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Solar Panel Install: review design?

Hello,

I'm currently in process with Tesla to install 8.5kW solar panels + 1 Powerwall. I've done extensive research and feel quite confident with my install. However just to be on a safe side (no surprises on the install day), I requested detailed design from Tesla.

I've attached the proposed plan for changes to the main electrical panel. Little background, my main panel is 125A and Tesla stated that they will be moving majority of the load to the load center (no MPU required).

Can y'all please review the following and provide any feedback/recommended changes to the plan? Also it would be helpful if you can please explain the changes in simple terms (no luck from Tesla). Much appreciated!

Electrical_Plan.PNG
 

slcasner

Active Member
Supporting Member
Feb 20, 2011
1,530
1,066
Sunnyvale, CA
This shows that all of your loads are relocated. My install was similar, but my existing main breaker is 100A. Because the feeder is 100A that means you won't be able to draw as much from the grid as you could before, but maybe that does not matter. Your loads can draw more from the combination of the grid and the solar + battery.
 
Because the feeder is 100A that means you won't be able to draw as much from the grid as you could before
That's not *quite* how it works. The max draw from the grid is 100a, however you will rarely actually use this amount now. This is because you will draw from the solar and power walls before the grid.

Specific to the OP's line diagram, the subpanel will have a load potential of ~165a. 100a for the relocated circuit of the existing subpanel, 30a from the power wall (max draw of 10kw), and ~35a peak from the solar. Going on the house is pulling a full 100a (it should *NEVER* be this much) the max you'll pull from the grid will be ~35a during peak solar output, and 70a without solar. They will still have the full 100a available, AND the output of the solar and powerwalls. it's like getting a free 65a service upgrade (during solar peaks).

I have a very similar setup, except I have a 10.5kw system (max you can back feed with a 100a service and a 125a rated main) and 2 power walls.
 

slcasner

Active Member
Supporting Member
Feb 20, 2011
1,530
1,066
Sunnyvale, CA
That's not *quite* how it works. The max draw from the grid is 100a, however you will rarely actually use this amount now. This is because you will draw from the solar and power walls before the grid.
Well, that is how the grid tie will work, but I agree with you that in most cases it will not matter, as I said. The only case in which it would matter is if the battery is depleted at a time with no sun and there is a need to draw maximum load. That is highly unlikely.
@slcasner got it, thanks for your input! I'm not sure if you can answer this but would it make sense to move my NEMA 14-50 feed from main panel to load center? Does it make sense to charge an EV using Powerwall? (I understand I might only get 10kW max charge)
The NEMA 14-50 will have to move to the new backup panel because per NEC 705.12.B.2.3.c it would exceed the main panel busbar rating to have it in combination with the 100A feeder breaker.
An advantage to having the 14-50 in the backup panel is that if the grid goes down and you have plenty of sun so the Powerwall is full you can hook up the car to charge and use up the rest of the solar power. You can adjust the car's charge current between 5A and 40A to match the power output from solar and avoid depleting the Powerwall.
 
Well, that is how the grid tie will work, but I agree with you that in most cases it will not matter, as I said. The only case in which it would matter is if the battery is depleted at a time with no sun and there is a need to draw maximum load. That is highly unlikely.

The NEMA 14-50 will have to move to the new backup panel because per NEC 705.12.B.2.3.c it would exceed the main panel busbar rating to have it in combination with the 100A feeder breaker.
An advantage to having the 14-50 in the backup panel is that if the grid goes down and you have plenty of sun so the Powerwall is full you can hook up the car to charge and use up the rest of the solar power. You can adjust the car's charge current between 5A and 40A to match the power output from solar and avoid depleting the Powerwall.
Great explanation! That's exactly what my thoughts were.
 
I appreciate all the feedback thus far. However, I've one more question for the TMC family!

I requested Tesla to redesign the solar panels layout and they responded with the following plan (8.5 kW/11937 kWh/yr).

I think it looks good but could it be improved? The 'X' area is under the shade from a tree and second story roof so that's not an option.

Capture.PNG
 

jboy210

Well-Known Member
Supporting Member
Dec 2, 2016
6,530
4,461
Northern California
I appreciate all the feedback thus far. However, I've one more question for the TMC family!

I requested Tesla to redesign the solar panels layout and they responded with the following plan (8.5 kW/11937 kWh/yr).

I think it looks good but could it be improved? The 'X' area is under the shade from a tree and second story roof so that's not an option.

View attachment 754739
Given setback requirements from vents, edges, and ridgelines it appears to me to be a good design for a Tesla install. Tesla will not install a system that violates thier internal solar install guidelines.

If you really want additional panels you will likely have to go with someone other than Tesla.
 

jboy210

Well-Known Member
Supporting Member
Dec 2, 2016
6,530
4,461
Northern California
Where I live (bay area), most of our solar comes from the South-southwest, so I wonder why you have five panels facing the northeast. I think I would've put them on the back southwest facing roof. Of course, I don't know all the particulars, and I would imagine Tesla knows more about it, but it's a curiosity.
They will put panels on the North side of a home if you ask them and layout works. And depending on slope and shading they will generate power here in Norcal. But, mostly for just a few months around the summer solstice.

My solar roof has quite a few active tiles facing due North. They don't do anything around the winter solstice, but around April/May start generating power. . We see production numbers as low as 8-9 kWh/day near the winter solstice and will go up to 70-80 kWh/day near the summer solstice when both the South and North facing tiles are generating. We never need this much power, but it builds a large credit that we chew through in the late fall and winter.
 

h2ofun

Active Member
Aug 11, 2020
3,621
867
auburn, ca
They will put panels on the North side of a home if you ask them and layout works. And depending on slope and shading they will generate power here in Norcal. But, mostly for just a few months around the summer solstice.

My solar roof has quite a few active tiles facing due North. They don't do anything around the winter solstice, but around April/May start generating power. . We see production numbers as low as 8-9 kWh/day near the winter solstice and will go up to 70-80 kWh/day near the summer solstice when both the South and North facing tiles are generating. We never need this much power, but it builds a large credit that we chew through in the late fall and winter.
I also have lots of north facing panels now. They clearly are MUCH lower this time of year, but not zero. In the best time, they are maybe 90% of the south facing?
 
I had a quote from one company in late november 2021
My house is east/west facing, 3 bed detached 6 year old property (standard project). Option for east/west Velux option is calculated in (as we are exploring this option).

Quote attached.

if I would like to add a battery, they ciuod also install a Solax 5.8KW battery with battery management system and charge controller with 10 years warranty for an additional £4,995.00.

Pp


In comparison I have fitted a 5.18 kWh system (14 x 370 Watt panels integrated into the roof, so the panels are flush with the tiles), a 5kWh hybrid inverter, an 8.2kWh battery and all the various isolators, EM115 and assorted gubbins. The panels are JA Mono MBB, the inverter and battery are both Givenergy.
The total cost was £10.5K inc VAT.

Your quote looks kinda pricey to me.
I Agree. I'm paying low 6K for a sonnen 10kwh battery. solax 5.8 is a far way off in storage, different brands for a bit of saving...
 

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