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

[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.

[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.]

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.

[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.]

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.

There may be some minor benefit to this, but it's more fluff than substance. It does not increase that irradiance on a panel. It can, in theory, improve efficiency some as I noted in a prior post to this thread.

[Drashya]

I am sorry for such a late intrusion, but I have a few points to mention. As has already been noticed in the previous threads, yes the NeON module is a 'mono-facial' module but uses bifacial cells. Yes, even with an opaque backsheet, bifacial cells have a better output compared to a 'standard' module.

A PhD project focused on "Bifaciality" at SERIS (I hope you are familiar with this lab) did theoretical and practical measurements and found that monofacial modules with bifacial cells stand to gain around 5% Isc compared to the ones with monofacial cells. (Chapter 5: http://scholarbank.nus.edu.sg/bitstr...pdf?sequence=1). This gain mainly comes from the reflection through cell gap that the back of the cell will be receiving.

Another observation everyone seems to be missing out on is that LG is using multi-busbar (12) in these modules instead of the traditional ones. This minimises the electrical losses due to interconnection and increases the CTM of the module.

One more thing, I don't know why LG mentioned 'Commercial use' in their data sheets, but I don't think if they are using an opaque backsheet, the underlying surface beneath the module and the distance between the two is going to make any significant contribution to the rear albedo.

Now what I don't know is, what's the price/kWp with these modules? Is it higher or lower than if you use a standard Yingli or Trina module, for the same project?

[SunEagle]

I am sorry for such a late intrusion, but I have a few points to mention. As has already been noticed in the previous threads, yes the NeON module is a 'mono-facial' module but uses bifacial cells. Yes, even with an opaque backsheet, bifacial cells have a better output compared to a 'standard' module.

A PhD project focused on "Bifaciality" at SERIS (I hope you are familiar with this lab) did theoretical and practical measurements and found that monofacial modules with bifacial cells stand to gain around 5% Isc compared to the ones with monofacial cells. (Chapter 5: http://scholarbank.nus.edu.sg/bitstr...pdf?sequence=1). This gain mainly comes from the reflection through cell gap that the back of the cell will be receiving.

Another observation everyone seems to be missing out on is that LG is using multi-busbar (12) in these modules instead of the traditional ones. This minimises the electrical losses due to interconnection and increases the CTM of the module.

One more thing, I don't know why LG mentioned 'Commercial use' in their data sheets, but I don't think if they are using an opaque backsheet, the underlying surface beneath the module and the distance between the two is going to make any significant contribution to the rear albedo.

Now what I don't know is, what's the price/kWp with these modules? Is it higher or lower than if you use a standard Yingli or Trina module, for the same project?

Hello and welcome to Solar Panel Talk

I appreciate your added information concerning the bifacial pv panels. There has been an interest in them but not a lot of good field data has been available to determine if the higher costs are justified or not.

[Drashya]

Hello and welcome to Solar Panel Talk

I appreciate your added information concerning the bifacial pv panels. There has been an interest in them but not a lot of good field data has been available to determine if the higher costs are justified or not.

Hello. I believe this thread is about the LG NeON 2 panels, which have a reflective backsheet and hence don't qualify as "traditional bifacial panels". In the case of these panels, the bifacial boost can be accounted for in the STC itself, hence eliminating any dependence on environmental features. The panels clearly give a 20W gain over the previous generation (MonoX NeON), however, only after knowing the price difference between the two gens can one identify whether the boost is worth the extra money (hence my question in the previous post).

But to answer your question, the only existing bifacial power plant in Japan released its 2014 data publicly early this year. Its reports suggest clear output gains from 18% (summers) to 48% (winters - snow). This data is highly convincing in the case of bifacial modules, I believe.
Here you go: http://www.nishiyama-s-denki.co.jp/ (Tip: Google Translate can help you get through the website, but not the PDFs).
Another article you may find interesting: http://www.pv-tech.org/guest_blog/bi...kwh_cost_reduc

[DanKegel]

the only existing bifacial power plant in Japan released its 2014 data publicly early this year. Its reports suggest clear output gains from 18% (summers) to 48% (winters - snow). This data is highly convincing in the case of bifacial modules, I believe.
Here you go: http://www.nishiyama-s-denki.co.jp/ (Tip: Google Translate can help you get through the website, but not the PDFs).

Google Translate had a little trouble with that site, but I gather from

http://www.nishiyama-s-denki.co.jp/pv/data/150222_PVGS_r13ni.pdf

that it was a ground mount system in a very snowy area -- precisely the
sort of installation one would expect to benefit from bifacial.
Do you know what brand and model of panel they used?

Thanks for the data!
- Dan

[Drashya]

Google Translate had a little trouble with that site, but I gather from

http://www.nishiyama-s-denki.co.jp/pv/data/150222_PVGS_r13ni.pdf

that it was a ground mount system in a very snowy area -- precisely the
sort of installation one would expect to benefit from bifacial.
Do you know what brand and model of panel they used?

Thanks for the data!
- Dan

Hello Dan. You're welcome. I'd like to ask you to try and focus on the positives, i.e., even in the peak summers, the plant got 18% higher power output from the rear. If that's real, I think bifacials are paying off. The panels used were from a company called PVG Solar, one of the only bifacial manufacturers on the map right now.

And as for the snowy areas, yes, I'd say they make a freaking amazing product for such places. Coz in heavy snow, the whole plant goes bust due to snow on the top of the panel, and this is when the rear still keeps producing. And in winters, demands go high in such places, so I think these panels will make a good case.

-Drashya

[Naptown]

Perhaps during winter months it could increase the production but
What about shadows on the back from racking.
How was the panel tested?

[DanKegel]

Thanks for the info.

I *am* focusing on the positive I like the idea of bifacial panels so much I'm
experimenting with them myself, see

http://kegel.com/energy/solar/retrofit2/

My site isn't as ideal -- no snow, and pitched roof -- but I might still
be able to provide a little useful data.
(If the array ever gets installed... still picking out shingles for the reroof, dang it.)

[Drashya]

Thanks for the info.

I *am* focusing on the positive I like the idea of bifacial panels so much I'm
experimenting with them myself, see

http://kegel.com/energy/solar/retrofit2/

My site isn't as ideal -- no snow, and pitched roof -- but I might still
be able to provide a little useful data.
(If the array ever gets installed... still picking out shingles for the reroof, dang it.)

Wow, Dan! great effort! But I am not sure if flush-mounting the bifacial panels will give you any benefit. You see, the mount height is very important for the bifacial boost to kick in your standard output. If you're just going to mount them directly over your roof tiles, you're basically setting them up for disaster. Without any considerable distance between the bifacial array and the rooftop, there will be no scope for the light to reach the surface underneath the panels, let alone bouce off and hit the rear of the solar panel.

By the way, how much did Sunpreme panels cost you? I'd like to know how much premium they're asking above standard monofacial panels.

In any case, good luck with your endeavours!

Drashya

[SunEagle]

Thanks for the info.

I *am* focusing on the positive I like the idea of bifacial panels so much I'm
experimenting with them myself, see

http://kegel.com/energy/solar/retrofit2/

My site isn't as ideal -- no snow, and pitched roof -- but I might still
be able to provide a little useful data.
(If the array ever gets installed... still picking out shingles for the reroof, dang it.)

I am curious as to what is the best surface to reflect the light back into the bifacial pv cells. Is just a white surface (like snow) better then a reflective (like stainless steel) or even a mirrored surface?

I would expect the cells respond to some light spectrum's better than others but a white surface would reflect just about all of the spectrum.

[Drashya]

Perhaps during winter months it could increase the production but
What about shadows on the back from racking.
How was the panel tested?

Hello Naptown. Well, there are shadows from the racking and from the arrays behind and ahead as well. But, the trick maybe to identify the optimum distance between the two parallel arrays to allow maximum light to hit the ground while also not wasting too much ground surface. However, various field tests done by the companies and labs involved in the technology, show that inspite of the shadow problems the bifacial module still delivers high gains. The data from the Japanese plant, show 18-25% boost in the summer months. When there is no snow. So while the shadow problem does affect the rear surface's potential, there's still a lot that can be gained from it. Nonetheless, a recent thesis sponsored by KTH, Sweden and EDF, France focuses on this exact problem. I haven't been able to finish reading through their procedure and outcome yet, but you can easily find it online and read it.

As for the panel testing, I still don't know how the people at the Asahikawa plant were able to tell the difference between their front and rear output, but I don't think it should be very difficult. Generally there are trackers and sensors that can be mounted with the panels, which in my opinion should have little extra cost compared to all the electronic equipment you'd add anyways to the plant (inverters, MPPTs etc etc).

Drashya