Creeping invasion of LG bifacial panels - is it happening? What does it mean?

[DanKegel]

LG's diagrams in

http://www.lg-solar.com/downloads/handbook/LG_Solar_NHB_EN_06.03.2014.pdf

talk about light entering at an angle between the cells, striking
the back film, and bouncing onto the back of the cell.
They specifically say it happens more when the sun is off-axis.

So this isn't like those ultraefficient multilayer cells, the cell itself is opaque here.

[J.P.M.]

I believe there has been a lot of research in multilayer pv cells so that the light that passes through the "first layer" of cells strikes the second layer which then produces more electrons and if the light is concentrated it goes through the 2nd layer to the 3rd yielding more production.

All this is being done in the lab but seems to be getting some hype and real % efficiency improvement data to show a possible commercial product.

I believe what you are describing is different than what LG is crowing about. Multilayer methods are how Boeing (I believe) got to ~ 40% conversion eff. Nice research, yet to come to market, if ever.

[SunEagle]

The cells may be 2 sided but the panels are not bifacial. The LG information is a good example of smoke/mirrors taking advantage of people's ignorance and using innuendo and implication. The "gaps" between cells or at the edges will indeed allow some light to "miss" a cell and be reflected from the back side of the panel on to the backside of a 2 sided cell.

If the panels were bifacial, I'm sure the advertising blurbs would want to show something other than panels mounted 6" above and parallel to a roof.

Note that the LG sketch of what's happening DOES NOT SHOW light as coming from the rear of the panel, but as penetrating the front side and being reflected in some fashion from the back of the panel.

That light that "misses" the cell will be of the same nature as the light thnat "hits" the cell until the light that "misses" the cell gets reflected off the back of the panel. The energy distribution of the light as f(wavelength) will change as will the ratio of direct to diffuse radiation in a rather complicated way.

I wonder if LG or anyone else has considered the possibility of enhancing the probability of increasing the absorption of the reflected light by manipulating the reflective properties of the backside for increased absorption by the back of a 2 sided cell ?

Two sided cells may be a nice touch provided it doesn't degrade longevity, increase cell degradation or cause other problems. In terms of increased efficiency, the overall effect is probably slight, with some of that increase PERHAPS due to a slight decrease in cell operating temp.

I believe there has been a lot of research in multilayer pv cells so that the light that passes through the "first layer" of cells strikes the second layer which then produces more electrons and if the light is concentrated it goes through the 2nd layer to the 3rd yielding more production.

All this is being done in the lab but seems to be getting some hype and real % efficiency improvement data to show a possible commercial product.

[J.P.M.]

The cells may be 2 sided but the panels are not bifacial. The LG information is a good example of smoke/mirrors taking advantage of people's ignorance and using innuendo and implication. The "gaps" between cells or at the edges will indeed allow some light to "miss" a cell and be reflected from the back side of the panel on to the backside of a 2 sided cell.

If the panels were bifacial, I'm sure the advertising blurbs would want to show something other than panels mounted 6" above and parallel to a roof.

Note that the LG sketch of what's happening DOES NOT SHOW light as coming from the rear of the panel, but as penetrating the front side and being reflected in some fashion from the back of the panel.

That light that "misses" the cell will be of the same nature as the light thnat "hits" the cell until the light that "misses" the cell gets reflected off the back of the panel. The energy distribution of the light as f(wavelength) will change as will the ratio of direct to diffuse radiation in a rather complicated way.

I wonder if LG or anyone else has considered the possibility of enhancing the probability of increasing the absorption of the reflected light by manipulating the reflective properties of the backside for increased absorption by the back of a 2 sided cell ?

Two sided cells may be a nice touch provided it doesn't degrade longevity, increase cell degradation or cause other problems. In terms of increased efficiency, the overall effect is probably slight, with some of that increase PERHAPS due to a slight decrease in cell operating temp.

[DanKegel]

I'm not arguing much light would be reflected, but I don't think there's much diffraction going
on in the pencil-sized holes at the corners of the cells.

[sensij]

I could buy that. http://ieeexplore.ieee.org/xpl/login...number=5615874 agrees, saying
"Non uniformity of back illumination and module elevation are among factors dramatically affecting the energy gain when using bifacial modules."

But note that there is some uniform illumination when mounted flat, even without edges, because of the gaps between the corners of cells. That's, what, 5% of the panels surface? So if the roof was 20% reflective, you might get a 1% boost. Tilting the panels on a sloped roof 25 degrees might get a 2% boost (one seventh of the sky being visible). Bah. If I had too much money, I might run the experiment.

Flat roofs traditionally have much whiter surfaces, so if I were doing my last house over again, I might get some actual boost by orienting the tilted arrays east-west and using bifacial panels.

No. The light passing through those small gaps will be diffracted (google.. light passing through a slit). Then, unless the reflective surface is a mirror finish, the light will be further diffused as it reflects. Some of the reflected light will pass back out through those same gaps. The angle of incidence of the light on the backside will not be nearly as direct as the light on the front. Angle of incidence affects how much of the light can be absorbed by the cell, with normal incidence resulting in the least amount of reflection. While atmospherically diffused light can and does contribute to the front-side performance, if that is the only light available to the backside, the boost would be a fraction of a percent, at best.

[DanKegel]

Even with true bi-facial panels, like those made by Sunpreme, getting a little bit of light reflected at the edges won't help. ... If the middle cells stays in series, then the edge lighting isn't adding anything at all, except maybe heat. To be effective, the backside illumination would need to be uniform

I could buy that. http://ieeexplore.ieee.org/xpl/login...number=5615874 agrees, saying
"Non uniformity of back illumination and module elevation are among factors dramatically affecting the energy gain when using bifacial modules."

But note that there is some uniform illumination when mounted flat, even without edges, because of the gaps between the corners of cells. That's, what, 5% of the panels surface? So if the roof was 20% reflective, you might get a 1% boost. Tilting the panels on a sloped roof 25 degrees might get a 2% boost (one seventh of the sky being visible). Bah. If I had too much money, I might run the experiment.

Flat roofs traditionally have much whiter surfaces, so if I were doing my last house over again, I might get some actual boost by orienting the tilted arrays east-west and using bifacial panels.

[DanKegel]

From their spec sheet:
The rear of the cell used in Mono X™ NeON is designed to contribute to generation; the light beam reflected from the rear of the module is reabsorbed to generate a great amount of additional power.

They list them as a commercial panel, which is usually ground mounted, so it can potentially get some reflection through the back, as opposed to mounting flush on a roof.

If you look at pictures of the panels, you can see the panels are opaque. I'm pretty sure it's just the cells that are bifacial. I admit, their datasheets confused me for a while.

[Amy@altE]

From their spec sheet:
The rear of the cell used in Mono X™ NeON is designed to contribute to generation; the light beam reflected from the rear of the module is reabsorbed to generate a great amount of additional power.

They list them as a commercial panel, which is usually ground mounted, so it can potentially get some reflection through the back, as opposed to mounting flush on a roof.

I know when Sanyo used to make bi-facials, people would make pergulas with them, and put white rock on the ground to reflect. We didn't sell many of them at all, but some.

If you are seeing a lot of people getting the LGs for their roofs, it's probably the typical "not being aware of what you are actually getting and falling for Marketing hype" syndrome.

[sensij]

Even with true bi-facial panels, like those made by Sunpreme, getting a little bit of light reflected at the edges won't help. Keep in mind that a panel is a bunch of cells in series, and the output of that series is limited by the weakest performing cell (roughly speaking). That is why the series is split up into 1/3's and bypass diodes are used, so that if a cell gets shaded, the other 2/3 of the array can continue to produce. If the bypass diode wasn't there, that shaded cell would become a hot spot and could eventually fail.

By leaking light only around the edges, those cells become higher performing than the cells in the middle. If it is extreme enough, the middle cells would be bypassed through the diode, and the panel would produce less power than it would have without the edge lighting. If the middle cells stays in series, then the edge lighting isn't adding anything at all, except maybe heat. To be effective, the backside illumination would need to be uniform, something like the East-West array that Bruce suggested somewhere, another thread I guess.

For what its worth, I think the LG300 marketing proposition is like Sunpowers, except the benefit is less and the premium is less. In any case, with the current product lines available, I would rather put 270 W panels +/- on my roof. If space was an issue, I'd look closely at the numbers before going to the more efficient panel. I found that with some installers, they simply marked the less expensive panel up at a higher rate than the more expensive panels, so that their profit was locked in either way.

[russ]

Solyndra tried to make a big deal of the 360° exposure - it is of no real meaning - the reflected light is not much.

[J.P.M.]

That would explain a lot, and http://www.lg-solar.com/downloads/ha...06.03.2014.pdf
backs it up; not only is there a photo showing the panels are opaque, but it
has a diagram showing a reflective back film. So they're not counting on
back illumination at all.

Thanks!

They are not bifacial panels.

[DanKegel]

That would explain a lot, and http://www.lg-solar.com/downloads/ha...06.03.2014.pdf
backs it up; not only is there a photo showing the panels are opaque, but it
has a diagram showing a reflective back film. So they're not counting on
back illumination at all.

Thanks!

[ericf1]

I could be wrong, but I don't think the LG's are bifacial PANELS, but use bi-facial CELLS. The only light striking the backs of the cells is that which is reflected off of the panel back sheet after passing through the front of the panel.

As far as the cables/connectors, they are the same as pretty much every panel on the market, with 2 cables terminated in MC4 connectors.

[DanKegel]

Plus and minus...
Microinverters (like everything else) need two cables to make a circuit.

I think you misunderstand. Let me rephrase.
Why does http://www.lg.com/us/commercial/sola...lg-LG300N1C-B3 say
"Length of cables 2 x 1000 mm / 2 x 39.37 in"
whereas http://www.lg.com/us/commercial/sola...lg-LG275S1C-B3 says
"Length of cables 1000 mm / 39.37 in"
?

Are they just messing with us, or do the Neon panels actually have more cables dangling off them than the non-bifacials?