Is charge on solar logic flawed?

[pmc1]

I have a Tesla solar with powerwall 3 setup. Powerwall is in self powered mode with charge from grid disabled.

During the day when solar is producing, it preferentially powers the house with any excess power going to charge the Powerwall . Nothing is imported from the grid unless production drops below the house load. If solar is producing a lot (more than house and battery want) it exports excess. So far so good.

When I add charge on solar to the mix, the distribution is as follows (see attached screenshot)

• Solar production all goes to Powerwall charging.
• Car charging goes to solar production-house load
• Grid starts importing equivalent to solar production

The net result is that when charge on solar is in use while the Powerwall is charging, it’s really being powered from the grid along with the house. Makes it kind of useless unless I’m missing something.

What would make more sense is that the excess solar power after powering the house is somehow split between car charging and battery charging. The grid should only kick in if the house load exceeds solar production.

Thoughts?

 

[arnolddeleon]

Sustained? Did you let it run a while and look at the accumulated data? Instantaneous readouts can be misleading.

Is the car below the minimum charge level for "charge on solar"? I don't think that's case in the screenshot because only 1 kW is going to the car.

Is the battery below the reserved amount?

 

[pmc1]

Sustained? Did you let it run a while and look at the accumulated data? Instantaneous readouts can be misleading.

Is the car below the minimum charge level for "charge on solar"? I don't think that's case in the screenshot because only 1 kW is going to the car.

Is the battery below the reserved amount?

I’ve only had charge on solar enabled for a couple of days but it has consistently shown this behavior. The charge levels are set at 50 and 80% with the vehicle battery level in the 65% range. The Powerwall reserve was set at 12% so we are well above that.

 

[Matt-FL]

Charge on Solar | Tesla Support

With Charge on Solar, your Tesla vehicle can charge using only excess solar energy produced by your solar system. Learn more about using the Tesla app to set Charge on Solar limits and more.

www.tesla.com

Some quotes on the support page:

'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.'

'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. Solar power and home loads are variables so if you ever want to charge faster, you can simply increase the lower charge limit to a desired range.'
'To maximize solar charging and have enough range, plug in your vehicle during daytime whenever you’re at home. Set the Charge on Solar sun slider at a level that ensures you always have enough range for daily driving if there is not enough excess solar to charge your vehicle above this limit.'

Sounds like if your vehicle charge is below the usual driving, it will charge from whatever means available. Once you reach that level, then any excess solar will charge the car. Excess solar is at least 1.2kw over what is currently being used, which it seems is not available at the time of your screenshot.

I'm not sure how the powerwall charge affects this, but I would prefer house load + powerwall charge over car charge. Once the powerwall is full, then excess solar to the vehicle.

I don't have the tesla charger, but I use an Ubiquiti charger. I setup a time to charge from 1pm - 5pm (powerwalls typically full by 1pm) and set the amperage setting based on my solar production capabilities It is wired and rated to 60 AMP, but I can set it in software to 20 or 30 AMPS to not drain beyond excess solar. Not nearly as sophisticated as charge on solar, but works well enough for me.

 

[pmc1]

Charge on Solar | Tesla Support

With Charge on Solar, your Tesla vehicle can charge using only excess solar energy produced by your solar system. Learn more about using the Tesla app to set Charge on Solar limits and more.

www.tesla.com

Some quotes on the support page:

'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.'
View attachment 1034188

'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. Solar power and home loads are variables so if you ever want to charge faster, you can simply increase the lower charge limit to a desired range.'
'To maximize solar charging and have enough range, plug in your vehicle during daytime whenever you’re at home. Set the Charge on Solar sun slider at a level that ensures you always have enough range for daily driving if there is not enough excess solar to charge your vehicle above this limit.'

Sounds like if your vehicle charge is below the usual driving, it will charge from whatever means available. Once you reach that level, then any excess solar will charge the car. Excess solar is at least 1.2kw over what is currently being used, which it seems is not available at the time of your screenshot.

I'm not sure how the powerwall charge affects this, but I would prefer house load + powerwall charge over car charge. Once the powerwall is full, then excess solar to the vehicle.

I don't have the tesla charger, but I use an Ubiquiti charger. I setup a time to charge from 1pm - 5pm (powerwalls typically full by 1pm) and set the amperage setting based on my solar production capabilities It is wired and rated to 60 AMP, but I can set it in software to 20 or 30 AMPS to not drain beyond excess solar. Not nearly as sophisticated as charge on solar, but works well enough for me.

Thanks for the suggestions. This is happening when the car is above the lower (usual driving ) limit but below the upper limit.

Once the Powerwall is full it behaves as expected: solar powers house first, excess goes to car charging, and any remaining power is exported.

The problem manifests when Powerwall is charging. As you pointed out the numbers are constantly fluctuating as solar production varies, but what appears to happen is when production is moderate it is split between the house and car. A roughly equivalent amount is then imported from the grid to charge the Powerwall.

I’ve tried turning off charge from grid on the Powerwall but to no effect. Given that, maybe what is happening is solar is being dedicated to the Powerwall, with an equivalent being imported for the house + car. Either way, the logic seems wrong as I don’t want to be importing during the day.

I’m using the Tesla charger (not the newest generation) with normal charge time set for 1am.

 

[jgleigh]

Are you sure the numbers in the app are accurate? It seems suspicious that solar/powerwall/grid are all exactly the same. Is your system fairly new?

We see a lot of misconfigured systems with CTs in the wrong spots with new installs.

 

[pmc1]

As far as I can tell they are fairly accurate. I have an independent device measuring the house load and it is pretty close to what the PW is telling me.

I just happened to catch them all equal when I did the screenshot but that's not generally the case. They're usually within +- .2kW or so.