Tesla 12kw design - most panels facing east?

[ucmndd]

A family member of mine has been interested in Solar and I suggested they look seriously into Tesla given the recent price drops.

Yesterday they sent me the proposed system design:

Can anyone think of a good reason why Tesla is stacking the entire east facing section of roof with panels and putting just a few on the west side?

There’s no difference in roof shading or exposure. The electrical panel is on the southeast corner of the house, but I can’t imagine that really matters one way or another.

Am I missing something here? Is this just stupid/lazy? I told them to push back on the design or at least get a solid explanation for this configuration, but it makes zero sense to me. Thoughts?

 

[arnolddeleon]

Current time of use hours have negated any advantage of west vs east production advantage/disadvantage. All you care about is total energy produced, particularly if you have powerwalls. Do you have any weather that might influence things (e.g. morning fog would make west more desirable)

Eyeballing it, I think you can at only get about 7 more modules on the west. The current set back requirements really limit placement.

I suspect the designers went for the easy conservative design. If they're still using the same mounting system from four years ago this also probably is slightly more efficient in the number of feet required. Fewer feet, faster/cheaper install. The installers also typical size up the situation once they are on site and can make tweaks.

I don't think it is stupid. I interpret as a "good enough" with a minimal effort which aligns with their "cookie cutter" approach to reduce cost.

 

[getakey]

Current time of use hours have negated any advantage of west vs east production advantage/disadvantage.???

 

[arnolddeleon]

Current time of use hours have negated any advantage of west vs east production advantage/disadvantage.???

Peak hours used to land CA in a way that favored west (later in the day) production so given equal situations you would prefer west over east. Now peak hours are pretty much when the sun isn't shining.

 

[getakey]

isn't Peak 4pm to 9pm?
that would favor west from 4pm to sunset

 

[arnolddeleon]

isn't Peak 4pm to 9pm?
that would favor west from 4pm to sunset

Ok, there is still a slight advantage to west all things being equal. I wouldn't bet on that staying. When I first got solar, south orientation was king as peak almost followed the sun. TOU rates have drifted to later and later in the day to a point where west gained some benefit. The rates continued to move to now diminish that benefit of a western orientation. The advantage of a western orientation in my view is practically gone. Powerwalls pretty much solve the issue.

I'm sure you can design system for the original poster that was slightly smaller and produce a similar net benefit with a slight western bias. Or you can just slap another module or two and call it a day. When installed solar was more expensive, trying to maximize the utility of each module was highly beneficial. I think Tesla is saying "we can make it cheaper if we don't hyper optimize it". This is somewhat analogous to standard vs custom cabinets.

 

[miimura]

Personally, I would prefer to have a more equal number of panels facing East and West.

 

[BrettS]

I have a number of panels on east and west facing mounting planes and one thing I have discovered is that in my location, at least, my mornings generally are cloudless, so my east facing panels produce well in the mornings. However I get a lot more clouds in the afternoons and evenings, so my west facing panels haven’t been doing as well. Obviously the weather in California will be different than it is here in Florida, but it is something to consider. Additionally, my system has only been installed for about a month now, so it’s possible that the weather patterns will be different here during different parts of the year.

 

[Troglodytes]

A huge assumption on my part, but if this is your initial design I think your 'lazy' guess is the right reason.

They put 36 panels on. I think almost all initial panel configurations without explicit buyer guidance are going to be certain numbers of panels; mine was 48 by the way. Back when marketing called that 48 X-LARGE. I ended up with 56 panels when it was all said and done.

If its your initial design then they want you to get comfortable with what you see from them for the design. If the price doesn't scare you off then you'll respond with additional guidance/wants. Based on that they'll revise and respond.

I think I had five material back and forths with the 'designers'. Likely 20+ small back and forths as well.

Designers are more mouse jockeys I think rather than solar designers. But, when you get close to being done, someone with solar designer experience does get involved for a review and in my case my annual solar production got a big haircut (20% reduction). When I asked about it reason given was tree shade that had not been included.

 

[ucmndd]

Thanks for all the responses. Good point about morning vs. afternoon weather - this is in the CA Central Valley which is subject to thick morning tule fog in the winter, usually burning off in the afternoons. The rest of the year however is sunny and dry, basically no measurable precipitation or even significant cloud cover from May to October.

I’ll tell them to keep following up and asking questions, advocating for a better east/west balance.

My assumption was that purely west facing panels might be ideal now, given the ever-later peak periods for TOU plans, but maybe I’m not considering all the variables.

 

[Mardak]

Eyeballing it, I think you can at only get about 7 more modules on the west. The current set back requirements really limit placement.

CA has a 4' skylight setback requirement, so probably closer to only 4 additional panels on the west side.

 

[charlesj]

... Now peak hours are pretty much when the sun isn't shining.

Next, it will be peak all the time.

 

[holeydonut]

You can go to PVWatts (PVWatts Calculator) and download a detailed hour-by-hour estimate of the output of of a hypothetical panel oriented facing due south. They take into account measured diffuse irradiance that is impacted by reported weather.

In my case (Bay Area California near SFO), production seems to slightly favor production in the morning; the fall-off is slightly faster approaching sunset. It's probably not going to be a huge dent to the ROI, but it's still a slight factor. Maybe mornings are just a bit more "clear" than the time after high noon?

 

[holeydonut]

CA has a 4' skylight setback requirement, so probably closer to only 4 additional panels on the west side.

View attachment 569297

Can you share where this 4' requirement for setbacks around a skylight is published? If what you're saying is true, then the solar that's about to go up on my roof would violate CA code.

This is the Winter 2019 version of the CA solar permitting guidebook...
https://opr.ca.gov/docs/20190226-Solar_Permitting_Guidebook_4th_Edition.pdf

"Skylights:Solar PV panels shall maintain a minimum clearance around the perimeter of skylights as not to interfere with the function of the skylight, as determined by the enforcing agency"

It also has language around setbacks at ridge are 18 inches to 36 inches depending on certain factors... but I can't find the 4 foot rule you described.

 

[sorka]

Current time of use hours have negated any advantage of west vs east production advantage/disadvantage. .

???? The current TOU is MORE advantageous to West than East than the old TOU which started peak in the morning vs where it is now at 3 or 4 pm depending on the schedule.

 

[Chuq]

Worth noting for anyone else in this thread, @ucmndd and @arnolddeleon are both in California and so any comments they make about rates and time of use, etc. may not apply to people in other states or countries.

In my case I had 8 kW of solar installed in 2012, all of it north facing for maximum generation. In 2014 my utility introduced time of use tariffs for the first time. The overnight rates (= prime EV charging time) being about half of what the previous rate was all the incentive I needed to change over after I got my Leaf. Peak rate was about 25% higher. In hindsight if I knew ToU was coming I would have had a split of east and west facing panels in order to have it generate more at the peak times.

 

[sorka]

Same sort of issue for me as well.

Post Your Tesla Solar Layout

 

[Dave EV]

Looks like everyone has it covered here. I would also suggest trying to get the east/west panels balanced as best as possible, favoring the west if possible because of the fog/clouds that tends to be in the mornings in your area.

Also, most households tend to use more energy in the late afternoon/early evening, so even if you do get Powerwalls, you'll pick up a bit of efficiency by using the energy directly.

Definitely look into a a couple Powerwalls, too!

 

[TheTalkingMule]

Designers are more mouse jockeys I think rather than solar designers. But, when you get close to being done, someone with solar designer experience does get involved for a review...

This seems to be the case with a lot of customers. What standard steps can we recommend to help optimize the avg homeowners experience with Tesla Energy? I've been advising people to "buy" the array one size larger than what you think is needed, then just push through the process until you get to a real designer who's an actual engineer. You can cancel/refund any time up to 7 days after turn-on anyway, so moving the process from sales to real installers quickly makes sense.

This super-lean onboarding process is NOT necessary to keep pricing this low. You can employ tons of legit online designers who do it properly from the start. You just can't give salespeople and lead generators $6k for every sale. Give them nothing and hire a few engineers. That's the Tesla way after all!

 

[Vines]

No residences have 4' setbacks from skylights, at least not in my experience.

As far as west vs east its pretty well covered. Your East roof would be better for Tesla (cheaper), the West might be better for you (better production)