Solar panels for the home...

The new fire code is really screwing up panel installs. A strip along the sides and then along the ridge line can eat up potential panel space.

Part of the issue with clipping is the panel orientation. I have two adjustable arrays and one fixed roof mount. The adjustable arrays do routine try to overproduce in winter as they are tilted optimally and get a lot of extra sun from snow reflection plus the back of the panels are exposed so they are quite cold. I had a prior setup with 1100 watts of Siemens panels on a 2K inverter. I saw a sustained 1250 watts off the array one cold clear winter day for about an hour. The same inverter now has 2100 watts of Evergreens and it does clip out at 2050 which is the inverters max output. My roof mount angle is definitely not optimal for winter. When its not covered with snow I haven't seen it putting out anymore than the panel ratings. It has an oversized inverter.

Its tempting to swap inverters but unfortunately they are built to different NEC code revisions so if I do swap, I end up with one system that is no longer built to code. One definite disadvantage to selling SRECs (owner has to certify that the system is built and maintained to code).

My panel/inverter matching is pretty good. Panels are rated at 6900 watts total (26x265) and inverters are rated continuous at 6500 watts total, but I regularly will see total output in the 6700+ watt range before clipping becomes apparent.

Vic99 said:

If you get microinverters, ask if and where they clip. My enphase have a max of 225 W. Might have higher rates ones now. Even though my panels are rated for 255W, I can never get that.

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The Enphase M250 is rated for peak 250w and continuous 240w output but averages $50 more than the M215 which is rated 215w continuous output. Reportedly the M215 will clip at around 225w. I notice that many installers and kits pair the M215 with panels ranging between 200-255w. I guess you have to do a cost benefit to what you lose when it clips on the occasions you manage to reach that point vs the added cost of the M250...

There is some logic supporting inverters with a continuous rating somewhat less than panel rating. My highest peak production so far has been in March and April, cold and clear. Since then clear skies with warmer temps and higher humidity have brought peak production down. Then add in pollen and dust on the panels, and that too brings peak production down. So saving a bit of money on less expensive inverters with a lower rating is a real savings. And don't forget to wash the panels once in awhile if possible to get the dust off.

The past failure prone part of an inverter was the capacitors as most inverters use them and capacitors seem to have a finite life made worse by heat. I lost an inverter due to a power company spike. My old inverter rode through it but the Fronius got hit and cooked a chip. I had delta transient surge suppressors on the panel and the inverter and they didn't pop but after reading several articles, the deltas don't clamp anywhere near low enough to protect much. I installed a couple of midnight solar suppressors which have a far lower clamp voltage. I hope no to test them.

Jags said:

So there is a significant cost difference between a 215 watt inv. when compared to 250w? (admittedly I know nothing about pricing for the supporting items of a PV system)

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Street prices from a reputable dealer I have used in the past:
M215=~USD$134.50 (without the integrated ground feature)
M215=~USD$139 (with new integrated ground feature)
M250=~USD$163.00

Over the weekend, I thought: I haven't washed my PV array since I put it on the roof a year ago, I should wash a couple panels and see if there is a measurable difference in output. Much to my surprise, I find the rain in South Florida does a fine job of keeping the remarkably panels clean. After 5 days of collection, I see no improvement in comparison to the adjacent panels versus the week before. (the tree in the distance in my avatar is a live oak tree).

Not sure on Enphases but some long term solar vets had told me that the concept of intentionally clipping an inverter in order to save a buck instead of buying the next bigger unit is not a good policy in the long run. Knock on wood I have fairly old Advanced Energy Inverter that is lightly loaded that keeps humming along after many years. Most of these units were maxed with more connected wattage than the rating so they clipped on occasion and most of them are no longer working. Maybe I am just lucky mine still works but I expect it has to do with running it at under its input rating . Of course mine is also in a nice cool basement not in the hot sun or far worse like an microinverter, bolted under a panel above a hot roof.

The vets I knew had been PV from the early days on high reliability systems in remote areas so they tended to be very conservative as a service call to Greenland was a major effort. Most installers now are in it to make a buck and go away so I expect they figure what is the lowest cost and figure the warrantee will cover it.

I don't know what I will do when that inverter dies, the array is small and the string voltage it too low for most grid tie inverters.

peakbagger said:

Not sure on Enphases but some long term solar vets had told me that the concept of intentionally clipping an inverter in order to save a buck instead of buying the next bigger unit is not a good policy in the long run.

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If you are competing on price for sales then this could definitely be the case. In a scenerio where you have say 20x250w panels and your microinverters clip at 225w then you are losing 500w of production if all panels were producing at max rate. That seems significant, but I wonder what percentage of the time you can really be producing at that rate for it to matter. Is that worth the 20x$30=$600 to go up a size in inverters? To you and me over the lifetime of the panels, probably yes. To the company who's solar package looks more expensive than the next guys, probably not. Maybe they should price the packages with the lower inverters and then talk you up once you commit to buy.

My comment

There is some logic supporting inverters with a continuous rating somewhat less than panel rating.

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was not suggesting that material under-sizing because of price control the decision on microinverter purchase, but was suggesting there may not be a benefit in over-sizing the inverters. My panels are rated at 265 watt and the highest output I have seen is 269 watts. My inverters are rated at nominal 250 watts, 265 watts maximum, usable with panels up to 300 watts. So far this summer maximum panel output has been about 240 watts, while maximum power output during the late winter (Mar-Apr) did hit 269 watts but more normal maximum was 265-268 watts, with periods (up to about 2 hours) above 260 watts on clear days. At 269 watts output that continued for more than a brief period of time, the inverters clipped back to about 268 watts. I never noticed any clipping at output in the 265-268 watt range.

So, should I have bought inverters with a higher rating (nominal 300 watt for Aurora)? I doubt it. I think that the inverters are just about exactly sized for the panels. Will operating the inverters towards the higher range of their rating result in failure at an earlier date? I don't know, but I think that the passage of time is more likely to result in failure than operating the inverter in the higher range of its rating. Absent real data, a person can only speculate.

WoodNotOil said:

If you are competing on price for sales then this could definitely be the case. In a scenerio where you have say 20x250w panels and your microinverters clip at 225w then you are losing 500w of production if all panels were producing at max rate. That seems significant, but I wonder what percentage of the time you can really be producing at that rate for it to matter. Is that worth the 20x$30=$600 to go up a size in inverters? To you and me over the lifetime of the panels, probably yes. To the company who's solar package looks more expensive than the next guys, probably not. Maybe they should price the packages with the lower inverters and then talk you up once you commit to buy.

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My M215s clip at 225 for 255W panels. At 25 panels, you'd think I would be losing over 600W. However, I only seem to hit 225 1) in the winter below freezing and for less than a couple of hours and 2) once in a while during a cooler day during the rest of the year. My panels face south (185 degrees) and 10 slope 28 degrees and 15 slope 56 degrees.