Charge on Solar

[+SpiceWare]

Tesla's added a new feature that lets you predominantly charge your car using excess solar:

 

Quote

With Charge on Solar, your Tesla vehicle can charge using only excess solar energy produced by your Tesla solar system.

...

Your vehicle will charge from solar and the grid when your current charge level is below the left sun slider. After your vehicle's charge level passes the sun slider, your vehicle automatically switches to only charge on excess solar up to your charge limit.

 

It requires your car, Powerwall, and phone app to have a minimum software version level.  My App is up to date, but both my Model 3 and Powerwall are not so I can't try it out yet.

 

For some reason Model S and X cars prior to 2021 do not support this feature.

[Thomas Jentzsch]

Sounds cool. Can you use your Tesla as battery too?

[+SpiceWare]

21 hours ago, Thomas Jentzsch said:

Sounds cool.

 

For me in Texas it does seem like it would make more sense to send excess to the grid during the day when it's needed to cover peak demand from AC usage, and schedule the car to charge at night when we have excess wind power. I do have net metering though so the power company pays me for my excess solar. For every 1 kWh I send to the grid they pay me the same amount I pay them to draw 1 kWh from the grid, so it doesn't matter financially when I charge the car.

 

For somebody without net metering it would make sense to use excess solar to charge their car rather than give it to the grid for free. Of course they would need to be at home when this occurs for it to be useful.

 

I have read that some people have net metering plans that are also TOU (Time Of Use). The utility pays more for each kWh during the day when demand is high than the customer pays for each kWh in the middle of the night when demand is low.  For those people it would not make sense financially to charge via excess solar.

 

 

21 hours ago, Thomas Jentzsch said:

Can you use your Tesla as battery too?

 

No, Tesla doesn't support V2G. I wish they would as it could be helpful after a hurricane.

 

Tesla CTO JB Straubel On Why EVs Selling Electricity To The Grid Is Not As Swell As It Sounds (Sadly the video they got the quote from is no longer available.)

 

Quote

Tesla CTO JB Straubel is one of the most respected battery experts on the planet, and a few weeks ago we shared an interesting video of him talking about batteries in which he touched on the topic late in the 36-minute video. 

 

Quote

“If we want to actually send energy back from the car to the electricity grid, this gets much more complex, and, you know, that’s something that I don’t see being a very economic or viable solution — perhaps ever, but certainly not in the near term. You know, the additional wear and tear and degradation on your vehicle battery has a fairly high cost, and many of the people and small businesses looking at this today, you know, don’t take into account fully that degradation cost, and also the additional interconnection cost, because if you interconnect your vehicle, you do have regulations that play a part — it has to interconnect in the same way that a solar system would on someone’s home or on a business, which have different standards so that they can protect line operators and people on the grid.”

 

This was back in 2016 though, when batteries were much smaller and more expensive.

[Thomas Jentzsch]

On 7/18/2023 at 6:00 PM, SpiceWare said:

This was back in 2016 though, when batteries were much smaller and more expensive.

It is mostly a matter of math calculations. We know how the batteries degrade quite well now. So if the price you are getting paid extends the degradation it becomes interesting. Plus you have some autarky if you can use the battery for your needs.  

[+SpiceWare]

My Tesla's on the FSD Beta software branch, which often lags behind on updates like the Charge on Solar feature.  It finally showed up with last night's update, so I'm giving it a try.

 

The Sun slider (on the left) is set to 40%, if the charge is less than that the car will charge up to that slider using the grid.  The max slider on the right is set to 80%.

 

Car's receiving 11A

 

Charging the car takes priority over charging the Powerwall. 

 

Some clouds reduced solar output, so car's now receiving 6A

 

A Charge Tip appears if you set the max above 80%. The recommendation used to be a range of 50% to 90%, and I had been leaving mine at 50% since I work at home.

 

 

[+SpiceWare]

The text above the slider changes while you're adjust it:

 

[+SpiceWare]

Since I work from home the day I usually drive the most is the first workday of each month as that's when I drive into Houston for our monthly meeting.

 

This graph shows solar production for the day and where it went:

 

• Blue = used directly by house
• Red = charging car
• Green = charging Powerwall
• Grey = sent to grid

 

As specified on Tesla's page:

 

Quote

Note: Your vehicle may delay the start of charging until there is at least 1.2kW of stable excess solar to maximize efficiency and lifetime of your charging equipment.

 

Which explains why the car stopped charging around 5pm even though it had not reached at 80%.  The car resumed charging the next morning when there was once again 1.2kW of stable excess solar.