So I've recently had a Powerwall 2 battery installed into my home. It comes with the gateway device that allows for mechanical disconnection from the grid. Therefore in the event of grid power loss, my home can be safely disconnected from the grid, and I can continue operating from the power available in the PW2.
Just last night I decided to try this off-grid functionality and turned off the electricity from the power box outside. I heard the mechanical "thonk" in the gateway device, as my connection was severed from the grid, and the house continued to run on the powerwall... super cool! The next day, my solar generation began (wonderful sunny day), and the battery charged up from 61% through to 98%, when I suddenly noticed that my solar generation went down to zero. I went into my loft to have a look at the inverter and noticed there was an error code on the display (see below).
Digging deeper it seems like my inverter has an AC frequency set range of 49.5 to 50.5Hz (UK grid frequency is ~50Hz), so this made sense as far as the error code was concerned. I also found out that I can adjust this range via an RS232 terminal on the inverter to increase this operating range should I so desire (can be adjusted anywhere from 40 through to 60Hz).
So my questions are:
- Why does my inverter show a frequency fault ONLY when the battery reaches near full charge?
- In the scenario where the grid is not available, where does the excess energy that isn't currently being used by the home, go? I was thinking that the inverter now needs to dump any excess electrical energy that my house isn't using at the time, but finds the external grid closed and therefore causes some kind of internal fault?
- If I were to change the acceptable frequency range on the inverter on the upper end, would there be any negative ramifications in doing so?
- What causes my PV meter to actually detect solar production? Does it require current draw of some form? So either the draw of my home, or the draw of the external grid "taking" my excess energy from me? Without these 2 draws... would the energy need to be dumped to some kind of heat sink and dissipated as heat energy, or would the inverter detect the required draw, and only "pull" electrical energy required from the panels?
Apologies for all the non-technical speak above. I'd appreciate any light that could be shed.
EDIT1: Inverter is a GroWatt 3600MTL - Manual here
EDIT2: It appears from the manual, that the default country when the inverter would have first been setup is Italy. There's a good chance the installers didn't change it from its default. Looking at this firmware software manual for the inverter, it shows that the range (R2 fac High) is 50.5Hz, whereas UK should be 52Hz... that would at least explain the error message.
EDIT 3: According to this chap, the raised frequency may actually be a feature of the Tesla Powerwall2! Looks like it somehow detects the maximum frequency of the inverter sensors, and then raises it's internal frequency to cause grid-tie inverter shutdown. In the video linked, it shows that his frequency went from 50 to 54, whereas mine only jumped to 50.7. Might be that Tesla isn't able to "know" what this upper limit frequency actually is, so it probably begins "probing" around 98% battery full, by incrementally increasing the frequency until it detects an inbound AC shutdown. It might remember that value for next time and allow itself to charge all the way to 100%, knowing it has an proven frequency target for inverter shutdown. Very clever!
EDIT 4: For anyone wondering how the PW2 Gateway works: I've just received a schematic of the work conducted by my installer. Hopefully it's a bit more meaningful to others, than it was to me!