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System 6.7 kWh + 2 PowerWalls - Will It Cover 100% of my Usage?

ftrv8

Member
Feb 2, 2016
16
6
Tracy, CA
Hello all,

I am getting two PowerWalls for a 2600 sq ft home with non Tesla solar panels. Due to code, and the roof layout of my two story home (very rectangular shape), 21 panels is a max I can fit up there. Based on my annual usage and the PowerWalls will I still be feeding from the utility. Would like to completely ween off them except for the damn interconnection fee. I am hoping the PowerWalls make up for the deficit somehow. Hopefully someone has been in the same situation has/had some experience with the same situation. All the bulbs in the house are LEDs and gas appliances. Two fridges though. Getting a Pacifica Hybrid minivan so will be installing a charger.

- NorCal (Central Valley) home, no shading.
- Annual usage last rolling year (the most) was 13,474 kWh
- System is 6.72 kWh (Panels are SilFab 320 NL), 2 PowerWalls, so using PVWatts site (no shading) system output comes out to 11,200 kWh annual.

Will the PowerWalls help in my situation?

Thanks in advance!

Bobby
 

wjgjr

Active Member
May 11, 2020
1,259
999
Silver Spring, MD
PWs do nothing to help you cover more of your usage (in fact, because they are 90% efficient in storing energy and have some basic energy use to operate on top of that, they actually will increase your usage.) What they do is increase your self-sufficiency. In your example, you are about 2,300 kWh short of covering 100% of your usage.

With solar only, what will happen is that at times, you will be producing more than you need, and you will send that energy to the grid. Then, when you are not producing as much or have higher home loads, you will take energy back from the grid. In other words, you rely more heavily on the grid.

With PWs, instead of sending the extra energy to the grid, you can store it in the PWs. Then, when you need more energy, instead of taking it from the grid, you take energy from the PWs. But even if you have enough PWs to never send any extra energy to the grid, that does not change the math, which says you will still need to take 2,300 kWh net from the grid over the course of the year. So PWs, reduce grid dependence, but they cannot generate any extra energy.

This is just addressing the energy balance. What this means financially depends on your utility and how they handle credits for energy you export to the grid.
 

BGbreeder

Member
Jun 19, 2020
297
190
Bay Area
@wjgjr makes great points about the effect of Powerwalls.

Winter will be tough to generate enough solar power to store; low sun angle, clouds (even in Tracy) make it hard to generate sufficient power, so I think the lack of sufficient solar is unlikely to do want.

As an aside, the PG&E solar limit of 110% of usage effectively means for almost all PG&E customers will have more than a little grid use during the winter, unless you have a huge roof, and large AC demand in the summertime, and next to no heating in the winter.

An EV makes the problem worse as more of your demand is spread year round, increasing the winter shortfall.

All the best,

BG
 

getakey

Active Member
Jan 28, 2020
1,325
429
95762
the key thing is not necessarily generating enough to cover all of your usage, but to reduce your usage from the grid during peak and send solar back to grid during peak. Thats what the PWs will do for you. So you could be a net user of grid power, but still have a zero or very low annual true up.
 

ftrv8

Member
Feb 2, 2016
16
6
Tracy, CA
PWs do nothing to help you cover more of your usage (in fact, because they are 90% efficient in storing energy and have some basic energy use to operate on top of that, they actually will increase your usage.) What they do is increase your self-sufficiency. In your example, you are about 2,300 kWh short of covering 100% of your usage.

With solar only, what will happen is that at times, you will be producing more than you need, and you will send that energy to the grid. Then, when you are not producing as much or have higher home loads, you will take energy back from the grid. In other words, you rely more heavily on the grid.

With PWs, instead of sending the extra energy to the grid, you can store it in the PWs. Then, when you need more energy, instead of taking it from the grid, you take energy from the PWs. But even if you have enough PWs to never send any extra energy to the grid, that does not change the math, which says you will still need to take 2,300 kWh net from the grid over the course of the year. So PWs, reduce grid dependence, but they cannot generate any extra energy.

This is just addressing the energy balance. What this means financially depends on your utility and how they handle credits for energy you export to the grid.
TY!
 

holeydonut

Supporting Member
Jun 27, 2020
1,868
1,251
East Bay NorCal
You're in a similar situation as me. I was using around 12,000 kWh per year before an EV. With an EV, I'll probably be up to like 14,000 kWh (rough math). I could only fit 23 panels, but I got 3 Powerwalls.

To determine why you may want 3 Powerwalls ... what you need to do (which is impossible) is to somehow predict:
  1. how you think PG&E will screw you on solar net metering for the first 12,000 kWh... remember we don't have 1:1 net metering in California due to TOU rates. And laws are ever-changing about obliterating NEM.
  2. separately try to predict how PG&E will screw you on trying to access that additional 2,000 kWh to power your EV.
No matter what you decide, you'll need to spend money. The challenge is trying to determine if you pay the $ up front in the form of buying batteries to sort of lock-in your costs; or risk the long run as you get slowly boiled by the relentless policies and ideology from PG&E as they extract value from you over time.

Remember, as a solar and EV customer, PG&E thinks you're part of the wealthy set that are kicking mud in the faces of disadvantaged people throughout the state. They want you to pay your fair share. And pay you will (eventually).

Since I hate PG&E, I was willing to pay up front to lock up some solar and batteries. This would buffer me from being exposed to the TOU rates. And, I could charge my future EV during the low off-peak EV2-A rate (remember, my solar array isn't large enough to generate power for an EV). Of course, I'm betting that PG&E continues to have off-peak EV charging rates low. But it is a real possibility that PG&E will just shaft EV owners in 5 years if PG&E sticks it to the silver-spooned EV population by making their charging rates triple.

So, to answer your question... with my annual base usage of 12,000 kWh (no EV), I need 3 batteries to effectively bridge the daily time gap from 3pm to midnight. This is the combined shoulder+peak time currently exposed on EV2A TOU. Thus, my feeling is your 2 batteries may not be sufficient to be completely free of TOU.

But the marginal cost of a 3rd Powerwall to really power through the shoulder+peak time may not be worth it. There is an incentive for a "large scale" residential ESS system, but the funds have dried up and I'm not sure you'll get this incentive now.

Keep in mind my approach to "size" an ESS is way different than what normal people use. Most people seem to think 1 Powerwall for every 4 kWp of solar production makes sense. They also typically size an ESS based on the types of loads that the system needs to operate in an outage. I'm exclusively looking at ESS sizing through the lens of hating on PG&E. And the only thing that helps a homeowner get distance from PG&E is more ESS.
 
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Reactions: pilotSteve

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
9,652
10,899
Riverside Co. CA
Hello all,

I am getting two PowerWalls for a 2600 sq ft home with non Tesla solar panels. Due to code, and the roof layout of my two story home (very rectangular shape), 21 panels is a max I can fit up there. Based on my annual usage and the PowerWalls will I still be feeding from the utility. Would like to completely ween off them except for the damn interconnection fee. I am hoping the PowerWalls make up for the deficit somehow. Hopefully someone has been in the same situation has/had some experience with the same situation. All the bulbs in the house are LEDs and gas appliances. Two fridges though. Getting a Pacifica Hybrid minivan so will be installing a charger.

- NorCal (Central Valley) home, no shading.
- Annual usage last rolling year (the most) was 13,474 kWh
- System is 6.72 kWh (Panels are SilFab 320 NL), 2 PowerWalls, so using PVWatts site (no shading) system output comes out to 11,200 kWh annual.

Will the PowerWalls help in my situation?

Thanks in advance!

Bobby

Your math shows you that it wont cover your usage 100%, on average. 11,200 generation, and 13,474 usage. Additionally, peoples usage goes UP when they get solar, not down. People always use more electricity because "we have solar, right?" (says the significant other as they crank on that AC lower).

It was already covered but powerwalls dont help generate more electricity, they only store what you make for use later in the day. Whether that helps you or not depends on how much peak energy you use now.
 

h2ofun

Active Member
Aug 11, 2020
2,684
492
auburn, ca
@wjgjr makes great points about the effect of Powerwalls.

Winter will be tough to generate enough solar power to store; low sun angle, clouds (even in Tracy) make it hard to generate sufficient power, so I think the lack of sufficient solar is unlikely to do want.

As an aside, the PG&E solar limit of 110% of usage effectively means for almost all PG&E customers will have more than a little grid use during the winter, unless you have a huge roof, and large AC demand in the summertime, and next to no heating in the winter.

An EV makes the problem worse as more of your demand is spread year round, increasing the winter shortfall.

All the best,

BG
I sure am going to be testing that 110% limit. Is it the last 12 months, period, or can it be 3 years? Can it be driven by how many batteries on has? Since I have 15K now, 47 panels, and have plans in motion for another 15K, 41 panels, which would put me at 88 panels, 29K, many not perfect directions, I keep asking my installer, has PGE approved before you put them on my roof, and risk at your cost having to remove?
 

BGbreeder

Member
Jun 19, 2020
297
190
Bay Area
I sure am going to be testing that 110% limit. Is it the last 12 months, period, or can it be 3 years? Can it be driven by how many batteries on has? Since I have 15K now, 47 panels, and have plans in motion for another 15K, 41 panels, which would put me at 88 panels, 29K, many not perfect directions, I keep asking my installer, has PGE approved before you put them on my roof, and risk at your cost having to remove?
Yes, I have suspected that it might come up for your expansion plans... ;)

In the past, PG&E has accepted customer requests for more than 110% when customers have made the case for anticipated increases in usage, e.g. new EV, new dryer, electric stove, etc. I would like to think that local grid demand patterns play into it, but that is probably giving them too much credit for overthinking it. Worst case is they say no, you demonstrate the need for additional power for a year and with additional demand and then do the additional solar installation.

I am sure that you will let us know how it turns out.

All the best,

BG
 

h2ofun

Active Member
Aug 11, 2020
2,684
492
auburn, ca
Yes, I have suspected that it might come up for your expansion plans... ;)

In the past, PG&E has accepted customer requests for more than 110% when customers have made the case for anticipated increases in usage, e.g. new EV, new dryer, electric stove, etc. I would like to think that local grid demand patterns play into it, but that is probably giving them too much credit for overthinking it. Worst case is they say no, you demonstrate the need for additional power for a year and with additional demand and then do the additional solar installation.

I am sure that you will let us know how it turns out.

All the best,

BG
Worst is I Try all that stuff and they say no. Costs me nothing but time. If NEM3 was not coming, I would NOT be even considering this!! I will never pay it back. And worst, if it gets approved and they eliminate NEM2, and charge per KW of panels, I am SCREWED.

The only reason I got approved for what I have is because of my house accident, I went to stand alone heaters, AC, and used 40,000 kw in one year!!
 

ftrv8

Member
Feb 2, 2016
16
6
Tracy, CA
You're in a similar situation as me. I was using around 12,000 kWh per year before an EV. With an EV, I'll probably be up to like 14,000 kWh (rough math). I could only fit 23 panels, but I got 3 Powerwalls.

To determine why you may want 3 Powerwalls ... what you need to do (which is impossible) is to somehow predict:
  1. how you think PG&E will screw you on solar net metering for the first 12,000 kWh... remember we don't have 1:1 net metering in California due to TOU rates. And laws are ever-changing about obliterating NEM.
  2. separately try to predict how PG&E will screw you on trying to access that additional 2,000 kWh to power your EV.
No matter what you decide, you'll need to spend money. The challenge is trying to determine if you pay the $ up front in the form of buying batteries to sort of lock-in your costs; or risk the long run as you get slowly boiled by the relentless policies and ideology from PG&E as they extract value from you over time.

Remember, as a solar and EV customer, PG&E thinks you're part of the wealthy set that are kicking mud in the faces of disadvantaged people throughout the state. They want you to pay your fair share. And pay you will (eventually).

Since I hate PG&E, I was willing to pay up front to lock up some solar and batteries. This would buffer me from being exposed to the TOU rates. And, I could charge my future EV during the low off-peak EV2-A rate (remember, my solar array isn't large enough to generate power for an EV). Of course, I'm betting that PG&E continues to have off-peak EV charging rates low. But it is a real possibility that PG&E will just shaft EV owners in 5 years if PG&E sticks it to the silver-spooned EV population by making their charging rates triple.

So, to answer your question... with my annual base usage of 12,000 kWh (no EV), I need 3 batteries to effectively bridge the daily time gap from 3pm to midnight. This is the combined shoulder+peak time currently exposed on EV2A TOU. Thus, my feeling is your 2 batteries may not be sufficient to be completely free of TOU.

But the marginal cost of a 3rd Powerwall to really power through the shoulder+peak time may not be worth it. There is an incentive for a "large scale" residential ESS system, but the funds have dried up and I'm not sure you'll get this incentive now.

Keep in mind my approach to "size" an ESS is way different than what normal people use. Most people seem to think 1 Powerwall for every 4 kWp of solar production makes sense. They also typically size an ESS based on the types of loads that the system needs to operate in an outage. I'm exclusively looking at ESS sizing through the lens of hating on PG&E. And the only thing that helps a homeowner get distance from PG&E is more ESS.
TY for the write up, I was initially at one wall, but went with two, but here is the kicker. I am with a worst utility than PGE… drumroll… MID! Now they are a very special breed of utilities company.
 

holeydonut

Supporting Member
Jun 27, 2020
1,868
1,251
East Bay NorCal
Wow you're in the Modesto Irrigation Whatevers?

BTW, your rates are nowhere near as bad as PG&E. That fixed $30 a month interconnection you have to pay to get access to the CAISO energy is peanuts in the grand scheme. Look at your summer peak rates vs ours!


1622067865560.png



Edit: PG&E summertime EV2-A is shown here.
1622067885791.png



And PG&E wants to blame their high rates on homeowners with solar. It's clear to me PG&E is just stupidly run with inefficiencies across the board driving up their rates.
 

ftrv8

Member
Feb 2, 2016
16
6
Tracy, CA
Wow you're in the Modesto Irrigation Whatevers?

BTW, your rates are nowhere near as bad as PG&E. That fixed $30 a month interconnection you have to pay to get access to the CAISO energy is peanuts in the grand scheme. Look at your summer peak rates vs ours!


View attachment 666605


Edit: PG&E summertime EV2-A is shown here.
View attachment 666606


And PG&E wants to blame their high rates on homeowners with solar. It's clear to me PG&E is just stupidly run with inefficiencies across the board driving up their rates.
Wow! Must be new. Last I checked prices were the other way around. Though with Covid and my wait times on permits (over a year and half), I wonder if things changed.
 

holeydonut

Supporting Member
Jun 27, 2020
1,868
1,251
East Bay NorCal
Wow! Must be new. Last I checked prices were the other way around. Though with Covid and my wait times on permits (over a year and half), I wonder if things changed.

Oh you’re right, that thing I posted may just be the transmission or generation charge. You may be billed separately for the total. I have no clue how MID operates.
 

sorka

Well-Known Member
Feb 28, 2015
8,170
5,946
Merced, CA
PWs do nothing to help you cover more of your usage (in fact, because they are 90% efficient in storing energy and have some basic energy use to operate on top of that, they actually will increase your usage.) What they do is increase your self-sufficiency. In your example, you are about 2,300 kWh short of covering 100% of your usage.

My EV2A on the summer schedule lets me leverage my solar production of 55 kwh / day into 78 kwh / day by selling high and buying low. That factors in the 10% round trip loss.
 

sorka

Well-Known Member
Feb 28, 2015
8,170
5,946
Merced, CA
Your math shows you that it wont cover your usage 100%, on average. 11,200 generation, and 13,474 usage. Additionally, peoples usage goes UP when they get solar, not down. People always use more electricity because "we have solar, right?" (says the significant other as they crank on that AC lower).

We're about to hit air conditioning season next month. We're going to probably use twice as much AC as we used because "we have solar" :)
 
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Reactions: jjrandorin

sorka

Well-Known Member
Feb 28, 2015
8,170
5,946
Merced, CA
I have 101 for Sunday. AC will be getting used and yep, setting to 74 :)

74? That's a bit over the top 😜

We'll be setting to 78 but it will get automatically drop to 76 from 2 to 3 pm before going back up to 78 for a bit of off peak pre-charge.

If my wife had her way, she'd set to 65F in the summer and 85F in the winter. I ask her why she wouldn't just want it set to the same temp all year around. Her reply is that when it's cold and freezing outside she wants to be nice toasty inside and when it's burning up outside, she wants it like a refrigerator inside. It makes no sense to me all why a human being would want it this way. I'm sure it's something psychological though.
 

h2ofun

Active Member
Aug 11, 2020
2,684
492
auburn, ca
74? That's a bit over the top 😜

We'll be setting to 78 but it will get automatically drop to 76 from 2 to 3 pm before going back up to 78 for a bit of off peak pre-charge.

If my wife had her way, she'd set to 65F in the summer and 85F in the winter. I ask her why she wouldn't just want it set to the same temp all year around. Her reply is that when it's cold and freezing outside she wants to be nice toasty inside and when it's burning up outside, she wants it like a refrigerator inside. It makes no sense to me all why a human being would want it this way. I'm sure it's something psychological though.
I have so much excess generation, I can do whatever. Now we shall see if thats too cold for her, if so we will try 76. And since I run off batteries 100% after 30, and basically all solar before, I prepaid for all this furn My wife wants it cold. So next winter, rather than my 60 degree, want to do 66 or 68. For 30 years never could do any of this, house to big and expensive. But with solar (any maybe more), and batteries, I can do ANYTHING!!!!
 

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