[RE-wrenches] Warranty Claim Based On Enphase Monitoring Data

[matt at solar-energy-solutions.com]

Kent,

Can you help me understand the 1.1%?  I had figured over 4% and allowed
that 1-2% may be voltage drop (though it is quite literally 12' of 10 awg
between the last enphase and the meter).

In a state with a semi-active SREC market all our systems are installed
with a revenue grade meter.  I see similar variations on almost every
string inverter installed.  I don't think this detracts from potential
Enphase value, I just don't see that this is an area where the Enphase
product stands out.

Matt



> Matt,
>
> The Enphase and revenue grade meter are in disagreement by less than
> 1.1% in the system you are describing - that's good agreement! According
> to the Enphase white paper, the wiring loss in the Enphase cabling
> between the first and 9th inverter is 0.6%. That only applies to the
> last inverter and the average loss for the system will be less, but it
> shows that the ac wiring loss is a significant part of the discrepancy.
> Also, even the revenue grade meter is not perfect - typically ±0.25%
> when new.
>
> Kent Osterberg
> Blue Mountain Solar
>
>
> matt at solar-energy-solutions.com wrote:
>> Mark,
>>
>> We have nine Trina modules on our roof with Enphase.  Enphase says the
>> array has produced 2,680 kWh to date.  The revenue grade meter 12 feet
>> away says 2,564.  Until I hear otherwise I am reluctant to consider
>> Enphase reporting precise.  It seems to be similar to what I would
>> expect
>> from a string inverter.  I would be delighted to hear more anecdotes
>> confirming your observations.
>>
>>
>> Regards,
>>
>> Matt
>>
>>
>> Matthew Partymiller
>> Solar Energy Solutions LLC
>> (859) 312-7456
>> matt at solar-energy-solutions.com
>>
>>
>>
>>> Folks,
>>>
>>> Has anyone used Enphase monitoring data to get warranty replacement on
>>> new
>>> modules with sub par yield?
>>>
>>> I have several interesting questions stemming from access to Enphase
>>> module
>>> level monitoring data.
>>>
>>> Looking at data from a larger site (80 modules) with no shading issues,
>>> instant power production indicates a high degree of uniformity in panel
>>> power (Sharp NU-U240F1 and D380) easily within 1%.
>>>
>>> So what can we now say about the precision and accuracy of this
>>> monitoring
>>> data? It seems the old school thinking for string inverters was all the
>>> monitors were 5% off and reporting 5% more power than actual.
>>>
>>> Based on the data that I am looking at, it seems the microinverter
>>> meters
>>> must be fairly precise and possibly fairly accurate as well. Uniformity
>>> of
>>> module performance must also be fairly high.
>>>
>>> In any case, this data clearly shows a single module that is not
>>> performing
>>> as well as it's cohorts. For power levels above 50% of STC, it averages
>>> 9%
>>> less power than all other modules in the system. So off to Sharp for a
>>> warranty replacement? Yes, but, what if I am 5% low on the report from
>>> my
>>> inverter meter and 5% lower on my power from this one module? What if
>>> the
>>> module gets back to Sharp and they say it is within spec, now the costs
>>> are
>>> all mine?
>>>
>>> Interestingly enough, access to this monitoring data is making more
>>> work
>>> for
>>> me as an installer. With a string inverter, I would monitor power
>>> production
>>> readings monthly and be happy so long as yields were higher than what I
>>> projected when I designed and bid the job. Pretty much fire and forget.
>>>
>>> Now I am spending time on evaluating this data and doing the work to
>>> change
>>> out the module under warranty and so forth. I am going to end up
>>> putting
>>> in
>>> quite a few hours into this for what: to recapture 10% of 1/80 of total
>>> system yield
.0.0013%.
>>>
>>> I am not complaining, just musing over this interesting evolution.
>>>
>>> Mark Frye
>>> Berkeley Solar Electric Systems
>>> 303 Redbud Way
>>> Nevada City,  CA 95959
>>> (530) 401-8024
>>> www.berkeleysolar.com
>>>
>>>
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Matthew Partymiller
Solar Energy Solutions LLC
(859) 312-7456
matt at solar-energy-solutions.com