TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC

Production expectations unrealistic?

Discussion in 'Tesla Energy' started by Eury, Mar 27, 2018.

  1. Eury

    Eury New Member

    Joined:
    Jun 30, 2016
    Messages:
    2
    Location:
    NH USA
    Hello, I had my PV system with 2 Powerwalls installed in early February. Not a lot of sunny days in NH between then and now, but I've had some that have been clear. My question is, are my expectations unrealistic as far as how many KW I should be producing?

    According to the plans and our purchase paperwork, we purchased a 7.2KW system, that has a "System Production" of 8924 kWh. I have 24 Hanwha Q Cells: QPeak G4.1/SC300 and a Delta Solivia 6.6 TL RGM Inverter.

    So, reading through all that. I don't see how I could ever produce anything near what they say I will with a 6.6kW inverter, just quick off the top of my head math would get me the 6.1-6.2kW that I am currently seeing from my PV system with the expected losses.

    Hopefully someone can help clear this up for me.
     
  2. liuping

    liuping Active Member

    Joined:
    Jul 23, 2013
    Messages:
    2,241
    Location:
    San Diego
    To calculate you expected daily production, you need to find the "Peak Sun Hours" for you location. That times your panel rating - losses should be roughly your average production.

    Annual System production of 8824kWh for 7.2kW of panels (assuming 10% losses) is using a peek sun hour rating of around 3.77 average over the year. That sounds about right for New Hampshire.
     
  3. SoundDaTrumpet

    Joined:
    Jun 22, 2017
    Messages:
    498
    Location:
    Bay Area, California
    #3 SoundDaTrumpet, Mar 27, 2018
    Last edited: Mar 27, 2018
    Winter solar production is depressing compared to summer. It's nearly 3:1.

    Use the gold standard PV Watts tool from NREL if you have doubts. It is excellent.

    PVWatts Calculator
     
    • Informative x 1
    • Like x 1
  4. miimura

    miimura Well-Known Member

    Joined:
    Aug 21, 2013
    Messages:
    5,521
    Location:
    Los Altos, CA
    Due to shading, my Winter low is 1/5 of the Summer peak generation in kWh/day.
     
  5. jsimon7777

    jsimon7777 Member

    Joined:
    Feb 1, 2018
    Messages:
    219
    Location:
    Castro Valley
    About the same for me at its worst. Typically more like 1/3rd, though. I'm also down in a canyon.
     
  6. miimura

    miimura Well-Known Member

    Joined:
    Aug 21, 2013
    Messages:
    5,521
    Location:
    Los Altos, CA
    Mine is really 5:1 every year. Typical Winter low is 5kWh/day and typical Summer peak is 25kWh/day. The gray line is a simple forecast model which does not account for the shading.

    Solar production Multi-Annual Chart.jpg

    My brother-in-law has the same type 18 micro-inverters mounted on his house without the shading and split directions and his really is 3:1.
     
  7. arnolddeleon

    arnolddeleon Supporting Member

    Joined:
    Jul 21, 2012
    Messages:
    522
    Location:
    SF Bay Area
    Doesn't seem that crazy, that's about 23 kWh/day. As a *very very* rough rule of thumb I've used is 4 to 5 "full hours" equivalent as an approximation for the bay area in CA including some losses. Your system is expecting about 3.7 "full hours" per day over the year (using 6.6 kW as the limit). (Forgot to hit post after I wrote this, I see @liuping makes a similar point)

    arnold
     
  8. Eury

    Eury New Member

    Joined:
    Jun 30, 2016
    Messages:
    2
    Location:
    NH USA
    Thank you for all the feedback. It doesn't sound like anyone considers the 6.6 inverter to be a limiting factor.
     
  9. wwhitney

    wwhitney Member

    Joined:
    Nov 2, 2017
    Messages:
    516
    Location:
    Berkeley, CA
    FWIW, it is normal to design solar installations in which the sum of the ratings of the panels exceeds the inverter rating. I think ratios of up to 120% or so are common. When the solar panels are able to produce more power than the inverter is rated for, the inverter will "clip" production to its maximum rating.

    But this clipping typically only happens for a short period of time around solar noon each day, and only in the summer. That means the economic value of the lost production is fairly small. Because string inverters only come in fixed sizes and are a fairly significant part of the equipment costs, using extra panels in this way can be economically optimal.

    Cheers, Wayne
     
  10. SoundDaTrumpet

    Joined:
    Jun 22, 2017
    Messages:
    498
    Location:
    Bay Area, California
    My breakdown between summer and winter months (with band splits at May 1st & June 1st). I get 62% of my solar production in the summer band and 38% in the winter band. I have zero shading, located inland near the Factory, and away from coastal clouds and fog. For the OP, the best summer band is yet to come.

    I get clipping in the early spring, where the winter rains have cleaned the panels, and low temperatures enhance PV performance. I was taken back by clipping in May-June for 1-2 hours a day. I voiced out to my contractor why a 4000VA wasn't spec'd out instead of my 3840VA inverter. I did the calculation and the money lost was only $50 over 25 years, so they send me a gift card for that amount. 3840VA is a perfect match for a 20A breaker. All-in-all, nothing wrong with clipping.
     
    • Helpful x 1

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC