Solar Roof

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SolarRoof power production

Hello,
I hope someone having gone before me has good info to share. I don't know too much at this point but am happy to share what I can, from a beginners standpoint.

I expected the Tesla website to provide a USA latitude-based chart or spreadsheet on the Tesla SolarRoof shingles so I could determine expected power production per sq-ft of my roof area assuming an optimize roof angle.

*** Does anyone know the power output of the Tesla solar shingles per sq-ft of roof area?

I'll take any measure you can offer, even if its not for the same latitude I need (35.2° for Charlotte, NC) as I think I can interpolate an adjustment based on gov't data on solar energy by region.

By the way, a "simplified formula" I found (https://solarpaneltilt.com/ ) regarding best roof angle was:
- IF your latitude is between 25° and 50°... "use the latitude (35.2° Charlotte), times 0.76, plus 3.1 degrees." So for Charlotte: (35.2*0.76)+3.1= 29.85° angle or about a 7:12 pitch roof.
- Please inform me if you think that is a wrong formula or roof pitch. They did provide an adjustment if you wanted to favor winter or summer energy gains... but that formula was for a year round best setting.
In case its helpful to others who my wish to favor winter or summer gains here is what they offered (based on the same latitudes between 25° and 50°):
• Adjust to Summer Angle March 30th ... The best tilt angle for summer is the latitude, times 0.93, minus 21 degrees.
• Adjust to Winter Angle September 10th ... The best tilt angle for winter is the latitude, times 0.875, plus 19.2 degrees.

Thank you!

Cheers,
Eric

Comments

  • The cost of the system is directly dependant on how many solar tiles are installed, not what they produce. When Tesla or any solar company makes a quote for you they will state a number, something like 12 kW. This is the maximum output if all the tiles (or panels) have 100% sun at the optimum angle at the same time. Rarely is this the case, unless you have a single south-facing solar system. And even then, it would only be valid two times during the year at some specific time during those two days.

    For example, our system was rated at 10.8 kW which is based on the number of solar tiles Tesla configured for our house. I have four facings (N, W, S, W). To turn this into some real numbers, in the Winter I get about 15 kWh over the day and about 45 kWh in Summer. Your number will be different, due to your roof size, location, orientation, number of facings, and perhaps other factors. I don't think a latitude-based chart is all that helpful, as there are so many other variables. It does make it a bit more difficult to compare systems and vendors.

    For me, I had a solar panel roof (not Tesla) and needed to reroof. I wanted a much larger solar system too. I had three quotes from roofers for a roof style I liked (it was super nice tiles). The quotes were more than the Tesla solar roof and did not include any solar. So for me, it was a no-brainer. That said, we're in a very expensive labor market area, so costs are high. You can also get a cheap asphalt roof that is likely cheaper than the Tesla roof, although you'd have to add in the cost of solar panels to make a fair comparison. Good luck with whatever you decide - I know it's not easy to figure it all out.
  • Oops, I forgot to be specific enough. The power production I was seeking was the production after the SolarRoof shingle array collection and after the impact of the Tesla Inverter converts the shingle DC power to home usable AC power.

    Maybe someone has been running a Tesla SolarRoof shingle system for several months (what's nearest city) and they recall their SolarRoof shingle sq-ft area?
    Along with that the actual energy collected over the same amount of months? :-)

    Haha, thanks!
    Eric
  • I think you're asking to compare apples to oranges. Every single installation is different. You might have an identical system to a neighbor, yet their annual production can be different. There are a myriad of variables to account for. This is why PV is rated at maximum theoretical output. It's up to the installer to input the specifics of an installation into their (usually proprietary) algorithm to establish an estimate of annual production. When Solar City did mine, they nailed the production with about a 2% error (in my favor) over their 24 month rolling time frame. That was five years ago.

    An estimate from *any* solar installation company should include an annual production projection. I wouldn't go with any company that doesn't provide a guaranty of said production, plus a remedy should it not be met. Also remember that a production warranty is only valid as long as the installing company is in business. This is one of the big reasons I went with SC/Tesla.
  • @"TeslaTap.com"
    Thanks so much! Good info, especially your general Winter/Summer (15 kWh/45 kWh) as I wondered how much of a hit in real-life that value was! Wow, I am stunned.
    You are so very correct about uniqueness of each home and solar orientation! But I figured the complexity of asking such details and me even being able to adjust for each variation would be tough.

    So my big take away from your data is that perhaps it would be wise for me to orient the house/roof somewhat to favor winter production. I'll need to consider carefully as my largest kWh usage avg. is summer. :-)

    My data needs are kind of different and specific since I am building the home on a lot of my choosing. I'll most certainly place the house with the long axis facing south on the front of the home. When I built this home 6yrs ago, I was only 8° off perfect south but solar shingles were not available nor sturdy like thr V3 Tesla shingles.

    Thanks again for sharing gr8 info!

    Cheers,
    Eric
  • Amen to that @gregbrew_98470014 !

    I too will look into any Tesla production warrantee. Great reminder!!!

    You guys are amazing with your super quick reply.
    Perhaps I needed to better share my challenge, Ha-ha.

    I'm trying get good general info and "BACK-INTO" 😀 how large a roof I would need to supply what I am "estimating" a new home would require. Based upon my existing energy audit and current 18-mo usage from my electric provider ... and my change to a smaller design home ... I'm expecting a daily average need of 30-35kWh.

    Of course with what you've taught me so far and knowing my Summer Avg Use is 125% above Yearly Average Use I must plan on making my roof 125% of that 30-35kWh goal... 37-44kWh. I also plan to be grid-tied so excess can be used by the Model Y or net metered to utility company for variations.

    Still my problem is that... I have NO idea whatsoever what the Tesla SolarRoof shingles (including the Inverter losses) can produce for the latitude I plan to build. I am at a loss as to my roof designs overall length and width. Its a big variable.

    So far what "I DO KNOW" is:
    1. Tesla's SolarRoof is the only solar tile we like so it's going to be a Tesla roof
    2. We will have Tesla PowerWalls (at about avg. 5.0 kW power with 13 kWh capacity each wall) to survive a 3-day outage. My current home daily avg use is 66kw but in emergency mode we get by on an 11kW Genrac Propane Generator in this larger home for HVAC, core lighting in stairs/halls, 2 bathrooms, 2 refrigerators, 2 TVs and the IT backbone... so in a smaller home I "guess" 8-9kW would be adequate.
    3. We'll be "grid-tied" to help me in low production days and help grid during my over production days.
    4. I will certainly have a near perfect Southern Exposure Long-Axis design exposing the front of the home south; Just like my current home.
    5. The roof will have NO penetrations and only one flat shed dormer roof with its south facing window... and total window glazing should be 6-8' wide x 3-4' Tall.
    6. The homes Latitude will be Charlotte at 35.2° (35.2*0.76)+3.1= 29.85° or 7:12 pitch roof).

    Now it's this roof that worries me. How big must it be to provide my expected need of about 44kWh?

    THANKS AGAIN for all the help! Now you have a better idea of what I'm planning and why I'm asking about how much energy the Tesla SolarRoof shingles are capable of producing.


    Cheers,
    Eric
  • Good questions, but I'm not a solar installer so I can't address much of what you're asking for. That said, if it helps, I have about 3,000 sq. ft. roof (a lot of big overhangs and covered patios, the house is quite a bit smaller). The solar titles cover about half the roof.

    I think you actually don't necessarily want all south facing. With some East and West, you get continued output over a longer part of the day. I had some north, as there weren't enough other areas to get to my 10.8 kW sizing. That's where I get the least output during Winter. I do have quite a few skylights, vents, and other limitations. Local fire requirements may also require solar tiles can't be 1-3 feet from the edge. That's going to vary by locale. For my area, the first row on the outside edge is all dummy tiles.

    I made a video and have other details of my installation here:
    https://teslatap.com/articles/tesla-solar-roof-installation/
  • Thank you! That's outstanding info. Can't wait to see your video.
    So about 1/2 of the 3000 sq-ft (1500 sq-ft) provided almost 11kW. Man, i need some roof area. :-)

    I'm glad you mentioned capturing a larger spectrum of the day. The new house, as my design looks so far, will have a 30° angle on the garage which will capture some of the afternoon sun.

    Thanks!
    Eric
  • @"TeslaTap.com"
    Brilliant job on the video & detailed story details! Your home looks amazing!

    So, how much of your designs 10.8kWh energy budget was added for your EV Charging?  I'll be charging a Model Y & have been wondering.

    A major takeaway on my mind after the video & our discussions is that I must reduce my energy budget more than anticipated. If you're living on... 10.8-kWh solar roof, two Powerwalls, two dual-channel solar inverters, and the gateway ... AND you can still charge your Tesla without any grid power... I'm blown away!

    OMgosh, my 18-mo average daily use here in VA is 66kW before Model Y impact (well, I do have HVAC in the garages). The next house, not here in VA but NC, was going to be smaller so I thought a goal of 40kWh was a stretch with a Model Y ... Brother, I must do better!!!

    Say... My home is all electric ... do you have natural gas for your heating or cooking?

    I'm also wondering about the "two dual-channel solar inverters" ... I know I'm not educated enough to ask the right questions but a couple might be:
    - why two?
    - what does the "dual-channel" provide you?
    - is your system tied into an emergency back-up generator?

    Ha-ha, I know I've tossed a lot at you... thank you!
    Eric
  • Dual-channel refers to having two Maximum Power Point Tracker (MPPT) input circuits in one inverter box. The MPPT finds the best combination of array voltage and current to output the most power possible. Essentially, it optimizes the power output of the array...on the fly.

    It's important to have separate MPPT circuits for separate PV arrays, if they face different directions or have different shading issues. With a single MPPT, output power is reduced to the lowest performing section or panels in the array. If the voltage of one panel's output is low (due to low illumination), all the panels in that section of the array are all pulled down to that voltage, which can greatly reduce power output of the entire array. So-called "micro-inverters" take this concept to the extreme, putting individual MPPT inverters on each panel. "Optimizers" do something similar.

    FYI, My 2015 ABB inverter has two channels, but the box reports to the app with a single, summed set of data. The front of the inverter has an LED display that shows them separately. It's kind of weird that mine has two MPPT circuits, because I have a single array, on the same roof plane, subject to zero shading. My inverter must have been the cheapest at that rating (4.2kW) at the time.
  • @ejkessler - I estimate at least 50% of EV charging is done via solar/PW over the year. In the winter, not much, but already this month I'm able to charge my Tesla from solar/PW. Of course, it varies depending on my daily travels and the amount of sun.

    Greg answered most about the inverters. I have four facings, so two dual-channel inverters are used to optimize the output from each facing during the day. If you only had two facings, then only a single two-channel inverter would be needed. Tesla will figure this all out as part of the planning stage, but good to understand too.

    I have gas for water heating and heating, no generator. Everything else is electric. With a new house, you're likely to have a far better-insulated house than what I have in my 59-year-old house. Then again, I'm in CA, so we don't have quite the weather extremes - just fires :(
  • > @ejkessler said:
    > Thank you! That's outstanding info. Can't wait to see your video.
    > So about 1/2 of the 3000 sq-ft (1500 sq-ft) provided almost 11kW. Man, i need some roof area. :-)
    >
    > I'm glad you mentioned capturing a larger spectrum of the day. The new house, as my design looks so far, will have a 30° angle on the garage which will capture some of the afternoon sun.
    >
    > Thanks!
    > Eric

    I believe each solar tile produces about 58W with area of 4.6875 sf. For example, if you order 16kW system, then it would require 160000/58x4.6875 = 1293 sf area of roof. The production of solar power is totally dependent on the location of your home, availability of sunlight, and how Tesla will install solar tile (which will be optimized, I assume :)). You can get rough estimate of usable roof area of your home for solar and available sunlight from Project Sunroof - Google (https://www.google.com/get/sunroof).
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