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

[DanKegel]

Lots of people on this forum seem to be going for LG 300 watt panels.
Looking at LG's site, I noticed that all their panels above 280 watts
seem to be bifacial. This brings up a few questions:

- Are people even aware they're buying bifacial panels?

- How are people mounting these panels, and how does that affect the power they're getting?
For flush mounts, does it now pay to leave as much of a gap as space allows between panels, so more light seeps through back there? What's that worth, another 1% output?
For tilt mounts, does it now make even more sense to point panels west instead of south?

- The data sheets seem to indicate there are *two* cables from the Neon panels. What, one for the front and one for the back? How does that fit with microinverters which expect one cable? Plz explain

- What's the price jump between 280 watt and 285 watt (or whatever the two closest common sizes are for the monofacial and bifacial panels)?

[Sunking]

Darn from the title I thought this was going to be a pornographic thread.

[DanKegel]

sicko

[foo1bar]

- The data sheets seem to indicate there are *two* cables from the Neon panels. What, one for the front and one for the back? How does that fit with microinverters which expect one cable? Plz explain

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

I don't think there's much of a price differential for bifacial vs. monofacial panels.
There is a price differential for 300W panel over a 280W
I think that most pricing of modules is dominated by their nameplate wattage. Then there are other perceived values that go into the mix as well - such as brand name, warranty, aesthetics. I don't think whether bifacial cells were used is much of a differentiator for purchasers. If it were, I'd expect to see it being more of a selling point that's featured prominently when you look at the places that sell them.

[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?

[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]

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!

[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.

[russ]

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

[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.

[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.

[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.

[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.

[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]

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.