Stacked Skyboxes with External CTs, math doesn't add up

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SHunsader
Forum Whiz
Posts: 48
Joined: Mon Feb 15, 2021 2:54 pm
My RE system: Identically configured pair of Outback Skybox Systems each with 12 - LG 340 panels, and a Discovery 6.5kwh 48V battery, both running as Masters. External CT's, one using L1 CT input and the other using L2 CT input so as to help share load more evenly.
Location: SF Bay, California

Stacked Skyboxes with External CTs, math doesn't add up

Post by SHunsader »

I have a pair of stacked Skyboxes, using external CTs (of course, connected only to the Master). Each time one of the systems displays either GridZero or AC Couple, the numbers don't add up.

Attached shows both the Optics for that moment, as well as both the Master (top) and Slave Skyboxes. In a 'normal' mode, where both grids show 'Selling' and Load is showing 'Powering', the math adds up.

For those of you not familiar with how the Skybox displays information when stacked WITH External Current Transducers installed, is that the Grid represents the Current AT the utility hookup (where they should be installed). The LOAD is the amount of energy being used by the entire location (everything that's hooked up to the Main Panel).

Since both the Slave (bottom right row) and Master (top right row) are selling power and the batteries are not contributing, the maximum power being produced is 7.0 kw. After subtracting the load of 2.1 kw, and another .2kw to power both Skyboxes, I would expect to see the Optics displaying that just under 5 kw (7-2.3 = 4.7kw) is being thrown back on the grid. I can confirm this number within 200w consistently.

Yesterday, the opposite was happening. The GRID for the master displayed GridZero, and again, the numbers didn't add up.

Is there a software setting that will KEEP either of these Skyboxes from entering AC Couple or GridZero modes so that information is displayed correctly on the Optics application?
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SkyboxAC_Couple.jpg
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Cottonwood
Forum Member
Posts: 10
Joined: Tue Dec 29, 2020 9:32 pm
My RE system: (48) Canadian Solar CS3U-350PB-Ag 350W panels; (3) SkyBox inverters; (3) 14 kWh LiFePO4 battery banks; Kohler 30RESA 30kW LPG generator. We are a rural Kansas farm family moving toward energy self-sufficiency.

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by Cottonwood »

I have a recently-commissioned, 3-SkyBox stack, also with properly located external CT's with which I'm encountering the same Optics calculation issue. Any feedback is welcome. I plan to check on this with Bo Magluyan as soon as possible and will try to update if a solution is available.
Attachments
Screenshot_20210307-103236.png
SHunsader
Forum Whiz
Posts: 48
Joined: Mon Feb 15, 2021 2:54 pm
My RE system: Identically configured pair of Outback Skybox Systems each with 12 - LG 340 panels, and a Discovery 6.5kwh 48V battery, both running as Masters. External CT's, one using L1 CT input and the other using L2 CT input so as to help share load more evenly.
Location: SF Bay, California

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by SHunsader »

Cottonwood,

I've spoken to Chuck (install support) about this over the past couple of weeks. He called me back out of the blue last week to let me know that there is someone else having the same 'problem', and that it's a confirmed bug. I believe it to be a sign error on one of your boxes. As you can see in my original post, I can access each of the consoles with a web browser, and have them displayed on the post. I believe the direction to be incorrect when in AC-Coupled mode. If it bothers you, you can often stop/start the grid connection to put it into it's correct mode. From time to time, I need to stop/start the inverter, but do so only as a last resort, because it takes all the inverters offline when in Master/Slave/Slave mode....something I'm also talking to Outback about.

If you want/need help seeing your console from a browser, I'll see if I have time to post a "How To".

Steve
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Cottonwood
Forum Member
Posts: 10
Joined: Tue Dec 29, 2020 9:32 pm
My RE system: (48) Canadian Solar CS3U-350PB-Ag 350W panels; (3) SkyBox inverters; (3) 14 kWh LiFePO4 battery banks; Kohler 30RESA 30kW LPG generator. We are a rural Kansas farm family moving toward energy self-sufficiency.

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by Cottonwood »

Apologies! I use the browser access all the time, just didn't include that in the screenshot.
SHunsader
Forum Whiz
Posts: 48
Joined: Mon Feb 15, 2021 2:54 pm
My RE system: Identically configured pair of Outback Skybox Systems each with 12 - LG 340 panels, and a Discovery 6.5kwh 48V battery, both running as Masters. External CT's, one using L1 CT input and the other using L2 CT input so as to help share load more evenly.
Location: SF Bay, California

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by SHunsader »

Please, post it in a format similar to what I've done. It'll help the both of us do the math. - Steve
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Cottonwood
Forum Member
Posts: 10
Joined: Tue Dec 29, 2020 9:32 pm
My RE system: (48) Canadian Solar CS3U-350PB-Ag 350W panels; (3) SkyBox inverters; (3) 14 kWh LiFePO4 battery banks; Kohler 30RESA 30kW LPG generator. We are a rural Kansas farm family moving toward energy self-sufficiency.

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by Cottonwood »

Here are a few combined view screenshots from mid-day today. (Note: Ignore the Total PV capacity of 29.12kW because there's an extra SBX still installed on my Optics site that Outback will be deleting - this was all due to a problem several weeks ago with that unit not being able to restart after a firmware update to which the solution was the installation of a new "beagle bone" board with a new MAC address.)
Cottonwood 01.JPG
Cottonwood 03.JPG
Cottonwood 05.JPG
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Cottonwood
Forum Member
Posts: 10
Joined: Tue Dec 29, 2020 9:32 pm
My RE system: (48) Canadian Solar CS3U-350PB-Ag 350W panels; (3) SkyBox inverters; (3) 14 kWh LiFePO4 battery banks; Kohler 30RESA 30kW LPG generator. We are a rural Kansas farm family moving toward energy self-sufficiency.

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by Cottonwood »

A couple of additional screenshots:
Cottonwood 06.JPG
Cottonwood 07.JPG
SHunsader
Forum Whiz
Posts: 48
Joined: Mon Feb 15, 2021 2:54 pm
My RE system: Identically configured pair of Outback Skybox Systems each with 12 - LG 340 panels, and a Discovery 6.5kwh 48V battery, both running as Masters. External CT's, one using L1 CT input and the other using L2 CT input so as to help share load more evenly.
Location: SF Bay, California

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by SHunsader »

Cottonwood,

Would you mind....Take a screenshot, then run out and see what the actual utility power meter says. I'm confident that the production numbers are correct, and pretty confident that the Slave grid and load information is correct. I'd like to confirm that you're getting what 'our' math is thinking that you're really sending to the grid. With that number, you can see what load you're really servicing with your top Skybox. From that, you can do the math to see what the the top Skybox's true grid number should be.

Of course, when you take a screenshot and run to see the meter, try to ensure that a family member isn't changing the load drastically....electric oven, blender, range, skill saw, cement mixer, etc. :)

I suggested to the install group at Outback that they should take advantage of that pulldown where you see "Skybox" and replace it with:

System
Sky 1 (This)
Sky 2
Sky 3

Where Sky 1, 2, and 3 are what you named your 3 systems. Without the 'real' Grid and Load information, it's harder to see what the math mistake in the system really is. - Steve
SHunsader
Forum Whiz
Posts: 48
Joined: Mon Feb 15, 2021 2:54 pm
My RE system: Identically configured pair of Outback Skybox Systems each with 12 - LG 340 panels, and a Discovery 6.5kwh 48V battery, both running as Masters. External CT's, one using L1 CT input and the other using L2 CT input so as to help share load more evenly.
Location: SF Bay, California

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by SHunsader »

Cottonwood,

It's been a few weeks since I've run into this problem, and needed to re-read my post to see what I was thinking then. It looks like I was pretty confident of the load number on the master. Let's apply the same math to your very first snapshot:

PV: 4.9 + 4.9 + 5 = 14.8
Load: 5
System usage: .3 + .3 + .3 = .9

The grid should be getting back 14.8 - 5 - .9 = 8.9 kw. That's 1kw off from what the Grid for the Master is saying that it's giving back. For my systems, it was off by .9 kw. Initially, it sounds like that might be the energy needed by the system, but the loads on my pair weren't that high to need 900w.

I DO believe that part of this error is is a sign issue. You shouldn't be seeing "AC Couple", instead you should be seeing "Powering" which is a down arrow, not UP.

Let me know what you find at the meter and the new screenshot. - Steve
User avatar
Cottonwood
Forum Member
Posts: 10
Joined: Tue Dec 29, 2020 9:32 pm
My RE system: (48) Canadian Solar CS3U-350PB-Ag 350W panels; (3) SkyBox inverters; (3) 14 kWh LiFePO4 battery banks; Kohler 30RESA 30kW LPG generator. We are a rural Kansas farm family moving toward energy self-sufficiency.

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by Cottonwood »

Unfortunately I was away from my system for several hours this afternoon so was not able to conduct your suggested test. I will plan to do so tomorrow. Thanks!
SHunsader
Forum Whiz
Posts: 48
Joined: Mon Feb 15, 2021 2:54 pm
My RE system: Identically configured pair of Outback Skybox Systems each with 12 - LG 340 panels, and a Discovery 6.5kwh 48V battery, both running as Masters. External CT's, one using L1 CT input and the other using L2 CT input so as to help share load more evenly.
Location: SF Bay, California

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by SHunsader »

Cottonwood,
I sent you a PM earlier today (Private Message). I'll be flying to FL tomorrow, definitely out of pocket tomorrow, but I'm sure there are others that may be able to help. - Steve
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BoMagluyan
OutBack Product Management
Posts: 40
Joined: Mon Mar 19, 2018 12:29 pm
My RE system: SkyBox
12x EnergyCell PLR batteries in an IBR3
no PV

Re: Stacked Skyboxes with External CTs, math doesn't add up

Post by BoMagluyan »

We've proven there is an issue with OPTICSRE display of CT data. It's is double-counting PV production from Follower units. The issue will be addressed in an OPTICSRE release in the future.
Bo Magluyan
OutBack Product Management

OutBack Power Technologies, Inc.
An Enersys Company
1628 W Williams Drive, Phoenix AZ 85027 USA
www.outbackpower.com
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