Solar Contractor in MA selected system with inverter undersized quite high, why?

VoodooV4

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Nov 14, 2021
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Hey folks,

Im about two weeks into this solar system stuff when I had a few local companys come out and draft a plan. Im located in southeaster Massachusetts - (Hyannis). In Massachusetts, were capped at 10kw a/c systems for residential. With that being said, im looking to use my roof space to meet the cap. One system that was drawn up is an LG 425 x 33 with Enphase IQ7+ inverters. Thats a 1.45 AC/DC ratio. Their rational was that while undersizing will cause clipping a few hours a day for a few months, the excess sideloading generated will be worth while throughout the year. Another company came out with LG425 x 27 with IQ7A and wouldn't recommend using the IQ7+ because the panel is rated too high for it, he says that it will cause clipping quite often, and it will prematurely cause failure to the inverter. Now im at the point that I dont know who to believe.

I know that MA is not the best locale for year round sun; but the roof is facing 248 degrees west, 8/12 pitch with lots of sun aimed at it. Those panels just seem excessive for the inverter. If I step up to a IQ7A then that puts me at a max of 27 inverters utilizing something like an LG440 x27. I cant go to a IQ7 and use more lower wattage panels because im out of roof space. My max panel fitment is roughly 34 panels.

Any help is appreciated.
Thanks.
 

Hedges

I See Electromagnetic Fields!
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Mar 28, 2020
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9,169
The microinverter vendors tend to advertise how large a panel it can take. Maybe because they can't keep up with fast market changes?
Panels are relatively inexpensive, and microinverters cost a bit more than string inverters, so over-paneling is reasonable.

Clipping shouldn't cause premature failure. It is just operating at 100% for more hours.

Do you have multiple orientations available?
I like two strings of different orientations feeding one inverter. Less clipping, more hours of power. I do that with string inverters, but microinverters would need smaller panels to use that effectively, and large panels are the sweet spot.

Will you want battery backup in the future? If so, plan for it. Some PV inverters play better with battery inverters than do others. Enphase has a battery offering. Some of their microinverters play well with other brand battery inverters (do frequency-watts) and such a system might be more economical and better performing.
 

VoodooV4

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Nov 14, 2021
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Unfortunately I don't have multiple orientations available with my roof setup.
As far as battery backup, its not something im considering.

At this point, im not sure if this setup is ideal or am I wasting $$ by going with these higher end panels for my area.
 

Hedges

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Mar 28, 2020
Messages
9,169
Panel efficiency 21.4%, quite good, so more power from a given area.


Are these the 440's, 22.1%?


You would get more watts and watt hours from same panel with a higher wattage inverter that didn't clip.
If you had inverters totaling max allowed 10kW, you would get more watt hours with larger panels (or smaller inverters) that clipped more.

Have you compared cost of power from PV with utility rates?
Do the companies provide an estimate of kWh per year or average per day, so you can amortize cost over say 10 years, or calculate how many years for break even?

Assuming no clipping, web sites for insolation would show effective sunlight hours. PV panel STC watts is test conditions, PTC watts is expected in field conditions, less inefficiency of inverter.
 
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