Tesla says I can't put solar panels on my rear porch roof

[Matt-FL]

I'd suggest multiple strings, especially if you can show which panels have partial shade at certain times of the day. Prior to having my design, I put a camera on my chimney to watch the locations where panels were going to capture (and timelapse easy) shading throughout the day. Just keep in mind that shading changes throughout the year/seasons, and the change can be considerable.
If your designer has it in the design, ensure the installers stick to the plan. My installers changed the design with what sounded legitimate to my non TMC educated reading, but as it turned out (in my opinion) was not helpful to me long run but helpful to simplify the installation.

 

[Jeremy3292]

I'd suggest multiple strings, especially if you can show which panels have partial shade at certain times of the day. Prior to having my design, I put a camera on my chimney to watch the locations where panels were going to capture (and timelapse easy) shading throughout the day. Just keep in mind that shading changes throughout the year/seasons, and the change can be considerable.
If your designer has it in the design, ensure the installers stick to the plan. My installers changed the design with what sounded legitimate to my non TMC educated reading, but as it turned out (in my opinion) was not helpful to me long run but helpful to simplify the installation.

What would be the reason for having multiple strings? Meaning based on my understanding from the videos you posted, the bypass diodes and MPTT of the Tesla string inverter would take care of any shading issues (to the best it can). So what would be beneficial in having 2 strings vs 1 string in regards to shading?

 

[Matt-FL]

If you know what areas are shaded, it can't hurt to separate those on a separate string. Also, if an individual MPTT fails, you only lose part of your array and not the whole thing. I think individual MPTT failure is not common, but it is possible. It might only be a few % increase, but that few % is only in the cost of some additional wire to the inverter.

 

[Matt-FL]

Here's the view from the two cameras on our chimney. One covering my south-facing array, the other mostly covering my east facing array (west is on the other side of the peak). I can pull a timelapse of the shading throughout the day, and I've been working to capture at least one timelapse per month so view the difference.

 

[Jeremy3292]

Update: Tesla agreed to the 9.315 kW system, 23 panels, which I accepted. For those curious I attached my price sheet below. I was only charged sales tax (6%) on the net Powerwall cost themselves ($16,500) and not any other equipment or labor.

Hoping the permitting process doesn't take awhile but I imagine it will.

 

[Jeremy3292]

Well the fun continues with Tesla. I just got an email to "Review and Accept Your Equipment Details" so I login and see the below. How does that make any sense at all? My heat pump compressor has a 153 LRA rating (5 ton unit) and according to Tesla's own link from the picture below 3 Powerwalls should be overkill for a full home backup.

I am hoping it is just another dumb mistake bc the picture shown next to it is also clearly a whole home backup setup. Notice no additional backup panel and also see in the link below the same pic is in the whole home backup section. I have a call with my advisor tomorrow morning anyways, but this seems so lazy and dumb.

Powerwall System Design | Tesla Support

When designing your system, Tesla will recommend the number of Powerwall units needed to back up your entire home (whole home backup). This means that during a power outage, your Powerwall system would be able to support all your appliances.

www.tesla.com

 

[Matt-FL]

I also have a 5 ton AC unit. My original design included 3 powerwalls which were configured in full house backup. I ended up increasing to four (a decision I absolutely do not regret).

I have replaced my AC unit post-install, but my original AC was from 2008, 5 Ton 14 seer, and had a significant initial load spike. Before the install, I added a soft-start which significantly reduced the initial draw. However, as much as I tried to pamper and maintain the old AC, it eventually got a pinhole leak in the air handler. I had to spend a stupid amount of money to get a new 18 seer 5 ton unit, and I went ahead with an inverter style. It's strange, the new AC uses less electricity to get started, but on hot days it uses far more than my old one for the cooling cycle. My old one would run about 5.5kw while cooling, but the new one will do close to 7kw on hot days, around 4kw on moderate temp days.

Anyways, got off topic. Are there other items in your house that might attribute to this? Maybe multiple hot water heaters, multiple kitchens, heat pump pool heater, etc?

 

[Jeremy3292]

I also have a 5 ton AC unit. My original design included 3 powerwalls which were configured in full house backup. I ended up increasing to four (a decision I absolutely do not regret).

I have replaced my AC unit post-install, but my original AC was from 2008, 5 Ton 14 seer, and had a significant initial load spike. Before the install, I added a soft-start which significantly reduced the initial draw. However, as much as I tried to pamper and maintain the old AC, it eventually got a pinhole leak in the air handler. I had to spend a stupid amount of money to get a new 18 seer 5 ton unit, and I went ahead with an inverter style. It's strange, the new AC uses less electricity to get started, but on hot days it uses far more than my old one for the cooling cycle. My old one would run about 5.5kw while cooling, but the new one will do close to 7kw on hot days, around 4kw on moderate temp days.

Anyways, got off topic. Are there other items in your house that might attribute to this? Maybe multiple hot water heaters, multiple kitchens, heat pump pool heater, etc?

Nope - a very normal, regular house lol.

Tesla Wall Connector, 5 ton HVAC compressor, washer, dryer, fridge, stove, electric 50 gallon water heater...nothing else I can think of. I do have a 60 amp breaker for the "emergency/backup/auxiliary heating strips" for if/when it gets too cold outside for the heat pump to generate enough heat by itself. Perhaps that is it??? But that is super normal for a heat pump HVAC in the southeast and a lot of other places. My house is brand new and has a 200 amp panel with a 225 amp bus bar also.

It has to be a mistake...no way 3 PW's can't handle everything I mentioned above. I'll find out for sure in a few hours hopefully.

Panel box below:

 

[BGbreeder]

Nope - a very normal, regular house lol.

Tesla Wall Connector, 5 ton HVAC compressor, washer, dryer, fridge, stove, electric 50 gallon water heater...nothing else I can think of. I do have a 60 amp breaker for the "emergency/backup/auxiliary heating strips" for if/when it gets too cold outside for the heat pump to generate enough heat by itself. Perhaps that is it??? But that is super normal for a heat pump HVAC in the southeast and a lot of other places. My house is brand new and has a 200 amp panel with a 225 amp bus bar also.

It has to be a mistake...no way 3 PW's can't handle everything I mentioned above. I'll find out for sure in a few hours hopefully.

The three powerwalls may be able to start the AC compressor load, but at the end of the day, three powerwalls only hold 40kWh of power. Even leaving out the TWC, you have a substantial list of loads, and it could be the total load that is driving the partial backup comment.

Good luck and keep us posted!

BG

 

[Jeremy3292]

Perhaps it is the electric heating strips...does anyone know if I can just back up everything EXCEPT that one 60 amp breaker for the heating strips? They literally won't get used very much at all here and it is only an issue if I am off grid/in a power outage also, correct? Everything works fine on grid even if I don't back it up...although I guess the question is what happens off grid/ in a power outage if the HVAC thermostat calls for the heating strips to be turned on but they aren't in the backup load panel?

 

[BGbreeder]

If you are lucky, your owners manual might have some information on whether your heat pump can work without the auxiliary heat. I think that some random person on the internet won't have sound advice on your particular HVAC system.

I suspect whether or not your heat pump can function without power strips is both a matter of

a) can the heat pump run without damaging itself due to cold refrigerant (heat pump transfer fluid), e.g. imagine solid refrigerant or solids in the refrigerant, and​

b) whether the amount of heat transferred drops so much that the heat pump doesn't actually provide enough heat, I.e. it runs but doesn't functionally transfer much heat.​

I doubt that the refrigerant would actually solidify, but I could imagine a high fluid viscosity might literally clog things, and damage the compressor or expansion valves. Specifically, I wonder at what temperature the oil in the refrigerant becomes too viscous for the system to work without auxiliary heat.

All the best,

BG

 

[Jeremy3292]

If you are lucky, your owners manual might have some information on whether your heat pump can work without the auxiliary heat. I think that some random person on the internet won't have sound advice on your particular HVAC system.

I suspect whether or not your heat pump can function without power strips is both a matter of

a) can the heat pump run without damaging itself due to cold refrigerant (heat pump transfer fluid), e.g. imagine solid refrigerant or solids in the refrigerant, and​

b) whether the amount of heat transferred drops so much that the heat pump doesn't actually provide enough heat, I.e. it runs but doesn't functionally transfer much heat.​

I doubt that the refrigerant would actually solidify, but I could imagine a high fluid viscosity might literally clog things, and damage the compressor or expansion valves. Specifically, I wonder at what temperature the oil in the refrigerant becomes too viscous for the system to work without auxiliary heat.

All the best,

BG

All good points.

Since I am in SC, auxiliary heat doesn't cut on very often. It is supposed to supplement the heat pump compressor should it not be able to keep the house at the set thermostat temperature. It can certainly function without the electric heating strips as that is the "normal operation" of the heat pump. It only turns on the electric heating strips when the thermostat calls for it bc it is 2-3 degrees beneath the set temperature point and realizes the heat pump is not keeping up.

But again this seems to only be an issue for my PW backup situation if the following 3 things occur:

1. Power outage
2. Very cold outside
3. Indoor temperature is 2-3 degrees beneath the set thermostat point (e.g. heat pump isn't generating enough heat to heat home)

I may just have to wait 6 months or more for PW3 since they can handle much more power...my budget does not allow for a 4th PW2. Never imagined 3 PW's wouldn't be enough...

 

[h2ofun]

All good points.

Since I am in SC, auxiliary heat doesn't cut on very often. It is supposed to supplement the heat pump compressor should it not be able to keep the house at the set thermostat temperature. It can certainly function without the electric heating strips as that is the "normal operation" of the heat pump. It only turns on the electric heating strips when the thermostat calls for it bc it is 2-3 degrees beneath the set temperature point and realizes the heat pump is not keeping up.

But again this seems to only be an issue for my PW backup situation if the following 3 things occur:

1. Power outage
2. Very cold outside
3. Indoor temperature is 2-3 degrees beneath the set thermostat point (e.g. heat pump isn't generating enough heat to heat home)

I may just have to wait 6 months or more for PW3 since they can handle much more power...my budget does not allow for a 4th PW2. Never imagined 3 PW's wouldn't be enough...

IMO, the cost to "need" PW's for what, is just dumb! Now, if one has lots of spare money, great, but never ever worth the value compared to things like more solar, etc.

 

[Jeremy3292]

IMO, the cost to "need" PW's for what, is just dumb! Now, if one has lots of spare money, great, but never ever worth the value compared to things like more solar, etc.

Well I have maxed out the # of solar panels my roof can fit. The PW's are necessary bc I must go on a TOU plan per my utility if going solar. So I need to be able to avoid the peak rate times which the PW's provide/allow for. My wife (and I) also like the idea of having backup power in case of a storm or outage.

 

[Jeremy3292]

I just got off the call with my Tesla advisor and I'll be damned that is not what I expected to hear lol. Lots to unpack here:

1. My advisor does not know why my HVAC unit is incompatible per the design team. He agreed this is an atypical answer for a typical/normal house. He has not seen this before and he said he has a lot of experience FWIW. He has submitted a request for the load calc/exact reason as to what the issue is to the design team.
2. My utility apparently only allows max 20 kW AC power which they have maxed out per my design plans. I did just find something similar in the solar rate schedule, pic below, but that seems to me to be related to solar power, not an ESS? Anyways the issue is not "amount of power" available it seems; it is specific to my HVAC unit. Again it is brand new 5 ton Trane heat pump with a 152.5 LRA rating.
3. I am getting one PW3 and two PW2's. They are apparently compatible/interoperable. The reason I am not getting three PW3's is bc my utility only allows for 20 kW AC as noted previously and 3 PW3's would be more like 30+ kW I think.
4. I pointed out to my advisor the PW3 FAQ page that says PW3 and PW2/+ are not compatible. He said that is written for existing installs but they are compatible/interoperable for new installs.
5. My advisor mentioned PW3 has a max 150 LRA rating, but then I pointed out per the Powerwall spec sheets available on Tesla's website that is per Powerwall and I have 3 total. Even if the other two are PW2's my HVAC unit should be compatible.
6. I just received my current spec plans via email so I need to digest all of the info in there as well.

A whirlwind of a call! I will find out design's answer as to why my HVAC is not compatible next week.

 

[Jeremy3292]

Update:

I just looked at my plans and it looks there is only one powerwall, not three in the plans. There is no mention of any other Powerwalls other than one PW3. Looks like definitely an error on their part which my advisor did not catch. So I have no idea if what my advisor said is correct or not regarding PW3 & PW2 compatibility as there are no PW2's in my design PDF anywhere. Just PW3 spec sheets and pics.

Also note they don't even have a backup panel in the design below; the diagram shows whole home backup.

See below:

 

[h2ofun]

Well I have maxed out the # of solar panels my roof can fit. The PW's are necessary bc I must go on a TOU plan per my utility if going solar. So I need to be able to avoid the peak rate times which the PW's provide/allow for. My wife (and I) also like the idea of having backup power in case of a storm or outage.

Have you done a spread sheet? IMO, you will never recover the peak times! And unless you lose power a LOT, cheaper by far to get a generator. Again, if you have money to burn, I love having my 7 PW's, but would never ever suggest it to anyone!!

 

[Jeremy3292]

Have you done a spread sheet? IMO, you will never recover the peak times! And unless you lose power a LOT, cheaper by far to get a generator. Again, if you have money to burn, I love having my 7 PW's, but would never ever suggest it to anyone!!

Yes, I have done an ROI but that isn't the driving force for me. It also makes no sense to go only solar from an ROI perspective bc of the TOU rates. It's either solar + PW's or don't do it at all. Plus you can't predict what the utility will require 3, 5, or 10 years from now. Better to go all in now than partially all in or nothing. Time value of money is also a factor.

I also have a 25% state tax credit coupled with the 30% federal credit for 45 cents on the dollar net out of pocket cost for me. Those tax credits won't be around forever - at the state and federal level. Tax code gets amended/repealed all the time.

 

[sunwarriors]

I just want to say Good Luck!

So glad I don't have to be a project manager to manage my own solar install anymore! Even non Tesla can be a lot of work and don't get me started on SGIP.

 

[Jeremy3292]

I just want to say Good Luck!

So glad I don't have to be a project manager to manage my own solar install anymore! Even non Tesla can be a lot of work and don't get me started on SGIP.

Thanks. It is pretty ridiculous. Took me 5 seconds to review the plans and see there was only one Powerwall vs three...was on the phone with my advisor for 30 minutes and he never caught it. Maybe he did see it and was covering for such a stupid error...