Tesla Solar plus Powerwall questions

[rsunny2012]

Hello,

i am planning for tesla solar panels 7.56 KW system plus 2 Powerwalls to my home. Currently i am using around approximately 12000 kwh per year ( i have model 3 and use AC a lot during night times) on my home electricity. Right now i have EV2-A plan with PG&E in bay area. i am getting approximately around $180 to 200 electric bill every month.

My question here would be will taking 2 powerwalls worth for my usage ? i dont want powerwall for backup as hardly i had power outage once within last 10 years. Only reason i am planning for powerwall is for high Pg&E rates within my area

even if i have my electric usage more in coming days, i can use the power from powerwall during peak rates

Am i thinking in right direction about powerwall or am i taking wrong step in spending 12K more on powerwalls

Kindly suggest me on my plan

 

[jrweiss98020]

If you size the Powerwalls properly to avoid using the grid on peak rates, it will likely be a good decision. The question is whether 2 Powerwalls will support your AC. The 5KW/Powerwall continuous load limit may be a factor. Also, the 7.5KW system may not be able to completely recharge the Powerwalls every day. Do a bit of analysis on your usage and seasonal variations...

 

[rsunny2012]

Tesla mentioned solar panels will be able to generate about 25-35 Kwh per day. without charging my Model 3, i use around 12 to 15 Kwh per day
2 powerwalls combines 27 Kwh. i can run A/C using 2 powerwalls ( not 1)

 

[SoundDaTrumpet]

2 PW will have the best “value” for you. I have 4.3kW solar in Bay Area and annually average 15 kWh per day. For 12 months, I discharged the batteries equivalent to 90 full discharges. Usually on a hot 90+ degree days, the batteries are drained to the user/app-defined “reserve for power outages” (mine set to 20%). The A/C is not backed up but is offset by PW system, which is does an admirable (~80%) job to avoid peak electrical rates.

My goal to avoid paying back the SGIP incentive was met 100% as I easily discharged 90X vs. the 52X required. I can easily do this for 5 years, as required. Avoiding peak charges fell shy at 80% of goal target.

3 PW will almost guarantee all A/C peak loads should be covered, and allows the nearly guaranteed option to backup A/C during an outage. I have a strong opinion that 2PW is not enough to kick start for mainstream A/C for technical reasons (see other A/C posts). Jumping to 3PW has other headaches (apply SGIP for yourself, and discharge requirements are 104 discharges).

 

[GenSao]

TLDR: Likely yes, but check to be sure.

I had a 5.7 kW solar array installed in the Bay Area in 2017. In the summer it produces up to 38 kWh (1st year production of 8,200 kWh). Since then, we added two Powerwalls. Even at 5.7 kW, they were able to fill them up. In 2019, a 3.8 kW solar array was added as our usage increased to 12,761 kWh since getting our Model 3. I wanted to mitigate for PG&E's rate inflation and the eventual panel degradation.

Do an estimate in the peak shave saving over the warrantied 10 year life of the batteries. Take the cost difference between the off peak rate (or your lifetime solar system cost per kWh) and the peak/part-peak rate. Take in the account winter and summer rates.

Use the online PG&E energy use data to estimate the peak period use. Take a select sample and average the data, or sum it all. Estimate the cost savings of Peak and Part-peak. In the below sample image image, 13.3 kWh for part-peak uses and 24.0 kWh for peak use under EV2-A. On cost alone, peak and part-peak cost was $32.35 in the below sample.

Add 6% annual inflation for rate cost for PG&E based on the below calculations. Feel free to adjust how you see it.

Since we have similar energy use, feel free to use the following data to make (or compare) your model. Assume the "From Powerwall" is only peak and part peak energy. This could be higher, but I chose to limit the battery use. Unfortunately Tesla removed the weekly/monthly/annual summary "To Powerwall" in June 2019.

I agree with SoundDaTrumpet, two Powerwalls are the best value. It should cover all your peak period and most of your part peak period. As you are not too worries about backup, a third Powerwall is not needed.

 

[SoundDaTrumpet]

2 PW will have the best “value” for you. I have 4.3kW solar in Bay Area and annually average 15 kWh per day. For 12 months, I discharged the batteries equivalent to 90 full discharges. Usually on a hot 90+ degree days, the batteries are drained to the user/app-defined “reserve for power outages” (mine set to 20%). The A/C is not backed up but is offset by PW system, which is does an admirable (~80%) job to avoid peak electrical rates.

My goal to avoid paying back the SGIP incentive was met 100% as I easily discharged 90X vs. the 52X required. I can easily do this for 5 years, as required. Avoiding peak charges fell shy at 80% of goal target.

3 PW will almost guarantee all A/C peak loads should be covered, and allows the nearly guaranteed option to backup A/C during an outage. I have a strong opinion that 2PW is not enough to kick start for mainstream A/C for technical reasons (see other A/C posts). Jumping to 3PW has other headaches (apply SGIP for yourself, and discharge requirements are 104 discharges).

Correction to above. It looks to be 52 discharges for residential. I hope there will another pull down item added for "Large Residential" instead of "Small Residential Storage" and "Large-Scale Storage" to their program metrics.

5.2.5 Operational Requirements
New non-residential systems are required to discharge a minimum of 104 full discharges per year. Residential systems are required to discharge a minimum of 52 full discharges per year. A “full discharge” is the equivalent of discharging the SGIP-incentivized energy capacity, whether it is during a single or multiple discharges.