Trying to understand the Grid Zero algorithm

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VHL
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Joined: Sun Mar 29, 2020 10:18 am

Trying to understand the Grid Zero algorithm

Post by VHL » Sun Mar 29, 2020 10:34 am

Hi there,
I am running a setup with 2 stacked Radians connected to the grid but in Grid Zero mode because we are not allowed to back-feed. Things more or less behave like expected except for the fact that the system always uses a considerable amount of grid power even if the batteries are fully charged and the PV could produce more energy than needed by the loads. In this situation the PV input is automatically reduced to between 40 and 60% of the load and mixed with grid power. If I am around and have time to take care for it I drop the grid input manually for the time of surplus PV which greatly improves my energy balance for the day. Obviously this situation defeats the purpose of an automated solar system. Can Grid Zero detect when no grid power is necessary and drop it automatically?
Thanks in advance!

fcwlp
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Posts: 295
Joined: Wed Jan 22, 2020 9:40 am
My RE system: GS8048A, FM80 w/3,600 W PV Fixed, FM80 w/2,700W on Zomeworks tracker, Mate3, 24 Trojan 2V L16 1100AH @ C20, Grid-Tied with Kohler 14RESA LPG Generator and MEP-803 Diesel if needed
I also install and maintain grid-tied and off-grid systems, details will be given for these system if required
Location: 80 miles NE of Phoenix at 5500'

Re: Trying to understand the Grid Zero algorithm

Post by fcwlp » Mon Mar 30, 2020 10:39 am

Hi VHL,
VHL wrote:
Sun Mar 29, 2020 10:34 am
Can Grid Zero detect when no grid power is necessary and drop it automatically?
The answer to your question is no, but it can be reduced to ~200W per hour. I would take a look at your Grid Zero settings on your inverter. On OpticsRE, for each of your inverters look at the bottom of the "Battery Charging" tab. There you can adjust the DOD DC Volts and DOD AC Amps. The default for the DOD Amps is 5Aac, which may be your issue.

I can sell back to the grid but have an on-peak rate plan that increases cost per kWh from 3pm to 7pm, so i switch to Grid Zero at 4pm currently. For my system with a 48V 1,100AH FLA Battery I use a DOD Volts of 48Vdc and a DOD Amps of 30Aac.

pss
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My RE system: 8330 watts in three strings, Flexmax 60 x 3, Radian 8048A, GSLC load center, Mate 3S, Hub 10.3, FN-DC and 900 Amp, 48V Trojan T105-RE battery bank.

Re: Trying to understand the Grid Zero algorithm

Post by pss » Mon Mar 30, 2020 12:43 pm

My system is three years old. In 2017, grid zero connections would show on Optics are 100 watts off and on. Then after several software updates to the Mate 3's and the Inverter, they started showing as 200-500 watts being used from the grid every hour, regardless of the PV, the battery SOC or load. When I contacted OB support, I was told this is the normal behavior. That to operate in Grid Zero, the system is constantly "connecting" to the grid to make sure its there and operating if needed. The problem was, at up to 500 watts per hour x 24 hours x 30 days, that's a lot of grid use that could be supplied by PV. And any extra PV you could be generating is not created if your loads and battery needs have been met. It is wasted potential. You may find you can do better when your batteries are charged and there is still PV available to disconnect from the grid, run off PV and batteries for a few hours, even past sundown and then go back to Grid Zero if you use grid in the darkness hours. You are going to have to play around some.

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Greg T Fordan
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My RE system: Radian, FM80, FNDC, 48V batt bank

Re: Trying to understand the Grid Zero algorithm

Post by Greg T Fordan » Mon Mar 30, 2020 4:01 pm

VHL,
Along with FWCLP's advise, ensure the Offset Enable is Y.
You can do this in Optics or in MATE3s.
Greg T Fordan
EngTech
Outback Power Technologies

fcwlp
Forum Guru
Posts: 295
Joined: Wed Jan 22, 2020 9:40 am
My RE system: GS8048A, FM80 w/3,600 W PV Fixed, FM80 w/2,700W on Zomeworks tracker, Mate3, 24 Trojan 2V L16 1100AH @ C20, Grid-Tied with Kohler 14RESA LPG Generator and MEP-803 Diesel if needed
I also install and maintain grid-tied and off-grid systems, details will be given for these system if required
Location: 80 miles NE of Phoenix at 5500'

Re: Trying to understand the Grid Zero algorithm

Post by fcwlp » Mon Mar 30, 2020 4:28 pm

VHK, in the spirit of myself understanding the Grid Zero algorithm a bit more, I sacrificed the sale of some kWh to the grid. We currently have a very good PV day here in AZ at 5,500 feet so there was plenty of PV.

From 2pm to 3pm, I ran with moderate loads and consumed 1.5 kWh with 0.3 kWh coming from the grid.

From 3pm to 4pm, I ran with some high loads and consumed 4 kWh with 0.6 kWh coming from the grid. During this period, some of the values I recorded for instantaneous power use were:

Load, Batt, Grid
1.7, 1.4, 0.3
2.6, 2.3, 0.3
3.0, 2.8, 0.2
5.0, 4.8, 0.2
5.6, 5.4, 0.2
5.7, 5.4, 0.3
6.1, 5.2, 0.9
6.8, 5.5, 1.3
7.2, 5.4, 1.8
7.5, 6.1, 1.4

These are with DOD Aac set at 30A or 7.2 kW. The Battery V ranged from 49.9 to 53.9 during the testing, again with a 48V 1,100AH FLA battery bank. So for this setup, I got minimal draw from the grid until I started hitting a load of 6.0 kW or 25 Aac.

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