Swapping micro inverters - how hard?

[desmo907]

In addition, 215 is 86% of 250; add inverter efficiency and you are at 90% of 250. It will be very rare to see your panels produce more than 90% of STC.

So to be clear, if i stay with 215 or 250 on my added panels, my array will be one and just look like it grew?

They mentioned using similar panels to what I have (maybe the Phonos are not available) but not add them to the end of my array on roof but separate them a bit.... so unsure yet how that impacts wiring, etc.

[jflorey2]

So to be clear, if i stay with 215 or 250 on my added panels, my array will be one and just look like it grew?

I can't speak to the aesthetics, since it can be hard to make it look seamless unless everything (panels, racking) is exactly identical.

But in terms of output it will look very similar. About the only time you will see a difference is during the rare "cloud lens" events, where:
1) It rains enough to wash off the panels
2) It rains enough to cool down the panels
3) The sun comes out through a hole in thin clouds.

At that point the panels are clean and cool (their most efficient state) and the sun is magnified by the clouds (you are getting direct sun plus diffused sun from the clouds.) At that point you might see 10% more power from the new panels. But other than cases like that, the output will look the same (new vs old.)

[J.P.M.]

I can't speak to the aesthetics, since it can be hard to make it look seamless unless everything (panels, racking) is exactly identical.

But in terms of output it will look very similar. About the only time you will see a difference is during the rare "cloud lens" events, where:
1) It rains enough to wash off the panels
2) It rains enough to cool down the panels
3) The sun comes out through a hole in thin clouds.

At that point the panels are clean and cool (their most efficient state) and the sun is magnified by the clouds (you are getting direct sun plus diffused sun from the clouds.) At that point you might see 10% more power from the new panels. But other than cases like that, the output will look the same (new vs old.)

The sun is not magnified by the clouds. The effective solar irradiance (some suggest that's a redundant term) on a surface or array can be increased by albedo from objects and/or conditions that may be terrestrial (ground based surroundings), or in the atmosphere (usually clouds), or extraterrestrial (usually the moon and usually effectively == zero). "Cloud albedo" or "cloud reflection" may be a better, more accurate, or at least less misleading or confusing term. The terms "lensing" or "cloud lens" or "cloud lens events" can be a bit misleading as a lens is usually used for the intentional redirecting light (or maybe sound). Clouds do not. Nor do they magnify the sun. They may simply and randomly reflect, mostly in a forward scattering manner, light from the sun, just like terrestrial albedo, except terrestrial albedo is not called "ground lensing".

Also, temporary albedo caused increases in PV device output do not need clean(er) panels, nor do albedo caused increases need cooler panels to be noticeable. The effect on PV output from cloud albedo or reflection can be quite noticeable on clear, dry weather under skies that are partly cloudy with scattered cumulus clouds.

[jflorey2]

Also, temporary albedo caused increases in PV device output do not need clean(er) panels, nor do albedo caused increases need cooler panels to be noticeable. The effect on PV output from cloud albedo or reflection can be quite noticeable on clear, dry weather under skies that are partly cloudy with scattered cumulus clouds.

Agreed. But the combination of all three is what might just push panel output to over 90% of STC. Or even over; I've observed over 100% of STC for a short time during the above-mentioned clean/cool panel and cloud lensing event. (Or "cloud scattering effect" if you like.) It dropped back under 100% pretty quickly as the panels warmed up.

[J.P.M.]

Agreed. But the combination of all three is what might just push panel output to over 90% of STC. Or even over; I've observed over 100% of STC for a short time during the above-mentioned clean/cool panel and cloud lensing event. (Or "cloud scattering effect" if you like.) It dropped back under 100% pretty quickly as the panels warmed up.

I agree that all three and more effects you note can conspire to synergistically increase output to beyond 100% STC output, or more to the point, cause noticeable and perhaps measurable changes in output (as, FWIW, I've measured on more than a few occasions), but the other effects you note besides albedo that are cloud irradiance need not be present and, more to the point, even when present, are usually of a minor nature when influencing array or cell output and ultimately, even when present, are either already smaller than the irradiance forcing function or so slow in their effect relative to the panel thermal time constant as to be immaterial to "changes" in output. For example, if we agree that an albedo caused increase in array output is often and usually noticeable by virtue of the relatively abrupt, sharp and short increase (or decrease if/when abrupt shading occurs) it causes in array output, as well as it's relatively short duration, and since a panel's thermal time constant is of the order of several to 10 minutes or so and somewhat variable depending on environmental conditions, that would make the effects by the other variables on the array output through the effects on array temp. much less noticeable as f(time) with respect to array output.

The primary cause of temporary spikes (up or down) in an array's output, and the time rate of change of that output is changes in the irradiance level, with that cloud albedo effect being nearly instantaneous. The other effects you write of are of much less importance, or may not need be present at all. Even when present, and by some SWAG reckoning on my part, and mostly anecdotally, those other effects seem to be maybe something like about an order of magnitude less of an influence on array output than changes caused by temporary increase in array input from cloud albedo, particularly when the effects that the thermal hysteresis/panel thermal time constant can have on the cell temps. are considered.

The other environmentally caused effects on array output through effects on array temp. you write of will change the array output by causing changes in the cell temperature. Because of thermal hysteresis, those environmentally caused changes in temperature will, for the most part, lag behind any noticeable changes in output caused by increased irradiance, and as a point of my observation and experience, may well not have any effect on output until such time as all or mostly all temporary albedo caused increase in output has run its course with the result that the time rate of decrease in output on the back end of an albedo spike may well be longer or less "spikey" than the rise time.

As for the cleanliness effects of rain, I strongly agree that a good rain can remove dirt. By some measurements I've done over the last 4+ years, I'd est. that a good rain can restore ~ ~ 2/3 - 3/4 of an array's output that's been lost to fouling, but that'll still only be a, say, maybe 2-4 % increase in output on average, and furthermore, without some pretty tight before/after measurements, be tough to quantify, and at any rate, sure not the 10+ % or so increase we seem to be 're talking about here.

To reiterate, to my measurement, learning and experience, the primary and overwhelming cause of temporary increases in array output are temporary increases in temporary irradiance on the array when caused by temporary increases in albedo, usually from clouds. Other environmental effects may or may not be present. Either or any way, those environmental effects which mostly effect array output through changes in array temp. are small contributors to observable and temporary increases in array output.

Respectfully,