question

hominidae avatar image
hominidae asked

how can I force chargeing from PV only / disable feed-in until batteries are full

Hi Folks,

during winter season, daily PV yield is not sufficient to fully recharge the batteries, especialy when direct consumption is also part of the usage.

My DSO does allow PV feed-in but does not allow chargeing from grid.

Using battery life alone, it would take weeks until a SoC of 100% can be reached, because discharging would still be allowed.

I'd rather find a solution to use almost all (and only) PV for chargeing, as well as prevent discharging until a SOC of 100% has been reached.

What would be the best option, given that I have Node-Red and the Cerbo with activated mqtt at hand?

My first guess is, to set the grid-setpoint to the value of the actual grid-consumption (so direct usage of PV will not take place, as all PV will be used for chargeing the batteries) .... do this until SOC of 100% has been reached, then return to a standard grid setpoint.

When minimum SOC has been reached, restart that procedure.

cerbo gxNode-REDgridbatterylife
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

3 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Hominidae,

Why not just manually set the ESS minimum discharge SOC to 95% so that the PV will always first go to charging the battery, and it won't be discharged below that (unless grid fails).

cleanshot-2022-11-30-at-123545.jpg

Then set the MultiPlus charge current limit to 0A so that it doesn't charge the battery from the AC input (but still allows pass through to the loads) as required by your DSO?

I think that should cover your limitations there?


cleanshot-2022-11-30-at-123545.jpg (100.2 KiB)
2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

hominidae avatar image hominidae commented ·

Hi @Guy Stewart (Victron Community Manager),

thank you very much for your answer.

I forgot to mention, that all my loads as well as the PV inverter are on AC-In. So what you suggested will not work for charging the batteries, won't it?. The Victron system is a retro-fit / add-on as the AC coupled PV has been installed several years ago.

Hence my idea of of "tricking" the ESS system of the GX into a state where the grid setpoint would allow for PV energy to be available to charge the batteries. If the power available for charging is deemed less than the actual power available from PV (i.e. calculated as 90% of actual PV), there will be no (noticeable) consumption from the grid for charging the batteries.

So the value given at the grid-setpoint would be calculated as "actual Grid Power + 90% of actual PV power". This would prevent feed-in and leave that 90% of PV for charging.

I would need some extra rules to take into account the SoC and allow discharge again, once 100% has been reached, then reopen the procedure when min-SoC has been reached ... and again, and so forth.

Maybe, what I have in mind is a simpler version of this: https://community.victronenergy.com/idea/116815/batterylifeai-and-forecast-based-battery-charging.html


0 Likes 0 ·
thomasw-1 avatar image thomasw-1 commented ·

This is exactly that what my "BatteryLifeAI" does in dependency of PV forecast.
It would be nice to have such feature in Dynamic ESS (assuming that the set point issue gets fixed and not consuming 4kW per day because of system design weakness).

0 Likes 0 ·
Richard Weir avatar image
Richard Weir answered ·

I tried what Guy suggested because i have a similar problem. I have PylonTech batteries and no solar and 2x multi 70A 48v. I charge my batteries at night and find that they are periodically discharging back to the grid when i don't want them to do. today I lost 13.5KWhs to the grid which is half of my batter capacity!! I really need some help on this please.

img-8650.png


img-8650.png (327.9 KiB)
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

hominidae avatar image
hominidae answered ·

...I did find a solution, finally.

This is, on general, what it does - implemented in Node-Red:

  • to exempt a certain load - or load level - from being backed (discharge) by the battery,
    the gid-setpoint is set set to that level.
    I am using this successfully with loads going to my heat pumps and EVs, so the loads for the rest of the house will be backed with ESS.
  • in order to disable discharging the battery completely for some time (i.e. until a certain SoC is reached while chargeing - either from grid or from PV, set "limit inverter Power" in ESS to zero watts.
2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Richard Weir avatar image Richard Weir commented ·

thanks ill try that - it didn’t work. All that happened is that it locked the batteries at 100%

0 Likes 0 ·
hominidae avatar image hominidae Richard Weir commented ·

Well, hard to tell with that little information, but when it "locked" the batteries at 100%", then - as it is my best guess - you forgot to disable the "limit inverter power" switch or to set the allowed inverter power to a level above 0 watts at some point in time later, after the batteries had been charged successfully.


Edit: here is an example, where you can see that the Battery (orange - discharge at this time) follows the load of the house (yellow), while the grid (red) follows the load of the heatpump (violet).

1703611564515.png

0 Likes 0 ·
1703611564515.png (89.9 KiB)