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Power wall without solar cost effective?

Power wall without solar cost effective?

I live in the San Fernando Valley Los Angeles and I'm wondering if the power wall without solar will pay for itself. Our electric bill is exceedingly high now that my wife works from home.

sashton | 03. Oktober 2017

In a lot of scenarios even storage with PV is not cost effective.
A crude calculation would be:-

Your saving per kWh = your expensive day electricity rate - ( your cheap night rate X your system turnaround losses ...about 1.12)

multiply this by your system capacity to give your daily savings then set this against the amortised cost of the kit.

This assumes you will use all the capacity of the system - ie you reach then end of your expensive day rate just as the battery goes flat. Any over specification is wasted in your costings.
This also assumes that your day load does not exceed the rate at which your kit can supply power.

Unquantifiable but guessable factors to consider are increase on electricity costs; degrading performance of the kit over time; maintenance/repair costs and whether you will continue to own the property against any improvement in sale value.

Benefit that can be harder to quantify is brownout cover if the optional disconnect equipment is purchased but remember there is no free lunch here. Implementing this will require you to set aside some battery capacity which you should remove from the above equation.

Personally I feel all the above is trumped by the fact that buffering your use is doing the right thing for the environment. Currently BEVs are mainly driven by enthusiasts but with the advent of the M3/Bolt (BEVs for the masses) or even higher capacity PHEVs, in greater numbers, I see peak grid loading as a real problem as many get home from work and just blindly put the car on immediate charge. Integrated, managed home storage could have a significant role to play. ....

zubinanary | 04. Oktober 2017

I don't have solar, but I wanted a way to reduce my PG&E electrical bill (excluding my Tesla vehicles of course). For me, I decided that If I were to get SGIP Step 2, then it would make sense, so I went with Quantity 2 Powerwall (the maximum for SGIP). My total cost was $13800, and my SGIP rebate (when it arrives) for Step 2 is $9200, so that leaves $4600 out of pocket.

I ran some numbers, and I calculated that I would save around 68% per month (this would be electricity I used at the two higher rates because I'm on the EVA plan). At the highest rate, I'm paying $0.416/kw, and at the lowest rate I'm paying $0.125/kw.

Based on my calculations, after around 3.5 years of ownership, I should be able to get a positive ROI only because my out of pocket is so low as a result of SGIP Step 2 and because my average daily consumption is around 12 to 15kw per day (the exception are those days when I have to run AC for almost the entire day, but that happens three to four times a year only).

Note: Right now, my Powerwall is setup for Whole Home Backup, because Time of Use Load Shifting is not yet available in the software (I'm running PowerwallOS 1.6.0). It should arrive by end of calendar year, but for now I'm doing my own "completely manual" Time of Use Load Shifting by flipping the breaker at 630am so I'm off grid, and then flipping it back at 11:15pm which puts me back on grid so I can charge the Powerwall.

I charge the two Powerwall and my Teslas every night at the cheapest $0.125kw rate.

jeff | 19. Juni 2020

I don't understand how your electric bill will go down if the only way you have to recharge your PW is via the grid. You're paying for electric that way, and because there's no such thing as 100% efficiency, it will likely cost more. Even if you charge your PW at night when the rate is lower, you're still paying the electric company.

Solar is a natural match for a PW. We have that setup and our electric bill has gone from around 100/month to somewhere between $10-20/month, and that's only because we use the grid when running the electric dryer. We don't have a Tesla vehicle.

bp | 19. Juni 2020

It's possible under a TOU (free nights) plan, a PowerWall-only configuration, charged from the grid, could save enough $ to justify purchase of the PowerWalls.

Though it's also likely the utility companies will ban homes with battery storage from those plans at some point.

TeslaTap.com | 19. Juni 2020

There are two other benefits, but hard to quantify the value.

In California, due to high winds, the local power utility may do blackouts, which could last several days. So with a Powerwall, you can keep critical items, such as a refrigerator and lights working. The time could be extended with more Powerwalls, less power consumption, or solar to recharge during the day. If you're in this situation of blackouts, consider the value of the loss of all your food in your refrigerator and freezer that might have to be tossed.

The second is a backup for your PCs. If you do a lot of work on a PC, the Powerwall prevents power interruption from the loss of that work. Now you could get a UPS and/or a laptop with a battery to handle that. Since the Powerwall is handling the entire house, it covers the internet connection such as the router, WiFi, and modem. It also allows DVRs to continue to record during a power failure. Hard to put value on these items, and may have no value to you.

gregbrew | 19. Juni 2020

There's a 10% round-trip efficiency loss into and out of a battery backup system.

Check with your utility. Many (most?) electrical utilities in the States won't allow a homeowner to charge from the grid at a low rate, and then discharge back to the grid at a higher one. The few PW-only installations that I've heard of are either in a different country (Australia and Britain come to mind) or have fixed, flat rates for electricity, day or night.