Guru
Joined: 21/06/2018
Location: AustraliaPosts: 1294
| Posted: 02:28pm 01 May 2026 |
A lot of water under the bridge but time for an update on the Sig system. I admit I was a bit naive after being told that if my system is set to self consumption, I would not get any more energy bills. The batteries are 48kWH and the inverter is 25kW. I have never exhausted the batteries or overloaded the inverter - either could require the grid to supply any deficiency at a cost.
During the March to April billing period, we received an account showing that we imported over 28kWH, over 16kWH was at peak rates. The Sig system showed only around 50 to 80 watts were imported daily- a big discrepancy. So someone is lying and I was determined to find out who or what was the issue. I talk to the Sig supplier who tells me to talk to the energy provider who tells me to talk to the SA Power Network distributors - the meter owner, going in circles.....
I got nowhere so eventually developed a theory. We no longer have net metering as there are different times and rates for importing and exporting. So how does an AC coupled system with the grid and house integrate together. The concept of self consumption is that our house tries to import energy from the grid but the battery inverter system then generates an equal amount of energy so no energy is imported.
But the mains voltage is varying by the second and the Sig (or any AC battery system) never knows if the next instant will be higher or lower or the amplitude. So in effect it is playing chasey and it tries to find a balancing point (on a moving target) and toggles slightly importing and exporting that in theory is a great plan.
The crap part is that imported energy accumulates in proportion to tariff time in an import register but the small toggle then to export accumulates in the export register. Remember the cost accumulates at around 10 times greater for an imported watt to an exported watt due to the almost non existent FIT.
Note when exporting excess solar although we are still chasing and trying to balance to a moving target, a bit more energy this cycle a bit less next cycle doesn't matter as the net all accumulates correctly in the same direction.
I asked our energy provider for a spread sheet of energy over the last few months and received it today and it was very revealing. My theory looks to be correct - my Sig is lying to me. It appears that the Sig uses net metering and if a small import is followed by a small export it cancels and there may be a small remainder each day of 50 - 100watts, nowhere near the ~1kW for the day reported on the spreadsheet.
When I revealed what I had found to SA Power Networks hoping they could suggest a cure they agreed about the unfairness but said there is an issue but we have no idea how to resolve it. I am thinking it is important enough to bring up with the energy ombudsman as there are ~ 75,000 battery systems in lil ol Adelaide and if they all behave like mine then the energy companys receive ~$1,000,000 dollars each month more than is fair from us suckers. I am not suggesting anyone set out to dud us but by the nature of how the system is set up and behaves was lucky to be in their favour. If it was in my favour I would not be posting about it in public
There would be few with a large battery and inverter like me who only want to have capable self consumption and maybe to return any excess solar to the grid for a pittance to help with the supply charges. In my case I expected to import zero and if it remained like that for 12 months I would say goodbye to the grid. That was why I had to understand why I was still receiving charges for imported energy.
Other than the above issue the Sig system itself has never missed a beat. I contacted Sig and suggested it would be nice if the system would automatically galvanically disconnect from the mains when not exporting and only reconnect after the battery is approaching full charge and there is excess solar to export and then reconnect again.
I'm not expecting them to do anything but you never know if enough people complain, at least they should fix the imported energy readout.
Sorry for the verbose post.
Edited 2026-05-02 00:35 by wiseguy