Is there a reason to not get bifacial panels?

[wopachop]

This would go on a toyhauler where i plan to tilt the panels when its not driving down the road. Nice white reflective roof. I did a few searches and not finding much. I saw these Renogy panels on amazon is what sparked the interest. Im in Socal if there is a better local option. https://www.amazon.com/gp/product/B0CC22M8ZR/ref=ewc_pr_img_1?smid=A1JVRIAVO15LDT&psc=1

 

[Will Prowse]

This would go on a toyhauler where i plan to tilt the panels when its not driving down the road. Nice white reflective roof. I did a few searches and not finding much. I saw these Renogy panels on amazon is what sparked the interest. Im in Socal if there is a better local option. https://www.amazon.com/gp/product/B0CC22M8ZR/ref=ewc_pr_img_1?smid=A1JVRIAVO15LDT&psc=1

If the bifacial is close to the roof (from studies I've read, a meter or less), then there is little to no benefit. I made some videos testing this a few years back.

If you live in the desert, bifacial should be avoided. Stick with traditional monocrystalline.

If you live in a cold climate, and you can lift the panels at least a meter off the ground, and you have a reflective surface (such as snow) and ample convective air flow during summer, bifacials are fantastic!

 

[NotToFast]

Is there any reason not to mix bifacials and mono, as far as setting them up in series? I am building my new rig with three 220watt panels, but the brand I bought sent me 2 and the third is on back order. So I have a loose Bifacial 220 watt I could mount up (Almost the same size). The VOC are 20.52v and 21.86v, Opt. Oper. Current is 12.24a and 12.60a. They should play well with each other, shouldn't they?

 

[Will Prowse]

Is there any reason not to mix bifacials and mono, as far as setting them up in series? I am building my new rig with three 220watt panels, but the brand I bought sent me 2 and the third is on back order. So I have a loose Bifacial 220 watt I could mount up (Almost the same size). The VOC are 20.52v and 21.86v, Opt. Oper. Current is 12.24a and 12.60a. They should play well with each other, shouldn't they?

Mostly. They do have different temperature coefficients. So in different temperatures are going to have different outputs.

But they are close enough, should be fine

 

[shadowmaker]

I am "Bi" fanboy, but there can be benefit even installed close to roof. White roof + "loose" panel installation can get you +25%.

 

[SeaGal]

Yes - they must be really good when you have 360 degrees of sunshine

 

[Will Prowse]

I am "Bi" fanboy, but there can be benefit even installed close to roof. White roof + "loose" panel installation can get you +25%.

That's false. Did you watch the video? The bifacials even produced less for their size as well.

 

[Will Prowse]

Furthermore the mounting configuration was not ideal for comparison testing. Different convective air flow and backsheet reflectivity. Look at how they are mounted.

 

[OffGridForGood]

Bifacials - are heavier. If you are putting these on a mobile set up, and close to the roof, they may be adding a lot of weight for little gain.
+1 on Will's commets - bifacials are best when elevated, used in temperate climates, have some chance to get light behind them, and air movement for summer cooling.

 

[Rednecktek]

Is there a reason to not get bifacial panels?​

Because it adds weight and cost for almost no benefit in your situation.

 

[rhino]

Just to clarify there are bifacials that have a clear encapsulant on back which makes them exact same weight as non-bifacial panels. The cons of that are however that they are not as transparent (80% compared to glass) and longevity would be less.

 

[wopachop]

So the biggest issue is heat. Also lack of performance. What would you guys consider too hot for summer temps? Assuming there is an air gap and pretend the wind blows 5-15mph all day. Is 80F already getting to hot? Or does it need to be 100F?

Im in the desert. It can get into the high 90s. So looks like these are not a good choice for my situation.
What would you guys toss on a toyhauler roof in the socal desert? Thinking around 1000-2000watt.
When i looked around this site last year i remember a place in San Diego that people recommended for local pickup of panels.

 

[shadowmaker]

Yes - they must be really good when you have 360 degrees of sunshine

Only summer. And then comes winter...

 

[shadowmaker]

That's false. Did you watch the video? The bifacials even produced less for their size as well.

Furthermore the mounting configuration was not ideal for comparison testing. Different convective air flow and backsheet reflectivity. Look at how they are mounted.

Well, 16,2% increase in production (compared to nominal power) even with calculated difference in favor of monos should count. If convection (=heat) plays a big role here, he got ~5% gain from left to right, meaning there is a production increase IF sunlight can hit bifacial backside (=loose installation).

I mean ultra white background and 5-10cm more elevation plus 15cm spacing to adjacent panels in every direction could give you something +25% production gain over monos. That's just my guess after seeing what happens to my setup when there's snow on the ground.

Yes, bifacials produced less for their size, but the same would happen between two monos if they have different module efficiency. I bet it is hard to find "identical" panels for testing (same nominal power, same module efficiency, same temperature coefficient).

If only there was someone who could do this comparison right... ?

 

[asot550]

Just to clarify there are bifacials that have a clear encapsulant on back which makes them exact same weight as non-bifacial panels. The cons of that are however that they are not as transparent (80% compared to glass) and longevity would be less.

I was trying to figure out how Renogy's 450W bifacial has the exact same specs as its 450W mono panel except being a couple pounds lighter than its opaque backsheet brother. Turns out its because they use the transparent backsheet mentioned by rhino.

I did quite a bit of searching and it's been tough to find good data. Trina solar uses glass-glass and claims its benefits are:

• Better light transmittance
• Less degradation
• Zero risk of water permeability
• Weather ability
• Corrosion resistance
• Abrasion resistance

Jinko solar uses transparent back (TB) modules and they claim when compared to dual glass (DG):
"The bifacial DG is better in terms of its resistance to humidity and mechanical properties, but inferior in terms of resistance to UV, saline-alkali, weight and ease of cleaning. The energy generation is also slightly lower than that of the bifacial TB."

It's interesting that overall energy generation is claimed to be better for TB modules because they run cooler than DG, not because they're better at light transmittance. The other interesting takeaway for me is that TB panels should be better at blocking UV, so for solar pergolas or car ports the TB panel should offer some UV protection to objects underneath.

With commercial and residential TB panels offering 30 year generation warranties I don't really see any increased risk going with TB vs DG. Trina solar guarantees 89% after 25 years, Jinko offers 82.5% after 30 years, and Renogy is 80% after 25 years. It does seem that the TB offerings don't have warranties as "good" as the DG, but I'd argue that both should protect you from catastrophic failures.

 

[TxSam]

I too am still considering bi-facials. I'm in the Texas panhandle where we get a lot of sun, only moderate heat, meaning only a few days that it hits 100*, fairly cool winters and usually some breeze blowing all the time. I have not settled on mounting as a result of still trying to decide which way to go (ground mount or roof mount). It seems roof mount (white metal roof) with some offset angle built-in to raise the panels off the roof at a steeper angle would be what I would need to do. I'm a little nervous about that approach because of occasional high winds we get. The other option is ground mount of course. I have plenty of room for that and considered laying some of the white, quartz rock underneath the array and possible building a white metal fence behind the array (Northside) for reflection and a potential wind block.

From what little bit of shopping I've done online, it doesn't seem the bi-facials are that much more expensive that the monos, especially if you factor in the additional possible gain. Weight would definitely be a consideration in my mind as it affects handling and mounting considerations.

 

[OffGridForGood]

I too am still considering bi-facials. I'm in the Texas panhandle where we get a lot of sun, only moderate heat, meaning only a few days that it hits 100*, fairly cool winters and usually some breeze blowing all the time. I have not settled on mounting as a result of still trying to decide which way to go (ground mount or roof mount). It seems roof mount (white metal roof) with some offset angle built-in to raise the panels off the roof at a steeper angle would be what I would need to do. I'm a little nervous about that approach because of occasional high winds we get. The other option is ground mount of course. I have plenty of room for that and considered laying some of the white, quartz rock underneath the array and possible building a white metal fence behind the array (Northside) for reflection and a potential wind block.

From what little bit of shopping I've done online, it doesn't seem the bi-facials are that much more expensive that the monos, especially if you factor in the additional possible gain. Weight would definitely be a consideration in my mind as it affects handling and mounting considerations.

I set my panels up to tilt and they are up above my shop roof (galvanized) which seems to help during certain times of the year and times of the day, with reflection off the metal.
The tilting doesn't really add that much to annual solar collection, if I didn't have snow, I wouldn't bother with tilting up and down. I would just set them up at my latatude angle and leave them there. LOL.

 

[ksmithaz1]

Well, 16,2% increase in production (compared to nominal power) even with calculated difference in favor of monos should count. If convection (=heat) plays a big role here, he got ~5% gain from left to right, meaning there is a production increase IF sunlight can hit bifacial backside (=loose installation).

I mean ultra white background and 5-10cm more elevation plus 15cm spacing to adjacent panels in every direction could give you something +25% production gain over monos. That's just my guess after seeing what happens to my setup when there's snow on the ground.

Yes, bifacials produced less for their size, but the same would happen between two monos if they have different module efficiency. I bet it is hard to find "identical" panels for testing (same nominal power, same module efficiency, same temperature coefficient).

If only there was someone who could do this comparison right... ?

My problem with bi-facials is simple. You are paying for a more expensive solar cell that can catch light from both sides mounted to a more expensive substrate, ~clear glass, which is also more fragile. And the cost / watt is not that different.

If you buy a 450W mono panel, face it to a perfect sun you get 450W. If you buy a '450'W bi-facial, and face it to a perfect sun, you get 400W. You *might* get another 50 if you mount it just right, and get a good reflection from the surface below. It "might" do better in the afternoon. It may, .... Then again you might just end of where you would have been just as well to get a 400W mono panel. So then the question becomes, for pretty much the same cost / watt do I want to dink around and maybe get the full potential of the panel, or just go ahead and get the panel I can just mount in the appropriate direction? Adding an additional 450W panel would be the same as the possible backside from 10 bi-fi's, only it's a sure thing.

Now if someone has mounted up 10 450 mono's and 10 450 bi-fi's in an empty field on mounts facing in optimal directions and you have numbers that say they produce the same or more output / $, let's see it, and I could change my mind if it's significant. Then again most people are not installing panels in an open field with a white surface underneath. Often times you have to put panels in sub-optimal locations on rooftops and buildings, which could eliminate 90% of the indirect lighting benefit. MEH. "KISS"... I don't want to have to over-think panel placement, I want to throw them up in generally the correct orientation and let it fly. To me they seem like more special purpose installation where there is a clear reflected light collection benefit, to the point above, perhaps more northern areas with snow and steeper pitch and limited area available for paneling.

 

[ricardocello]

If you buy a 450W mono panel, face it to a perfect sun you get 450W. If you buy a '450'W bi-facial, and face it to a perfect sun, you get 400W. You *might* get another 50 if you mount it just right, and get a good reflection from the surface below. It "might" do better in the afternoon. It may, .... Then again you might just end of where you would have been just as well to get a 400W mono panel. So then the question becomes, for pretty much the same cost / watt do I want to dink around and maybe get the full potential of the panel, or just go ahead and get the panel I can just mount in the appropriate direction? Adding an additional 450W panel would be the same as the possible backside from 10 bi-fi's, only it's a sure thing.

This is not true for my 480W QCELLS Q.Peak-Duos, the 480W rating is for the front side only.
Anything you get from the rear is gravy on top of that, here is an excerpt from the data sheet:

Are they more expensive? I didn’t think so at the time, as they were on sale.

But clearly, don’t buy them unless it is justified.
I’ve got mine mounted 5’ off the ground with reflective white nylon on the ground.

 

[shadowmaker]

My problem with bi-facials is simple. You are paying for a more expensive solar cell that can catch light from both sides mounted to a more expensive substrate, ~clear glass, which is also more fragile. And the cost / watt is not that different.

If you buy a 450W mono panel, face it to a perfect sun you get 450W. If you buy a '450'W bi-facial, and face it to a perfect sun, you get 400W. You *might* get another 50 if you mount it just right, and get a good reflection from the surface below. It "might" do better in the afternoon. It may, .... Then again you might just end of where you would have been just as well to get a 400W mono panel. So then the question becomes, for pretty much the same cost / watt do I want to dink around and maybe get the full potential of the panel, or just go ahead and get the panel I can just mount in the appropriate direction? Adding an additional 450W panel would be the same as the possible backside from 10 bi-fi's, only it's a sure thing.

Now if someone has mounted up 10 450 mono's and 10 450 bi-fi's in an empty field on mounts facing in optimal directions and you have numbers that say they produce the same or more output / $, let's see it, and I could change my mind if it's significant. Then again most people are not installing panels in an open field with a white surface underneath. Often times you have to put panels in sub-optimal locations on rooftops and buildings, which could eliminate 90% of the indirect lighting benefit. MEH. "KISS"... I don't want to have to over-think panel placement, I want to throw them up in generally the correct orientation and let it fly. To me they seem like more special purpose installation where there is a clear reflected light collection benefit, to the point above, perhaps more northern areas with snow and steeper pitch and limited area available for paneling.

Hmm... I think you are confused how bifacials are labelled with their nominal power ratings. Like ricardo above mentioned, nominal power rating is for front side only. Backside production is just a plus to that and varies with available backside irradiation.

Also why would two tempered glass in one panel be more fragile than just one? I mean you can walk on mono panel because of the tempered glass, not because it has thin white plastic sheet on the backside. I'd assume that two tempered glass is twice as robust?

I don't think bifacials are always the best option. It really depends on many things. For me and for my vertical installation they are fine. I paid 1c/W more than if I had went with mono P-type panels. With that 1c I also got robust panels (wind load), shingled cell technology with N-type cells, so that was a no brainer for me. My friend got these same panels and installed those on his roof so he has little or no benefit at all from bifaciality, but he got the other perks for 1c too. Bifacials are twice as heavy (because of that double tempered glass), so they might not be suitable for every installation.