[SOLD] Bifacial 405W Monocrystalline Solar Panel

[Sailmonkey]

I thought this was a “for sale” post……how has this devolved into a discussion?

[BenBowSirocco]

Originally Posted by capn_billl

If you are going to post on a topic as an "expert", at least make sure you know what you are talking about.

Albedo
As mentioned earlier, an ideal blackbody will absorb all incident light, but in the real world, things absorb only part of the incident light. The fraction of light that is reflected by an object is called the albedo, which means whiteness in Latin. Black objects have an albedo close to 0, while white objects have an albedo of close to 1.0. The table below lists some representative albedos for Earth surface materials. Most of these albedos are sensitive to the angle at which the sunlight hits the surface; this is especially true for water. When the Sun is at angles of 40° and higher relative to the horizon, the albedo of the water is fairly constant, but as the angle decreases from 40°, the albedo increases dramatically, so that it is about 0.5 at a Sun angle of 10° and 1.0 at a sun angle of 0°. You are aware of this in the form of glare coming off the water in the early morning or in the evening before sunset.

with source.

https://www.e-education.psu.edu/earth103/node/1002

AN albedo of 1.0 is 100% reflection, your burnt eyes, and evening sunburn aren't figments of your imagination, they are a real phenomenon.

The real advantage here isn't that the panels produce more at high noon, it is that they get a second wind when the sun is low in the sky, and peak output has dropped.

The FINAL measure of a solar system is Watt hours per day with clear sky.

And getting an extra 5% to 10% watt hours when the sun is low in the sky makes a difference.

But then an expert would know that.

I am thankful you posted this. I had felt this was the case, that when the panels could use it most, the reflection off the water would be at its most. But I am not knowledgeable enough in the field to quantify it and a provide sources.

[Popcorn]

Hey guys:
Stop the haggling and accept the forum's opportunity to share information.
Users of this forum are not to criticize by telling someone their posting (using improper language) is not based on your thinking, unless their posting is dangerous and possibly downright possibly injurious.
Don't speak with insulting or insinuating language, it's not part of this forum.

[BenBowSirocco]

Originally Posted by redneckrob

Again I think there's a fundamental misunderstanding of this technology here. This is not two solar panels glued together with the back side working just as effectively as the front but for the fact that it's pointed down, that's a popular misconception. That is not the case at all, in fact if you flipped the panel over and put the back of it in full sun (and covered the former front) it would produce at most 30% of the panels power. It's a very fascinating technology that allows the rear of the same cell to generate power, in ideal circumstances where 70%-90% of the irradiance is reflected it will produce somewhere around 20% of the rated power of the front, with a boat not being close to ideal conditions. So a claim that "a bifacial panel takes advantage of this by receiving light on the bottom/back of the panel just as effectively as the front." is in fact an outrageous and completely incorrect claim that demonstrates someone doesn't grasp the very basics of the technology and is being led astray in a way that's detrimental to them.

If one had actually read what I had posted, where I clearly talked about alternatives, addressed the potential benefits from white boats, and provided resources to do actual modeling of the question at hand, I can't understand how I could be accused of "not reading what is being posted"? I'm sorry but if someone posts that the earth is flat, it's not condescending or unnecessary to point out that the statement is simply wrong, given that we're sailors here and it matters, even if they decide to take it as condescending.

To bring this back to CF, it's the equivalent of someone who has no experience with sailboats posting here that they plan to add a mizzen mast to their 40' sailboat because it will receive double the wind of their single mast. It would in no way be condescending for those who have actual hands on experience with mizzen masts to point out that the physics don't work that way, they'll probably see a very minor increase in speed if any, and that optimizing the main sail or jib would probably be a better way to achieve what they're trying to accomplish. For bonus points they might tie in the physics of how sails more sailboats through the water. That's exactly what I did here. If the guy wanting to put the mizzen mast in then questioned the "experts" on mizzen masts, called them trolls, and accused them of being pessimistic and condescending, we'd all think they were someone who clearly didn't understand the subject, heard something they didn't want to hear about it, and reacted inappropriately. I can't image we'd tell the people with experience with mizzen masts they were being condescending, pessimistic trolls and question their expertise!

RedneckRob, you are absolutely hopeless. No one is arguing its the same. Never was. You just cant seem to let it go man. Its been clear since post #3 that the manufactures claims of 20% increase due to bifacial is exaggerated and that all I am am looking for is every watt I can get.

[Jenta]

I bought 4 of the LG Bi-Facial panels - LG405N2T-J5 - to install on the back of our catamaran. I'm still putting the frame together and don't have them mounted yet but do anticipate there will be SOME benefit form the back side.
One of the purported benefits is on days with more clouds they perform better than a standard panel. I'm sure it's a small fraction, but none the less I thought it worth seeing how it goes.
I'm not worried that the numbers will or won't match up to some perfect expectation. I just like trying new things and thinking a bit outside of the box. Our dinghy is on the davits pretty much any time we are not in it and that is going to take a big bite out of output from the backside as well.

I had to look up albedo to know what that even is. But based on what I read water can actually be quite good at high angles of incidence.
Anyway - I think of LG as a pretty intelligent company and am willing to bet they feel there can be a benefit to this product in certain situations to make it worth developing. Certainly I can imagine on the back of a boat was not one of their scenarios and over water was not part of the design.
However, I've decided to just try it and see because - why not?
I'll always take real world results over scientific calculations.

ANYWAY... BenBo -
Due to shipping snafu's I have 3 extra panels if you haven't ordered yet. But they are up here in Virginia. The cost and hassle of shipping them would not be worthwhile, but if you happened to be driving by with a truck I could help you out. Send me a PM if that would help.

On the + side - I think these panels look cool and they're quite strong.
Even just at face value (pun!) I'm going from 600W to 1620W so I don't think I'll be too sad.

[redneckrob]

Originally Posted by capn_billl

If you are going to post on a topic as an "expert", at least make sure you know what you are talking about.

Albedo
As mentioned earlier, an ideal blackbody will absorb all incident light, but in the real world, things absorb only part of the incident light. The fraction of light that is reflected by an object is called the albedo, which means whiteness in Latin. Black objects have an albedo close to 0, while white objects have an albedo of close to 1.0. The table below lists some representative albedos for Earth surface materials. Most of these albedos are sensitive to the angle at which the sunlight hits the surface; this is especially true for water. When the Sun is at angles of 40° and higher relative to the horizon, the albedo of the water is fairly constant, but as the angle decreases from 40°, the albedo increases dramatically, so that it is about 0.5 at a Sun angle of 10° and 1.0 at a sun angle of 0°. You are aware of this in the form of glare coming off the water in the early morning or in the evening before sunset.

with source.

https://www.e-education.psu.edu/earth103/node/1002

AN albedo of 1.0 is 100% reflection, your burnt eyes, and evening sunburn aren't figments of your imagination, they are a real phenomenon.

The real advantage here isn't that the panels produce more at high noon, it is that they get a second wind when the sun is low in the sky, and peak output has dropped.

The FINAL measure of a solar system is Watt hours per day with clear sky.

And getting an extra 5% to 10% watt hours when the sun is low in the sky makes a difference.

But then an expert would know that.

Again, I struggle with why you felt the need for the "But then an expert would know that" comment? Did it make your overall point more clearly? Did it help others understand what you were trying to convey? What, exactly, did you hope to accomplish with that?

Ignoring the gratuitous comments, there are a couple issues with low sun angle that one needs to take into account. First, the sun is only at low incidences for a very short percentage of the day. Obviously it's at zero for about a minute between the upper and lower limb, and it's actually only between 10 degrees and 0 degrees for very short percentage of the day. The second issue is irradiance. The sun has to go through a much bigger portion of the atmosphere as it gets lower on the horizon, so much less of the sunlight makes it to earth. So basically very little of the sun's light is reaching the surface at the times when the sun is low in the sky, to put it in basic terms even if albedo is 50% when the sun is 10 degrees above the horizon, its 50% of a very small number.
To put that in graphical form

And for those who want to play with the math, the formula for calculating it can be found at https://sinovoltaics.com/learning-ce...ar-insolation/

So basically if we're only getting 20% (the bifacial portion) of 50% (the albedo) of something like 20% (the insolation at a few degrees above the horizon) it's a very small number. If we're only getting it for a few minutes of the day it becomes de minimis.

On the other hand, as I pointed out above there are places you can actually buy a panel that costs 20% less but will produce from the top face the same as these bifacial panels will produce only in ideal conditions that without question don't exist all the time on a boat. I'm baffled as to why you've decided you need to attack someone who points that out. The normal response to someone who tells you something you weren't aware of before that saves you money or makes your project more efficient is a simple "thank you", but I'd be happy with basic civility.

[redneckrob]

Originally Posted by BenBowSirocco

RedneckRob, you are absolutely hopeless. No one is arguing its the same. Never was. You just cant seem to let it go man. Its been clear since post #3 that the manufactures claims of 20% increase due to bifacial is exaggerated and that all I am am looking for is every watt I can get.

You're right, I correctly pointed that out in post #2 and yet five of the subsequent posts consist of calling me a troll, condescending, questioning my expertise, saying I'm just a pessimist....and that was before just disagreeing with what I pointed out. You obviously got it in post #2, but I'm not sure the folks insisting I was a troll did

As I pointed, if getting every watt you can is what you're looking for, you can not only do that more effectively with a more efficient panel that is not bifacial, but it will also save you 20%!

[BenBowSirocco]

Originally Posted by redneckrob

You're right, I correctly pointed that out in post #2 and yet five of the subsequent posts consist of calling me a troll, condescending, questioning my expertise, saying I'm just a pessimist....and that was before just disagreeing with what I pointed out. You obviously got it in post #2, but I'm not sure the folks insisting I was a troll did

As I pointed, if getting every watt you can is what you're looking for, you can not only do that more effectively with a more efficient panel that is not bifacial, but it will also save you 20%!

RedneckRob,



Please post the panels that with shipping will work out 20% cheaper and perform better. I am open to all ideas. (I hope)

[redneckrob]

Originally Posted by BenBowSirocco

RedneckRob,



Please post the panels that with shipping will work out 20% cheaper and perform better. I am open to all ideas. (I hope)

It's buried up in post 28...

Originally Posted by redneckrob

In the interest of providing actual actionable data, the bifacial panels under question are $300 each and according to the spec sheet at STC bifacially producing 443 watts including the bifacial part working at STC (they're nominally 405 watts).

Alternately, you could get a LONGi panel that's effectively the same size that puts out 445 watts at STC with no question about albedo underneath it for $241 per panel (https://ressupply.com/solar-panels/l...5m-solar-panel).

I don't have any affiliation with that company and I'm sure shipping varies by where you're at compared to them, so I'm not pushing that LONGi panel specifically and couldn't even tell you if that is the best price to get one at as I just picked it randomly as an example comparable to the panels we're talking about in this post. I'm just saying that in general you're better off getting a higher true wattage panel, which is of a comparable size as the bifacial if it's more efficient. Depending on your size constraints there are lots of choices of inexpensive efficient panels.

[Wilyum]

Originally Posted by redneckrob

calling me a troll, condescending, questioning my expertise, saying I'm just a pessimist

and then four posts later he asks if you can point out some options to help save him some money, and you actually oblige him lol. Wow sir are a gentleman and a scholar.

[PhilC]

@redneckrob thanks for persisting in your scientific factual discussion on this topic. Reading this has improved my understanding of the pros and cons of bifacial panels. The time you spent has helped clarify my plans for my next set of panels.

[SVTwilight]

Originally Posted by redneckrob

Again I think there's a fundamental misunderstanding of this technology here. This is not two solar panels glued together with the back side working just as effectively as the front but for the fact that it's pointed down, that's a popular misconception. That is not the case at all, in fact if you flipped the panel over and put the back of it in full sun (and covered the former front) it would produce at most 30% of the panels power. It's a very fascinating technology that allows the rear of the same cell to generate power, in ideal circumstances where 70%-90% of the irradiance is reflected it will produce somewhere around 20% of the rated power of the front, with a boat not being close to ideal conditions. So a claim that "a bifacial panel takes advantage of this by receiving light on the bottom/back of the panel just as effectively as the front." is in fact an outrageous and completely incorrect claim that demonstrates someone doesn't grasp the very basics of the technology and is being led astray in a way that's detrimental to them.

If one had actually read what I had posted, where I clearly talked about alternatives, addressed the potential benefits from white boats, and provided resources to do actual modeling of the question at hand, I can't understand how I could be accused of "not reading what is being posted"? I'm sorry but if someone posts that the earth is flat, it's not condescending or unnecessary to point out that the statement is simply wrong, given that we're sailors here and it matters, even if they decide to take it as condescending.

To bring this back to CF, it's the equivalent of someone who has no experience with sailboats posting here that they plan to add a mizzen mast to their 40' sailboat because it will receive double the wind of their single mast. It would in no way be condescending for those who have actual hands on experience with mizzen masts to point out that the physics don't work that way, they'll probably see a very minor increase in speed if any, and that optimizing the main sail or jib would probably be a better way to achieve what they're trying to accomplish. For bonus points they might tie in the physics of how sails more sailboats through the water. That's exactly what I did here. If the guy wanting to put the mizzen mast in then questioned the "experts" on mizzen masts, called them trolls, and accused them of being pessimistic and condescending, we'd all think they were someone who clearly didn't understand the subject, heard something they didn't want to hear about it, and reacted inappropriately. I can't image we'd tell the people with experience with mizzen masts they were being condescending, pessimistic trolls and question their expertise!

This is all very good info. Honestly, I cannot find any condescension on this side of the conversation while the other side is HEAPED with it! :-)

I have the name brand bi facial panels and while interesting, the extent of increased output claim is largely marketing spin from ideal conditions. ‘Nuff said….

[SeanPatrick]

Originally Posted by redneckrob

First, the sun is only at low incidences for a very short percentage of the day. Obviously it's at zero for about a minute between the upper and lower limb, and it's actually only between 10 degrees and 0 degrees for very short percentage of the day.

Well, that's not quite true for all latitudes and times of year. But ...

Originally Posted by redneckrob

The second issue is irradiance. The sun has to go through a much bigger portion of the atmosphere as it gets lower on the horizon, so much less of the sunlight makes it to earth. So basically very little of the sun's light is reaching the surface at the times when the sun is low in the sky, to put it in basic terms even if albedo is 50% when the sun is 10 degrees above the horizon, its 50% of a very small number.

This is true, and in astronomy it is known as "extinction". It's why you can look directly at a sunrise/set without straining or damaging your eyes and why most stars and planets are not visible at all when very low in the sky. It is also not dependent on the latitude or time of year.

[RedneckRedcoat]

I just bought 4 x 410 watt bifacial panels from signature solar. Some ET panels. I have have been absolutely delighted with them. I installed 3 of them and have been clocking between 390 and 425 watts per panel. They were slightly bigger than advertised but I couldn’t be more happy.

[Jenta]

After watching a recent episode of Will Prowse on Youtube that talked about Bi-Facial panels I was reminded of something I had kind of forgot, which is that the Bi-Facial panels are not just picking up reflections from the backside that come from the side, they actually pick up reflections of the light that passes through the panel to a substrate below and then reflected on to the back of the panel. Maybe the 30 inches (or whatever it was) standoff distance is to somehow maximize that effect, but Will indicated that even without that optimal standoff, in cloudy conditions the Bi-Facial panel out performed the other two panels he had when measured as output percentage of capacity. But his conclusion was that in a bright sunny location the advantage for the cost was lost.
Anyway - my takeaway for my situation is that perhaps my dinghy being mounted below the panels won't be such a big negative after all and that reflecting off the water (regardless of it's albedo) would not be the biggest contributor anyway.

Maybe I just need a white cover for my dinghy...

Got my frame in place, but still have a lot of other work to do before mounting any panels so it will be a while before I have any real world result data.