[RE-wrenches] Enphase v. string inverter

[Joel Davidson]

Hello Drake,

I have observed hundreds of PV systems in the early morning and can say without doubt that string inverters are not inherently slow to wake up.

For example, today my 12 year old SW4048 with a single crystal PV array facing south at 12 and 18 degrees tilt and my SB2100 with a single crystal PV array facing south at 18 degrees both were putting out power at 7:45 am when the sun was 9 degrees above the horizon at azimuth 105 degrees. Today the sky is clear and the sun rose in Los Angeles at 6:57 am.

I have seen systems with 100 kW Xantrex inverters and flat Unisolar arrays wake up before the morning sun rose above the horizon. Granted the systems were putting out less than 5 kW, but the inverters were on.

See you all at the solar conference.

Best regards,
Joel Davidson


----- Original Message ----- 
  From: Drake 
  To: RE-wrenches 
  Sent: Monday, October 11, 2010 6:39 AM
  Subject: Re: [RE-wrenches] Enphase v. string inverter


  I'm now monitoring a 5.376 kW system we recently installed. The sun is barely up, with light clouds, and a portion of the array is still in shade.  The system is putting out 700 watts.  A string inverter would probably be waiting to start. 

  My main problem with the Enphase is the 199 watt limit to its output.  The inverters are rated for up to 235 watt modules.  This 224 watt module array spends a fair amount of time at full inverter capacity during cool sunny days.  Maybe these inverters should not be used with over 210 watt modules.  

  Drake 



  At 12:50 AM 10/11/2010, you wrote:

        The main advantage of Enphase is the module level monitoring.  However, the increased output due to partial shading can be significant.  I was at a 6 year old PV site this week, and a tree had grown up near the base of the roof.  Branches were casting a few minor shadows on the array, but was wiping out 75% of the production.  I can assure you, those 9 modules would have been producing '50+% greater output'
    Nick Soleil
    Project Manager
    Advanced Alternative Energy Solutions, LLC
    PO Box 657
    Petaluma, CA 94953
    Cell: 707-321-2937
    Office: 707-789-9537
    Fax: 707-769-9037



    From: Jamie Johnson <jjohnson at spefl.com>
    To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
    Sent: Sun, October 10, 2010 5:38:55 AM
    Subject: Re: [RE-wrenches] Enphase v. string inverter

    Marco,

    The last I heard the NREL was testing enphase vs. a string inverter, they were also suppose to test enphase vs. A competitors module level mpp tracking.  Not sure if that performance test is complete yet.  

    I have seen 1 independent unshaded test ( potentially biased ) which IIRC showed enphase ~1% less than a string inverter, this seems to match the inverters CEC rating.

    What we see around here is an over estimate of kWh production by the selling contractor using enphase, sometimes by 50+% greater than unshaded kWh estimates.

    Performance guarantees with monetary compensation back to the customer if estimates are not met can be a good thing and improve the industry IMHO.

    Jamie Johnson
    General Manager
    SOLAR POWER ELECTRIC TM
    NABCEP Certified Solar PV Installer #031310-118
    (941) 380 - 0098
    www.SPEFL.com
    Commercial & Residential
    FL State Certified # EC13001765

    Sent from my iPhone

    On Oct 9, 2010, at 7:07 PM, "Marco Mangelsdorf" <marco at pvthawaii.com> wrote:


      Does anyone know of any reports out there from a neutral, 3rd party which compares an Enphase array with an array using a string inverter with both arrays on the same unshaded surface?

       

      Some Enphase peddlers here are saying that the energy harvest from an Enphase system is going to be better since they supposedly come on sooner and stay on later in the day.

       

      One guy is actually saying that the Enphase inverters come on before the sun comes over the horizon.   Maybe from the same family that claimed that a-Si modules produced power from the moonlight.

       

      Thanks,

      marco

       
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