Tesla to add the ability to Charge EV with excess solar

[Gwgan]

Then CoS is not too helpful. I need all the batteries charged. I was using Charge HQ and the car would charge during peak and I kept the PW in backup mode and it would also charge.

This is the first sunny day in weeks where I could see how the CoS system behaves.

With net metering I have no actual spend on electricity but Tesla app has no way to factor that into their AI.

 

[Gwgan]

M3 stopped charging

Maybe because the excess power is not sufficient; it’s not just a value but sufficient over enough time to be expected to remain so. What does the car screen show?

 

[rando]

If excess solar falls below the minimum CoS limit (I think around 1kW) then car charging stops. It doesn't immediately resume once excess returns. I think someone said it checks at the top of the hour. I know my system initially would top off the Powerwalls before starting to charge but these days it seems to alternate between cars and Powerwall until one or both is full. It's possible this is some predictive algorithm that tries to guess how much car charging it can spare and still achieve a full Powerwall before peak rates start.

 

[rando]

Here is an example of the alternating CoS does between powerwall and cars. On this day, Powerall reached 100% just before the peak rates started at 4pm. Also notice the data glitches where it looks like the home has a spike in use each time the car starts charging.

 

[offandonagain]

Also notice the data glitches where it looks like the home has a spike in use each time the car starts charging.

The way CoS is implemented, it separately tracks your home usage (as usual using the solar/grid CTs) and the car charging rate (using Tesla's API that talk to the car). When CoS is active, it will subtract the car charging rate from the home usage. This can lead to some weird data glitches:
- Because two APIs are not in sync, there are timing differences which can lead to the spikes you see.
- If the wall connector is not backed up / not monitored by CTs, the data will look completely off (subtracting no longer makes sense and so you see 0 home usage and vehicle charging rates that are too low). That's not the case for you, just pointing out glitches that other users might see.

These issues are sort of understandable, you'd need a separate CT for car charging to get better data. But I think trying to line everything up on one chart was a bit too ambitious by Tesla.

 

[rando]

I understand ... was sharing an example of the artifacts created by their current solution. The car could sample data more frequently and assure time sync a bit tighter and I think most of these glitches would disappear. It's no doubt not a priority as it's a small portion of their customer base that can and will use and we all know Tesla isn't exactly customer focused.

 

[ArizonaJon]

As I read through this thread, I found Gwgan's post 218 interesting. I an not sure what his buy and sell rates are. I think he is on net meeting and they are the same. If they are the same, maybe the system decides it doesn't care if it uses grid or solar. Anyone know about this?

 

[rando]

He attached his rates in #218 and does have the same buy/sale rates within each TOU period. Still his peak and off-peak are different but unfortunately, his peak period covers nearly 100% of sunlight hours leaving little room for arbitrage.

 

[Gwgan]

Yup. As long as net metering is in effect, which is about another 3 years under contract, I don’t pay for electricity. There is no way to represent that in the app.

There is essentially no arbitrage opportunity.

With CoS the PW will quickly empty if the car needs to charge up to the “all sources” level so now that Winter is coming I set the backup reserve to 90%.

 

[rando]

Set your cars charge schedule to start at 8pm (end of your peak rates). Based on your rate plan, it should then charge to the all sources limit nightly, from grid, not the Powerwall. I think your Powerwall is going to hang out at the reserve until the weekends if you use TBC independent of CoS.