utility like a back up generator.

I hope this helps.
How would I go about putting the entire load of my house on those two outlets? Is that possible?

Thanks for the help.

withoutatrace
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Re: Power used by house inaccurate

Post by withoutatrace » Sat Oct 19, 2013 11:13 am

jnh wrote:A few points,

1. the AC ammeters built into all Outback FX inverters are notoriously inaccurate, and can be off by as much as 1.5A or so, usually reading lower than they should since fractional amps are truncated rather than rounded. I don't know why they were designed this way, but it's a definite weak point in an otherwise excellent product.

To get reliable numbers you have to add extra metering equipment. I use a Brultech ECM-1240 multi-channel/bidrectional power logger on the AC side, and an Outback Flexnet-DC on the DC. The FNDC can display its readings on the Mate, but the Brultech, not being an Outback product creates its own independent data stream.

2. Whenever a GVFX is operating in grid-tie mode, its AC-In and AC-Out terminals are always tied together. The inverter will supply as much AC power as it can while still maintaining a target battery voltage, and any not taken up on the AC-Out side will automatically flow to AC-In. In particular, it has no way of knowing how much AC-In current is going to loads back at your main panel, as opposed to flowing out to the utility. If you don't want to "sell" any power back, the only way to guarantee that won't happen is to turn 'grid-tie authority' to OFF (no sell).

(I think there were early plans to offer something like what you want, where the GFX's unused "XCT" terminals could receive sense inputs from an eXternal Current Transformer placed across incoming bus bars at the service-entrance panel, and a control loop would seek to drive this current to zero, but not to a negative value. The necessary software support was never completed, though).

3. If you really want to avoid grid-tie, read up on "HBX" (High Battery Transfer) mode, where the inverter can be programmed to take itself, and all AC-Out loads off-grid during times when you're getting adequate sun to operate independently. This can take a lot of careful adjustment to get good results, though, will wear out your batteries a bit faster, and will yield lower overall efficiency than running grid-tie. The combination of cycling losses, plus not having an "infinite load sink" available means some PV energy will end up wasted every day-- especially if, as in many households everyone is away at work, school etc. during the sunniest hours.

I'd suggest just setting up net metering if you can. I was leery at first of the inspection and paperwork requirements, but as it turned out that wasn't so bad. Having most components already integrated in the Flexpower enclosure should reduce the amount of work you need to bring things up to code.
1. I have the Flexnet-DC incorporated into the PowerFlex One, but I'm not sure I want to invest more into more monitoring equipment.

2. If I switch to "no sell", then the only power generated by the panels is what I need for the batteries and the two 110V plugs on the side of the inverter. That would save nearly nothing in electric costs.

3. This sounds like an excellent option, however, I would only do it if I could maintain the 90% battery level, as battery life is extremely important to me.

I'll do some research. Thank you very much for your in-depth response.

jnh
Forum Guru
Posts: 387
Joined: Fri Jun 01, 2007 11:56 am
My RE system: GVFX-3524, FM-80+FM-60, ~4.9kW PV in mixed panels on movable platforms, 300 Ah AGMs @ 24V, 80Ah @ 12V, Hub4, Mate, FNDC, Brultech GEM 32-ch AC datalogger, Midnite E-Panel, homebrew DC-DC crossfeed to 12V system, Honda EU-1000i, Iota DLS-27-25
Location: St. Augustine, FL, US

Re: Power used by house inaccurate

Post by jnh » Wed Oct 23, 2013 2:50 pm

Do you not have a protected-loads subpanel connected to the AC-Out terminals of your inverter? In a typical grid-interactive but no-sell setup, this is what would be powered from your harvested PV energy during the day. Not having one also means you miss out on one of the nicest features of this style of inverter, the ability to serve as a (nearly) "whole-house UPS," where power just stays on when the utility goes away, without having to take any manual steps like running extension cords out to your shed.

For my system, I just mounted a second breaker box next to the main one, fed this with a dedicated cable from the inverter (separate from the AC-In cable going to a main panel breaker), and moved over all circuits I wanted to have on backup power. The main panel required some filler plates to close off all the extra spaces afterward, since it was only about 1/3rd full after nearly all 120V house circuits were moved.

withoutatrace
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Re: Power used by house inaccurate

Post by withoutatrace » Fri Nov 15, 2013 2:22 pm

jnh wrote:Do you not have a protected-loads subpanel connected to the AC-Out terminals of your inverter? In a typical grid-interactive but no-sell setup, this is what would be powered from your harvested PV energy during the day. Not having one also means you miss out on one of the nicest features of this style of inverter, the ability to serve as a (nearly) "whole-house UPS," where power just stays on when the utility goes away, without having to take any manual steps like running extension cords out to your shed.

For my system, I just mounted a second breaker box next to the main one, fed this with a dedicated cable from the inverter (separate from the AC-In cable going to a main panel breaker), and moved over all circuits I wanted to have on backup power. The main panel required some filler plates to close off all the extra spaces afterward, since it was only about 1/3rd full after nearly all 120V house circuits were moved.
That is EXACTLY what I wanted. My installer just didn't understand. So I need to mount a second breaker box next to the main box. Move all 120V breakers to the new box and run a line from the same terminal as before. And now all 120V breakers HAVE TO go through the FlexPower One.

When the grid goes down, how does it keep powering? When I've simulated a "grid-down" by shutting off the breaker at the meter, the (original) line I have running from the AC on the inverter to the breaker box cuts off (for safety reasons, I'm sure). I guess I'm just not understanding where the wire connects to the FlexPower One that goes to the new breaker box I will be installing.
Last edited by withoutatrace on Sun Nov 17, 2013 11:31 am, edited 1 time in total.

withoutatrace
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Re: Power used by house inaccurate

Post by withoutatrace » Fri Nov 15, 2013 2:38 pm

After looking closer at the schematics, I figured out the breaker that is not being used on the FP1 that I need to run to the new breaker box. THANK YOU. I was beginning to think I'd never have this setup the way I wanted it.

withoutatrace
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Re: Power used by house inaccurate

Post by withoutatrace » Sat Nov 16, 2013 9:16 am

How do I put my 240V breakers on backup?

Or, if that route is not cost effective, how would I add another GVFX3648/FM80 combination for more power? I already have the panels, batteries and controller. I just have to purchase the inverter. Thanks.

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