Back to square 1.

[Eric99]

After waiting 6 weeks for a redesign, (i asked for panel placement and a ~10kw system) it came back Exactly the same as the original….8.16 in the same spot.
I wanted 10kw and 2 PWs.

Now i am considering cancelling and ordering a 12.75kw and 1 PW system. For roughly the same cost as 8kw and 2 PW.
My primary goal is money savings and using the 1PW for load/rate shifting. I dont care about backup.
If i go this route, what inverter(s) would i get? I want to make sure it is properly sized. I assume im in the minority of people that want a 12kw system with “only” 1 PW

 

[holeydonut]

There are a few threads about this already, but a 12 kWp DC system with 1 Powerwall seems to be an odd combo. The PV system would overpower the 1 battery if the PoCo goes offline. And your single Powerwall (while still a great thing) is probably undersized for your home in terms of backup and time of use balancing.

Last, if you want a vendor that will accommodate what you want instead of just taking what they give you; Tesla is not the best vendor for you.

 

[Eric99]

Thanks,
8kw would probably just cover my current usage. Hence the reason for the redesign to 10kw. But i recall reading recommendations to invest in more panels vs PWs given the option.

 

[holeydonut]

Thanks,
8kw would probably just cover my current usage. Hence the reason for the redesign to 10kw. But i recall reading recommendations to invest in more panels vs PWs given the option.

Hmmm I guess if your extra solar is just to handle a future EV or 2, then you may only benefit from a single PW for your normal home loads. TBH I think you need to consult with a better staffed and more responsive Solar Team for your purchase. Tesla isn't known for curating their designs to a particular home when it's a novel situation.

 

[SMAlset]

Everyone’s goals are different but we have an 8.16kW system with 3PWs and while it seems to be a good solution for us presently, I regret we didn’t add a 4thPW at the time we changed from 2 to 3.

We will sometimes charge both of our cars during the week and AC is probably the biggest daily load during the summer. We have gas cooking but electric double oven, gas water heater and furnace. With summers getting hotter and smoke in the air decreasing solar production sometimes, I’m thinking now more towards the future here. Sadly with code changes the single PW and stacked two we have are probably all we will ever be able to have. No more stacking by code which would have been easy for us at the time to add that 4th to the single.

I think it will be easier to add solar panels later if we decide to, but not PWs.

 

[h2ofun]

Everyone’s goals are different but we have an 8.16kW system with 3PWs and while it seems to be a good solution for us presently, I regret we didn’t add a 4thPW at the time we changed from 2 to 3.

We will sometimes charge both of our cars during the week and AC is probably the biggest daily load during the summer. We have gas cooking but electric double oven, gas water heater and furnace. With summers getting hotter and smoke in the air decreasing solar production sometimes, I’m thinking now more towards the future here. Sadly with code changes the single PW and stacked two we have are probably all we will ever be able to have. No more stacking by code which would have been easy for us at the time to add that 4th to the single.

I think it will be easier to add solar panels later if we decide to, but not PWs.

This is why I added about 15KW of panels to my about 15kw of panels, for about 30kw. And if you think ac takes power, I converted to total mini split heat pumps. The amount of electricity they use in the winters is in the same league as AC. This is why I have yet to hear anyone say they have TOO much solar.

 

[holeydonut]

Haha, basically the sentiment is one cannot have too much solar or too many batteries If only these things didn't cost so damn much.

I'm with SMAlset. I have a 8 kWp DC system with 3 Powerwall 2's and wish I could have had a 4th. And I wish I had more solar. And I wish I had more money

 

[wjgjr]

If i go this route, what inverter(s) would i get? I want to make sure it is properly sized. I assume im in the minority of people that want a 12kw system with “only” 1 PW

Just to address this part of the question - in the past it seemed like Tesla was pairing 3.8 kW of inverter with each size increment, so I would have expected you to get a 7.6 kW inverter and a 3.8 kW inverter with their 12 kW panel option. However, with the PW+, there have been reports of 12 kW systems with just the single 7.6 kW inverter due to a supposed "overdrive" feature which allows it to operate beyond the 7.6 kW spec. So, it is something to check with them about, assuming you go that route.

 

[ericl]

After waiting 6 weeks for a redesign, (i asked for panel placement and a ~10kw system) it came back Exactly the same as the original….8.16 in the same spot.
I wanted 10kw and 2 PWs.

Now i am considering cancelling and ordering a 12.75kw and 1 PW system. For roughly the same cost as 8kw and 2 PW.
My primary goal is money savings and using the 1PW for load/rate shifting. I dont care about backup.
If i go this route, what inverter(s) would i get? I want to make sure it is properly sized. I assume im in the minority of people that want a 12kw system with “only” 1 PW

I did countless hours of research on this (see my annoying threads).

So I'm assuming this is for solar panels and not roof. For the roof, I think one 7.6 inverter is enough.

For panels you might want to consider Tesla 7.6 + 3.6. However just keep in mind this combo is at 1.13 DC/AC ratio so if the array degrades as it ages you might see energy loss due to inefficiencies (eg it approaches 1:1).

Also depending on where you live and it's not everyday is sunny, you might want the larger array to convert as much as it can and keep it just a single 7.6 inverter. If you live in a cloudy area or if the solar panels are not in optimize positions; just go with the oversize with one powerall+ (and inverter).

 

[jboy210]

Everyone’s goals are different but we have an 8.16kW system with 3PWs and while it seems to be a good solution for us presently, I regret we didn’t add a 4thPW at the time we changed from 2 to 3.

We will sometimes charge both of our cars during the week and AC is probably the biggest daily load during the summer. We have gas cooking but electric double oven, gas water heater and furnace. With summers getting hotter and smoke in the air decreasing solar production sometimes, I’m thinking now more towards the future here. Sadly with code changes the single PW and stacked two we have are probably all we will ever be able to have. No more stacking by code which would have been easy for us at the time to add that 4th to the single.

I think it will be easier to add solar panels later if we decide to, but not PWs.

What is your system yielding in fall-spring? We have a 12.75 kW Solar roof and struggle to keep 2 PWs full during the late fall through early Spring. We can fill them by 10AM on a mid summer day, but that is not often enough for me to justify a 3rd PW.

 

[h2ofun]

What is your system yielding in fall-spring? We have a 12.75 kW Solar roof and struggle to keep 2 PWs full during the late fall through early Spring. We can fill them by 10AM on a mid summer day, but that is not often enough for me to justify a 3rd PW.

Yep, which is why I invested in a lot more solar. If you cannot charge batteries, what good are they , ESPECIALLY in the winter with low solar

 

[EVRider-FL]

We recently installed 10.56kW solar with 2 Powerwalls on our newly-constructed home. Since it was new, the installers (third-party Tesla certified) didn’t have any electrical usage history to go on, but they did a pretty good job sizing based on the electrical plan. We did want full backup capability, and after living with the system a while we realize the 2 Powerwalls wouldn’t get us through the night during a grid outage, so we added another Powerwall. With our normal home loads, the solar can’t fully charge the 3 Powerwalls (even though we’re in south FL), so we’re going to add another 3.96kW of solar. However, even without 100% charge, the 3 Powerwalls let us operate grid-free most of the time. I have the reserve set to 15% right now, but will increase it if a storm is coming.

 

[SMAlset]

/What is your system yielding in fall-spring? We have a 12.75 kW Solar roof and struggle to keep 2 PWs full during the late fall through early Spring. We can fill them by 10AM on a mid summer day, but that is not often enough for me to justify a 3rd PW.

Let me answer you this way, and for benefit of newbies who might be curious on the month to month basis. Our system for a 2-story, 3800 sq ft home: 8.16kW (24 Hanwha Q.Peak Duo Blk G6+ 340), 3 PW2 (40.5 kWh ESS); Major loads: 5-ton 2004 Carrier A/C split system--10 SEER, double oven, 2 Teslas charged off and on during the week sometimes. My Model 3 almost 100% home charged. With covid pretty much WFH vast majority of time. Other appliances are natural gas. First full month of data after PTO was 11/2020, so not full year yet. Tesla estimated our annual solar production @ 13,339 kWh (currently @ 12,144 kWh short of 2 months and will probably just exceed their projected by 10/31). We have 13 panels facing SW, 11 panels facing SE. SF South Bay area interior valley.

Month/Solar Energy kWh/Home Usage kWh - % Self Powered /% Solar/% PW
November/897/655 - 97%/49/48
December/859/667 - 97%/43/54
January/766/631 - 93%/40/53
February/978/649 - 100%/52/48
March/1280/680 - 99%/54/45
April/1466/725 - 100%/66/34
May/1633/674 - 99%/67/32

Our home usage was pretty consistent during the above, averaging 668kWh.

With Summer and A/C usage starting to be reflected (A/C set to 77F pretty consistently):
June/1530/832 - 100%/59/41
July/1450/956 - 100%/53/47
August/1285/952 - 100%/52/48

With our 3 PWs we were pretty much self-powered throughout the year and don't believe since receiving PTO we've incurred any cost for electricity so far from PG&E/SVCE other than that PG&E monthly fee they get you for. Future-wise: we will eventually replace our A/C system with a more efficient unit, but once return-to-office comes into play we can expect our Teslas will be charged more frequently at home. My husband's MS has free supercharging as long as he keeps it and his office does have charging there so hard to project how much additional charging our cars will require from home.

During a few week-periods of really hot (high 90 and 100s degree) consecutive days of heat, we have had our PWs reach our reserve limit, I think set in the low 20% range. And there were some days when the PWs didn't reach 100%. A few of those days we also used the sun to charge our cars so not all went back into the PWs. With our usage and during the summer we generally will see our 3 PWs filled by noon-1pm at which time we will charge our cars a bit. Overall been very happy with our system and enjoyed a very comfortable house this summer.

I'll also add thankfully no PSPSs here this year. One day in March and one in July we had a 20+second shift to backup power. And a 2 minute shift in July when PG&E came out to swap out a SmartMeter that was no longer displaying. So haven't had to live yet thought a power outage. Our app is showing our lifetime solar value based on SVCE EV2-A rates at $2624. True-up with SVCE is in November.

 

[jboy210]

Let me answer you this way, and for benefit of newbies who might be curious on the month to month basis. Our system for a 2-story, 3800 sq ft home: 8.16kW (24 Hanwha Q.Peak Duo Blk G6+ 340), 3 PW2 (40.5 kWh ESS); Major loads: 5-ton 2004 Carrier A/C split system--10 SEER, double oven, 2 Teslas charged off and on during the week sometimes. My Model 3 almost 100% home charged. With covid pretty much WFH vast majority of time. Other appliances are natural gas. First full month of data after PTO was 11/2020, so not full year yet. Tesla estimated our annual solar production @ 13,339 kWh (currently @ 12,144 kWh short of 2 months and will probably just exceed their projected by 10/31). We have 13 panels facing SW, 11 panels facing SE. SF South Bay area interior valley.

Month/Solar Energy kWh/Home Usage kWh - % Self Powered /% Solar/% PW
November/897/655 - 97%/49/48
December/859/667 - 97%/43/54
January/766/631 - 93%/40/53
February/978/649 - 100%/52/48
March/1280/680 - 99%/54/45
April/1466/725 - 100%/66/34
May/1633/674 - 99%/67/32

Our home usage was pretty consistent during the above, averaging 668kWh.

With Summer and A/C usage starting to be reflected (A/C set to 77F pretty consistently):
June/1530/832 - 100%/59/41
July/1450/956 - 100%/53/47
August/1285/952 - 100%/52/48

With our 3 PWs we were pretty much self-powered throughout the year and don't believe since receiving PTO we've incurred any cost for electricity so far from PG&E/SVCE other than that PG&E monthly fee they get you for. Future-wise: we will eventually replace our A/C system with a more efficient unit, but once return-to-office comes into play we can expect our Teslas will be charged more frequently at home. My husband's MS has free supercharging as long as he keeps it and his office does have charging there so hard to project how much additional charging our cars will require from home.

During a few week-periods of really hot (high 90 and 100s degree) consecutive days of heat, we have had our PWs reach our reserve limit, I think set in the low 20% range. And there were some days when the PWs didn't reach 100%. A few of those days we also used the sun to charge our cars so not all went back into the PWs. With our usage and during the summer we generally will see our 3 PWs filled by noon-1pm at which time we will charge our cars a bit. Overall been very happy with our system and enjoyed a very comfortable house this summer.

I'll also add thankfully no PSPSs here this year. One day in March and one in July we had a 20+second shift to backup power. And a 2 minute shift in July when PG&E came out to swap out a SmartMeter that was no longer displaying. So haven't had to live yet thought a power outage. Our app is showing our lifetime solar value based on SVCE EV2-A rates at $2624. True-up with SVCE is in November.

Thanks for the great data. It looks like you are getting great production numbers. Because of shading we see about 120 kWh for the month of December and don't go over 1000 kWh until April. We have to pull from the grid from November through April.

 

[h2ofun]

Thanks for the great data. It looks like you are getting great production numbers. Because of shading we see about 120 kWh for the month of December and don't go over 1000 kWh until April. We have to pull from the grid from November through April.

Yep, this is what I see, so much less in the winter. And we had little rain last year so was actually better than it will usually be. And with the smoke, my summer has been down too, like the last few years. Oh well,still hoping I have enough panels to get me enough NEM credits for winter time with my heat pumps

 

[SMAlset]

Thanks for the great data. It looks like you are getting great production numbers. Because of shading we see about 120 kWh for the month of December and don't go over 1000 kWh until April. We have to pull from the grid from November through April.

That’s low. At least you’re on Winter rates I guess. If our other appliances were electric of course our % self-powered would be different. For us the goal for solar/PW was to have backup during outages, be able to run A/C comfortably during summer, and charge cars using as much or all off solar when possible.

@Eric99 let us know what you decide to do. Some backup during outages is good to have for refrig/freezer and normal life at home functions including computer etc. My concern given you live in East Bay and I assume see foggy mornings during winter (and hopefully we see rain as well) will be how low your production will get then. A second PW when charged during sunny days will just give you that added protection and hours of usage if a winter storm knocks out power. I’m also concerned going with one PW unit initially and wanting to upgrade to a second later might be a problem for you down the road. You would also have to pay an install fee (what is it now?) twice due to the additional plan drawings required, permit fee, rolling another truck, getting new utility agreement and triggering a new PTO and true-up period and maybe new rate structure plan. I just see living with the 8.16 kWh solar being the easier road long term. Not sure how Tesla Energy is working through things now but some panel adjustments have been made on site at time of install when we had ours done.

 

[Eric99]

Thanks for all the details SMAIset, probably one of the best user experiences ive read. Very helpful

​

 

[SMAlset]

@Eric99 However you go with solar I will add seriously consider adding pest screening to your install early on. Tesla back then was able to add it to ours at install, not sure about now but there are companies that do this work in bay area as well. If Tesla is still doing it, it saves having another team walking up on your roof. You would need to arrange before hand with them and it is an additional charge.

Tesla’s solar panels have a skirt panel that gets added to the panels that comes down quite a bit but the roof peak side of the panels does not get this and critters still can get in underneath either way. This will prevent birds from nesting underneath (mess to clean out), keep out roof rats (prevalent in bay area I understand due to fruiting trees) and squirels from getting underneath and chewing on connectors (reducing potential panel power issues).

Adding screen protection is something new panel owners say they wish they heard about so in case you haven’t run into that thread yet putting out there again now.

Another thing to throw out there about 1 vs 2 PWs is that an A/C unit may require 2 in order to have enough power to start up.

 

[jboy210]

That’s low. At least you’re on Winter rates I guess. If our other appliances were electric of course our % self-powered would be different. For us the goal for solar/PW was to have backup during outages, be able to run A/C comfortably during summer, and charge cars using as much or all off solar when possible.

With the exception of our oven and A/C, we use mostly gas (heating, stovetop). I appreciate you showing how you can make use of 3 or even 4 PWs. I guess unless we can improve the shading we cannot make use of another PW.

But, while I would like more solar I am not cutting down my favorite trees in the backyard.

 

[SMAlset]

With the exception of our oven and A/C, we use mostly gas (heating, stovetop). I appreciate you showing how you can make use of 3 or even 4 PWs. I guess unless we can improve the shading we cannot make use of another PW.

But, while I would like more solar I am not cutting down my favorite trees in the backyard. View attachment 707100

So you are in a similar situation as us then with electrical load. I remember your install photos of your backyard and would be hard pressed to want to lose that tree too. The weight of that one branch may give way at some time though. Hopefully our years of drought will see the tree come through healthy. Increased pests during drought can be a factor too. We have two mature mule palms that flank our dining pergola (designed landscape for the placement) and know we’d hate to lose one or both of those not only for the large canopy shade but aesthetics.