Dual Glass or Bifacial PV panels

I have always used PV panels with non-transparent backing.
The last time I purchased panels that made no difference to me.
I was considering buying shade cloth for a future small veg patch, but I thought why not use these dual glass panels instead of shade cloth.
I can’t see on the WWW the % shade these panels approximate.
I am not even sure they are available in SA.
Has anybody any experience of a pergola or carport or such good or bad they can relate?

Interesting. I saw some Canadian solar ones https://www.itnerfricashop.co.za/product/canadian-solar-300w-poly-bifacial-biku-frameless/ not even more expensive than the normal ones.

They look like they are packed quite dense and there won’t be much light coming through?

The way I understood it, these panels generate PV power from the main side as well as from the secondary(back) side which would be from reflections of a wall or floor.
So it’s not for passing through light, but for generating power from both sides.

So it seems that even though it could be somewhat transparent, that is not the goal. So it would be a small %.

You are dead right, but I have seen panels now that the cells are actually sitting in clear glass. The cells themselves are not transparent but an inch or so framing each cell is.

I read that they perform best if you throw something reflective on the ground underneath them like white stone pebbles or some such.

Will be keeping an eye on this thread if it grows.

Yep. Concrete, and believe it or not grass is surprisingly reflective.
There are also some interesting applications where they mount them stand-alone like a fence E-W and vertically.
Two power peaks a day (early and late) and a power valley at noon.
Very little loss in overall daily product, but big farms can sell the power for a higher price at non-conventional solar peaks.

2 Likes

I have just had a chuckle.
All these municipalities, with there drones and aerial photo’s to identify these unregistered solar
panels, would probably be stymied by vertical panels in the back garden.

1 Like

I had the exact same thought after reading your comment. Of course the Tesla solar roof idea would also be hard to pick out on an aerial photo.

Do you use one MPPT or two on them? Presumably it only has one positive and negative terminal so would have to use on one MPPT? Does this impact performance?

Just one MPPT, there is only one set of panel outputs.

So how does this impact efficiency? It isn’t really optimal running different orientation panels on the same MPPT, especially not in series (like this seems to be)?

You loose very little. See the doc in the thread for calcs
Solar panel direction East/West vs North

Wasn’t that only when you put them in parallel, then you end up just adding the amps, so not a big deal if some of your strings are “flat”?

You have a point. But I have assumed a “fence” of panels will be all in one direction. Perhaps they could be in more directions.

Consider two panels at the same orientation on the same day:

The first a normal PV panel makes electrical power from direct light that strikes it on one side. The reverse side is covered.
The second a bifacial PV panel makes electrical power from direct light that strikes it on one side as well, but it also makes electrical power from diffuse or reflected light on it rear side.

More light = more electrical energy/cell = more efficiency.
Different things behind the panel reflect different amount of light on the other side. Consider how much more effective this could be in a snowy climate.

The MPPT is agnostic to whatever panel is used, it doesn’t know it just optimizes what it is given.

Ok. that said lets just forget about reflected light for the time being.
One side of a bifacial panel is only about 90% as responsive to light as the other side.
If the panel was mounted vertically E-W, lets say with the better side towards the East, then in the AM it would respond like a standard vertical panel.
But in the PM the standard vertical panel backsheet would be facing the sun so it not produce, but the bifacial panel would produce 90% power.

So if you combine those two properties:
A) That it produces more power generally, and
B) That you would need two standard panels back to back to match one bifacial panel.
Then bifacial panels may become an attractive option if your application suits.

Yes, but E-W is best. If the you are in a place where the sun is nearly always North of your position N-S wouldn’t be best use of their bifaciality.

Perhaps this little production comparison pic will be worth a thousand words:

image

The asymmetry of the two peaks is because one side is better than the other. It’s called the bifaciality factor.

1 Like

Ah so it doesn’t have more cells, the cells are just able to generate energy from both sides?

1 Like

You have it.

1 Like

Look at me catching up! One of these days I’ll quit my boring day job and become an electronic engineer.

4 Likes