[RE-wrenches] Enphase v. string inverter

Mon Oct 11 16:05:54 PDT 2010

Hello Joel,

The issue is that over half the array was in shade.  I don't think 
there would have been enough string voltage to start a string inverter.

Cheers,

Drake

At 11:33 AM 10/11/2010, you wrote:
>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: <mailto:drake.chamberlin at redwoodalliance.org>Drake
>To: <mailto:re-wrenches at lists.re-wrenches.org>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
>><http://www.SPEFL.com>www.SPEFL.com
>>Commercial & Residential
>>FL State Certified # EC13001765
>>
>>Sent from my iPhone
>>
>>On Oct 9, 2010, at 7:07 PM, "Marco Mangelsdorf" 
>><<mailto:marco at pvthawaii.com>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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>>>List sponsored by Home Power magazine
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