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Newbie install option / system design

JJBTXModS

Member
Mar 3, 2020
26
14
Austin TX
Hello,
New to this forum section. We are a ModS and ModY household and are in the planning stages for solar + Powerwall(s). We are in south central Texas so there will be plenty of sun. Our purpose is to have backup power for as long as reasonable (2 days?) as well as offset the cost of electricity for the house. We use quite a bit of energy at the house with teens at home all day due to pandemic etc....

We have used anywhere between 1500 KWh to 4000 KWh per month depending on the time of year (hot summers in TX). As I mentioned, we have 2 EVs that charge at the house (one of them 2x per week since I drive a lot), 2 AC central units, and pool equipment (pump etc..). All our appliance except for oven/washer/dishwasher and microwave are gas operated.

Tesla recommends their large system (16.32 I think) and 4 Power walls. In reading here, seems like most people do not go with the Large system and have more PWalls. We would like to have a stable backup process when off grid with the panels replenishing the PW as much as possible during an outage. I know we will load shed some things (only run 1AC, go to Supercharges instead of charging at home, etc...) but wanted some opinions as to what size of system to install. Definitely new at this and looking for input. How about the inverters/tesla gateways? What else am I missing that I may need (like panel upgrades - house is 3 years old so dont expect much here)

We actually put order in with Tesla and hope that it can be modified after assessment.

Thoughts/recommendations?

Thanks, JJ
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
7,650
8,434
Riverside Co. CA
Hi!

Given your desires and information you provided, the size system and number of powerwalls sounds about right. things like central AC and pool pumps take a LOT of power, more than people are aware of until they start tracking it actively.

Even with shedding loads in an outage, you will likely still have pool pumps and AC running in the summer for example.

There are a few members here in Texas who have systems who might be able to provide you with more "local" type information. If the primary goal is "backup power" then you might also want to look into whether a generator is right for you. If the primary goal is "more power independence, while also having some capability of backup power" then PV (solar) + some form of battery backup can be a good fit.

Given the historically low cost of electricity in Texas compared to some other places like where I am in CA, I would advise not looking at this from a "return on investment" type situation. PV + batteries are going to cost significantly more than just getting a generator, but a generator doesnt provide "more power independence", its purpose is generally strictly disaster recovery / backup.

Tl ; DR ... system size and number of powerwalls looks "right" for stated goals to me, given stated objectives and amount of power use.
 
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JJBTXModS

Member
Mar 3, 2020
26
14
Austin TX
Thanks JJ. I am definitely not looking for an ROI for sure. It will never pencil out. Currently the PV+PW system quoted by Tesla is about 2X a generator (20 KW) after federal credits. If it is strict disaster, the generator is a great idea unless they decide to cut the gas supply (we have natural gas at the house) which they threatened to do during the crazy weather a couple of weeks ago. There is desire to be "off grid" dependent as well to a degree.

I am afraid of the unknown or "additional" things that may be required after the initial Tesla assessment (panel upgrades, multiple inverters, gateways or whatever else will be needed) People trying to sell me on micro inverters vs. String with optimizers etc... etc... etc... We are happy with our Tesla cars, chargers etc... They know a thing or 2 about energy and software to control control, store and optimize. And their price is significantly better than others. I will continue to follow the forum for more info.

Thanks again, JJ
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
7,650
8,434
Riverside Co. CA
Thanks JJ. I am definitely not looking for an ROI for sure. It will never pencil out. Currently the PV+PW system quoted by Tesla is about 2X a generator (20 KW) after federal credits. If it is strict disaster, the generator is a great idea unless they decide to cut the gas supply (we have natural gas at the house) which they threatened to do during the crazy weather a couple of weeks ago. There is desire to be "off grid" dependent as well to a degree.

I am afraid of the unknown or "additional" things that may be required after the initial Tesla assessment (panel upgrades, multiple inverters, gateways or whatever else will be needed) People trying to sell me on micro inverters vs. String with optimizers etc... etc... etc... We are happy with our Tesla cars, chargers etc... They know a thing or 2 about energy and software to control control, store and optimize. And their price is significantly better than others. I will continue to follow the forum for more info.

Thanks again, JJ

Well,

Tesla doesnt do micro inverters, so you dont have to worry about them trying to sell you that. I dont think they do optimizers now either, but I am not sure on that. Tesla sells solar like you are buying it from home depot or lowes. They are the cheapest almost always, and the products they sell are good, but just like the cars there is not much customer service during the process.

They will also tend to let you buy something that you likely should be talked into or out of... for example, they might let you buy a 14-15kW system and say "i only want 2 powerwalls cause thats all I want to pay for", when that size system should likely have a minimum of 3 powerwalls.

Tesla (for the most part) does not tend to "up charge" or try to suggestive sell you on add ons, HOWEVER, they also tend to not "fight" something that might or might not be needed. An example of this would be needing a main panel upgrade because of reason X or Y. Maybe it could be avoided with some technical acumen and wrangling of the local AHJ ("authority having jurisdiction" or people who sign off on your permits in your local area). Tesla would, in general, just tell you "you need the upgrade" because its faster to move forward that way.

They (tesla) are not bad (at all), they just focus on moving fast (and to code). Arguing with AHJs takes time and effort and they dont tend to do that. Many other companies dont either. You usually need a local type installer who is focused on the customer (and charges enough to have people to work on that stuff).

As long as you are aware (which it sounds like you are) that Tesla will tend to communicate very little during the process, the pricing is in general lower than you will find with others. Also, in general, people tend to be very happy with their actual install crew. Its not like there are never any reports of issues, but for the most part, what I read here is people tend to be happy with the install team. They tend to be frustrated a bit with communication with the office staff.

Good luck, hope you hang around.
 

JJBTXModS

Member
Mar 3, 2020
26
14
Austin TX
Well, I have their design and they quoted me a 16.32KW system but they state that it will offset 55% of the energy "only" based on our past year usage (yes we are not very stingy with power at the house). I also do not like the way they placed (stacked) the panels. I thought the desired offset is typically 80% if possible. I know we can reach that based on the south facing real estate on our roof but not the way they designed it. Trying to get a hold of the advisor has been shall we say challenging to say the least. Will Tesla accept modifying their design? Will they allow me to go to a, lets say 20KW system as opposed to the 16.32? Also they did not include the PW on their system design. Thoughts?



1615481664538.png
 

h2ofun

Active Member
Aug 11, 2020
1,551
249
auburn, ca
Well, I have their design and they quoted me a 16.32KW system but they state that it will offset 55% of the energy "only" based on our past year usage (yes we are not very stingy with power at the house). I also do not like the way they placed (stacked) the panels. I thought the desired offset is typically 80% if possible. I know we can reach that based on the south facing real estate on our roof but not the way they designed it. Trying to get a hold of the advisor has been shall we say challenging to say the least. Will Tesla accept modifying their design? Will they allow me to go to a, lets say 20KW system as opposed to the 16.32? Also they did not include the PW on their system design. Thoughts?



View attachment 643577
I hear tesla gives you want they have. Want changes, may have to go with a 3rd party. May have cost me more money, but so glad I went with 3rd parties. I got to be totally involved in the design process. Doing another bid now and get to ask LOTS of questions and design trade off options with GREAT real time communications.
 

bevo

Member
Mar 10, 2021
35
14
Irvine
They were designing to the x-large system spec. Tell them you want as many solar panels as necessary to offset 80% (or 100%). They will then give you a design with more panels as others have been able to do here...
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
7,650
8,434
Riverside Co. CA
Well, I have their design and they quoted me a 16.32KW system but they state that it will offset 55% of the energy "only" based on our past year usage (yes we are not very stingy with power at the house). I also do not like the way they placed (stacked) the panels. I thought the desired offset is typically 80% if possible. I know we can reach that based on the south facing real estate on our roof but not the way they designed it. Trying to get a hold of the advisor has been shall we say challenging to say the least. Will Tesla accept modifying their design? Will they allow me to go to a, lets say 20KW system as opposed to the 16.32? Also they did not include the PW on their system design. Thoughts?



View attachment 643577

Tell them you want the percentage of coverage you want (80%, 100% etc), they will re design it with more panels.
 
Mar 1, 2021
117
31
San Diego, CA
Well, I have their design and they quoted me a 16.32KW system but they state that it will offset 55% of the energy "only" based on our past year usage (yes we are not very stingy with power at the house). I also do not like the way they placed (stacked) the panels. I thought the desired offset is typically 80% if possible. I know we can reach that based on the south facing real estate on our roof but not the way they designed it. Trying to get a hold of the advisor has been shall we say challenging to say the least. Will Tesla accept modifying their design? Will they allow me to go to a, lets say 20KW system as opposed to the 16.32? Also they did not include the PW on their system design. Thoughts?



View attachment 643577
Any interest in solar roof? You can get an instant quote for exactly the size of system you want from the website based on tweaking the "cost of electricity" input.

I feathered my system to a target cost, above our "need" based on current usage. Before installing we were using ~7,000kWh/yr, and our designed system gets ~10,000kWh/yr.
 

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