Bifacial solar cells vs separate cells on each side?

[DasKleineWunder]

Bifacial solar cells can produce electricity from light coming from both sides.
Reportedly they produce up to 20% more electricity with diffuse sunlight coming from the back.
However their price is much more than 20% higher.

What about just using a separate solar cell on each side?
What cell materials are better suited for the back side, thus gathering indirect, diffuse sunlight?

 

[IRstuff]

Wouldn't a separate panel incur 100% more cost for only 20% more production?

20% is probably a best case, which probably includes an unobstructed view of the ubobstructed back, which is rarely the case for panel arrays, where there are other arrays or structure or shadows that reduce the solar flux.

TTFN
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[racookpe1978]

A very few heat-collectors do accept reflected and diffuse radiation from the back side as a secondary heat source. I have never heard of any photovoltaic cell able to do that. Amorphous silicon cells can get more energy from diffuse radiation than the more efficient straight silicon (solid Si cut) cells. Let's assume some kind of cell could get diffuse or re-reflected solar energy on the back, maybe even at 20% of the front energy recovery.

You'd still be more effective spending the money on a solar tracker and frame and foundation and controller to get more energy fro the front of the flat panel!

 

[VEBill]

Is "diffuse" sunlight really as high as 20% of the maximum solar flux? Considering that our perception of illumination is logarithmic, it might be easy to overestimate. Especially if the ideally brightly reflective ground is shaded by the array.

"Wouldn't a separate panel incur 100% more cost for only 20% more production?"

If you flipped it over, right side up, in its own spot, you should get 100% more production.

Perhaps I'm biased because I'm in Canada and have a three acre yard, but it seems to me that the only solar cell efficiency figure-of-merit worth discussing is power/cost. Any 'improvement' that negatively impacts the fiscal efficiency is inherently for a niche market where space is limited (satellites, Tokyo, etc.)

 

[racookpe1978]

Sort of. Some of the time.

Assume you actually have what the climate "scientists" actually assume is a "perfectly clear atmosphere" (no dust, no clouds, very, very low humidity. At high solar elevation angles, you get about 8% diffuse radiation, in addition to the direct radiation. Look at your shadow: It is dark (obviously) but is not "black as night" but the edges are pretty sharp. Still, it would be easy to read a print or small type in the shadow from the diffuse radiation. As the sun gets lower in the sky (dawn or dusk) Soviet diffuse-to-direct radiation ratios measured in the high Arctic on what they called clear days greatly increased as more and more light bounces around before getting to the ground. So, even on clear days, diffuse radiation could be as much as 50% of the direct radiation - in the morning and evening. But, the amount of direct radiation goes down so much compared to the amount at noon that you still really can only use solar power 6 hours a day. 9:00 AM to 3:00 PM local solar time.

Now, take a high, thin cloudy day, completely overcast. Almost no direct radiation, everything is diffuse. Your shadow line is very indistinct. Direct to diffuse ratios don't make much sense, and a double sided receiver might appear logical. BUT! There is little radiation getting through those clouds, so you still are not very efficient even if you gathered energy from both sides of the collector. Neither is getting much energy, but the back side is getting more relative to the front.

 

[VEBill]

Going one step further, both sides will perform equally well at night.