# Charge only using solar power



## ER1C8 (Jan 1, 2018)

I am having solar and 3 Powerwalls installed at my new house. I'm wondering if anyone has found a way to only charge their Tesla when there is solar production. If I come home at night and plug in, my model 3 will deplete my Powerwalls rather quickly. In the UK they sell an EVSE (Zappi) that tracks solar production and ramps up and down charging but it's not sold in the US. It looks like Juicebox used to sell a Juicemeter that did he same thing, but they don't make it anymore. I can't believe Tesla doesn't have this feature.


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## MelindaV (Apr 2, 2016)

assuming your state does net metering, your whole house will benefit from any excess solar no matter the time of day unless you have a dedicated meter/system just being used/powered for the car and nothing else.


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## ER1C8 (Jan 1, 2018)

My state does have net metering. The problem is, if I run Powerwall in self power mode. When I get home at night after my 80 mile commute with no sun out my car will mostly drain the Powerwall. If the car would just wait to charge until there was sun generating energy the car would get power from the panels not the Powerwall. I just feel like charging a battery to only drain it to charge a different battery is kind of pointless. I could turn off self power mode but that would remove one of the benefits of Powerwall.


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## garsh (Apr 4, 2016)

ER1C8 said:


> My state does have net metering. The problem is, if I run Powerwall in self power mode. When I get home at night after my 80 mile commute with no sun out my car will mostly drain the Powerwall. If the car would just wait to charge until there was sun generating energy the car would get power from the panels not the Powerwall. I just feel like charging a battery to only drain it to charge a different battery is kind of pointless. I could turn off self power mode but that would remove one of the benefits of Powerwall.


If you can't find an ideal solution, then a semi-useful workaround could be to set the car's scheduled charging to begin around sunrise.


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## Ed Woodrick (May 26, 2018)

I'm confused. If you get home at night and leave in the morning, when do you expect the car to charge from solar?
Electric providers use batteries for this explicit reason.
At 80 miles, you will indeed drain your batteries.
Do you have enough solar to charge the car?


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## Bigriver (Jan 26, 2018)

ER1C8 said:


> I just feel like charging a battery to only drain it to charge a different battery is kind of pointless.


I totally agree. Not only is it philosophically pointless, it adds another inefficiency as there is a small loss as energy goes in/out of the power wall. (My estimate is that the power wall inefficiency costs about 40 kWh a month for me.)

I have solar and 2 powerwalls, and as inelegant as it is, I usually turn off self-power mode while I charge. I actually find myself turning off the self power mode for other occasions. For example it is off right now (i.e., I'm running my house on the grid) because the forecast for today and tomorrow is to be quite cloudy. My solar production will be pitiful. I'd rather use whatever solar I get to fully replenish the powerwalls just in case of a grid power outage with the upcoming weather system. Of course the power wall is supposed to have a storm mode that it would automatically do this, but I've never had that kick in.

My favorite thing, although this doesn't happen often, is to charge in the middle of the day on a very sunny day. That takes some ratcheting too, tho, because I need to wait until the solar kW are high enough and need to lower the amps to the car, as my peak solar production comes in slightly below 10 kW (for my 11.97 kW system), and there is still the load from the house.

While it's fun to be fully self-sustaining, I agree with @MelindaV that net metering makes it possible for the grid to support high rates of usage, and then solar just puts it back to the grid in its own timing.


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## gary in NY (Dec 2, 2018)

Bigriver said:


> While it's fun to be fully self-sustaining, I agree with @MelindaV that net metering makes it possible for the grid to support high rates of usage, and then solar just puts it back to the grid in its own timing.


With my panels running full tilt (3-5kw), the car easily consumes twice as much power (8kw on level 2 charging). To match production, I either have to switch to level 1, or ramp down the amperage on the screen. While a device that would do that automatically would be nice, net metering works well for me. I also find it difficult to time my charging at home to daylight hours.


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## Frully (Aug 30, 2018)

This gets asked from time to time...
A guy used a bit of a hack tricking the wall connector into slave mode, then driving it with a raspberry pi connected to the solar controller to adjust charge to solar production.


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## ER1C8 (Jan 1, 2018)

So to answer some questions. I'm having 12 KWs installed and use the UMC so the 12 KWs in full sun should cover the charging.



garsh said:


> If you can't find an ideal solution, then a semi-useful workaround could be to set the car's scheduled charging to begin around sunrise.


Sadly this seems like the closest I'm going to get. The car and Powerwall use the same app you would think this would be easy to implement.



Ed Woodrick said:


> I'm confused. If you get home at night and leave in the morning, when do you expect the car to charge from solar?


I leave for work at around noon so plenty of day light with the car plugged in.

@Blgrlver I totally agree, completely pointless to charge the Powerwall only to loose the 10% while pulling the power back out to charge the car. There is also the wear and tear on the battery. I'm having three installed. If I could plan charging the car during the daylight I would use a fraction of the Powerwalls capacity to self power over night meaning they would cycle less and last longer.


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## BI_EV_Solar_Advocate (Mar 19, 2021)

Solaredge has 2 ev charging solutions that can be set to only use "surplus" solar power. The 1st is a 7.6 kW inverter with integrated ev charging cable. The 2nd is their free standing ev charger. Both require installation of a wattnode type electric meter that detects when your system would normally begin exporting surplus solar power to the grid and diverts it to the ev charger. I don't know if their free standing ev charger will work with any other brand of inverter.
Another partial option could apply in states that have a large amount of solar +or wind generation. Charging during sunny or windy periods will result in a good % of your power coming from renewable sources. If you can effectively load shift, you could sign up for TOU rates, which is 9a-5p in states with plenty of solar, to lower the cost of charging.


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## BI_EV_Solar_Advocate (Mar 19, 2021)

Certain Fronius & SMA solar inverters can also charge EVs with only surplus solar.


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## Enginerd (Aug 28, 2017)

While experimenting with my system and awaiting PTO, one of my main goals is to avoid exporting excess to the grid... because I'm not supposed to be doing that yet. So in order to sink all the excess into the car, I switch off the Gateway main breaker (to/from the grid) , set the app "Vehicle Charging when Off-Grid" to the current Powerwall charge state, and manually set the car to start charging. There appears to be a PW SOC target tolerance of maybe +/-3%. If the PW's are above that setting, the car charges at about 10 kW and draws them down. When the PW's reach about (target - 3%), primary solar goes to the house demand first, and excess goes to the car. This is exactly what I want... for the car to accept any excess production. When the PW is at (target - 3%) and clouds blot out the sun, I've seen the car stop charging entirely, then resume again when the sun appears.

I wish that this logic was available while on-grid. Sinking the solar straight into the car also eliminates the AC-to-DC conversion for PW storage, then DC-to-AC for the return trip to the car (which converts yet again from AC-to-DC). I don't know what the conversion losses are, but I'm trying my best to avoid them.


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