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Why is my neighbor using his power walls daily (will they last long)?

jboy210

Supporting Member
Dec 2, 2016
4,921
3,015
Northern California
how about a generator?
I have one but it is small. Not enough to power the entire house. Also, there are associated maintenance costs and fueling hassles. We cannot store much gas or propane in our homes.

And, the TEG and Powerwalls can be used every day to reduce the amount of money we send PG&E monthly. And this is something I try to do as much as possible. Nothing brings a smile to my face like seeing my PG&E bill shrink.:)
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
8,102
8,969
Riverside Co. CA
It sounds like your neighbor just enjoys spending money and the latest tech gadgetry. Powerwalls rarely pencil-out from a financial standpoint, especially in this situation.

"penciling out" depends on what you are putting in the equation. It doesnt have to be 100% financial, unless thats your criteria. I think I remember you mentioning somewhere you were in finance? If so that might mean that, for you, maybe the "penciling out" has to be 100% financial.

For others, it can be a combination of things, and all of them may not fit on a spreadsheet.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
8,102
8,969
Riverside Co. CA
Just like there are people for whom they say "man I never would buy an EV. Where do you charge?! What happens when you have to replace the battery? I take a road trip every month and cant get there without stopping to charge, doesnt that take, oh 2 hours or so?"

This is the same back and forth, just for home batteries.
 
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jboy210

Supporting Member
Dec 2, 2016
4,921
3,015
Northern California
Just like there are people for whom they say "man I never would buy an EV. Where do you charge?! What happens when you have to replace the battery? I take a road trip every month and cant get there without stopping to charge, doesnt that take, oh 2 hours or so?"

This is the same back and forth, just for home batteries.

Agreed. My response is pointing out that in the US over 75% of driving is done for commuting, and the average commute is under 20 miles one way. So for most of us if we charge our car's like a phone (at home, largely at night), we seldom need to charge anywhere else.

And if you want to be really mean you can mention the free Supercharging for Life you got with your Tesla.;)
 

jboy210

Supporting Member
Dec 2, 2016
4,921
3,015
Northern California
If backup is the concern, then (1) Powerwalls really aren't the best/most economical option and (2) Draining them overnight isn't a good idea. It would make more sense to set a pretty high reserve percentage, which would leave capacity for outages, and also reducing the cell degradation. We all know lithium ion cells degrade with each charge/discharge cycle.

Not sure what is worse for cells. Cycling through their capacity but never to deep discharge (I never let my Powerwalls go below 25-30%), or holding them at a very high state of charge for long periods of time. I know on the cars Tesla suggests only going above 90% on trips, and not for everyday driving.
 

pdx_m3s

Active Member
May 18, 2019
1,285
1,120
Portland, OR
"penciling out" depends on what you are putting in the equation. It doesnt have to be 100% financial, unless thats your criteria. I think I remember you mentioning somewhere you were in finance? If so that might mean that, for you, maybe the "penciling out" has to be 100% financial.

For others, it can be a combination of things, and all of them may not fit on a spreadsheet.

To "pencil-out" (colloquially) generally refers to the financial impact. I agree there are other non-financial motivators as well. Perhaps reducing climate impact is one, which would be achieved by draining solar-filled Powerwalls at night as opposed to draining from a fossil-fueled grid when the sun isn't shining.
 
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MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,564
8,741
Colorado
To "pencil-out" (colloquially) generally refers to the financial impact. I agree there are other non-financial motivators as well. Perhaps reducing climate impact is one, which would be achieved by draining solar-filled Powerwalls at night as opposed to draining from a fossil-fueled grid when the sun isn't shining.
That's what we do. We power our house and approximately 22 hours a day via solar energy, thanks to our Powerwalls. While we do take some power from the grid, last year we sent ~4200 kWh more back to the grid than what we took from it.

We aren't worried about using our Powerwalls for their intended purpose.
 

sorka

Well-Known Member
Feb 28, 2015
7,858
5,778
Merced, CA
I am somewhat surprised that Tesla does not give an option to charge PW batteries to less than 100%, similar to this option for Tesla cars.

This is perplexing. I'd love to be able to set the max charge to 80%. As it stands now, if I leave it in advanced mode with peak from 3 pm to midnight, my PWs charge to 100% every day before peak begins but only discharge to 50% before the sun starts shining again. I'd much rather have it cycle from 30% to 80% than 50% to 100%.
 

sorka

Well-Known Member
Feb 28, 2015
7,858
5,778
Merced, CA
Ok looks like my neighbor's system is undersized....I saw close to 100A on his heat coils (only when deep cold) Otherwise it's on a 3 ton Heat Pump.

What bugs me the most is that his system is only 9.6kw and slated to produce 9800 Kwh a year. That's not even half his early consumption.
And it a fairly large house (2000sqft roof) with nice exposure. Is solar roof less efficient? I get 13Kw on 40 solar panels (600sqft)



Is he using electric for heat? My house if 4000sf and I consume about 1300kwh / year which includes charging my car for commuting. My 8.16 kw system is estimated to produce 13.5 kwh / year.
 

sorka

Well-Known Member
Feb 28, 2015
7,858
5,778
Merced, CA
Another reason to use energy from the batteries is surcharges, which may be levied against the power drawn from the grid as opposed to the net usage from the grid. May or may not apply where you are. In PA, if excess power is generated over the course of a year, the amount rebated is retail price minus the distribution costs. It isn't clear to me what is exactly meant by "retail price", but the distribution cost is 4.4 cents/kWh.

You still get credit for power put back on the grid including distribution. But you do eat the NBCs. The NEM round trip cost is about the same as the efficiency loss round trip from the battery. Of course you still want to put all peak production you can onto the grid for later consumption off peak, but if your comparing off peak into grid with off peak from grid, the 2.1 cents out of 17 cents / kwh is about 12% compared to 10% in and out of the PWs.
 

fbitz777

Member
Apr 6, 2016
421
549
Wexford, PA
Is he using electric for heat? My house if 4000sf and I consume about 1300kwh / year which includes charging my car for commuting. My 8.16 kw system is estimated to produce 13.5 kwh / year.
Yes he uses a heat pump (about 4kw or so) but when it's cold (under 20F) it gets into resistive mode (20kw or so)
My 13kw system produced 13Mwh first year although it was guaranteed by Solar City to produce 10 percent more...got a credit after two years (was like 65$) They had estimated I could get as high as 16Mwh but the shadow of a chimney is making me loose a lot (I guess one panel in the shade creates losses across multiple panels)

Here typical (PA) a is 1-1.1 Mwh per year per one kw of installed panels ..you obviously get more sun than us.
Below is my install and next one is my neighbor
 

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MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,564
8,741
Colorado
Does Colorado pay you for that overproduction? Washington prohibits it, by forcing the utility companies to zero out production credit every year (Apr 1, IIRC).
Yes. Typically we wouldn't have had such a large surplus but I worked from home most of last year after we expanded our solar system at the end of 2019. We can either get paid for the surplus or have it rolled over. We chose to just have it rolled over to help offset our usage during the winter months.
 
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RKCRLR

Member
Apr 13, 2020
307
121
Garden Valley, CA
Rather than “I see no good reason”, I take it you meant ‘I see no financial reason’.
I myself like minimizing my reliance on the grid. As such, I use battery power overnight in the summer. In the winter, I do have most of the PowerWalls reserved for backup as power is critical.

There are valid reasons, other than financial.
Maybe I shouldn't have said "no" good reason, I understand wanting grid independence.

But wanting to be greener may not be a valid reason in his case. ~10% of the solar being stored in being lost to inefficiencies. If the utility doesn't have a greater need for the power during the period when the power is being consumed from the batteries over when the solar would be directly fed to the grid then he is actually being less green. And needlessly depleting the battery life isn't green either.
 

wjgjr

Active Member
May 11, 2020
1,158
891
Silver Spring, MD
But wanting to be greener may not be a valid reason in his case. ~10% of the solar being stored in being lost to inefficiencies. If the utility doesn't have a greater need for the power during the period when the power is being consumed from the batteries over when the solar would be directly fed to the grid then he is actually being less green. And needlessly depleting the battery life isn't green either.
I think this is the important distinction to make. Sometimes, grid independence or a higher Tesla "self powered" score is directly linked to being the greenest, when that is not always the case. It depends on a number of factors, including, as you point out, when the PWs are discharged, and the mix of fuels used by the power company. There is nothing wrong with prioritizing being self-powered, or maximizing income, or maximizing environmental benefit, but these goals can sometimes be in conflict. However, in pretty much all of our cases, exactly how we use the system probably has a much smaller impact on the environment than the simple fact of having solar power installed.
 

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