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Powerwall Economics in Bay Area?

Powerwall Economics in Bay Area?

I can't figure out what the economics are for installing a powerwall or two. Has anyone done any analysis in the bay area as to whether this makes sense if you have solar, a tesla, and are on the EV TOU PG&E plan? I know that every situation is slightly different but would love hearing about anyone who has moved forward and why.

cwied | 25. April 2018

I don't think there's a way to make it look attractive financially unless you're really interested in backup. The restriction of charging only from solar in order to qualify for the ITC means you can't take advantage of the cheap overnight rates to charge up the powerwalls for use during the day. Furthermore, since the powerwall isn't eligible for net metering, you also can't offset more than your usage during the higher rate periods.

Financially, what you'd save is the difference between peak and part-peak on the usage from 2pm-9pm (minus 10-15% efficiency loss due to the battery roundtrip), provided your solar generates enough power before 2pm to cover that. You can discount the cost of the powerwalls by the 30% you'll get back for the ITC. That will give you your pay-back period.

I went ahead because there is a chance I can still get the SGIP and my inner survivalist likes the idea of a backup solution that can go indefinitely if the big one hits.

PatientFool | 26. April 2018

@cw_tesla i'm not familiar with the 30% ITC mention. What is that about? Assuming that you get both that and SGIP what would you expect your out of pocket costs to end up being on a powerwall?

cwied | 26. April 2018

The ITC is the Federal Investment Tax Credit - the 30% tax credit (see https://www.tesla.com/support/energy/own/powerwall/federal-investmenttax...).

If I get into step 3 of the SGIP, I will get $4060 back per Powerwall (I have 2). My installed cost was about $13,803, so SGIP would take my cost down to $5683. After the ITC it would be $3978. If I don't get the SGIP, the cost will be $9662. The problem is there is a huge backlog of Tesla customers waiting for SGIP and they may use up their allocation before it's my turn.

PatientFool | 26. April 2018

Thanks I hope that you get it. $4k our of pocket for two powerwalls is a nice deal

vernon | 24. Mai 2019

There is a different approach to looking at the cost for powerwall. I'm in California USA with net metering. PGE acts a 100% efficient battery so pw for backup is the only straight forward use. However, using powerwall can allow one to displace grid usage with solar power if that is a user preference. 'Cost justifying' in this case just means displacing (substitution) cost. For example, I might buy a Ford instead of a Chevy for the same price. I did not save any money, but exercised a preference for how it was spent.

For me, I purchased a 14 panel system with 2 pw. My analysis shows: using E-TOU-B and being able to fully charge pw off-peak and use pw for all usage on peak (40% of total usage on peak) 1510 kWh/month, if 12% of off peak usage cost can also be offset, over 10 years I break even on cost versus no pw; 12 years with no off-peak offset. PW cost + solar panels cost after incentives is $22,964.09. I use Samsung DVM eco system for HVAC and electric induction range, so heavy on the kWhs, light on gas.

If, instead, usage is 900 kWh/month, it would take 17 years to break even with no off peak offset.

In any case, my point is cost justify can include merely not losing money as an expression of user preference with a bonus of backup power.

dortor | 28. Mai 2019

there is _NO_ ROI to power walls - change your approach - I lose power for 15 min or more (some times for hours) in the Watsonville area 2 or 3 times a month - I approach them as a home appliance so I can live my life and not worry about how flaky PG&E is - I've run numbers desperately trying to find an ROI story - it's just not there - but they are cool home accessories and if you have power outages really really useful.