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Arizona Powerwall Installs

Chancellor32

Member
May 10, 2018
719
485
Queen Creek, AZ
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PW is a stud! Highest demand peak has been .2kw!
 
Dec 2, 2017
358
339
Arizona
Pulled the trigger today for 8.19kW solar + 2 PW through Tesla.
Exactly what I signed on for as well recently - SRP just approved the design today. I agree that 4 kW and 1 PW might have been a better ROI but like you said it depends on whether your house can make it through peak. Anyway, with 2 PW I can back up our A/C that we just replaced with more efficient variable speed units.

I was wondering why Tesla couldn’t use the newer Panasonic 325W panels though since the 315W panels are discontinued on the Panasonic web site. (I’m assuming you have 26 315W panels in your design too.) Sent an Email to my advisor but no response yet. Not a big deal and would probably clip on the 7.6kW inverter sometimes but 8.45kW max would be a little better for cloudy days.
 

SOULPEDL

Supporting Member
Jul 25, 2016
3,119
11,952
Arizona
Anyway, with 2 PW I can back up our A/C that we just replaced with more efficient variable speed units.

They wouldn't back up our A/C because the startup pull is crazy high amps (60A small, and >100A on the main) without a 3rd PW or another service box (costing more from SRP too). So we plan to upgrade the A/C and then add it to the branch circuit. They tell me it needs to be a Scroll compressor AND if we use their power conditioner (probably a huge capacitor). What did you use exactly? And was a power conditioner used?

As I understood, without A/C backed up, it can still run my A/C 100% from the battery, but not if there's a power outage from SRP. There must be something in the gateway that disconnects that branch when SRP power fails. At least that's the only logical explanation. A schematic would help. I've heard bad stories here about added costs, and they neglected to put "Install battery in garage". In fact the contract specifies everything near the service box. Oh well, 3 days to get that in writing.

The way I see it, 55% (of current full demand) has become a new goal (and that's with the Model 3). New A/C will be the priority, but everything becomes a candidate for scrutiny (like the pool pump, add some Pink Panther in the rafters, more shade on walls... We're already on gas for stove and hot water, but some sunny day I could switch back to an electric kitchen.
 
Dec 2, 2017
358
339
Arizona
They wouldn't back up our A/C because the startup pull is crazy high amps (60A small, and >100A on the main) without a 3rd PW or another service box (costing more from SRP too). So we plan to upgrade the A/C and then add it to the branch circuit. They tell me it needs to be a Scroll compressor AND if we use their power conditioner (probably a huge capacitor). What did you use exactly? And was a power conditioner used?
Our A/C units were pretty old so we replaced them with two Lennox XC20. They have a startup current of only 20 amps each. Tesla checked the specs and they said they could be backed up.
 

SOULPEDL

Supporting Member
Jul 25, 2016
3,119
11,952
Arizona
I was wondering why Tesla couldn’t use the newer Panasonic 325W panels though since the 315W panels are discontinued on the Panasonic web site. (I’m assuming you have 26 315W panels in your design too.)
Yes, 315's here. Discontinued? Geeze, it's always a moving target with Tesla - they move so fast. But power is power. And since I have plenty of roof, they could put 100kW for all I care. I'm sure we're paying for watts here. Guaranteed 80% at 25 yrs is what really matters.

They say my "system lifespan" is 30 yrs. Those batteries will be toast by then. Unlike PVs, Lithium batteries die quickly when they decide. I'll be happy 85% in 10 yrs, 75% in 15 if they make it? We'll see... I'm going to try and vent my garage. Too many batteries in there now. I always bring my rechargeables in the house. I think the car is now cooling more at night in fact because it's still 105F in the garage in the evening.
 
Dec 2, 2017
358
339
Arizona
View attachment 442856 View attachment 442854

These are the two panels Tesla offers, I went with the Q cell hanwha because the warranty was slightly better.
Thanks for the info. Looks like the trade off is in the temperature coefficient: the Hanwha panels lose 0.37% per degree C whereas the Panasonic lose 0.258%. But since we’re playing the demand game here maybe it doesn’t make much difference.

Link to the “discontinued” Panasonic 315W is: N315K Photovoltaic Module HIT® BLACK. The 325W is here, but you’re probably correct that Tesla won’t offer them: N325K Photovoltaic Module HIT® BLACK, 40mm.
 
Dec 2, 2017
358
339
Arizona
They say my "system lifespan" is 30 yrs. Those batteries will be toast by then. Unlike PVs, Lithium batteries die quickly when they decide. I'll be happy 85% in 10 yrs, 75% in 15 if they make it?
Sounds like healthy skepticism. Tesla battery chemistry and thermal management is pretty impressive on their vehicles that have been out there a while though, so I’m cautiously optimistic. When the batteries die I guess we should still have pretty decent PV arrays.
 
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SOULPEDL

Supporting Member
Jul 25, 2016
3,119
11,952
Arizona
View attachment 442821 View attachment 442820 PW is a stud! Highest demand peak has been .2kw!

Whoa! An interesting graph you have. Been staring at it for an hour. Here's what I can gleem:
  1. That 200W was at 3PM (slight white line above 0).
  2. Solar energy charges battery in the morning.
  3. You're PW is fully charged by 1PM.
  4. From 2-8 you do not use any SRP (but 200W mentioned).
  5. Peak solar output is about 3kW
  6. About 2PM you fed the grid, twice.
  7. About 8:30PM you start charging your vehicles, done at 4AM (Drive much?)
  8. Your A/C unit is not variable speed.
Close?
 
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Dec 2, 2017
358
339
Arizona
Whoa! An interesting graph you have. Been staring at it for an hour. Here's what I can gleem:
  1. That 200W was at 3PM (slight white line above 0).
  2. Solar energy charges battery in the morning.
  3. You're PW is fully charged by 1PM.
  4. From 2-8 you do not use any SRP (but 200W mentioned).
  5. Peak solar output is about 3kW
  6. About 2PM you fed the grid, twice.
  7. About 8:30PM you start charging your vehicles, done at 4AM (Drive much?)
  8. Your A/C unit is not variable speed.
Close?
I’d also guess a bit of cloud cover passed over about 1 pm. You can see the power output dip and then jump above the rest of the curve. Presumably the array cooled off a little and temporarily gained efficiency until it warmed up again.
 

Chancellor32

Member
May 10, 2018
719
485
Queen Creek, AZ
Whoa! An interesting graph you have. Been staring at it for an hour. Here's what I can gleem:
  1. That 200W was at 3PM (slight white line above 0).
  2. Solar energy charges battery in the morning.
  3. You're PW is fully charged by 1PM.
  4. From 2-8 you do not use any SRP (but 200W mentioned).
  5. Peak solar output is about 3kW
  6. About 2PM you fed the grid, twice.
  7. About 8:30PM you start charging your vehicles, done at 4AM (Drive much?)
  8. Your A/C unit is not variable speed.
Close?
Spot on! Basically anytime my AC kicks on it draws .1-.5kw from grid unless solar is on. #6 seems to be most important! The software knows that later in the day I will pull from grid a little so it backfeeds grid at 2pm since there is excess. This offsets any grid usage later in the day. I used to charge at 11pm on the EV plan but since there is no super off peak I start charging at 8:30 and the AC kicks on at 8pm to cool to 74 degrees for sleeping. System works flawlessly!
 
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CSFTN

Member
Aug 24, 2014
924
507
Memphis, TN
I'm going to try and vent my garage. Too many batteries in there now. I always bring my rechargeables in the house. I think the car is now cooling more at night in fact because it's still 105F in the garage in the evening.
Concern of mine .... if 4 PW2s in a closed 3 car garage, housing running >90% off solar + PWs, how much heat do the PW2s give off?

edit: the garage contains no ICEs. If it helps, 1st proposal from installer calls for 43288 kWh/12 months, 33 kW to run my house 100% solar. I figure I will knock that down substantially before install. My current power provider says 18 kW from the panels to supply 80% of my usage. They don't know about the batteries.
 
Last edited:

brur

Member
Nov 17, 2018
358
202
Prescott AZ
Concern of mine .... if 4 PW2s in a closed 3 car garage, housing running >90% off solar + PWs, how much heat do the PW2s give off?

edit: the garage contains no ICEs. If it helps, 1st proposal from installer calls for 43288 kWh/12 months, 33 kW to run my house 100% solar. I figure I will knock that down substantially before install. My current power provider says 18 kW from the panels to supply 80% of my usage. They don't know about the batteries.

Off topic but a good idea for those living in the valley, you can get water heaters that heat water via an incorporated heat pump. The net effect is a cooler garage.
 
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azdryheat

Member
Jul 6, 2016
405
580
Mesa, AZ
Pulled the trigger today for 8.19kW solar + 2 PW through Tesla. At first they recommended more solar and 3 PWs to cover 100% demand, but that drags down the ROI because you can't compete with SRP costs during off peak. Next round, they recommended 55% and 2 PWs. As Chancellor points out, 40% is the sweet spot and the first PW is a no brainer. I may be able to do this with only 1 PW but if go over then it's really expensive power from SRP. So that's the game we play.

Here's another thing, I just posted on Nextdoor. Nextdoor is the free private social network for your neighborhood community.
In case you can't see this (without signup or something), I'm claiming (IMHO) that the reason when SRP asks us to pre-chill our homes is because they make money selling electricity (duh). When you pre-chill, you don't just shift demand and save $, but you also increase total demand because of the Laws of Thermodynamics (Heat exchange is faster at a higher temp differential, so you lose energy faster trying to get the house cooler than normal).

Another interesting fact, utility companies have renewable mandates. Seems Arizona is not meeting its mandate and seems congress can grant exceptions, not a very strong sense of urgency here in Az. If they consider making their own farms, their infrastructure also needs to be grown so I bet it's cheaper to have us create our own power and just control how much they pay us for it so they don't lose out $$$.

I pre-cooled my non-solar house the last few years (just moved to a grandfathered solar home). Yes the demand was higher, but with time of use, I figured I saved about $100/month minimum in the summer. Waiting for SRP approval to add another 10 KW on the house.
 

SOULPEDL

Supporting Member
Jul 25, 2016
3,119
11,952
Arizona
I pre-cooled my non-solar house the last few years (just moved to a grandfathered solar home). Yes the demand was higher, but with time of use, I figured I saved about $100/month minimum in the summer. Waiting for SRP approval to add another 10 KW on the house.

Thanks for confirming. You just moved my theory closer to practice, and it does make sense it would cost more energy (not $) to pre-chill. I'm calling this a scam that hurts our environment, and no longer just my opinion.
 

Chancellor32

Member
May 10, 2018
719
485
Queen Creek, AZ
Thanks for confirming. You just moved my theory closer to practice, and it does make sense it would cost more energy (not $) to pre-chill. I'm calling this a scam that hurts our environment, and no longer just my opinion.
I still precool because it allows me to sell back for 1-2hrs and keep my demand low. Also prolongs the battery. I would still do it unless you know your PW will 100% last till 8pm. In terms of renting the panels it’s not a good deal at all, read the fine print. Prices can go up with only a 30day notice, $1500 to remove them. After 7 years it costs more to have rented them.
 
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SOULPEDL

Supporting Member
Jul 25, 2016
3,119
11,952
Arizona
I still precool because it allows me to sell back for 1-2hrs and keep my demand low. Also prolongs the battery. I would still do it unless you know your PW will 100% last till 8pm. In terms of renting the panels it’s not a good deal at all, read the fine print. Prices can go up with only a 30day notice, $1500 to remove them. After 7 years it costs more to have rented them.

I haven't had a chance to read it, thanks. That's what I figured.
 

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