Staying below 100%

[Myke Hines]

I’ve recently installed my system but I’ve already wished there was tighter integration with my Model X. I wish my car was smart enough to start charging when the PW get close to 100% and stop charging when I’m 10% from my reserve (so that I can get through the night without the grid).

It would also be great if it wouldn’t charge at all if the next day is predicted to be cloudy.

It seems you could handle this all via the Tesla APIs but hopefully it will be supported via the app some day.

 

[Shygar]

That is the nice thing, there's API's for all of this to play nicely and smarter in the future. I expect more of this to come by Tesla.

 

[ewoodrick]

It sounds as if you want the car to only charge from the utility or that you don't have enough power generation and storage to support car charging?

I don't think that many people would want their car to stop charging, unless you are detached from the grid. In which case it definitely sounds as if you don't have enough generation/storage.

 

[MorrisonHiker]

I was just wishing for this feature (once again) over the weekend. It wouldn't be hard at all for the cars to hit the Powerwall APIs and see if/when they should charge. They could also adjust amps or charging times to try respond to solar production if charging during the day.

 

[Myke Hines]

It sounds as if you want the car to only charge from the utility or that you don't have enough power generation and storage to support car charging?

No I only want the car to charge via the Powerwall system, I don't want it pulling from the grid. The issue with a 100kwh Model X pack is that it's vastly larger than a Powerwall system. So it can be used to help offload any energy once the Powerwall gets full. I don't really care if my car is @ 60% vs 80% - but I do care if:

- my car is at 50%, the Powerwall is 100% and the solar system is pushing it's power to the grid.
- my car pulls 20kWh and drains the Powerwall when it's cloudy tomorrow

 

[miimura]

No I only want the car to charge via the Powerwall system, I don't want it pulling from the grid. The issue with a 100kwh Model X pack is that it's vastly larger than a Powerwall system. So it can be used to help offload any energy once the Powerwall gets full. I don't really care if my car is @ 60% vs 80% - but I do care if:

- my car is at 50%, the Powerwall is 100% and the solar system is pushing it's power to the grid.
- my car pulls 20kWh and drains the Powerwall when it's cloudy tomorrow

If you have Net Metering, what you're asking for is illogical. I have Powerwalls and I set them up with the Advanced - Time Based Control -Balanced feature. It will charge and discharge the Powerwalls to minimize my total electric bill. If I choose to charge my car during the Peak rate period, it will try to satisfy that demand with Powerwall energy until it hits the Reserve % setting. If I charge my car during the cheap Off-Peak time, then it will not do anything and the car will draw from the grid.

If you don't have Net Metering, then describe you utility billing situation and we can help you figure out the best way to use the Powerwall.

 

[Myke Hines]

If you don't have Net Metering, then describe you utility billing situation and we can help you figure out the best way to use the Powerwall.

I do have Net Metering but I want to consume my own green energy. I want to prevent pushing energy to the grid that I could have consumed myself via the car.

 

[miimura]

I do have Net Metering but I want to consume my own green energy. I want to prevent pushing energy to the grid that I could have consumed myself via the car.

Do you have Time of Use utility rates? If not, then the warm fuzzy green feeling of using your own solar power has little cost. I would suggest you look into the thread below that allows you to vary the HPWC pilot signal to follow your solar export. Near the end of this thread, there are people actually using it that way.
New Wall Connector load sharing protocol
Then you could use the Powerwall in Self-Consumption mode and it will automatically power your house through the night and avoid grid draw.

In theory, Tesla has the grid draw data from the Powerwall energy monitoring system, so they could command the car to soak up the surplus solar if it was plugged in. If they exposed the ability to change the car's charging current through the API, it would be possible to do it on your own with a RaspberryPI, reading from the Powerwall API and sending commands to the car.

 

[Bigtanuki]

No I only want the car to charge via the Powerwall system, I don't want it pulling from the grid. The issue with a 100kwh Model X pack is that it's vastly larger than a Powerwall system. So it can be used to help offload any energy once the Powerwall gets full. I don't really care if my car is @ 60% vs 80% - but I do care if:

- my car is at 50%, the Powerwall is 100% and the solar system is pushing it's power to the grid.
- my car pulls 20kWh and drains the Powerwall when it's cloudy tomorrow

Mike,

I completely understand your logic. I did just exactly what you are describing for months prior to getting the TOU update on my two PWs. Whenever I approached 100% on the battery during the solar production period I used my Model S battery as a "surge volume" to make my usage more "green". I did have TOU and NEM at the time but not an EV TOU rate. I reset my MS charging rate not to exceed the output of my solar/battery combination and manually started charging to bring down the SOC on the battery to a level that would still allow full battery supply throughout the night. That system worked well but was VERY manual and a serious PIA. When I finally managed to get PG&E to swap me to an EV TOU rate I went with the software solution and just fed back into the system using the Tesla software. I've been reducing my feed back into the grid by using a modified "peak rate" period to force the battery to start discharge sooner and maintain longer in the evening. By controlling the length of the peak period and reserve level I've been able to minimize, but not eliminate, my sell back without having to do a bunch of manual operations. I do force the car to charge at off peak rates because they are so low, relative to peak rate here in PG&E territory (~.12/kWh vs ~.48/kWh). I realize that I'll be making seasonal adjustments but that's better than doing it every day.

Having worked in a power plant for PG&E for 28 years I have a bit of experience with grid ops and you should know that taking "some" load in the wee hours probably helps the environment a bit by reducing the up/down cycling of the power plants in the system which causes more inefficient operations and potentially more GHG emissions. It's a pretty obscure connection but hey, we are looking to make a difference with our battery systems however small right?

 

[MorrisonHiker]

Mike,

I completely understand your logic. I did just exactly what you are describing for months prior to getting the TOU update on my two PWs. Whenever I approached 100% on the battery during the solar production period I used my Model S battery as a "surge volume" to make my usage more "green". I did have TOU and NEM at the time but not an EV TOU rate. I reset my MS charging rate not to exceed the output of my solar/battery combination and manually started charging to bring down the SOC on the battery to a level that would still allow full battery supply throughout the night. That system worked well but was VERY manual and a serious PIA. When I finally managed to get PG&E to swap me to an EV TOU rate I went with the software solution and just fed back into the system using the Tesla software. I've been reducing my feed back into the grid by using a modified "peak rate" period to force the battery to start discharge sooner and maintain longer in the evening. By controlling the length of the peak period and reserve level I've been able to minimize, but not eliminate, my sell back without having to do a bunch of manual operations. I do force the car to charge at off peak rates because they are so low, relative to peak rate here in PG&E territory (~.12/kWh vs ~.48/kWh). I realize that I'll be making seasonal adjustments but that's better than doing it every day.

Having worked in a power plant for PG&E for 28 years I have a bit of experience with grid ops and you should know that taking "some" load in the wee hours probably helps the environment a bit by reducing the up/down cycling of the power plants in the system which causes more inefficient operations and potentially more GHG emissions. It's a pretty obscure connection but hey, we are looking to make a difference with our battery systems however small right?

It sounds like we've both taken a similar approach. I used Self-powered the first couple of weeks until TBC was enabled. I still switch back to it from time to time and might stay on it if it had a few other settings (such as time periods). I am trying TBC Balanced again and have modified part-peak/off-peak times like you. It works ok but sometimes it just stops charging the PWs for no (known) reason and sends power to the grid...even in part-peak.

 

[Bigtanuki]

It sounds like we've both taken a similar approach. I used Self-powered the first couple of weeks until TBC was enabled. I still switch back to it from time to time and might stay on it if it had a few other settings (such as time periods). I am trying TBC Balanced again and have modified part-peak/off-peak times like you. It works ok but sometimes it just stops charging the PWs for no (known) reason and sends power to the grid...even in part-peak.

I've seen the same thing using Balanced mode. I suspect that the partial peak power to the grid is driven by their algorithm deciding that you'll likely have enough to get through the peak period based on your "usual" usage. I would have to say that it seems to work pretty well. I've only dipped into grid power once when I reached my reserve before the end of peak. We had been using a much larger amount of power that day due to an unexpected completely overcast day. We live at a spot that can change very quickly depending on the depth of the marine layer. Just an increase in depth of a couple of hundred feet more than forecast results in a pretty complete cloud cover. I try not to overreact and remember that it's a long game with NEM.
Since I have and electric vehicle to charge that I puchased after we installed solar I know that I'll always end up paying some at the end of the NEM true up.
My plans are to upgrade solar sometime in 2019 or 2020 with higher power, more efficient panels since I don't have room to expand from 15 panels to 20. My current panels are relatively low efficiency 275 W panels. The newer panels are closing on 400W and that will likely be my trigger for the upgrade. By then I hope to have a third PW (via a referral prize). When I had my PW system installed I had them do all the wiring for a third, stacked unit so once Tesla actually makes enough PW units to send me my referral prize it should be a drop-in installation.

 

[AndreSF]

I do have Net Metering but I want to consume my own green energy. I want to prevent pushing energy to the grid that I could have consumed myself via the car.

You are basically using your own green energy, as long as you generate enough for your needs with your PV system. Not sure why it matters where it stored prior to you consuming it. If you want to be completely self-powered, one PW is likely insufficient.

 

[MorrisonHiker]

You are basically using your own green energy, as long as you generate enough for your needs with your PV system. Not sure why it matters where it stored prior to you consuming it. If you want to be completely self-powered, one PW is likely insufficient.

That's a good way of thinking about it.

One thing I don't like about the app is the Self-powered graph. For example, if I use 20 kWh in the morning before the sun comes up and then 20 kWh more throughout the day, it really skews the self-powered percentage. It might show only 25% to 50% self powered even if I send 80 to 100 kWh back to the grid throughout the day. Yes, I did use some from the grid, but shouldn't I get "credit" for sending excess production back to the grid? I could move the car charging to be at 11 pm instead of 5 am and it would flip the reported results as it would show nearly 100% self-powered throughout the day.

 

[Myke Hines]

This is a very nice solution to half of my problem:

 

[CA-Gbm84]

That's a good way of thinking about it.

One thing I don't like about the app is the Self-powered graph. For example, if I use 20 kWh in the morning before the sun comes up and then 20 kWh more throughout the day, it really skews the self-powered percentage. It might show only 25% to 50% self powered even if I send 80 to 100 kWh back to the grid throughout the day. Yes, I did use some from the grid, but shouldn't I get "credit" for sending excess production back to the grid? I could move the car charging to be at 11 pm instead of 5 am and it would flip the reported results as it would show nearly 100% self-powered throughout the day.

That, by definition is not self-powered. You are thinking of offset %. There is also no guarantee that just because you sent a green electron to the grid, that a green one will be sent back.

Without NEM credits - you would be much more interested in the self-powered score...