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Fill Powerwalls first, Tesla EV second, extra to grid third?

I’m 99% sure this isn’t possible without manual intervention, but thought it cannot hurt to ask...

Now that great full solar days are here my Powerwalls are filling up before noon each day and then after that extra solar power is being sent to the grid.
Is there a way to leave my Tesla EV plugged in to the wall connector and only charge once the Powerwalls are full, using the solar only? Essentially topping off the EV after the Powerwalls are topped of but before sending power to the grid. Of course the EV could only charge at a rate that matched the solar production minus the house load and ideally not pulling anything from the grid.

The only way I can come close to this now is manually starting the EV charge once I notice the PWs are full at a fixed lower amperage, like 18 to 24, to match the output of my solar but leave some headroom for house load. Not something I want to manually do each day.
 
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gpez

Member
Apr 25, 2019
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658
USA
I personally do not have experience but if you have a gen 2 TWC what your asking for should be possible with some technical know-how and TWCManager (dracoventions/TWCManager).

TWCManager lets you control the amount of power delivered by a Generation 2 Tesla Wall Connector (TWC) to the car it's charging. This can save around 6kWh per month when used to track a local green energy source like solar panels on your roof. It can also avoid drawing grid energy for those without net metering or limit charging to times of day when prices are cheapest.

Due to hardware limitations, TWCManager will not work with Tesla's older High Power Wall Connectors (HPWCs) that were discontinued around April 2016. TWCManager will also not work with Generation 3 TWCs released around Jan 15th 2020. Sadly, gen 2 TWCs are no longer sold by Tesla and may become hard to acquire over time. We don't expect to add support for gen 3 TWCs unless their wireless protocol is reverse engineered by a third party.
 
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Its not possible with only tesla app / etc afaik. There might be some third party solution that would let you do that. It would be nice of tesla would enable that but they currently only enable that setting during "no grid" charging scenarios.
Exactly. I wish in the app there was a setting to only car the Tesla EV after the Powerwalls reach a certain percentage even when the grid is available. Just like the current setting in the app fro when the grid is out.
 

miimura

Well-Known Member
Aug 21, 2013
7,187
7,145
Los Altos, CA
Exactly. I wish in the app there was a setting to only car the Tesla EV after the Powerwalls reach a certain percentage even when the grid is available. Just like the current setting in the app fro when the grid is out.
With the information Tesla has in the cloud from the Powerwall and the car, they could easily implement a feature for the car to absorb the surplus solar power that would otherwise go to the grid. I really wish they would do it.
 
I’m 99% sure this isn’t possible without manual intervention, but thought it cannot hurt to ask...

Now that great full solar days are here my Powerwalls are filling up before noon each day and then after that extra solar power is being sent to the grid.
Is there a way to leave my Tesla EV plugged in to the wall connector and only charge once the Powerwalls are full, using the solar only? Essentially topping off the EV after the Powerwalls are topped of but before sending power to the grid. Of course the EV could only charge at a rate that matched the solar production minus the house load and ideally not pulling anything from the grid.

The only way I can come close to this now is manually starting the EV charge once I notice the PWs are full at a fixed lower amperage, like 18 to 24, to match the output of my solar but leave some headroom for house load. Not something I want to manually do each day.
That is exactly the problem I have--I don't want to send anything to the grid. I'd rather "store" that energy in the 2 EVs in the garage for travel purposes. This manual process should be a fix from Tesla for the app to make this matching automatic: if solar is covering normal house demand, excess solar should automatically go into the EV until it reaches the set limit for the car charging. Only after that should the grid receive energy. The manual process I assume you use is to lower or raise the car charging amp settings and that requires constant attention. That should be automated.
 
They do have the ability to do that since there is some sort of communication between the UMC/wall connector and the gateway. I know this because in off-grid mode you can set a limit for how much power (in % of Powerwall capacity) is allowed for charging. Once the Powerwalls get down to that state of charge, the amps the car is using to charge are adjusted to match the excess solar above house utilization.

This only happens when the grid is out. It would be nice to be able to trigger that behavior when on-grid (effectively setting it so no energy from the Powerwall can be consumed).
 
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This is something I plan to tackle once I get PTO. My plan is to use a Zigbee device to talk to my meter, then use OpenEVSE charger for charging. That way I can charge based on the current excess going back to PG&E. I do not have powerwalls, but basically the same premise. I will also try to interface with my pool equipment and have been looking into smart thermostats etc. Its really too bad that Tesla does not already have this working with existing software, or anyone else for that matter. I seem to see a lot of people looking for this functionality and up to this point have not been able to find a simple way to do it. At first I thought I could do with the Tesla API, but this does not allow changing charging current. I have yet to spend much time on it, but from general research looks like it could be done. The downside is, it would be difficult to setup and you would need to run a server to control it all.
 
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This is something I plan to tackle once I get PTO. My plan is to use a Zigbee device to talk to my meter, then use OpenEVSE charger for charging. That way I can charge based on the current excess going back to PG&E........
Keep us informed. I am using a Rainforest Zigbee device just for data. With NBCs I would like to have a similar system. I currently have been using a crude system that controls a relay to turn on my EVSE when solar hits a kW setting.
 
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I've been watching these Zappi chargers in the UK for a while now. I think they could do what you'd like.


I think they've got their own CT clamps and they look for excess flow and when they see that they adjust your charge rate. So in theory if the CTs where on your grid ties and could see power leaving your house they'd compensate by charging your car.

I may be totally wrong BTW.
 
Keep us informed. I am using a Rainforest Zigbee device just for data. With NBCs I would like to have a similar system. I currently have been using a crude system that controls a relay to turn on my EVSE when solar hits a kW setting.
How is the Rainforest working for you? I have seen some complaints of dropped connections to the meter. I have been looking at the Universal Devices isy994, its more expensive but looks to have many features. I have many years programming experience, but never done any home automation stuff, so still trying to see how all this stuff can work together. In an ideal world, I would like to create my own app, that could track usage, track production, and help balance out loads. Once I get going I will post updates in a new thread.
 
I wish this feature would be implemented too. I'd prefer to top the car off with whatever solar isn't needed to fill the PW until he sun goes down. It may not get the car to 90%, but that just less sent to the grid then pulled back later in the night.

Even being able to adjust the charge amperage via the phone app would be helpful. I wonder why they left that feature out of the app.
 
I’m 99% sure this isn’t possible without manual intervention, but thought it cannot hurt to ask...

Now that great full solar days are here my Powerwalls are filling up before noon each day and then after that extra solar power is being sent to the grid.
Is there a way to leave my Tesla EV plugged in to the wall connector and only charge once the Powerwalls are full, using the solar only? Essentially topping off the EV after the Powerwalls are topped of but before sending power to the grid. Of course the EV could only charge at a rate that matched the solar production minus the house load and ideally not pulling anything from the grid.

The only way I can come close to this now is manually starting the EV charge once I notice the PWs are full at a fixed lower amperage, like 18 to 24, to match the output of my solar but leave some headroom for house load. Not something I want to manually do each day.
You need an intelligent charger such as myenergi Zappi to do this
 
I have wanted this for about two years. If you look at the release notes of the latest version of the car software 2021.12.25 it states it can now do this but only while off-grid.
"Your vehicle coordinates with Powerwall for enhanced charging during a power outage, without exceeding the energy and power capabilities of your Powerwall system. Powerwall continuously responds to the changing power needs of your home and will slow or stop your car's charging, keeping your home loads powered. During a power outage, your car will charge from the Powerwall whenever it is above the threshold set in the Tesla mobile app. You can change this threshold to balance your home and transportation energy needs, putting you in full control of your energy ecosystem. Powerwall can also use surplus solar to charge your vehicle during an outage if you keep your car plugged in while the sun is shining."

It has done the "slow or stop charging based on set threshold" thing for a while but what's new in this release is the " use suplus solar to charge". It used to get to the threshold then stop, now it seems like it will start charging again when the Powerwalls are above the threshold. I have not tested it out yet and it only works off-grid. Hopefully this means an option to do this while on-grid is coming soon.
 
Is there a difference in efficiency between charging at a reduced rate versus the maximum rate? I’ve been experimenting with lowering the amps in my Model 3’s charging UI so that I charge at 3-5 kW, and then I manually start/stop charging from the Tesla app during times of the day when I’m only charging via excess solar and not pulling from the Powerwalls. I have a gen3 TWC so it’ll be nice if Tesla implements this behavior automatically while on-grid like @Er1c* and @morph3ous discuessd.
 
I have heard there is an efficiency difference between L1 and L2 charging but no idea if lowering your amps while charging a 240V changes the efficiency.
I asked an EE colleague and they told me that there shouldn’t be any efficiency difference in charging my car at any of the amperage settings that the TWC supports. The efficiency has more to do with energy conversion, which is why there’s a difference in efficiency between 120V and 240V charging like you mentioned.

I’d still like to understand more, in particular how the energy flows from the panels > inverter > Powerwall > loads like my car charging at home. For instance, with the way I’m charging my car currently by limiting the amperage and only charging during times when I have excess solar production, is that energy going directly from the inverter to my TWC or does it “pass through” the Powerwalls to some extent where there’s any effect?

Disclaimer: I’m not an EE. I know how to plug things in, unplug them, and often, break them.
 
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Tesla should be able to add this.

We mainly just need a (auto) toggle next to charging options to dynamically set the speed.
Though you could still have excess solar even after maxing out the carr charging, so excess beyond the draw would still need to go to the grid after PWs are 100%. (16kW PV+).

If the GRID is off, then this does work as you seem to be requesting, any excess solar goes to the plugged in EV and the amperage throttles as needed to balance against the production.
 

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