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Powerwall with solar = no grid charging
- Thread starter racpuc
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- Powerwall Tesla Energy
kev1n
Active Member
when i spoke with Swell Energy about this, i was under the impression that you can charge the powerwall at any given time and you can schedule it, is this not true?
from what the rep said, you technically can get a powerwall without solar, go on EV-A plan and charge your powerwall overnight and use it during the day to avoid the 30 something cents and pay 12cent flat(assuming you dont use over what can be stored by the powerwall)
from what the rep said, you technically can get a powerwall without solar, go on EV-A plan and charge your powerwall overnight and use it during the day to avoid the 30 something cents and pay 12cent flat(assuming you dont use over what can be stored by the powerwall)
SoundDaTrumpet
Member
Accurate statements overall with caveats:
If money matters: please be aware that the 30% federal incentive tax credit (ITC) has specific requirements. The requirement to fully receive the ITC is that batteries be charged with renewable energy (e.g. solar). ITC gets prorated if non-renewable charge the batteries up to a threshold. Once over the threshold (i.e. 20% of capacity), you are not allowed to claim the ITC. The aforementioned requirements are in effect for 5 years.
I have discovered that rate arbitrage only works for those on the EV-A rate schedule. There is an inherent wear-and-tear cost when charging/discharging the Powerwall (PW). Those on the ETOU rate schedules are better off using Powerwall strictly for backup. To make matters more complex, those trying to apply for SGIP (California's self generation incentive program) rebate are required to discharge 52 equivalent discharges per year. Those on EV-A benefit for discharging to the grid while those on ETOU just barely need to discharge to keep the SGIP rebate legitimate.
Also, charging with grid power changes the PW warranty from Tesla. There are two warranty paths.
If money matters: please be aware that the 30% federal incentive tax credit (ITC) has specific requirements. The requirement to fully receive the ITC is that batteries be charged with renewable energy (e.g. solar). ITC gets prorated if non-renewable charge the batteries up to a threshold. Once over the threshold (i.e. 20% of capacity), you are not allowed to claim the ITC. The aforementioned requirements are in effect for 5 years.
I have discovered that rate arbitrage only works for those on the EV-A rate schedule. There is an inherent wear-and-tear cost when charging/discharging the Powerwall (PW). Those on the ETOU rate schedules are better off using Powerwall strictly for backup. To make matters more complex, those trying to apply for SGIP (California's self generation incentive program) rebate are required to discharge 52 equivalent discharges per year. Those on EV-A benefit for discharging to the grid while those on ETOU just barely need to discharge to keep the SGIP rebate legitimate.
Also, charging with grid power changes the PW warranty from Tesla. There are two warranty paths.
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@SoundDaTrumpet Thanks for the clarification. Whats the powerwall warranty if using the grid to charge? Are we allowed to discharge the powerwall to the grid to get credit from PGE?
SoundDaTrumpet
Member
The PW warranty is here: https://www.tesla.com/sites/default/files/pdfs/powerwall/powerwall_2_ac_warranty_us_1-4.pdf
The two cases I pasted from the table for your convenience:
Case 1
Application: Solar self-consumption/backup only (storing solar energy generated by an onsite array, and using that stored solar energy (i) for daily self-consumption and/or (ii) for use as backup power.)
Energy Retention: 70% at 10 years following initial installation date
Operating Limitations: Unlimited cycles
Case 2
Application: Any other application or combination of applications
Energy Retention: 70% at 10 years following initial installation date
Operating Limitations: 37.8 MWh of aggregate throughput (measured at the battery AC output)
For grid to charge: I imagine Case 2 applies. I imagine charging the batteries for backup and trickle charging would be allowable under Case 1.
For the purposes of rate arbitrage using grid power. It will fall under Case 2.
I plan to recharge with only renewables (i.e. excess solar that would have resulted in credits), and do self consumption from sundown to 9pm. Right now the Tesla app does not look to be supporting this to my liking. On ordinary days when I am home a 50% backup setting makes logical sense, yet when I am not home the app would have PW charge the EV, which isn't advantageous. Hopefully Tesla comes up with an automated scheme / app update so one need not to fiddle with the backup % each day. I also plan to operate the PW only during the summer because during the winter the EV-A rate schedule pricing difference isn't as great from a rate arbitrate standpoint and not worth deploying the PW.
The two cases I pasted from the table for your convenience:
Case 1
Application: Solar self-consumption/backup only (storing solar energy generated by an onsite array, and using that stored solar energy (i) for daily self-consumption and/or (ii) for use as backup power.)
Energy Retention: 70% at 10 years following initial installation date
Operating Limitations: Unlimited cycles
Case 2
Application: Any other application or combination of applications
Energy Retention: 70% at 10 years following initial installation date
Operating Limitations: 37.8 MWh of aggregate throughput (measured at the battery AC output)
For grid to charge: I imagine Case 2 applies. I imagine charging the batteries for backup and trickle charging would be allowable under Case 1.
For the purposes of rate arbitrage using grid power. It will fall under Case 2.
I plan to recharge with only renewables (i.e. excess solar that would have resulted in credits), and do self consumption from sundown to 9pm. Right now the Tesla app does not look to be supporting this to my liking. On ordinary days when I am home a 50% backup setting makes logical sense, yet when I am not home the app would have PW charge the EV, which isn't advantageous. Hopefully Tesla comes up with an automated scheme / app update so one need not to fiddle with the backup % each day. I also plan to operate the PW only during the summer because during the winter the EV-A rate schedule pricing difference isn't as great from a rate arbitrate standpoint and not worth deploying the PW.
SoundDaTrumpet
Member
In August 2016 I had 9.8kW of solar and a Powerwall 1 installed. I can charge it from the grid or from my solar panels.
Tesla support told me that the powerwall can't do both at the same time. You have to switch it between the two modes yourself.
I would like to charge the battery to 70% at night, not discharge whilst my car is charging in the early morning and then the rest of the day self consume and use the battery when nesasary to avoid buying electricity at the higher day rate.
Nothing like this is possible in the software. Settings are extremely basic. Either self consume or time shifting.
I would like to charge the battery to 70% at night, not discharge whilst my car is charging in the early morning and then the rest of the day self consume and use the battery when nesasary to avoid buying electricity at the higher day rate.
Nothing like this is possible in the software. Settings are extremely basic. Either self consume or time shifting.
Agree. The minimum new function I want is to automatically block discharge during Super Off-Peak 11pm-7am unless the grid is down.
Up until your question, everyone has been talking about behind the meter. If you want to go through the meter to the grid, it would need to have a transfer switch or safety programming that is found in Grid Tie inverters. PG&E may also have restrictions.
Ulmo
Active Member
I'd like to know more for completeness's sake, for when PG&E offers programs to buy energy from our batteries. For instance, is the hardware present in my installation of PowerWall 2 + transfer switch?
I updated my power use website to make it easier to remember for my off-the-shelf Tesla PowerWall 2 installation, using the well known domain name format of the DIY trailblazer in the topic: http://ulmo.solar/
We know that there is renewable curtailment for and hour or two on some mornings. I have also seen some reports that Cal ISO is paying some neighboring states to take some of that renewable energy so they don't have to curtail it. I hope that trickles down to the IOUs. I would love to get paid by SCE to charge my Tesla in the morning. I could even program my electric water heater to put load on the system. My wife would love to use the electric dryer in the morning.
Ulmo
Active Member
Correct. I believe when they first installed it, they charged from grid on the first day, but I could be wrong. Ever since then, my PowerWalls are entirely charged from solar power. It's done by the interaction between the solar power monitors, and the switch that reads that information and sends it to the batteries to charge up by that exact amount. So, the batteries are actually using whatever electricity happens to be bumping on the wires to charge with, be it PG&E, solar, the backfed energy from some source that sends electricity back (such as a motor), or whatever, but at an instant rate equal to what the solar panel inverter is putting out. So, essentially, it is not getting anything from the grid in amounts it isn't also sending to the grid; the grid power remains net flat all day. Unfortunately, there's a murmur of a few watts all day long that I'm concerned might show up in the PG&E bill somehow.
Ulmo
Active Member
I can test it today. Here goes:
At around 3:03AM:
Currently, it is discharging at 56% charge level, with 15% backup minimum, in Self-Powered mode. (Self-Powered refers to charging only with solar power and using only that solar power from the battery when solar isn't enough.)
I just set the backup minimum to 75%. Let's see what it does over the next half hour.
Something else I can also test is putting it into Backup mode (100% for backup).
:::::::::::::::::::::::::::::::::
Result 1: It stops discharging the battery at 3:30AM and starts using grid for home use, but not to charge the battery.
So, I set it back to 15% reserve for backup for self powered mode, then set it to Backup Only mode, at 3:51AM. Waiting again.
:::::::::::::::::::::::::::::::::
At around 3:03AM:
Currently, it is discharging at 56% charge level, with 15% backup minimum, in Self-Powered mode. (Self-Powered refers to charging only with solar power and using only that solar power from the battery when solar isn't enough.)
I just set the backup minimum to 75%. Let's see what it does over the next half hour.
Something else I can also test is putting it into Backup mode (100% for backup).
:::::::::::::::::::::::::::::::::
Result 1: It stops discharging the battery at 3:30AM and starts using grid for home use, but not to charge the battery.
So, I set it back to 15% reserve for backup for self powered mode, then set it to Backup Only mode, at 3:51AM. Waiting again.
:::::::::::::::::::::::::::::::::
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Ulmo
Active Member
4:25AM: Still no change; battery still in standby. Putting back into Self Power mode with 15% reserve.
So, it appears that I do not have the capability to charge from grid once Tesla provisions it as a self-generation user.
It is said that Tesla will update the software to have more control. They imply that they will update the software to do great things. We don't know completely when or what, but it should be "soon". Personally, I'd only want to charge from grid if grid was paying me to during high clean energy times when PG&E is sending me clean energy to store for them or for my later use. Daytime rates for electricity would have to drop to negative. For that to happen, we need to get a lot more solar panels online in California.
:::::::::::::::::::::::::::::::::
At 4:30 AM, the PowerWall switch started discharging the powerwall, and I'm back on clean energy again, and off of the backup dirty energy grid power. Belch! That was disgusting. I didn't like using dirty energy.
So, it appears that I do not have the capability to charge from grid once Tesla provisions it as a self-generation user.
It is said that Tesla will update the software to have more control. They imply that they will update the software to do great things. We don't know completely when or what, but it should be "soon". Personally, I'd only want to charge from grid if grid was paying me to during high clean energy times when PG&E is sending me clean energy to store for them or for my later use. Daytime rates for electricity would have to drop to negative. For that to happen, we need to get a lot more solar panels online in California.
:::::::::::::::::::::::::::::::::
At 4:30 AM, the PowerWall switch started discharging the powerwall, and I'm back on clean energy again, and off of the backup dirty energy grid power. Belch! That was disgusting. I didn't like using dirty energy.
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