Best Practices for Vehicle Charging with Solar + Powerwall – Tesla Motors Club

Tesla made me complete forms for the incentives.

Obviously, saving money is always preferred, but not a big fan of penny-wise dollar foolish.

I think my ideal scenario is charge the car(s) at off-peak rates and not draw from the batteries as I’d much rather use those to power everything else. Although based on what I’ve seen so far, when the sun goes down and PWs kick in to power the house starting at 100% SOC, I only use about 20-25% power from them before the sun is out again the next day and starts charging them back up to 100%.

Just curious to hear what more seasoned solar + PWs users have been doing.

Do you happen to know if you have discharge requirements. For example because my first two Powerwalls are on SGIP I need to discharge a minimum amount per year (easily achieved for me with my usage).

I started off running advanced/cost saving mode. I then switched to advanced/balanced mode to trigger more self consumption. The downside of self consumption is the roundtrip loses through the batteries. The downside of using the grid storage are the non-bypassable charges. I also ran export limitations (long side story) which pushed me towards more self consumption.

With my previous solar and 2 batteries I was not riding through enough hours to my liking during the time of year when we were running air conditioning. At end of the day I decide I wanted more self consumption during the night hours for a variety of reasons. So I added more solar and battery. I now have 3 Powerwalls and about 17 kW of solar (effectively less but another long side story).

Right now with mild weather I’m charging cars during the day to avoid the round trip through the Powerwalls. This is easy to right now since I’m working from home. My reserved set at 20% but I’m currently not reaching that. It appears that I will have enough solar to fill the batteries before peak once some summer rates hit, likely before part peak during low air conditioning days.

I’ve seen the system discharge to offset car charging during some of the times and other times it didn’t. I suspect this Tesla trying to forecast how much energy it will have left.

Knobs to turn:

Reserve (what is the minimum you want for a power outage)

Advanced Time Base Controls

Price Schedule (you don’t have to follow your tariff exactly). Currently I’m still in winter schedule but I’ve put in peak and part peak hours to bias which hours the system will self consume if it thinks it doesn’t have enough energy in the batteries before solar charging begins (I’m choosing to support the grid as much as possible from to 4 pm to midnight) I noticed when I didn’t have enough solar/batteries it tried to start self consumption as late as possible to minimize the time it was a low state of charge. For example it would stop discharging at 9:00 pm and resume discharging at 3:00 am. At the moment it’s pretty moot because I’m in the period of excess battery and solar.

My recommended settings for you based on your goals:
Time based control/balanced (this will encourage self consumption to the system).
Lower your reserve to the what you are comfortable with
Set your car to delayed charging/departure schedule. This will make it charge at around 3 to 5 am (assuming you have a departure time of around 7 am.

Note: If your system is new you might need to give Tesla time to get data for the behavior to stabililze. When you a change a setting or usage patterns you may need to let the system “settle” or “learn”. I don’t think anyone has official documentation on the exact details but observed behavior is Tesla is trying to be “clever” by predicting consumption and production. It appears to factor in historical data and things like weather forecasts.


May 5, 2021 sally Wood