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 Post subject: Tesla Powerwall 2
PostPosted: Mon Apr 17, 2017 2:01 pm 
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Joined: Thu Jan 12, 2017 10:04 am
Posts: 23
Location: SF Bay Area
Anyone with rooftop solar considering a Tesla Powerwall 2? Even with the CA SGIP incentive and federal ITC, it would never pay for itself in my situation. To me, the benefits I see are:

1. To be on the bleeding edge of technology
2. Have backup power if the grid goes down while also allowing the PV system to stay up and produce
3. Protect against high TOU rates in the evening when solar isn't producing. I am still on the E-6 rate and NEM credits currently cover all my usage.

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2016 SE with DCFC
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 Post subject: Re: Tesla Powerwall 2
PostPosted: Mon Apr 17, 2017 3:43 pm 
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Joined: Fri Mar 27, 2015 4:13 pm
Posts: 1003
Location: Los Altos, CA
I put a deposit for a PowerWall 2 with Swell Energy. The deposit is refundable if they cannot get the SGIP rebate on my behalf. I still pay $1,000/year to PG&E due to the small size of my solar array. I cannot make the array bigger because it would push me into NEM 2.0 which would increase my cost of EV charging. I have wanted to install a natural gas backup generator since I had my house built in 2012, but never got around to pulling the special permit for that. So, throwing in $3,500 that I would have spent on the generator and installation, I will definitely get some financial benefit from the PowerWall after SGIP and ITC tax credit. Also, our area is changing to a CCA (Silicon Valley Clean Energy) and they will pay out generation credits even if you are a net consumer. It's small money because it's only the generation portion, not distribution or transmission, but it is something when PG&E would wipe out your credits if you are still a net consumer. The PowerWall will further exaggerate my strongly off-peak usage.

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 Post subject: Re: Tesla Powerwall 2
PostPosted: Mon Apr 17, 2017 5:26 pm 
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Joined: Thu Jan 12, 2017 10:04 am
Posts: 23
Location: SF Bay Area
Actually now that I think about it, I remember reading your post on the Tesla forum. I got a quote from Swell Energy as well, but the two installers they use for "my area" were based more than 100 miles away in the Sacramento area which I thought was interesting. Perhaps they might have a second office in the Bay Area? Swell definitely pads the install cost as you mentioned. I know that they would just need to add a small sub panel near my main panel and move/add a few breakers to it, should be relatively simple. I am still getting quotes from a few other places just to compare.

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 Post subject: Re: Tesla Powerwall 2
PostPosted: Mon Apr 17, 2017 9:10 pm 
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Joined: Fri Mar 27, 2015 4:13 pm
Posts: 1003
Location: Los Altos, CA
Yes, I did post about PowerWall on TMC.

The more interesting thing will be to see how much Swell Energy wants for installation after they actually do a site survey. Since the deposit is fully refundable if they can't do it for the initially quoted price, they are motivated to pad the number from the start, just to accommodate complicated installations or old main breaker panels that need upgrading.

My main point is that if you don't pay anything at your NEM true-up, you will have a much harder time justifying the cost. In my case, I burn through almost all my Peak period generation with household usage between the sun going down and 9pm when that TOU period ends. Part-Peak on the EV rate schedule is the only period that is significantly negative in the summer. The PowerWall would soak up that morning and noon-time generation and push it out during the peak period. So, during the course of the year, given the rate differential between Peak and Part-Peak and time shifting 10kWh/day, I would save about $600/year. In theory, you could get more arbitrage payback by using the rate differential between Off-Peak and Peak, but you need to charge the stationary batteries from solar 75% of the time or more in order to qualify for the ITC tax credit.

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