Bifacial panels performs better than monofacial panels under low light conditions?

[Battouter]

i need somebody to point me in the rights direction regarding this matter either through articles or based on your own experience.

EDIT: low light might be the wrong terminology. i meant during cloudy days or when there is any kind of shading on the panels also early and late day sunlight.

EDIT 2: to be more clear. the information i am getting regarding the advantage of bifacials is regardless of mounting location, ground or roof, bifacials generally can harvest more energy on shady/low light conditions even if you deliberately cover the entire back side.

 

[Norwasian]

i need somebody to point me in the rights direction regarding this matter either through articles or based on your own experience.

I'd like to see what others think on this subject, but in my opinion the bifacials seem nearly the same as the monofacials in low light. I have two separate setups, though, one with bifacials and one with monofacials. I never compared them against the same setting and equipment to see the actual differences.

The bifacials surprised me a little when I saw them for the first time. It's basically just a see-through panel, so light coming from any direction could theoretically enter it. In my mind, however, it seems like the light could just pass through and not be "caught" by the panel. I assume this is just a counterintuitive phenomenon, though, as the panels do function well.

My bifacials are roof-mounted in the same manner as standard panels would be, with only inches of clearance between them and the roof, so there probably is not much additional percentage of production to be expected from light entering on the reverse side. In theory, the placement of the panels and the form of light (hard or soft) to which they are exposed should have measurable impacts. I would guess that if bifacial panels were oriented vertically, they might catch more light on a cloudy day than monofacials would catch in the same location. I'd be interested in hearing from those who may have experimented with this.

 

[Mattb4]

I went to mostly all bifacial after testing since they performed better than the standard in my ground mount setup. They do need to allow as much backside exposure as can be obtained. Some I tried had outstanding low light production (as well as exceeding panel ratings routinely) Commercial bifacial style panels are much better than RV styles in my recent experience.

 

[PVGeezer]

It would depend on how you define low light and how you mount the modules.

If by low light you mean early and late on a clear day and/ or with your array at a low tilt angle or over a low albedo (dark) surface then there won't be much improvement with bifacials. On clear days most of the solar irradiance is direct beam so it will mostly fall on the module front surface. Relatively little will be reflected from the ground and if you're at a low tilt angle the module backs won't see much unshaded surface to collect light from.

If you want to enhance performance on a cloudy day with your array at a high tilt angle above a high albedo surface (like snow) then you should get a significant performance boost. On cloudy days most of the solar irradiance is diffuse so a lot will get reflected off the ground surface and will be scattered in all directions. If you're at a high tilt angle the module backs will see a lot of exposed ground surface to collect light from.

You can get an idea what the difference might be by running some cases through the PV Watts model which has options for bifacials and ground albedo if you open the advanced tab.

 

[Madcodger]

In my experience, bifacials perform about 15% better in low light, but azimuth and tilt remain the big factors. We have two bifacial strings at 45 degrees, one mono at 67, and one mono at 90. Each has its role.

 

[PVGeezer]

In my case, PVWatts has my improvement in performance from bifacials at about 4 percent. My array is at 14 degrees tilt and we don't get a lot of snow here. Since my array also has a pretty low ground clearance I suspect the 4% is probably optimistic. I bought bifacials anyway because they were cheaper due the the tariff exemption.

 

[chrisski]

IME there is nothing practical you can do in low light conditions for more production short of get more panels.

So, now for my rant.

Although not bifacial, I tested two types of panels in low light and found that although one was more efficient, 10% I think, with a 100 watt panel producing 20 watts, the other better panel only produced 22 watts.

10% better power production in cloudy conditions of the rigid versus flexible panels is a whole lot better sounding then 2 more watts.

I saw a video will did where he got similar results for a PWM versus MPPT where the PWM was better at making power, but when you look at the actual extra watts produced not much.

There’s very little real data out there about production in cloudy conditions. There’s claims like “more power” “much better” “I’m very happy with,” but lack data.

 

[PVGeezer]

The reason it doesn't matter so much about improved low light performance of PV is because in most cases not very much energy is collected under low light conditions. Even in winter most energy is collected on sunny days. Most of what you hear from the manufacturers about low light performance is marketing hype.

Id suggest just using the annual (if net metered) or monthly (if off grid) output of PV Watts or another good performance model to decide what module type, orientation, and quantity to get. If you want to look closer at hourly or daily data you can download that.

 

[PVGeezer]

Another excersize you can do with the PV Watts output for your system if youre confortable managing spreadsheets.

Download the hourly data and open it in excel or sheets. Find the column labelled plane of array. That is the hourly irradiance falling on your array surface in watts per square meter, so 1000 would be one full sun.

Sort the sheet on this column from low to high. Now you can sum your production up to any irradiance level cutoff you want and compare it to your annual or monthly total.

 

[Kornbread]

Among others, this guy has a series on bifacials. Interesting results.

 

[Battouter]

Among others, this guy has a series on bifacials. Interesting results.

I've watched this video and read other discussions where people with bifacial panels, whether ground- or roof-mounted, claim that these panels can capture more light, even when the backside is completely covered.

 

[Norwasian]

That youtuber has ground-mounted panels with much higher potential incidence of light from the backside. In his situation, bifacials make sense. In any case, judging by the local markets here, we may not have much option going forward. I purchased the LONGi Hi-mo 6 panels, which are monofacial. The company had only 16 of them left at the time, so I felt fortunate to be able to have my order filled. But now they market the Hi-mo 7 panels, which are bifacial. It's getting hard to find the hi-mo 6 ones here anymore. They're going extinct.

I suspect that the Southeast Asian market, being nearer to the manufacturers of these panels (China), is more quick to respond to the changing trends. The North American market may take a little longer for these changes to saturate the market.

 

[Battouter]

That youtuber has ground-mounted panels with much higher potential incidence of light from the backside. In his situation, bifacials make sense. In any case, judging by the local markets here, we may not have much option going forward. I purchased the LONGi Hi-mo 6 panels, which are monofacial. The company had only 16 of them left at the time, so I felt fortunate to be able to have my order filled. But now they market the Hi-mo 7 panels, which are bifacial. It's getting hard to find the hi-mo 6 ones here anymore. They're going extinct.

I suspect that the Southeast Asian market, being nearer to the manufacturers of these panels (China), is more quick to respond to the changing trends. The North American market may take a little longer for these changes to saturate the market.

even in southeast asia bifacials are becoming mainstream. they are also about the same price and sometimes cheaper than the same spec monofacial panel.

but back to the topic in hand. this is only "experiment" comparing the two is the one done by will.

and also dave

.

 

[Norwasian]

Those both look like solid reviews, and more realistic than the first one posted @Kornbread. I guess one's results may vary, but I found it quite interesting that the watts per square meter turned out to be fewer with the bifacials. I hadn't given much thought previously to the bifacials being of a larger size for an equivalent rating.

 

[PVGeezer]

I would be wary of any evaluation that assumes the increase due to bifacial effects between the modules from different manufacturers is due to one being bifacial and the other not. There are numerous other variables in play.

Rather than YouTube videos a better place to look for properly validated performance data would be the NREL literature. Google "NREL Bifacial Study" and you'll find detailed studies of bifacial module and system performance as well as a tool kit theyve developed for modeling bifacial systems.

 

[shadowmaker]

I found it quite interesting that the watts per square meter turned out to be fewer with the bifacials. I hadn't given much thought previously to the bifacials being of a larger size for an equivalent rating.

Bi-panels can also be smaller than monos with equivalent rating. It's just what efficiency panels you are using in your test. It has nothing to do with panel being bi or mono.