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Discussion Starter · #1 ·
Sorry, I have a diagram but I can't get it uploaded, my computer freezes whenever I try.

Installation of the Tesla Powerwall 2 in a rental home I own was completed last week. It is currently waiting for an inspection by Tesla and permission from my local utility before it is commissioned. Until then I have received no information about the Powerwall 2, so the following is how I think it works based on discussions with the tech staff and the installers.

System – The heart of the system is the Tesla Gateway, this is where the flow of electricity in the home is controlled. The Gateway has three inputs, the grid, solar via the solar panels and an inverter, and the battery. There are two electrical service panels connected to the Gateway to direct power into the home. The first is the Main Panel which is connected directly to the grid. In my case all heavy load 240 AC circuits such as for the A/C, electric range, electric dryer and EVSE are connected to this panel. These circuits are not backed up, so if the grid goes down, these circuits will also go down. The rational for connecting these circuits to the Main Panel is they can exceed the 5 KW continuous power output capability of the battery. The other circuits, in my case, all the 120 VAC circuits are connected to the Backed-Up Panel. As such, the frig, microwave, lights and computer will continue to operate as normal during a power outage.

Normal daytime operation – The Gateway combines solar and grid power to support all circuits in the home. Excess power from the solar is used to charge the battery via an internal rectifier. The battery has a thermal management system to prevent overheating during charging.

Normal evening operation – When the sun goes down, the Gateway uses battery power in lieu of grid power to power the house. This is the primary means by which the system is able to lower electric costs. In my area power from the utility (SDG&E) can be as high as $.40/KWH during this time. The battery discharge level can be programmed. So initially it can be set at a higher level to minimize degradation and as the battery ages it can be reprogrammed to go deeper into the battery. While drawing power from the battery is prioritized over grid power, heavy loads, such as the A/C operates on a combination of battery and grid power (I don’t have a clue how the Gateway does this, but this is how the tech staff says it operates). When the battery is depleted the Gateway shifts solely to grid power. If programmed to do so, the battery can be programmed to be charged using off-peak power. This is rather complicated as the main source of power to charge the battery is from the solar array, so this feature must be intended to compensate for average shortfalls from the solar.

Backup operations – If the grid goes down the system uses the battery to provide power for the backed up circuits. The way this works is the Gateway disconnects the Main Panel from the system and the inverter in the battery provides a 240 VAC source for the circuits connected to the Backed Up Panel and importantly, for the external solar inverter to synchronize. By providing a 240 VAC source to the solar grid-tied inverter it allows the solar portion of the system to continue to operate during a grid outage to power the house and to charge the battery. Southern California is earthquake territory, if the big one hits the grid could go down for many days or weeks, so this is an importantly capability for me.

Cost – This cost discussion pertains only to the battery portion of the system. The scope of the battery subsystem included the following:

Tesla Powerwall 2 AC battery (13.2 KWH, 5 KW charge/discharge continuous, 7 KW peak) including 10 year warranty (must be connected to the internet for online monitoring)

Tesla Backup Energy Gateway.

Tesla Cloud-based Monitoring Platform

Backup Load Subpanel.

Installation including design, plan, permitting, inspection support, and initial battery programming.

Also included in the original price was additional work to upgrade the Main service, however this was not done due to code issue which would have increased cost considerable, so a workaround was done. The cost (reduction?) of the workaround is not reflected in the figures below.

Total Contract Amount for the Battery Subsystem - $10,500
Less estimated rebate - $5,200
Less estimated tax credit - $3,150
Estimated Net Cost - $2,150

The rebate is from the California Self Generation Incentive Program which provides rebates for qualifying distributed energy systems installed on the customer’s side of the utility meter. I was lucky enough to qualify for the Step 1 rebate which opened May 1, 2017, Step 2 which is about 10% lower opened June 5, 2017 and is probably sold out. Further steps are planned but I don’t have the opening dates. If you live in California and are interested in a battery, I strongly recommend looking into this rebate.

With a net cost of $2150 for the battery subsystem I expect the system to pay for itself rather quickly by offsetting the cost of peak power with self generated solar power. As am landlord that means an increase of monthly rent of about $19/month would cover the cost of the battery subsystem over the 10 year warranty period. I expect the tenant will save more than that on their utility bills plus they will have unlimited backup power in emergencies.

Sorry, I don't have more information. There is a glaring lack of details from Tesla on how the Powerwall 2 works of what I'm supposed to do to program it's operation. I should get more info when the system is comissioned. If anyone is willing to help, PM me and I can send the PDF file showing the system interconnection. Perhaps you will have better luck getting it posted.
 

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I have two of these (and possibly a third) coming soon because of the referral program. Here in Texas, I have an electricity plan that gives me free power from 9PM to 6AM, so I'm looking forward to scheduling the charge/discharge cycles to take advantage of them. I LOVE the fact that the Tesla app will be able to manage my Powerwalls and my two Teslas with the app, as well.
 

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The California Self Generation Incentive Program applies to batteries? Good deal.
I have grid tie solar, which I was able to get a Self Generation rebate from my local utility, but Batteries don't generate power.

Likewise, there is no mention of batteries in IRS form 5695, the Residential Energy Credit form.
 

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The California Self Generation Incentive Program applies to batteries? Good deal.
I have grid tie solar, which I was able to get a Self Generation rebate from my local utility, but Batteries don't generate power.

Likewise, there is no mention of batteries in IRS form 5695, the Residential Energy Credit form.
My understanding is that battery systems only qualify for the credit if they are installed with a new solar panel system. If they are installed after, they are not eligible for the credit.
 

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The California Self Generation Incentive Program applies to batteries? Good deal.
I have grid tie solar, which I was able to get a Self Generation rebate from my local utility, but Batteries don't generate power.

Likewise, there is no mention of batteries in IRS form 5695, the Residential Energy Credit form.
Since batteries don't generate power they don't qualify by themselves.
 

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Can you break cost down for the components that were included in $10.5K?

How much was the labor?

Is $5200 rebate gone already?
 

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Discussion Starter · #8 ·
Can you break cost down for the components that were included in $10.5K?

How much was the labor?

Is $5200 rebate gone already?
The $5200 rebate sold out the first day of was offered. The next level rebate is 10% less. It opened for applications in June, check with an battery installer to see if it is still available.

Sorry, I was given no breakdown of the $10,500, but it includes a new service panel and service upgrade. My guess is the Tesla stuff is around $7500, the rest went to labor and electrical work unique to my house.
 

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If anyone is willing to help, PM me and I can send the PDF file showing the system interconnection. Perhaps you will have better luck getting it posted....
FYI, I PM'd you the first day with my email but I never heard from you. Happy to help if I can.
 

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The $5200 rebate sold out the first day of was offered. The next level rebate is 10% less. It opened for applications in June, check with an battery installer to see if it is still available.

Sorry, I was given no breakdown of the $10,500, but it includes a new service panel and service upgrade. My guess is the Tesla stuff is around $7500, the rest went to labor and electrical work unique to my house.
I see. Not sure how I missed it... Blog on solar forums, been looking at Powerwall II without incentives. I already dropped 3/4" underground conduit for my battery install, made room for battery at my pool pad. Sent email to SCE SGIP group - hopefully there is still room...
 
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