Change in grid draw behaviour when plenty of solar available

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dr-t asked Apr 5, '24

Change in grid draw behaviour when plenty of solar available

I have an ESS installation with two parallel connected Quattros 48/15000, two MPPT RS 450/200 solar chargers and one MPPT 150/45 solar charger. The system is controlled by a Cerbo GX, and I use MG batteries.

I had a burglary where one of the builders who built the shed in which the system is housed stole my batteries, so the system was offline for a few months while I replaced the stolen and damaged components. After I reconnected the system, I noticed that the system was now constantly drawing power from the grid, even when there was plenty of solar power available. This draw was between 600W and 1kW (averaging 700W) - even when there was 18kW worth of solar power available, of which 12kW was being fed into charging my batteries. I asked my dealer to look into it and he did something and now the draw is more in the 300W-800W (averaging 400W) range. The system is never feeding any power back to the grid, not even a few Watts. My dealer says that this is normal and that the draw cannot ever be exactly zero, and I understand from the posts on this forum that this is indeed the case.

However, what is strange is that last summer, before I had the burglary, the system was fluctuating between -150W and 300W when there was plenty of solar power - according to VRM. According to my Carlo Gavazzi meter, the meter was, however, stopped. The "meter stopped" LED was on. And my utility meter was not advancing at all - during the sunny months, it would not advance even by 0.1kWh over the course of a week. So even though the Quattroes were sometimes drawing 300W, sometimes feeding back 150W, it seems that the fluctuations were taking place with high enough frequency that the utility meter registered no net energy consumption.

Now, however, my Carlo Gavazzi meter confirms a constant draw of 300W-800W from the grid, and my utility meter is constantly advancing - even when there is enough solar power to supply all my energy needs twice over. My pre-Victron installation average consumption was about 1.5kW, so this 300W-800W is not a small amount of power draw - when taking into account the overheads of the Quattros and other Victron components and the UPS and the ventilation fans and the fact that I get no solar power on dark winter days, I'm not sure if on an annual average basis, my average utility power consumption is higher or lower now that I've installed all those solar panels than it was before I installed the Victron system.

I've asked my dealer and he says it is what it is, this is the best we can do. But this can't be the case, as last summer, on sunny days, there was no net draw from the grid.

In ESS settings, my Grid setpoint was set to 70W last summer and I had reduced it to 50W more recently. I have now reduced it still further to 0W, but there is still net draw from the grid when it isn't needed.

However, in the meantime, we have upgraded the firmware of all my devices a few times. For example, my Cerbo GX is now running firmware version 3.30, whereas before it was running an earlier version (unfortunately, I do not know which version).

What could have resulted in this change of behaviour? And how can I get the old behaviour back?

Thank you.

grid solar

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Alexandra ♦ commented · Apr 08 at 07:10 PM

@dr_t

Resistance is the key in parallel set ups to get balance.

Makes sure everything is torqued.

Sometimes repairing wiring is not enough. Needs to be replaced if there are kinks/bends.

DC wiring needs to be exact.

AC wiring needs to be long enough to help balance it out.as well.

Make sure everything is updated to the latest FW. That way it is all current.

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dr-t Alexandra ♦ commented · May 15 at 11:04 AM

Thank you very much for your very kind and helpful reply.

All the firmware is updated to the latest version.

It is not very easy to check wiring length because everything is in ducts and conduits. We checked the DC cables between the batteries and BMS. They are all between 2.03m and 2.06m long. I think the AC wires are not of equal length but it's a nightmare to change them now, or even to measure their lengths.

However, any mismatch is the same as last summer - when there was no net draw from the utility for extended periods of time (a week at a time is the longest I tested for - the utility meter did not move even 0.1kWh) when there was enough sunshine. However, now there is a constant net draw from the utility.

I have permitted grid feed-in of up to 1kW and set the grid setpoint to -170W. However, even now, there is a net draw from the utility, although I have reduced it from 800W to about 100W.

I switched off the utility altogether during the solar storms and it turns out I do not need it at all on most days, as there is more than enough solar power. During the solar storms, I used the generator once, and at the end, I manually re-connected the utility. Is there a way in ESS mode to ask the Cerbo to have the utility completely disconnected unless battery charge level falls too low - and in those cases to treat utility power just like another generator, i.e. either for the Quattro to switch on its internal relay, or for the Cerbo to control an external contactor using one of its relays to start the utility as a "first" generator (I still want to have my generator as a "second" generator backup)? If not, is this not a feature that would be useful?

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Modifications Space

Node Red Space

Answer 1 · 2024-05-15T20:33:05Z

Alistair Warburton answered · May 15 at 08:33 PM

If you take the grid away with any external method that will fix the draw issue, not that I disagree with anything said earlier mind. Obviously your system works when Islanded.

You could try ignoring AC input but I don't have ESS enabled so that is just a suggestion, that at worst, will not hurt anything if it doesn't work.

If you are not using DVCC for anything else you can use that system to directly control the AC charger. However if you are also using AC coupled solar that isn't an option because the frequency has to be able to change in order to control the PV inverter/s, which it cant if the grid is also connected. (Unless you export of course... Why are you not doing that? the new G100 rules are great, install and inform up to 16A/phase I think. Do not do that without checking, I could be wrong.)

You can manage this stuff from Node Red, running on the Cerbo but these are just suggestions and would need careful consideration along with far more detailed information about your setup/equipment before you could call them 'potential options' let alone a plan!

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