Adding panels and how much oversized to inverter

[sandbagger]

So I had a system installed a little over a month ago and am not thinking I should have gone bigger as the output does not look to be enough. When I did this I knew it was going to be undersized but its what I could afford to pay cash for so that is what I did.

Its a grid tie with a net metering agreement with the power company (Detroit Edison) so if I change the inverter I will be breaking the agreement and I will loose the net metering. I am currently grand fathered in for 10yrs as I got in just before Michigan changed the laws.

Solar Edge SE5000HD 16XJKM310P-72 panels for 4960W with Solar Edge optimizers P320's in a single string.
zip code 48141 230deg and a 40deg tilt fixed roof mount

Having it for most of july and that being the highest radiation month per PVWATTS at 682kwh actual average for 31 days should have had me at 616kwh so its close.
Over the last 45+ days, most days peak at about 3.8kw and have only had 3 days get to 4.1kw
It is mostly shade free, only very late in the day on 2 panels from the chimney

I have room to add one more row of panels up to 8. roof currently has 2 rows of 8 in a single string.

So the million dollar question is, should I add another row?
I am more than capable of installing this my self/help

Per the inverter specs I can go to 155% of the 5000 so up to 7.75kw
I also cant exceed 5700W on a single string even though they allow up to 25 panels. so it will have to be on its own string
I also have to have a minimum of 8 panels on a string.
I would prefer not to mess with the dealer installed string as they do monitor it.

8 more 310 panels (+2480) on a 2nd string would bring me up to 7440kw
Based on the 3.8kw current max looks like I would peak at about 5.6kw without clipping but I know I will.
Also while max per PVWATTS is 682kwh I do have 5 months below 450kwh

How bad is clipping for the inverter?

Is there a way to model the 7.75kw system with clipping at 5kw?
Is it going to be worth it in the long run

Thanks

[NEOH]

My Net Metering agreement only allows for a 10% increase in output.
Otherwise, I need to notify them of the change in design.
Do you have the same type of restriction?

[sandbagger]

I am already at 5kw on the inverter and that is what I am approved for. I could have been approved for a much higher system as I had a much higher load last year( crypto ) but have turned the miners off. I thought the install company was submitting the app at the higher usage but they only submitted for the 5kw system install. Even at that here they will allow up to a 20% increase based on previous year.

[ButchDeal]

The P320 is not really appropriate for the JKM310P-72 . You should be using the P370 or P400 for a 72 cell module.
You can model the set up on PVWatts for output and clipping.

[nwdiver]

How bad is clipping for the inverter?

Is there a way to model the 7.75kw system with clipping at 5kw?
Is it going to be worth it in the long run

Thanks

Clipping isn't really bad for the inverter at all. The lost energy isn't dissipated by the inverter it's simply not harvested. There may not necessarily even be that much more heat generated since SE inverters kick the DC bus up to ~440v when they're saturated... at least the HD Wave I recently installed does.

I'm a huge advocate of array oversizing. PV Watts estimates your loss from saturation at <3%. We recently expanded a SMA system from 4.45 to 5.6 and it's on a 3.8kW inverter. Since the new SMA inverters have multiple MPP channels and when saturated they only curtail one channel I can actually see how much energy is 'lost' due to saturation. 'Losses' so far for August are <3%.

Another point to keep in mind is that NEM cannot last forever and the energy you're losing due to having an oversized array is the most likely to be exported vs self-consumed => the least valuable energy once NEM goes away and the energy you're adding in the mornings and especially in the evenings is far more valuable.

[sandbagger]

The P320 is not really appropriate for the JKM310P-72 . You should be using the P370 or P400 for a 72 cell module.
You can model the set up on PVWatts for output and clipping.

Yea I know about the P320 vs the 400, that is what the installer used and per the specs on the panes, are still in spec for the optimizers. I would be using the 400's and doing it right but the both have the same limitations regarding the string and output max so....

went back to PVwatts and noticed the ac/dc ratio under andvanced so plug in 1.488 (7440/5000) ?

[sandbagger]

Another point to keep in mind is that NEM cannot last forever and the energy you're losing due to having an oversized array is the most likely to be exported vs self-consumed => the least valuable energy once NEM goes away and the energy you're adding in the mornings and especially in the evenings is far more valuable.

NEM is grandfathered for 10yrs, I plan to be retired and living in south america or something by that time Payback right now looks to be 8yrs at our old rate but DTE just got a 7% hike and just requested a 9% for 2020. We are already I think top 10 in the country for costs. at this rate it will pay back much quicker than 8yrs.

Thanks for the info

[sandbagger]

Anyone else have any recommendations/suggestions ?

[J.P.M.]

PVWatts is a model for preliminary system design. It is not a predictor of system performance, particularly short term preformance. Nor does it handle or account for shading. Using it as a comparison to short term system output can lead to incorrect conclusions.

Read the PVWatts help screens with respect to model limitations for further information. Give it a year, keep an eye on output and see what happens. Chances are, over a year, your system's output will be +/-10 % or so of whet a model's output might be if the inputs match reality fairly well and your system has no/little shading.

In the meantime, see and keep informed about what's the fine points with your POCO rules/regs with respect to NEM, particularly as regards system expansion(s).