More Powerwalls or Solar

[Ngenn]

Does it make sense to get more than two Powerwalls due to net metering or are you just better off getting more solar? I can understand it depends on the usage and use case but is there a general rule?

I’ve got 9.9 KWh capability w/2 walls and during the summer can fill the Powerwalls before 1pm. I can see getting more capacity to carry me longer through the night and morning but since that’s off peak it seems like I should just see if I can add more solar (not sure it will be as productive).

 

[arnolddeleon]

Sorry, no easy general rule.

You didn't describe how you use your powerwalls: backup only? self consumption? cost savings? How much, if any are you reserving for powerfailures? I can guess that it is not backup only since you mentioned filling them. Without knowing the answer to that your question is impossible to answer.

I will point out a couple of probably obvious points:

No amount of additional Powerwalls is going to change the amount energy you produce. All they can do shift when you use it (assuming that is a goal). So if you want more energy produced you need more solar. Additional batteries will however increase the amount power available to you in addition to increasing your energy storage.

Additional solar will on help you battery capacity if you are using battery during the day. So assuming you are not using batteries during the day (which you can for cost savings reasons) you will need more batteries if you want more energy stored/available at night.

 

[BrettS]

@arnolddeleon provided a great answer. If you give us some additional details that could help. You mention that you have net metering, so is your solar system producing 100% of your power demand (or close to it) over the year? If so then adding solar will probably provide little benefit as even with net metering most utilities provide very little or no compensation for overproduction. If your system is only meeting, say 50% of your demand then more solar could definitely be beneficial.

If you have TOU rates and you’re using the powerwalls to get through the peak usage times do they have enough capacity to do so or are they running out of power before the end of peak? Especially on hot days when you’re using the air conditioner a lot? If not, then an additional powerwall could be helpful.

Are you using the powerwalls as back up for grid outages? Is this in addition to load shifting? Do you feel that you have enough reserve to help get you through an extended outage? Again, if not then an additional powerwall could be helpful.

 

[Ngenn]

Thanks guys. I have switched the powerwalls to cost savings. I am reserving 6% for power failure since the ones to date have been for 30 seconds. I did get these partially to deal with a longer term outage due to firestorms (in CA) which took us out for 3 days (several times) last year but I should be able to reduce usage in that case.

Understand the batteries only help if I have excess generation which I seem to have over the summer. Not had them through the winter yet. But given I do have net metering I’m debating if I should just use the grid as my battery. Assuming that’s probably the most cost effective though at some point I’d prefer to be generating and using just what I produce.

Here is a pic of my usage from yesterday.

 

[Ngenn]

Seem like before getting more solar I should capture that which I am sending to the grid. I suspect though that this excess will reduce substantially over the winter and the powerwalls will be just sitting there.

 

[jjrandorin]

Yes, your winter production will likely be half of your summer production. You wont be using AC but may be using heat, and with 1/2 the production you will likely need to draw from the banked credits you have with the utility (which is what net metering is for).

Before you plan to add anything at all, you should live with the system for a year (through an entire 12 month cycle) so you can see what your true up situation is (whether you are a net consumer for the year, or a net producer).

 

[Ngenn]

I can’t see how I’m not a net consumer. I’ve been one for the last two years owing $1,000 each end of period and can’t imagine the power walls are going to make that much of a difference.

 

[SoCal Dave]

I can’t see how I’m not a net consumer. I’ve been one for the last two years owing $1,000 each end of period and can’t imagine the power walls are going to make that much of a difference.

How are you owing $1,000 every year? Is the app screenshot not representative of your normal usage? Looking at the screenshot you roughly seem to buy and sell the same amount of power. You also sell a lot back during peak. So from a net perspective you look positive in your favor.

You do have what looks like ~2kW * 12 hours of buying so 24kWh of NBCs. But that should only be about $0.55.

 

[jjrandorin]

I can’t see how I’m not a net consumer. I’ve been one for the last two years owing $1,000 each end of period and can’t imagine the power walls are going to make that much of a difference.

You need to see if that 1k charge is because you are using power during peak, or because you simply dont have enough solar.

 

[jakespeed]

when you say you charge your powerwalls by 1pm in the summer is that while also utilizing solar for power your home. if so then it sounds like you have plenty of panels

however, more panels could decrease the usage of the powerwalls & therefore lengthen their lifespan due to their limited number of cycles

if your utility is paying you less than full rate or full credits for your solar production then another powerwall could be beneficial to avoid being short-changed when selling back energy

 

[Ngenn]

You need to see if that 1k charge is because you are using power during peak, or because you simply dont have enough solar.

Great point. Will be interesting to see the impact of using cost savings as time goes on.

 

[Ngenn]

when you say you charge your powerwalls by 1pm in the summer is that while also utilizing solar for power your home. if so then it sounds like you have plenty of panels

however, more panels could decrease the usage of the powerwalls & therefore lengthen their lifespan due to their limited number of cycles

if your utility is paying you less than full rate or full credits for your solar production then another powerwall could be beneficial to avoid being short-changed when selling back energy

It’s a bit hard to tell now since I have switched to cost savings which charges the powerwalls completely first and uses the grid for the house during that time. Before I came to this forum and was convinced to run that way I was attempting to minimize all grid usage and so was getting my house powered and walls charged before 1pm.

Even with cost savings there are still a couple of hours before peak at 4pm when the walls are charged and It’s sending back to the grid. Once winter comes I doubt I will have that.

I also wonder if I should stay on this plan by PGE where the peak is 4-9pm. From what I hear people telling me maybe I should have stayed on a plan where peak matched my best solar output?

 

[Ngenn]

How are you owing $1,000 every year? Is the app screenshot not representative of your normal usage? Looking at the screenshot you roughly seem to buy and sell the same amount of power. You also sell a lot back during peak. So from a net perspective you look positive in your favor.

You do have what looks like ~2kW * 12 hours of buying so 24kWh of NBCs. But that should only be about $0.55.

Couple reasons I think although I was surprised with this hit (again had the same last year).

I just got the powerwalls really working this month. It took them due to covid, inspections and many corrections to get it passed, about two months. Before that I only had solar and was on a no time plan. I am now on the EVA-2 plan which I “hope” is better although PGE models say it won’t be (but this forum said it would).

I am also not driving my Tesla so that is certainly reducing my usage. The reduction in miles and working from home is driving me crazy. I know it’s crazy to want a commute...

 

[jboy210]

Here are our costs from PG&E before and after installing a Solar Roof and Powerwalls. I bet you can guess when they came online. The dates are billing dates. We are on TOU with a peak from 4-9 M-F.

It would be great to see how other's bills have changed.

Note, this is when we "playing with the system" and avoiding pushing power back to the grid. So we never filled the Powerwalls. Now we allow pushing back to the grid and letting the Powerwalls get to 100%. We are happy with the change!

 

[dancudds]

Here are our costs from PG&E before and after installing a Solar Roof and Powerwalls. I bet you can guess when they came online. The dates are billing dates. We are on TOU with a peak from 4-9 M-F.

It would be great to see how other's bills have changed.

Note, this is when we "playing with the system" and avoiding pushing power back to the grid. So we never filled the Powerwalls. Now we allow pushing back to the grid and letting the Powerwalls get to 100%. We are happy with the change!

View attachment 583190

You can see the PSPS outages too!

 

[miimura]

It’s a bit hard to tell now since I have switched to cost savings which charges the powerwalls completely first and uses the grid for the house during that time. Before I came to this forum and was convinced to run that way I was attempting to minimize all grid usage and so was getting my house powered and walls charged before 1pm.

Even with cost savings there are still a couple of hours before peak at 4pm when the walls are charged and It’s sending back to the grid. Once winter comes I doubt I will have that.

I also wonder if I should stay on this plan by PGE where the peak is 4-9pm. From what I hear people telling me maybe I should have stayed on a plan where peak matched my best solar output?

What plan were you on before? The plans that have Peak mostly during solar generating hours have been closed to enrollment for many years.

Also, PG&E has started actively changing the TOU schedule of rates now. E-6 will go through fundamental changes to make it more like the others. Before, they would not make schedule changes to rate plans, they would just close them to new customers and then force people to choose another after some time.

E-6 through 12/31/2020
Summer Season May 1-October 31 (6 months)
Peak 1pm-7pm M-F
Part-Peak 10am-1pm, 7pm-9pm M-F, 5pm-8pm Sa/Su
Winter
Part-Peak 5pm-8pm M-F
Off-Peak all other times

E-6 during 2021
Summer Season June 1-September 30 (4 months)
Peak 3pm-8pm M-F
Part-Peak Noon-3pm, 8pm-10pm M-F, 5pm-8pm Sa/Su
Winter
Part-Peak 5pm-8pm M-F
Off-Peak all other times

E-6 during 2022
Summer Season June-Sept (4 mo)
Peak 4pm-9pm M-F
Part-Peak 2pm-4pm, 9pm-10pm M-F, 5pm-8pm Sa/Su
Winter
Part-Peak 5pm-8pm M-F
Off-Peak all other times

In 2023 customers must choose another TOU plan available at that time.