[RE-wrenches] Enphase IQ7A 3 phase limitations

Thu Mar 4 15:45:27 EST 2021

Mac Lewis was nice enough to run some Helioscope simulations for me (thank
you, Mac). The numbers were almost identical to PVWATTS in that per kW, you
get about 1% less energy yield with a 420W/IQ7A than a 385W/IQ7+ when
operating at 208Vac. Given that the IQ7A is more costly, and presumably the
higher powered modules will start off at a higher $/w cost, it probably
doesn't make sense to use the 420W/IQ7A on a commercial building, but the
energy yield differences were much smaller than I anticipated. On the flip
side, higher energy density is an obvious choice if maximum utilization of
the roof is more important than a small difference in ROI.

I'm still trying to get a definitive reason that Enphase lists the IQ7+ at
a constant 290W for 240/208 (1.21A/1.39A output currents, respectively),
but the IQ7A is rated at 349W for 240V and 290W for 208V (1.45A current for
both output voltages).

Jason

On Wed, Mar 3, 2021 at 8:36 PM Dave Tedeyan <dtedeyan at taitem.com> wrote:

> I've never really trusted PVWatts on this. I just did a quick test using
> my location in the northeast, with all the standard values and then just
> changing the DC to AC ratio. It's telling me that a ratio of 1.5 is almost
> exactly the same as a ratio of 1, and that around 1.3 is best. You actually
> lose about 2% at 0.5 and about 8% production at a ratio of 2.
>
> So I can only conclude that either PVWatts does not have a great
> calculation, or the efficiency loss due to not running the inverter at
> rated power is worse than I assumed.
>
> Cheers,
> Dave
>
> On Wed, Mar 3, 2021, 6:14 PM Jason Szumlanski <
> jason at floridasolardesigngroup.com> wrote:
>
>> I've used that document many times when clients question the ratio. I
>> wish I knew exactly how the PVWATTS ratio calculation worked. I know
>> there's information on how this is all done, but I don't really have the
>> time or inclination to study it. I'm wondering if someone knows how
>> accurate It is.
>>
>> On Wed, Mar 3, 2021, 4:04 PM Jay <jay.peltz at gmail.com> wrote:
>>
>>> Emphase has a white paper showing production vs module size and
>>> locations around the country.
>>>
>>> I don’t know if it’s more accurate than pv watts but you might check it
>>> out.
>>>
>>> Jay
>>> Peltz power.
>>>
>>> On Mar 3, 2021, at 12:13 PM, Jason Szumlanski <
>>> jason at floridasolardesigngroup.com> wrote:
>>>
>>> 
>>> I'm wondering how accurate the DC to AC ratio is when using PVWATTS. I
>>> did a quick PVWATTS analysis at my local area using a typical commercial
>>> roof tilt and found that using a 420W module on an IQ7A versus a 385W
>>> module on an IQ7+ yields almost identical results. The 420W module has 1%
>>> less annual production at to the 145% ratio compared to the 132% ratio with
>>> the 385W module.
>>>
>>> Given that, I can't imagine why anyone would use the IQ7A versus the
>>> IQ7+ on a 208V system. Why incur the additional cost if the AC output
>>> current is identical for both inverters?
>>>
>>> If PVWATTS is right, I guess it's a non-issue in my local area, but it
>>> may vary in other locations where clipping is more common. The heat here
>>> results in little clipping at a 132% ratio here, and I guess at 145% the
>>> morning and afternoon advantages largely outweigh the mid-day clipping
>>> increase.
>>>
>>> Jason Szumlanski
>>>
>>>
>>>
>>> On Tue, Mar 2, 2021 at 10:00 AM Jason Szumlanski <
>>> jason at floridasolardesigngroup.com> wrote:
>>>
>>>> I was surprised to learn that the IQ7A is limited to 290 W continuous
>>>> at 208 volts. That pretty much puts Enphase out of the running for light
>>>> commercial jobs with new high-powered 72 cell panels. Any thoughts on this?
>>>>
>>>> Jason
>>>>
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