Your trusty Commercial Solar Guy has sacrificed much to sneak out to the Mandalay Bay Convention Center in Las Vegas, Nevada for Solar power International 2017. The blue skies, colorful drinks and 90°F are really taxing my ability to stay focused on solar panels – but I’ll do my best to tell you about the coolest solar panel technology on the planet.
Bifacial solar panels are being marketed *almost* everywhere. Visiting each of the big players – LG, LONGi, Hanwha Q Cells, Yingli, BYD, Panasonic and others – gave me a bit of unique information from each manufacturer’s perspective.
First off, LG has the best visual representation of bifacial solar panels in action. The basics of the presentation, shown in the two images side by side below, were this: have two solar panels, one bifacial and one not bifacial, in a similar lighting situation. Specifically, a lighting situation with a highly reflective surface surrounding the panels. You’ll note that on the left – the two solar panels show a different wattage – in the standard light. To prove that the difference in wattage comes from the backside – from reflected light – of the solar panel and not from a technical difference in the panel, you then cover the solar panel with a thick piece of cardboard. And the image on the right shows that this chunk of solar panel would generate five watts of electricity from that reflected light. And that is the fundamental value of a true bifacial solar panel – the ability to capture light reflected off of surfaces surrounding the product. In this case, in this near perfect setup, a 22% boost in total electricity created. Pretty cool.
And, again from the LG booth in the image below, is a nice computation of how to understand the amount of additional electricity you might get from a bifacial solar panel in your setting. And this, very important for all readers, is where we must focus for now with this technology. What’s it gonna do for me? The greatest driver of the wattage boost is the ‘albedo‘ – the proportion of the incident light or radiation that is reflected by a surface – of the material that the panels sit above. As you can see in each of the three charts below, different materials are going to reflect different amounts of light – even asphalt will add a 0.7% increase to productivity.
However, where then have a question: Is the electricity production bump that I will get be worth the extra money I am spending? I had a great conversation at the Hanwha Q Cell booth about why they don’t sell a bifacial solar panel product. And it has to do with the above chart compared with the additional cost of the solar panel – all about extra glass versus a standard backsheet, the weight of that glass and the extra space needed to maximize the reflection benefit.
First – what are the odds that we are going to be able to build on a material that has that higher level of reflectivity? In the commercial rooftop world we’re starting to see more and more white rubber roofs (EPDM), and these roofs really are the ideal location for this product. But how many people have this type of product on their house? Most of us have asphalt shingles – and that 0.7% boost isn’t worth it. What’s interesting is that even grass and lighter soils have higher levels of reflectivity than the additional cost of the solar panels…so I do expect to see large scale ground mounts to use this technology. Along with white roof commercial locations that have more roof space than electricity is needed.
Second – if you notice in the lower right of the above image, to get the highest levels of additional electricity the panels needed be laid out at 30° – that is a great angle to put panels in many places as it helps maximize the amount of sunlight hitting the panels on an annual level…however – angling panels at that level, while possibly increasing efficiency, actually lowers the total amount of energy that can be produced by many rooftops. This is because the panels must be set a larger distance away from each other to limit shadows. In places where the price of energy is high, and the desire to generate as much energy as possible is the goal, many folks installs at 5-15°.
Now, even with these challenges – it looks like the marketplace is moving forward. LONGi (with the LONGi superman below) is ready to offer their customers a guarantee of at least an 8% gain in electricity production. I’ve not delved into that guarantee – and I’d guess there must be some caveats for how you install the product, but at minimum we see a powerful player willing to put their money where their mouth is.
Now, there is one hard warning I want to put out there about what ISN’T a ‘bifacial’ solar panel – and here is where I have questions for Panasonic’s marketing team. The image below is from a Panasonic marketing device I grabbed from the booth and describes their definition of ‘bifacial’.
Every single other solar manufacturer I spoke with would definitely not call this a bifacial solar product – but would instead point out that this technique, catching electrons as they bounce off of the inside backsheet as a standard practice in module manufacturing. Is Panasonic taking advantage of a hot marketing term to show off an old technology? The below image of two almost exact solar panels show that this reflection effect is real – and, in a slight nod toward the possibility that this bifacial concept might have been around a lot longer than I am aware of, it is almost the exact same effect as photons bouncing off of a white roof. Note, solar panel wattage with white (on the left) vs black (on the right) backsheets at the Panasonic booth.
There is a clear difference in productivity – and every booth that I visited that had the same solar panel in white versus black backsheet showed a similar difference. This makes sense because of physics – darker materials hold onto the photons that drive electricity production. Its same albedo effect talked about in the paragraph at the top of this article.
However, its definitely is not a bifacial solar panel as the broader market is talking about these days. So be conscious of that.
As an aside, there were many other manufacturers with BiFacial panels plus many others panels type that would be considered standard products. So please, don’t consider this an exhaustive review.
So there you have it – bifacial solar panels are coming. I happen to believe they’ll be a significant player in the longer run in this industry. I don’t yet have the tools to sell them yet, and banks are going to have challenges in underwriting them due to the challenges of predicting their production levels – but those issues will be ironed out. Rock on manufacturers.
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