Bi-Facials, installation height matters just as much as the angle of the dangle

Choco

Solar Enthusiast
No offence intended, is it really worth the bother of the extra rigging and support for such minimal gains?
I would take the bifacial performance stats with a rain of salt, for residential in AU not many bother with this tech, put that extra investment into more panels?
 

Jennifer

Electricity kills, think twice before acting.
No offence intended, is it really worth the bother of the extra rigging and support for such minimal gains?
I would take the bifacial performance stats with a rain of salt, for residential in AU not many bother with this tech, put that extra investment into more panels?
No offense taken my friend, you are ABSOLUTELY correct, it's probably not... the money I spend on extra racking etc would probably take years to make up in bi-facial gains.... you hit on the real question.... why the heck bother, just bolt the BEEEEEEEEPS down already... lol..... (I was thinking about that all day)..

That's what sets us players apart from those doers... we over engineer and over diagnose and by the time we get it installed, there are new panels out and we start all over again..... that's half the fun.. but no, you are absolutely correct... it's probably not worth it in any way.. .just seems a shame to have a perfect spot for them and not use it but the more I look at it (in fact I was up on my toy hauler roof today and the sizing between obstructions is more applicable to just putting them up there and moving on. Bi-facials ares so cheap now if I want to get more for the Shed-O-Doom..... I always can...thanks for your "give your head a shake and get'er dun" post.. some times we need some logic smacked into our craniums. 🤪

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svetz

Works in theory! Practice? That's something else
... is it really worth the bother ... for such minimal gains?

Back when I looked at Bifacial panels they were also "double glass", so extremely resistant to corrosion and had 30 year warranties that made me drool a little. So, even without power from the backside they might be warranted if they've comparable prices. I eventually bailed on the concept because I couldn't overcome the elevation issue... but these forums didn't exist back then, now people can get help for stuff like this.

it's probably not... the money I spend on extra racking etc would probably take years to make up in bi-facial gains....
I wouldn't be so sure!

At 12 cents a kwh, each 340 watt panel with an average insolation of 4, the savings per year per panel would be:

.12 $/kWh x .34 kW x 4 x 365 x Y% gain = 60 x Y%​
10%20%30%40%
Yearly $$ at Average$6$12$18$24
Value $$ at 20 years$120$240$360$480
$$ Saved 12 Panels @ 20 Years$1440$2880$4320$5760

So, if it costs $12 more per panel with mounting hardware, even at 10% gain it pays itself back in two years. Fine-Print: Assuming my calculator is correct....

... we over engineer and ... that's half the fun...
Amen!

What's to the north in this picture? Is the property surrounded by a brim like the one behind the shed? If so, you might be able to use the tilt of the brim for mounting similar to how Will mounts them flat on his driveway. A top-down google-earth type snapshot would be nice too.
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While I love the idea of using the roof reflectivity, I can't help but wonder if some member might be able to look at the property and suggest an alternative where you can get the back-side to work for you without breaking the bank.

But I wouldn't give up on the shed either. Possibly it's strong enough, or possibly it can be reinforced? For example, when I lived in Colorado I sistered the rafters so the roof could take the weight for concrete tile and snow. Here in Florida a nearby house was retrofitted with hurricane tie-down straps just to get the insurance break (pays for itself in a few years and your roof is less likely to get sucked off).

So, possibly some pics of the shed's foundation, the wall members, and the roof supports? If the roofing members and wall studs are all still exposed in the shed it might be easy to reinforce them without any/much disassembling. Take a look at the "hurricane strapping" article, it'll give you some ideas as to what to take photos of in the roofing.

How tough is it to get a building permit there? Here you can't do anything alternative without a couple of engineering companies swearing to it and even then insurance won't touch it. But there are a lot places you can't even get a building permit/review if you want one. The reason I ask is that it might even be possible to build an elevated ground superstructure on the exterior of the shed that allows the panels to be over them and gives the needed support.

The community would need to know more about the local building codes though to help you with that, primarily wind and snow. You can find what the "hazards" (e.g., max wind speed, max snow load) are for your area here.
 
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Jennifer

Electricity kills, think twice before acting.
Ok booooyes n goyles... I think I decided where to put my bi-facials....... I'm in the process of building a 12' x 24' shed... and was just going to use the fancy new roof for rainwater catchment, which I still can.... and every morning when I get the laser shot of reflection in the back of my head through the window I kept debating it... but finally gave in.... the 1st shot below shows me looking west at the shed roof, all brand spanky new shiny corrugated...... ALL MORNING this roof gets an absolute flogging from the sun... the second shot shows me looking east, ALL AFTERNOON till the burning ball of hell fire goes down this west exposure gets a flogging as well....

I just checked my bi's.... I can easily put a 2 high by 3 long = 6 on each side in a landscape config, into a separate charge controller for each side, and while my lower edge won't be the meter above the ground/surface, I think having these mirrors behind them should light them up pretty good and make up for it..... and the run up to my toy hauler in the background wont' be far at all. It'll all happen in this shed, by run I mean split phase, (not solar PV voltage) this will be the power center for the lower part of the property where I plan to put in some cabins/rv spots maybe at some point. Then on the roof of the toy hauler I'll load it up with flat non bi's, putting these on there would be a waste, putting them on this mirror finish should kick donkey and give me crack of dawn till dusk generation... The compass shot shows the N/S layout of the shed, not ideal but pretty good none the less.

370 watts each, X 6 per side... and I'll still have a few left for another shed.... YAY

I'll probably go S-5 rib mounts and some Iron Ridge rails, (unless all you wiser than I have suggestions, I'm totally open). They won’t be flat,I’ll throw some tilt on them to get as much reflectivity on the back side as I can.


Note, directions of the white arrows means nothing, I was just over excited and drew too many white arrows... it's not indicative of the rays from the burning ball of hell in the sky.

What'ya'all reckon?

Jen
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YAY... new present arrived last night, 2, SCC's, count them TWO!!!!! SCC's, in one box... (one for morning/east, one for evening/west)... UH UH UH UH in my best count voice... 2 charge controllers, one for each side....

https://www.solarflexion.com/produc...6l3izvNuHbploj1ZCvFJgskDUOM-_jyYaAuzBEALw_wcB

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Below numbers, each side so twice this amount...

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Hopitrout

New Member
I work in Academia and so I'm used to the lingo. "Bifacial gain would be saturated" - just means - after this point it's not getting more - it's saturated.

When you look at the curves they are flattening- You always have to consider the audience those documents are written for. So this is written for a solar field installer - and every cm higher - is additional material and cost. So they want to know what's the least amount to elevate the bifacial to get gains.

In your and my case - I don't care to make the post of my carport 1m or 4m long . (4ft or 14ft) that's maybe a hundred or two hundred bucks - on a one term expense. The remainder you have to pay anyhow on the racking. Doesn't matter if it's one meter above ground or four.
I appreciate this thread. I’m considering bifacials for a pole or rack mounted system but the base of the panels will need to be at least 6ft / 2m off the ground because of very significant winter snow conditions and sluffing. It didn’t think that gain would decrease with increased height, or that the chart showed that. Thanks for interjecting on Jen’s great post.
 

Hopitrout

New Member
And one other question regarding bifacials from this superb thread.…. Though my imaginary system has not been purchased or built yet, it will be (hopefully by this fall). I think it will have bifacials. Another positive aspect would seem to be that even though I hope to have a steep winter tilt angle for my panels, if I get snow sticking on the front or top face, the underside of the panels will still function giving me some PV charge capability to my batteries, correct??? This is important to me as winters are HARSH at my cabin and I will not be there for periods over a month + and want to have some confidence that some solar charging is getting to my batteries if the top of the panels get plastered. If so, this would seem like a great benefit of pole mounted, elevated bifacials.
 

Jennifer

Electricity kills, think twice before acting.
And one other question regarding bifacials from this superb thread.…. Though my imaginary system has not been purchased or built yet, it will be (hopefully by this fall). I think it will have bifacials. Another positive aspect would seem to be that even though I hope to have a steep winter tilt angle for my panels, if I get snow sticking on the front or top face, the underside of the panels will still function giving me some PV charge capability to my batteries, correct??? This is important to me as winters are HARSH at my cabin and I will not be there for periods over a month + and want to have some confidence that some solar charging is getting to my batteries if the top of the panels get plastered. If so, this would seem like a great benefit of pole mounted, elevated bifacials.
You're doing this exactly right.... asking all the questions BEFORE dumping money into a system that ends up being incorrect or buying items you don't need..... well done!!!!!

I'm not sure if the bi-facial manufacturers are putting bypass diodes in the strings between front and back or not. You'd need something like that just like you would if you had two regular panels side by side with shading on one panel...... I'd suggest checking with your panel manufacturer to check the front to back shadowing / bypass issue. I would think there has to be some sort of bypass as a large amount of the time in some situations the back side of the panel will be in shading (compared to the front side) unless perfectly setup.... but it may be only protecting loss/bypass for shade on the backside, again probably manufacturer dependent.

PS: Keep in mind, a lot of that sun that comes through to reflect onto the backside is coming through between the half cut cells and if the front is covered in snow, that'll greatly reduce that light source.... rather than worry about all this stuff, just go buy a soft bristle broom at the dollar store.. LOL

Explained here:

Jen
 
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Hopitrout

New Member
You're doing this exactly right.... asking all the questions BEFORE dumping money into a system that ends up being incorrect or buying items you don't need..... well done!!!!!

I'm not sure if the bi-facial manufacturers are putting bypass diodes in the strings between front and back or not. You'd need something like that just like you would if you had two regular panels side by side with shading on one panel...... I'd suggest checking with your panel manufacturer to check the front to back shadowing / bypass issue. I would think there has to be some sort of bypass as a large amount of the time in some situations the back side of the panel will be in shading (compared to the front side) unless perfectly setup.... but it may be only protecting loss/bypass for shade on the backside, again probably manufacturer dependent.

PS: Keep in mind, a lot of that sun that comes through to reflect onto the backside is coming through between the half cut cells and if the front is covered in snow, that'll greatly reduce that light source.... rather than worry about all this stuff, just go buy a soft bristle broom at the dollar store.. LOL

Explained here:

Jen
Thanks Jen, I really appreciate your input. I‘m struggling to find an answer to how the bifacials output is effected when so much more of the PV energy is typically interacting on the top surface of the panels. I assumed having snow for half the year would help reflect a lot of light toward the bottom side of the panels and be a big plus for bifacials. But what happens if the top of the panels get encrusted in snow? It’s a winter wonderland at my very off grid cabin and unfortunately I won’t always just be able to run up (snowmobile in) to use that soft bristle broom from the dollar store you advised me of….😘. So if folks out there know what I should expect for bottom side PV output if I am fully snow covered on the primary or top side, I’d appreciate it and if there are specific bifacials out there that are good this way, by all means, let me know. Cheers all.
 

eXodus

Solar Addict
Thanks Jen, I really appreciate your input. I‘m struggling to find an answer to how the bifacials output is effected when so much more of the PV energy is typically interacting on the top surface of the panels. I assumed having snow for half the year would help reflect a lot of light toward the bottom side of the panels and be a big plus for bifacials. But what happens if the top of the panels get encrusted in snow? It’s a winter wonderland at my very off grid cabin and unfortunately I won’t always just be able to run up (snowmobile in) to use that soft bristle broom from the dollar store you advised me of….😘. So if folks out there know what I should expect for bottom side PV output if I am fully snow covered on the primary or top side, I’d appreciate it and if there are specific bifacials out there that are good this way, by all means, let me know. Cheers all.
when you got enough tilt snow just slides off the panels. It's very slick glass a solar panel. On my panels in a snowy region it sometimes takes till noon until the snow falls down after a hefty snowstorm. Just account for this with extra storage.

I would think there has to be some sort of bypass as a large amount of the time in some situations the back side of the panel will be in shading (compared to the front side) unless perfectly setup...
there should be a bypass, since like you correctly observed - the backside is in the shade most of the time.

My understanding is that the rear is in series with the front. A bifical panel are basically two panels.
So the total voltage gets higher, but not much current.

Like when you got multiple panels in series - when one is shaded - the bypass takes over.
 

Bluedog225

Solar Enthusiast
I get the saturated. Thanks for confirming. But for those of you smarter than me, what does this mean?

”This is important because irradiance uniformity results in mismatch loss from the module and array, which ultimately leads to energy loss.”
 

Jennifer

Electricity kills, think twice before acting.
110 degrees in the shade, NW Arizona, working on the sun facing side of a hot tin roof... IN SHORTS cus it's too hot for pants... ... mamma didn't raise no fools.... (it's a shame I'm adopted)... 1 down, 13 more to go (7 each side, 370 watt Longi bi-facials)....

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Jennifer

Electricity kills, think twice before acting.
Perfect fit.... 7 down, 7 to go (on the other side facing the west / setting sun) for a total of 14 on this shed, then another 2 stings in a SW and SE facing set of strings..... 7 Longi 370 watt bi-facials on nice shiny roof, 7S1P running around 340 SOC, each string going into one side of a 4 string capable Victron Energy SmartSolar MPPT RS 450/200... thank the lord for Kubota, she sure makes a single person job a lot easier, that's all I'm sayin....

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