Prioritise PV vs Grid

[WyattSmith101]

I have an older system, which is sometimes run off-grid and sometimes grid tied:
Mate 3
2 x GVFX3048E
2 x FX80 48V
24 x 12v200aH batteries (Lead Acid)
6kW PV panels
At the moment I try not to Offset PV because we are charged for doing that. That might change in the near future.

When the load is greater than the PV I connect to the grid and the MATE "shares" the load between the PV and grid. Except sometimes it doesn't, it just ignores the PV and uses the grid.
Is there a way to prioritise the PV over the grid?
(Absorb voltage is set at 57.2, Float voltage at 54.4 and Sell voltage at 52.4)

[Mike Curran]

If your battery voltage is less than your float setting then all your PV will go to the battery, while grid covers the load.

[WyattSmith101]

Today I had 4kW coming in from the panels while off grid. Battery voltage was 52.6. I changed float voltages on both the inverters and charge controllers to 50.4. I then connected the grid. PV dropped to zero and input from grid was 4kW. The battery voltage was 54.4
So it seems that battery voltage higher than float has the opposite effect to what I want.....

[Mike Curran]

Do your FM80s have grid-tie mode enabled?

[EA6LE-ONE]

Today I had 4kW coming in from the panels while off grid. Battery voltage was 52.6. I changed float voltages on both the inverters and charge controllers to 50.4. I then connected the grid. PV dropped to zero and input from grid was 4kW. The battery voltage was 54.4
So it seems that battery voltage higher than float has the opposite effect to what I want.....

set you inverters battery charger absorb and float 0.4V lower than on the CCs. also try to calibrate the voltage on CCs and inverters when is no sun production and no loads.

[WyattSmith101]

Mike, yes they are and I can sell back but I don’t want to because we get charged for it.

[WyattSmith101]

Eagle, what do you mean by calibrate?

[EA6LE-ONE]

on the inverters and CCs you can calibrate the battery voltage to have all reading the same value.

[Mike Curran]

Mike, yes they are and I can sell back but I don’t want to because we get charged for it.

So, with grid-tie mode enabled, are you saying that connecting to grid causes your FM80s' output to drop to zero? Or are you disabling grid tie to avoid selling? Because with grid-tie disabled I suspect that might be causing what you're seeing.

If that's the case you might try setting your inverters' AC input mode to generator instead of grid. That setting would prevent selling and possibly allow your FM80s to continue producing.

[WyattSmith101]

Mike, no I can sell without any problems but in certain circumstances when there is insufficient pv to cover the load if the grid is connected it will share (I think it’s called support), in other cases it will bypass the pv and use almost exclusively grid.

[WyattSmith101]

Thanks for your assistance everybody. It seems Mike was right. If the battery had been partly discharged before I connect to the grid then the grid powers the load while the battery recharges with pv. Once the battery is charged it doesn’t switch to using pv for the load.

If the battery isn’t discharged before the grid is connected the load is shared between grid and pv.

This will become academic when I’m able to offset the pv from July, hopefully.

Thanks again.

[EA6LE-ONE]

Mike, no I can sell without any problems but in certain circumstances when there is insufficient pv to cover the load if the grid is connected it will share (I think it’s called support), in other cases it will bypass the pv and use almost exclusively grid.

That might happen when you have the float and absorb voltages identical on CCs and inverters, both will try to keep float and if the inverter is trying to push the same voltage which can be marginally higher than CCs then the CCs will dial down the PV production. the fix for that is to have the float and absorb 0.4V lower on the inverter battery charging settings.

[Mike Curran]

Once the battery is charged it doesn’t switch to using pv for the load.

Note Ea6le's post - he has probably identified why your system doesn't continue using PV once the battery is charged. Your inverter float setpoint is too close (or equal) to your FM80 float setpoint, and so the inverter takes over while the FMs back off. To repeat his advice, be sure the float settings on your FM80s are 0.4 volts higher than those on your inverter. That will keep them working.

[pss]

As part of my graduate work towards my Ph.D in Outback product support via this forum, I have read this thread. This is my 2 cents of observations. Outback has cleverly written into the charging algorithm software a period of time labelled "SILENT". When the charge controller or inverter's charger is in this period, there will be no charging or PV harvest, regardless of available PV or GRID power. This UGLY phase (my label for it, not Outback's) generally occurs after a period of absorption charging (possibly float charging too) and is present until the the RE-BULK voltage or RE-FLOAT voltage is reached for the batteries. So if you actually lowered your float , re-float and re-bulk voltages, and you were in the absorb part of the charge cycle, then after that timer is completed, the SILENT period is in effect until the next voltage setting is reached. And if your load is small, it may take a long time for the voltage to drop and therefore a lot of SILENT mode. Some of this behavior is written and illustrated in the Radian manual under the inverter's charger section.

In my case, I keep my inverter's charger on, but I have a low RE-BULK and RE-FLOAT voltage set for my batteries which they do not reach. Then during PV time, my chargers are in grid tied mode, BULK and the voltage rapidly exceeds the SELL voltage. Selling begins ( I have auto grid tie control disabled) and charging continues and SOC 100% is reached. I go to GRID ZERO in late afternoon and voltage spike of batteries finishes things off above the SELL voltage for the day. When PV is no longer present, my batteries run down to about 80% then I reconnect to the grid when utility prices decrease at 9 PM. But because my battery voltage never got as low as the inverter's RE-BULK or RE-FLOAT setting, no charge cycle begins until the next solar PV day starts.

I am starting my 5th year of Outback studies at present. Learning never stops.

[EA6LE-ONE]

As part of my graduate work towards my Ph.D in Outback product support via this forum, I have read this thread. This is my 2 cents of observations. Outback has cleverly written into the charging algorithm software a period of time labelled "SILENT". When the charge controller or inverter's charger is in this period, there will be no charging or PV harvest, regardless of available PV or GRID power. This UGLY phase (my label for it, not Outback's) generally occurs after a period of absorption charging (possibly float charging too) and is present until the the RE-BULK voltage or RE-FLOAT voltage is reached for the batteries. So if you actually lowered your float , re-float and re-bulk voltages, and you were in the absorb part of the charge cycle, then after that timer is completed, the SILENT period is in effect until the next voltage setting is reached. And if your load is small, it may take a long time for the voltage to drop and therefore a lot of SILENT mode. Some of this behavior is written and illustrated in the Radian manual under the inverter's charger section.

In my case, I keep my inverter's charger on, but I have a low RE-BULK and RE-FLOAT voltage set for my batteries which they do not reach. Then during PV time, my chargers are in grid tied mode, BULK and the voltage rapidly exceeds the SELL voltage. Selling begins ( I have auto grid tie control disabled) and charging continues and SOC 100% is reached. I go to GRID ZERO in late afternoon and voltage spike of batteries finishes things off above the SELL voltage for the day. When PV is no longer present, my batteries run down to about 80% then I reconnect to the grid when utility prices decrease at 9 PM. But because my battery voltage never got as low as the inverter's RE-BULK or RE-FLOAT setting, no charge cycle begins until the next solar PV day starts.

I am starting my 5th year of Outback studies at present. Learning never stops.

the only silent period I see is from when absorb is reached and then the battery goes down to float voltage. but I am not selling to grid.