Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Arizona Powerwall Installs

cwied

Member
Jan 13, 2015
869
617
San Mateo, CA
Curious, the left-most box doesn't look like a normal Gateway, is that really what it is? Main difference is the lack of antennae on the top, do the two boxes share a Neurio or something?

Comparing to my (California) installation, I'm guessing that Backup Gateway 1 is what's called the "generation panel" in my case. It has the breakers for the Powerwalls and solar in it and feeds into the Gateway. This actually looks quite similar to my installation except I only have one solar inverter and none of the cutoffs.
 
  • Like
Reactions: SSonnentag

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
They are looking into their options. They claim SRP won't allow sharing my conduit. It's possible SRP needs dedicated feeds because they hook up their monitoring equipment as part of their survey program. But that's a wild guess.

Well, I just adjourned a special meeting with Tesla (2) and SRP (3) at my house. The reason SRP doesn't want to share wires in my conduit is because they lock the box where my wires would need to pass through and I would have no way to access my own wiring. I offered to accept this lock-out (why would I ever need to pull my Model 3 charging wires anyway). They didn't say no, and wanted to see the full schematic first, but it's against the general rule it seems.

More worrisome is that my roof paper has about 1/2" of lifted curl under the tile - it's about 20 yrs old. The total overlap is about 2-1/2" so I figure it could curl for another 80 yrs? Anyone know costs of re-papering a ceramic tile roof. (I could get away with half the roof). Cheaper in the winter I bet.

Doing this for an ROI is weak now, but it still feels right. And because I can't back up my A/C units until I get more efficient ones, we talked about pre-wiring for that eventuality. That's also a costly route and now I may have to live without A/C if there's an SRP outage. Not quite the system I envisioned, but not a lot of options either. Plus, the deductions are fading fast... so then when, right?

I really wanna be a player (so I don't feel guilty when I drive fast anyway). This Tesla stuff is life-changing.
 

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
Ultimately I stuck with it because I have wanted solar for years and with their price drop it made my ROI at a level I was comfortable with. Plus I wanted to support the brand. Biggest hesitation was after sales support I have heard horror stories so I’m hoping that only gets better. First month in it looks like my bill dropped about $160.

Net $160 savings on total power, or off the SRP bill. Are you saving in other words compared to your monthly payment. That's the result that would get others going. People looked into this in the past and SRP was not worth it. But a 40% design has merit. People don't know that yet. Close friend ruled it out and never re-considered it because of poor ROI in the past.
 

Kenne74

Member
Mar 6, 2013
131
31
Arizona
I paid $16000k to re-paper my roof and a few other things before I added solar. My home is 25 years old and 2800 soft, so I figured I did not have much of a choice. I’m not sure why you can’t back up your AC units perhaps I missed it, but I have mine backup with no issues.
 

Chancellor32

Member
May 10, 2018
711
479
Queen Creek, AZ
Net $160 savings on total power, or off the SRP bill. Are you saving in other words compared to your monthly payment. That's the result that would get others going. People looked into this in the past and SRP was not worth it. But a 40% design has merit. People don't know that yet. Close friend ruled it out and never re-considered it because of poor ROI in the past.
$160 in bill savings. Overall savings was only about $60. Not amazing but feels great knowing almost 50% of my power comes from panels/PW and that for all the other power I am paying $.03-$.04! I was paying about $6 a day to SRP and now it is $2.20 a day. Monthly payment on panels is $100. Demand charge was $2.05
 
  • Like
Reactions: vickh

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
Pushing for whole-home backup redesign, and re-thinking my AC units. Gotta have AC in case of an outage, and I'm assuming I can easily add more PVs if I want to cover 100% demand. At 8kW panels, it's only covering 55%. But my demand is exaggerated because of other inefficiencies. My AC is my worst energy drain, currently at 11 seer, 19 yr old Tranes.

At bit off topic... my heater is a gas furnace in the attic in-line with the AC coil, so I can't get more than a seer 14 without completely replacing the heater too. That's because higher efficiency AC units need a variable speed fan and my current fan is part of the heater box. The advanced fans have controller boards and communication wires tied in so they won't fit in my existing box. So to get really efficient, it's a complete rebuild.

The AC compressors have to be Scroll types so that they can install a "soft start" which virtually eliminates the demand spikes when the compressor turns on. My 2 powerwalls can deliver up to 56 Amps, so I can't go over that for any compressor. The Soft Start makes it so you can take a higher rated AC unit and regulate the load down quite a bit.

SRP has rebates on AC upgrades, but you need min seer 16 to qualify. A 4 ton system can get you $900 back, but the heater part costs about $1,200 (plus install), and the system is more complex (more to fail with 2 compressors), plus the install is harder. The door to the attic is smaller than the boxes, so some ceiling has to be removed or the unit disassembled and reassembled in the attic. So most just replace their coil only in the attic and the unit outside with a 14 seer (Goodman is actually 14.5 seer). There are diminishing returns on going to higher seer numbers, but one advantage is comfort because the temps are more stable. There are some savings on the AC bill with a more efficient system, but if we're only paying 3-4 cents per kW from SRP, the savings are only 1/3 of what they claim on their website.

Just thought I'd share some of this... was a lot of info to figure out. Who knows, someday I may want to switch from gas to electric heat and add more panels, so I think I'll just go for the seer 14 units, 4 ton, low cost but still works when the Grid's offline. You can get these AC units for just $1,400 + coil $500, + line set, plus install (varies widely). They come pre-charged so there should be no fee for evac or charging (unless you're coil is more than 25' apart. Initial quote was $4,500 but confirming with an inspection next week.

TMI?
Maybe...
 

miimura

Well-Known Member
Aug 21, 2013
6,161
5,754
Los Altos, CA
Facing those difficulties, I might be inclined to install some mini-split type A/C in critical rooms like your bedroom, so those can be kept cool during an outage and also provide more efficiency so you can run the central unit less.
 

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
I paid $16000k to re-paper my roof and a few other things before I added solar. My home is 25 years old and 2800 soft, so I figured I did not have much of a choice. I’m not sure why you can’t back up your AC units perhaps I missed it, but I have mine backup with no issues.

My A/C is old and needs too many Amps to start-up on Battery only. So I'm scoping new A/C while they explore pre-wiring for full backup maybe next year. I would need more PWs to backup it all today.
 

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
My A/C is old and needs too many Amps to start-up on Battery only. So I'm scoping new A/C while they explore pre-wiring for full backup maybe next year. I would need more PWs to backup it all today.

One down, one to go (Yes!). New Condenser and Coil = $2,500 installed. Found a Tech to help me out on Nextdoor... challenging in the attic, but a good sweat!

Get this, at temps over 105F, all those expensive units with 20+ seer ratings lose performance to as low as 13-14 seer. Not a chart you're going to find in the public domain. So seer 14 is just fine for Arizona, and very cost effective.

This is the new coil in the old furnace, slides in (mostly). Keep the heater and fan part too.

20190928_104535.jpg


Need the Soft Start now to lower my peak surge current as needed for the powerwall batteries. Only works with scroll compressors per Tesla. Goal was for whole home backup - why miss out on the best part, right?

20190928_161530.jpg
 
  • Like
Reactions: JayClark

azdryheat

Member
Jul 6, 2016
404
580
Mesa, AZ
One down, one to go (Yes!). New Condenser and Coil = $2,500 installed. Found a Tech to help me out on Nextdoor... challenging in the attic, but a good sweat!

Get this, at temps over 105F, all those expensive units with 20+ seer ratings lose performance to as low as 13-14 seer. Not a chart you're going to find in the public domain. So seer 14 is just fine for Arizona, and very cost effective.

This is the new coil in the old furnace, slides in (mostly). Keep the heater and fan part too.

View attachment 461464

Need the Soft Start now to lower my peak surge current as needed for the powerwall batteries. Only works with scroll compressors per Tesla. Goal was for whole home backup - why miss out on the best part, right?

View attachment 461465

Where did you get your info on HVAC's losing efficiency? I would think this would also apply to a 14 SEER unit.

I agree that it starts to make little sense cost wise to go with the highest SEER unit, but solar and Tesla's are in the same category.
 

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
Where did you get your info on HVAC's losing efficiency? I would think this would also apply to a 14 SEER unit.

I agree that it starts to make little sense cost wise to go with the highest SEER unit, but solar and Tesla's are in the same category.

I'm still looking for a graph like this. The tech said he learned this in HVAC school. If true, it's a dirty little secret, doubt it's very public. Impression I got was that my seer 14 would not drop that much, but lots of variables here. Plus, given there's no standard rate on anything in the HVAC industry, I wouldn't be surprised by a coverup here.

Not sure what you meant by "Tesla and solar are in the same category."
 

cwied

Member
Jan 13, 2015
869
617
San Mateo, CA
I think your tech is confusing EER and SEER. EER is the unit's efficiency at a given temperature. SEER is the unit's efficiency over a "typical cooling season." (Seasonal energy efficiency ratio - Wikipedia). Given the definition, it doesn't make sense to talk about SEER relative to a temperature (since it's actually EER averaged over a bunch of different temperatures).

The higher the outdoor temperature, the more energy it takes to cool your house to a given temperature. That's just physics. A 14 SEER AC would be affected by this just as much as a 20 SEER unit. While a 20 SEER unit at 105 degrees might be functioning like a 14 SEER unit would at 95 degrees, at 105 degrees a 14 SEER unit is now using as much energy as a 10 SEER unit at 95 degrees.
 
  • Like
Reactions: D3xDt3Reaction

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
I think your tech is confusing EER and SEER. EER is the unit's efficiency at a given temperature. SEER is the unit's efficiency over a "typical cooling season." (Seasonal energy efficiency ratio - Wikipedia). Given the definition, it doesn't make sense to talk about SEER relative to a temperature (since it's actually EER averaged over a bunch of different temperatures).

The higher the outdoor temperature, the more energy it takes to cool your house to a given temperature. That's just physics. A 14 SEER AC would be affected by this just as much as a 20 SEER unit. While a 20 SEER unit at 105 degrees might be functioning like a 14 SEER unit would at 95 degrees, at 105 degrees a 14 SEER unit is now using as much energy as a 10 SEER unit at 95 degrees.

... and maybe my facts aren't exactly correct (seer/eer sound the same to this old fart). I'll follow up with the guy for some details. What I'd like to know is whether the effect is greater on higher err ratings - getting at true cost savings vs theoretical in places like the Arizona deserts.

My utility company tells me how much money I can save with the higher seer #s, then they do an ROI using 11 cents/kWh as the cost basis. But I'm going to be buying electricity (if needed) at 3 cents/kWh (cheap at night). So seer 14 seems most cost effective, and I bet it's cheaper to get more solar panels than more A/C efficiency over the useful life of the solar (+3 A/C units).

It's almost like paying more for the Model 3, and save on fuel. Except not how I drive... 350 watt/mi around the city says I'm no grandma.
 

azdryheat

Member
Jul 6, 2016
404
580
Mesa, AZ
I'm still looking for a graph like this. The tech said he learned this in HVAC school. If true, it's a dirty little secret, doubt it's very public. Impression I got was that my seer 14 would not drop that much, but lots of variables here. Plus, given there's no standard rate on anything in the HVAC industry, I wouldn't be surprised by a coverup here.

Not sure what you meant by "Tesla and solar are in the same category."


Solar power and buying a Tesla are something you do more for the fun and using less fossil fuel. If you look at the cost of ownership, they are still at best a break even. Same with buying a 20 SEER HVAC. Break even point is way into the future at best.
 

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
Solar power and buying a Tesla are something you do more for the fun and using less fossil fuel. If you look at the cost of ownership, they are still at best a break even. Same with buying a 20 SEER HVAC. Break even point is way into the future at best.

Mine was more for comfort in having a stable temp throughout the day (hate Time of Use plans), and in case of major outages or attacks. ROI is only about 15 yrs on my system. Panels should be good for 30, batteries... not even close but it balances out.

Not sure a seer 20 cost difference will ever "break even" because you also have more frequent repairs. Neighbor is getting a seer 16 (for the utility rebate), but paying $7,500. He's at least $4,000 more than my system... and will never recoup over 10 yrs on a delta seer of just 2. Assuming Solar is cheaper than grid (in Az anyway), it may be smarter to get the lower efficiency A/C and have fewer repairs.
 
Dec 2, 2017
358
339
Arizona
Not sure a seer 20 cost difference will ever "break even" because you also have more frequent repairs. Neighbor is getting a seer 16 (for the utility rebate), but paying $7,500. He's at least $4,000 more than my system... and will never recoup over 10 yrs on a delta seer of just 2. Assuming Solar is cheaper than grid (in Az anyway), it may be smarter to get the lower efficiency A/C and have fewer repairs.
We actually replaced two four-ton 13 SEER units with 20 SEER units here in AZ. First full month in September showed about a 30% decrease in overall energy usage YOY, implying greater than 30% of A/C energy decrease as advertised. I’m not sure the high temperatures bothered them.

Will they ever pay back over just putting back lower SEER units in energy savings alone? No, but they are variable speed (even temperature and reduced allergens), quiet, start/run on about 20 amps (can be backed up with Powerwalls), and have a great user interface to geek out on. A pure financial play probably would have involved lower SEER units, though.
 

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
We actually replaced two four-ton 13 SEER units with 20 SEER units here in AZ. First full month in September showed about a 30% decrease in overall energy usage YOY, implying greater than 30% of A/C energy decrease as advertised. I’m not sure the high temperatures bothered them.

Will they ever pay back over just putting back lower SEER units in energy savings alone? No, but they are variable speed (even temperature and reduced allergens), quiet, start/run on about 20 amps (can be backed up with Powerwalls), and have a great user interface to geek out on. A pure financial play probably would have involved lower SEER units, though.

Got a couple of Soft Starts that keep the amps low, so these are backed up as well.
I'm looking forward to the Tesla energy app for sure!
 

SOULPEDL

Supporting Member
Jul 25, 2016
2,984
11,305
Arizona
The higher the outdoor temperature, the more energy it takes to cool your house to a given temperature. That's just physics. A 14 SEER AC would be affected by this just as much as a 20 SEER unit. While a 20 SEER unit at 105 degrees might be functioning like a 14 SEER unit would at 95 degrees, at 105 degrees a 14 SEER unit is now using as much energy as a 10 SEER unit at 95 degrees.

I did a follow up question with my installer, and I agree I should use EER. But I still disagree with your statement. The reason high efficiency units drop out rapidly at higher temperatures (Arizona especially) is because the system cannot maintain an easy 1 deg F change. So it has to use the larger compressor or both compressors, which brings them back to EER 13'ish. (Likely along with my unit as well but nowhere "neer" as much EER.) If you want to compare specs, be my guest. I'm sure this has a gradient effect and may be just a curve function of 2nd stage compressor duty cycle.
 

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top