My new bifacial solar panel

[Marco Flamingo]

I had not even heard of these until a few weeks ago. I was looking to add a solar panel and came across the concept. Basically, a solar photo cell that collects on both sides isn't that difficult to make, but it has had little practical application (the Soviets first used them in outer space). Unless the background is white (like snow), the shade underneath a solar panel isn't enough to add much electrical power from the backside. That is why bifacial solar panels are mostly used suspended such that sunlight gets underneath them. The other issue is that the mounting system can't block light to the backside.

There seemed to be a couple of benefits for bifacial on a boat. First, there is an odd tariff on Chinese solar panels right now that (for some unknown reason) does not apply to bifacial panels. The tariff is such that the price of a 200W bifacial solar panel is the same as a regular panel even though they are more costly to produce. The main structural difference is that the back of a bifacial has another sheet of glass instead of the "normal" opaque white plastic. Bifacial are heavier, sturdier and, right now, the same price.

The panels are rated by their "right side" production. A panel rated at 200W should produce 200W under perfect conditions even with the back covered. The "back side" watt production isn't included. Various manufacturers claim a 10 to 30% increase from bifacial. The highest gain I saw in a laboratory test was 50% by maximizing the ambient reflected light behind the panel (called albedo).

So, same price and the possibility of a 30% kicker, I went with bifacial. It actually fit my application as I was intending to hang the panel to the outside of the boat from the flying bridge railing. Plenty of opportunity for light to bounce up from the water to the underside of the panel. You can get the idea from the pictures below.

As a bonus, some of the detailed measurements of bifacial panels have found that they have an additional advantage in partial shade conditions. Shading from something as little as the shadow produced by a mast stay can drastically effect output. Bifacial panels, when benefiting from albedo, suffer much less. Instead of a little shadow producing a 75% drop in wattage, it might only produce a 40% drop. Sounded interesting.

I'm in covered moorage, so no testing without cruising. I'm also near Seattle, so no sun until next May. Actually, we went out this rainy weekend and did monitor the panel through my new bluetooth MPPT controller. Sunday morning at 9 a.m., with complete cloud cover and rain, it was producing .5 amps. I tipped it towards where I thought the sun might be and got .7 amps. Later at noon, I guessed where the sun probably was and got 3.2 amps. So only a trickle charge on dark, cloudy, rainy days. Can't wait for some actual sunshine. We say that a lot here.

 

[mike66]

Nice! Can you give any details on your mounting system?

 

[Marco Flamingo]

It is all DIY. Along the entire outside edge is a 1.5x1.5" aluminum el stock to make sure that it is well supported ($30). On each end of that are two expandable stainless mop handles that swivel at the upper end ($50), allowing adjustment of the panel angle. The mop handle end was modified to fit a spring clip ($20) to attach to the SS rings on the bottom of my stanchion posts. The panels are attached with Seadog stanchion clamps ($40), the attachment point also reinforced with the aluminum el stock. A "normal" solar panel would likely have a couple of aluminum bars across the back for attachment, but I had to keep the panel back open to the light.

 

[Peter B]

Marco, it appears to me that one other advantage in this type of panel on a boat, as opposed to eg mine, mounted on my house roof, is that they might work quite well mounted vertically. Especially if mounted where nothing shaded them, and they could perhaps be rotated to optimise the angle, and the boat swinging round would mean the other producing side was facing the sun. Just a thought..? ?

 

[twistedtree]

It’s just anecdotal, but I recently installed new pole mounted panels at home that happen to be bi-facial. I wasn’t looking for bi-facial when I bought, but the panels I selected happened to be.

By all indication they really do work better. If nothing else I get much better low and partial light production on cloudy days. I can’t say whether that’s due to being bi-facial vs other improvements, but I’m very pleased with the results.

 

[mvweebles]

About 2 years ago, I was part of an audience where the a senior exec of BP Lightsource was speaking (one of the worlds largest producers of renewable energy). I had never heard of bifacial modules before. She said they were proactively replacing conventional panels with bifacials rather than waiting for the old panels to age-out. Tells me the business case is pretty strong.

However, my panels are mounted to my hard top. Not a lot of light to scavenge.

Peter

 

[twistedtree]

However, my panels are mounted to my hard top. Not a lot of light to scavenge.

Peter

I think that's the challenge. Only certain installations can benefit. My boat panels are similarly mounted, and I doubt would benefit.

 

[Marco Flamingo]

they could perhaps be rotated to optimise the angle, and the boat swinging round would mean the other producing side was facing the sun.

I've seen some discussion on TF about the whether angling the solar panel is worth the complication of a special mounting system. Like other things, it depends on where one boats. I remember seeing a picture in the Emma B thread that was taken in the Broughtons on December 20th at about noon. That would be noon on the winter solstice at (or above) the 50th parallel. At it's zenith that day the sun would only be 20 degrees above the horizon, meaning that a solar panel would be tipped up 70 degrees! Actually, because of the amount of light reflection off the water, 90 degrees might provide the maximum solar gain. Sounds crazy to those who boat down south.

But yes, the panel should produce a little even when in the "down" position.