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If I had an extra panel I'd already put it outside with back side facing the Sun covered by piece of carton so it could only pick up radiation with its face surface from the back and measure Isc to get an idea of the 'production' ballpark. Is anyone out there with extra panel interested enough to bother? My own guess it will be less than 2% of STC value. Too bad all my panels are already on the roof.
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In the case of this equipment, STC is based in front side of module. One manufacturer has suggested a new bSTC value, but standard treatment has been to ignore the backside for STC and provide info for different percentages of boost. Multiple years of data suggest more kWh production than should be possible with a standard module with equal STC rating.
Point is, they CAN produce more kWhs in my experience. IF volume drove price to near pairity with standard modules (not happening real soon), it would not be a scam perpetrated on all with less understanding of albeto.Comment
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That's probably a decent 1st approx., and, FWIW, a good example of Canadian elegance of thought and approach to analysis I've seen over the years (seriously), but keep in mind that, depending primarily on irradiance and wind vector, and to a smaller degree the color of the cover used, the cell temps. will be ~ 20 - 25 C. or more lower than if not covered, with irradiance (or lack of it) being the primary driver of (cell temp. - amb. air temp.), with wind vector being of secondary but still measurable effect..
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Thank you for the post, the links and your opinions. IMO, the links you include generally seem to support my opinions and past findings that bifacial gains are relatively slight. I'm not in complete agreement with the graph of measured vs. simulated output in the first link that shows an approx. 18 - 20 % gain in bifacial/monofacial output, I suppose a larger gain than the other two links suggest (of what looks to me anyway, and very ~~ 2-5% gain) might be possible given the height of the test modules, but I'd reserve judgment on that until I saw how those 20% gains were calc'd. The rest of the text in that first link is very familiar to me.I'm not sure anyone is suggesting using bifacial panels in a residential roof mount application. Most of the bifacials I've seen advertised to date by MFG have been 72-cell panels. And when used in commercial applications they need to be mounted in such a way that as much of the rear face of the panel is available to receive reflected light from the ground -- aka fixed or tracking ground mount at least 3 to 6 feet off the ground. Ideally more like 10-20 feet off the ground such as in a parking lot or walkway canopy.
While I agree the contribution of albedo is only a small percentage -- I'd be shocked if it ever reached 20% of total output -- in applications with snow, sand, white or light colored concrete or tarmac there may be an added benefit.
But the real questions is how much more does a bifacial panel cost versus the identical non-bifacial. For the MFG, the added MFG cost of the bifacial is very small -- the cells themselves are already double sided for the most part, and the surface area is even slightly greater on the back as there are no bus bars. Add in the extra material costs for a transparent back sheet, and mark them up how much?
Bifacial is a "premium" feature to increase MFG margin, but it's targeted at the commercial customer rather than the residential customer.
IMHO, there's plenty of data/information. It may not pass JPM's muster, but there's enough to see the impact of bifacial is limited at best ~5-15% (usually less than 5-8%) in most cases.
I stand by my original, grossly simplified assertion, the cheapest ($/Watt) panel that isn't crap will be the most cost effective in terms of kWh/$. Does anyone know how much more MFG will be charging for bifacial? If it's more than ~5-10% you'll never recoup this added cost.
As for who suggested the use of bifacial panels in a more standard residential application, that is, ~ 0.2 m or so off a roof deck, I'm probably the loudest and most obnoxious among those here who called out mfgs. and peddlers for putting the message of bifacials in such terms that, IMO, make it easier for the uneducated and crowd following solar wannabes running in near panic from self inflicted high electric bills to fall for the ideas that:
1.) Bifacials are effective in common rooftop applications where, most likely, little/no irradiance is available under an array.
2.)They are (more ?) cost effective because of claims of greater output even though those claims are mostly unsubstantiated (like LG's "up to 30% greater output")
with those (what I call bogus) claims easy to get uninformed folks to swallow because they affirm claims that seem to make life easier, and therefore make the product easier to sell, even though the claims are at least greatly exaggerated if not completely bogus and based on what's still, IMO anyway, somewhat sketchy information. So, I'm probably the one saying it's mfgs. and vendors hawking their wares, or greenwashing R.E. wannabes who probably know about as much as the solar ignorant or less, all spreading the bifacial gospel in a less than candid and truthful way and in so doing, then make it easier for the solar ignorant to infer bifacials are a no brainer cost effective must have choice for their home.
As for commercial applications, carports in particular, even though my opinion is that any increase in cost effectiveness may be minimal to negative, not having seen every application worldwide, there may be some valid applications. However, I'd suggest that caution and a "show me the numbers" kind of tough skepticism and analysis with respect to savings from using bifacials vs. std. panels in terms of things such as LCOE reductions and meaningful, realistic life cycle costs be very carefully done (and never by the vendor) before and without some headlong rush into bifacials that may or may not yield expected or fewer savings than claimed or worse, produce lower LCOE, from increased first cost and/or maint/failures.
As for your general assertion that the cheapest ($$/STC Watt) panel of fit for purpose quality will be the most (cost ?) effective in terms of kWh/(initial cost ? $), I'd say perhaps, maybe even likely, depending, as with any serious cost analysis, on the other application requirements, how the cost analysis is done, and a lot of other intangibles. It's been my experience that while first cost is usually the overriding consideration for most projects (and sometimes even at the expense of safety), and that overriding first cost syndrome shortcoming has been an ongoing curse to American business as long as I was in it, not everything can always be tied to a $ sign. However, and trying to be somewhat realistic, that's the way things usually work out and the world still goes around.
Thanx again for your input.Comment
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Baseline being annual kWh anticipated from a system of equal STC size, location, and orientation based upon production determined by standard estimating tools and calibrated with other standard systems in same geography that provide a indication of variance from the mean (or by purchasing access to satellite based meteorological data for the time period evaluated).Comment
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That's not how it works and won't give you what you're claiming in terms of a way to see possible performance enhancement of bifacial panels. You are calling modeled performance == actual measurements. That's not how it works. Actual system output of any panel will vary from std. as f(off std. test conditions) mostly as f(weather), but also cleanliness of the array and other factors. Some years more than others, sometimes more, sometimes less, never the same. A system will never see the same weather as modeled, either in quantity, duration, pattern or sequence. It will be, and is, impossible to quantify or evaluate system output compared to a model with the degree of accuracy you're claiming.
Side by side performance measurements with identical panels in identical orientations and test fixtures except one panel being bifacial is the only way to do it. All else is speculation.Last edited by J.P.M.; 09-25-2017, 05:44 PM.Comment
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Without meaningful methods and approaches, including stated conditions, actual side by side testing, and results that are reproducible, you have nothing.
I'm not sure you understand much about the scientific method.
I don't think I can spend any more time explaining it to you.
I'm moving on.Last edited by J.P.M.; 09-26-2017, 10:30 AM.Comment
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Back to Neon R discussion, will the 25 year product warranty come standard with purchase in the US, or be an add option?Comment
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and where are those data? Post them here and we can all see if they can be made sense of or indeed 'experimental noise'. Why continue theoretical discussion when the actual production data supposedly exist? This forum tries hard not to fall under 'approved' guidelines and remain open but sober to the new inventions so who knows this tech might get a nod.Comment
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I'm not sure I do either. Seems like the more I learn the more I realize there's a lot more to learn than I thought, meaning that on balance, I'm getting more ignorant. At this rate of intellectual curiosity, If I live long enough, I'll become a complete nitwit. Also probably means my wife is prescient but maybe a bit premature in her opinion.Comment
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Some short term data points provided by a module manufacturer (of standard and bifacial modules) for those interested: http://en.longi-solar.com/Home/Event...echnology.html
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