Panels too much for inverter?

I just had a 15.4 kWh solar system installed on my roof.  It is designed to provide 15.4 kWh max output.  My Inverter is a Solar Edge se11400h.

The inverter clips at 11.4 kWh Max.  The install company said I can only use 11.4 kWh max because of my 200 amp electrical panel.  I understand that I get to my max output of 11.4 kWh faster with so many panels but it seems like a waste of 4 expensive solar panels when I am at full output.  Can I add another inverter? Do I need an upgrade on my electric panel.  I saw a video where someone added a max output panel with 175 amp breaker to feed the whole house.  If I add batteries to my system can I harness the 4kWh that go unused during max output.

Thanks  

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,689 admin
    For most folks, "over sizing" the solar array and derating to ~77% of array "standard" Watt rating is normal...

    Solar panels have their output voltage drop as the panels/cells get hot. The "panels" are rated at 75F/25C--But in normal full sun on a warm/hot day/no wind, the cells can get to upwards of 175F... And their output voltage can fall to 80% or so.

    Remembering that AC inverters take Power In Array = Power Out Grid (plus some losses). Where Power=Voltage*Current... Falling voltage, falling power (solar array current does rise very slightly as cells get hot, but is usually ignored because the rise is so little relative to voltage drop):
    • 11.4 kW inverter / 0.77 typical derating = 14.8 Watt "suggested" max array
    • 11.4 kW inverter / 15.4 kW array = 0.74 derated array
    Which is perfectly OK... Some folks use 75% derating instead.

    Generally, you are losing something on the order of (2% of 15.4kW=) 0.308 kWatts = 308 Watts

    Which, even in California is around $0.06 to $0.12 of "loss" production (assuming 2% "extra" losses) per hour... And usually, you only see the 77% "clipping" maybe an hour or couple hours per day, for a few days on cool/clear spring/fall days... So, not that much money is wasted (few $10 of dollars per year?).

    There are sometimes other considerations too in designing the solar array... The input voltage has to be within a certain min/max input to the inverter... And these can only be "adjusted" by the number of panels in series and parallel. Too low of voltage, the inverter won't start (or won't work efficiently). Too high of array voltage and damage the inverter during winter cold snaps (as array gets colder, the array voltage rises) if there are too many panels in series.

    I guess you are somewhere around Fort Collins Colorado? You have hot summers and cold winters... Depending on the exact panels chosen (Vmp/Voc/Imp/Ioc panel ratings) and your min/max temperatures--The designer/installer may have had to meet other requirements from the invert.

    There are lots of trade off that can be made... Brand/model/price/specifications of the AC inverter--Brand/price/models/availability of solar panels/roof space/roof arrangement/aesthetics/etc... Electrical wiring requirements for roof top solar and your main panel. Could he have taken (for example) 2x solar panels off of your roof... maybe.

    At this point, I don't see that the installer made any fauxpas here... It appears that you most likely got an "optimum" cost/performance design.

    Adding batteries will add costs... Batteries are expensive, and last 3-15 years. You would need to a solar charge controller, AC inverter too... You may want to do this for other reasons (such as emergency power--Which a standard GT Solar System cannot provide--Utility power goes out, so does your GT solar). But that is a different set of questions (and a lot more costs).

    Yes, he could have (possibly--Details matter here) changed the 200 amp breaker and installed a 175 Amp main breaker and added more solar/larger GT inverter--But that also depends on your power needs (I have natural gas and a 125 Amp main breaker--More than enough power for me and my family)... A/C, electric heat, stove, drier, well pump, etc. may need more than 175 amp service...

    At this point solar panels are ~$0.50 per Watt (very roughly)... If you could have dropped 2x 300 Watt panels--It would have saved ~$300 in costs (plus markup). Solar panels are very cheap these days (not that many years ago, solar panels were $5+ per Watt or 10x as much).

    Assuming everything works and was installed correctly--I would not worry. "Clipping" a few hours a year is normal for an "optimum" cost design. (panels are cheap, GT inverters are not that expensive--And Labor+permits+wiring+racking is pretty expensive).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,579 ✭✭✭✭✭
    edited May 4 #3
    I just had a 15.4 kWh solar system installed on my roof.  It is designed to provide 15.4 kWh max output.  My Inverter is a Solar Edge se11400h.

    The inverter clips at 11.4 kWh Max.  The install company said I can only use 11.4 kWh max because of my 200 amp electrical panel.  I understand that I get to my max output of 11.4 kWh faster with so many panels but it seems like a waste of 4 expensive solar panels when I am at full output.  Can I add another inverter? Do I need an upgrade on my electric panel.  I saw a video where someone added a max output panel with 175 amp breaker to feed the whole house.  If I add batteries to my system can I harness the 4kWh that go unused during max output.

    Thanks  
    If you are south of the Mason Dixon, I certainly wouldn't worry about it.

    Panels today are often rated with both the STC - Standard Test Conditions and NOCT - Normal Operating Cell Temperature values.

    Here's an example of 2 labels with NOCT values, note that they are about 75% of the STC values;


    I'm not saying you will not produce more than the inverter will handle, but it should be rare unless you live in a very cold climate.

    I suspect if you look at your estimate, if they provided one, that the array was NOT "...designed to provide 15.4 kWh max output. " but was designed to maximize production with your current 200 watt panel and the specified inverter.

    Buying batteries would require a different system than what you have. I don't believe Solar Edge inverters are design to charge or use batteries in case the grid shut down. That would be a different type of system.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,971 ✭✭✭
    Your installer is correct, you are limited by the bus-bars in your 200 amp panel, you can't add more AC generation.

    Panels are not expensive and it is standard practice to add more name-plate rating than an inverter can produce. In my system, the panels are lowest cost part of the system.


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