Is Sunpower price difference worth it? -- thoughts, posting as new topic

[Mike90250]

and now, this tiresome thread closes.

[solar pete]

Howdy, just thought of a place where you can get some data, the desert knowledge centre in Alice Springs, Australia have been testing various panels for years.

I havnt looked at this for years but last time I did I found a graph where the different solar panels performance for the day were all on the same graph and it was so close that it was easy to conclude that there really aint much difference between most of them.

Any way here you go, some interesting reading awaits http://dkasolarcentre.com.au/historical-data/download ...knock ya selves out....

[LLB]

After reading your response and finding no facts I tried to reply seriously but eventually gave in to my other side. Otherwise the only thing people would be reading is Where's the facts?
Cell construction makes a difference, inter-connects increase reliability, diode moved out of the cell, both help with reverse bias and partial shading.
Purity of materials matter

LLB: I believe you are one of maybe 3 or 4 posters who have had/done posts longer than some of mine.
Except for the work experience part of your resume I believe you have managed to repeat everyone of your fact-less opined points again, just packaged differently.

I'll not get into a lengthy discussion of the benefits/drawbacks of S.P. with you.
Why? Is that not what this forum is for? To have logical fact based discussions (obviously only when facts are required) to come to reasonable conclusions? Sure people can always refuse to agree at the end, but you've never even presented one bit of evidence. You seem to be proud of your pro bono work, mentioned it many times, while also saying you don't care if you get your point across. I don't see the point in spending time attempting to educate people pro bono AND not caring that you are actually not making sense to them. Maybe that's why you are having the results you are with your HOA and many here. I know if I had 10k posts under my belt I would already have created .docx files on my computer and used them in posts and then saved or pinned those posts so to easily send newbs to the info, so you wouldn't have to retype the obviously certain facts that you have now forgotten and told me to go searching for.

Opinions and interpretations are what they are. We have both stated some of ours in a place that's purposed for opinions and information exchange. So be it.
Correction, I have presented both opinion and published facts. You have only opined.

I will only comment on how your interpretations of what I've done and what I may think may need correcting as they relate to my experience or qualifications. I believe that's within my purview.

It seems that my brief re-counting of some of my community pro bono work may have led you to think that's my only experience in energy related matters.

While I believe I'm a normally reserved and private person, I don't like confusion or being misrepresented, intentionally or otherwise, so I'd like to comment on what I believe may be some of your misinterpretations as I see them relating to me.
Let me perhaps provide others and maybe even you a little linguistic assistance. Anything I wrote in reply to you is my "opinion" and not open to interpretation by you, but I can change my opinion. You presented and opined what you wanted, "how you came to know SP was an overpriced company via your HOA experience and dealing with AHJ". If you presented insufficiently and/or incomplete facts that is on you, but not misinterpretation on my part.


Before I start and for the record: Formal education is not something that means a whole lot to me. I relate any such experience I may have been lucky enough to receive and build on only as clarification. FWIW, I'm wary of the abilities of folks whose first statement after their name is something like : "and I have degree in so and so". Well, so, and so what ? Do you know anything ? About the best and most savvy P.E. I ever met was a mustang who got a P.E. license the hard way : No formal education and at least 12 years of qualifying experience, that is, being in responsible charge of engineering work. P.E''s know what I'm writing about and know that drill.
Not sure what brought on this part of your rant, strictly rhetoric imho. Perhaps some kind of preemptive strike.

I was trained (some would say formally educated) in the 60's as a physicist. Not being able to afford further education, and finding that the job market in the field for mere baccalaureate physicists being slim, I became a peddler of industrial equipment and made decent $$ in a boring way for ~ 10 years. I got the solar bug ~ '75 while trying to learn how to stay warm in a cold climate. The curiosity I had, lucky circumstances and getting tired of the B./S. I got from other peddlers (of solar products) all seemed to coalesce at one time and place: I quit working, got more training (returned to school and parked my ass in classrooms long enough to get another tuition receipt), began a real engineering education and got a job as a mechanical engineer designing power and process equipment not unlike some of the stuff I formerly peddled, and, most importantly, learning more of how to think and see the world like an engineer sees and interprets the world. All the while keeping and developing the interest in solar and renewable energy that sparked my return to school in the first place. Along the way, as well as learning to think and see the world like an engineer, and speaking what I believed to be truth to the often B.S. from solar conmen and peddlers, I obtained a P.E. license (mechanical) and got more training (M.S.M.E.) that took about 6 years on a part time basis + 2 yrs. to write the required thesis, the subject of which was far from solar or R.E. and dealt with vibration analysis with respect to some particular aspects of the failure modes of shell and tube heat exchangers of the type and nature that would later produce the San Onofre failures. In true Peter Principle fashion, over the years, I progressed into several levels of engineering management. Last job title (which admittedly means little in the bigger scheme of things) before retirement was Director of Special Projects. I was always active in promoting my profession and was active in professional organizations such as he ASME, ASHRAE, local P.E. society chapters and others, and also the International Solar Energy Society, particularly the Resource Assessment div. I've also kept active and up to date in solar and R.E. developments as less than a job but more than a hobby. I've also, from the '70's on been active in community pro bono work, usually of the type that tries to educate and help folks understand and improve their lives through energy conservation and more efficient ways to use (or not use) energy. My recent stint on the ARC in my HOA is probably a continuation of that effort at community involvement. 10,000+ posts here may also perhaps be attributed to some sense of maybe giving back.
I haven't seen such a healthy case of self-esteem in years, congratulations. The name Sheldon come to mind. You also have an interesting way of showing how you give back, very selectively apparently.

I've never been reimbursed by or been involved with companies that mfg. or installed solar equipment, but I have worked for a few companies that have what I believe to be good reputations in the engineering and manufacture of power generation and process equipment.
Sounds like your answering in a deposition.

As for why I have S.P. on my roof while railing about it's poor cost effectiveness relative to other equipment, and the level of half truth I see in their marketing:
You really should learn to let that anger go or focus it to do some good. EVERY industry sells half-truths! Big Pharma, Wall St., Big Ag "made with ALL natural ingredients" those things steal your quality of life AND your life. Get mad at them, even if your SP claims were true and they are not because you never presented any facts, the effects to your health and quality of life are minuscule in comparison financially and physically.

Biggest reason is I wanted to investigate the S.P. claims of superiority on my own. I believe I've satisfied my curiosity. I've described my efforts at investigating their equipment's performance at some length on this forum, probably ad nauseum in some opinions. I'll not repeat them here. If you're curious, start digging.
So many ways to go with this childish response of yours. I already deleted mine, but it felt good to type them out. Mentally mature people have enough composure to edit themselves.
Never crossed your mind to make a sticky huh, shame. Shame for the ones that come after me and shame on you.
I find it ironic with all your mentioning of pro bono work, you actually have a audience who wants to know, unlike your HOA and you don't execute, classic.
But that's OK because I know they really doesn't exist.

They're public record. I knew S.P stuff was not cost effective long before I signed a contract.
Well now your just being sloppy, which is it, you wanted to investigate or you already knew. Pick a story and stick with it. I'm kind of losing interest and starting to doubt the accuracy from this point on. Since you are fond of going to school can I suggest some creative writing classes, they help with world building and story development.

I didn't get S.P. for its for cost effectiveness. Hell, no PV is cost effective for me by my criteria. I only use about 7,000 kWh/yr. The LCOE for most any system I'd consider is still greater than the LCOE of what the POCO would supply me. Most passions about things (what some call hobbies) are not cost effective anyway. For me, the PV on my roof satisfies my curiosity and keeps me off the streets. Knowing nothing else, the knowledge of local PV pricing and vendor quality gained from my HOA/ARC experience would have shown that S.P. is not cost effective even if I didn't have other means to see it.
Flag on the play - off topic. Can we stick to, where are the SP facts? Everyone knows solar doesn't pencil without the credit and sometimes not even then.

Jealous or remorseful about my choice ? No. Quite the contrary. I accomplished what I set out to do - see the truth or B.S. of the S.P. claims on my own terms as best as my own engineering abilities allow me to analyze. I also learned and continue to learn a lot about residential PV that I would not know of without having made the effort. Some of which information I've shared here. Some agree with some of my spoor, some don't. Most probably either don't understand it, or care, or both, or something else. Either or any way, it matters naught to me. I'm having fun. That I do so while having the good fortune and luck to have made a buck off S.P. stock while saving some $$ in electric bills (but in so doing gaining less by not having used the funds for alternate and more productive investments rather than PV equipment) is icing on the cake.

My guess is I've probably forgotten more about the engineering aspects of solar and renewable energy and resource assessment, as well as how to market and peddle such products (and so more easily spot he B.S. that goes with the marketing) than some others may know for quite some time to come. Maybe even you.
And there it is, ending with a zinger, you're feeling proud right about now, am I right, up top! I get a chuckle every-time I hear someone use that line, "I've forgotten more ...",
I haven't forgotten that there is always someone bigger, faster, smarter than I and that it serves one best to keep it in mind.
You disappoint me and do a disservice to all who enter here by not delivering factual useful actionable knowledge. So go climb up back to your mountain on high and tell everyone that makes it to the top that the answers they are looking for they already passed by and they should search for them on the way down. (When in reality the facts aren't there)

Rant mode off.

We (the forum) could have had good times poking fun at SP's vivid and creative marketing verbiage, while you pontificated about where their facts where lacking, wrong or exaggerated, but you chose to take your ball and go home.
Feel free to respond if you change your mind.

[J.P.M.]

My feeling of the gist of this, is unless you are really tight on space, and need the extra % that SP offers, they are over priced, with lotsa technobabble in their sales pitch

As another possible alternative to S.P. if space constrained: Consider measures and the costs from reductions in usage that will allow a reduction in the (electrical) size of the PV. Lower bills, and lower PV costs from both a smaller array and lower per Watt costs.

[J.P.M.]

LLB: I believe you are one of maybe 3 or 4 posters who have had/done posts longer than some of mine. I'll not get into a lengthy discussion of the benefits/drawbacks of S.P. with you. Looks like your latest post(s) deal mostly with respect to S.P. as well as interpretations and opinions of such reference data as that information may apply to S.P. and other mfgs.

Opinions and interpretations are what they are. We have both stated some of ours in a place that's purposed for opinions and information exchange. So be it.

I will only comment on how your interpretations of what I've done and what I may think may need correcting as they relate to my experience or qualifications. I believe that's within my purview.

It seems that my brief re-counting of some of my community pro bono work may have led you to think that's my only experience in energy related matters.

While I believe I'm a normally reserved and private person, I don't like confusion or being misrepresented, intentionally or otherwise, so I'd like to comment on what I believe may be some of your misinterpretations as I see them relating to me.

Before I start and for the record: Formal education is not something that means a whole lot to me. I relate any such experience I may have been lucky enough to receive and build on only as clarification. FWIW, I'm wary of the abilities of folks whose first statement after their name is something like : "and I have degree in so and so". Well, so, and so what ? Do you know anything ? About the best and most savvy P.E. I ever met was a mustang who got a P.E. license the hard way : No formal education and at least 12 years of qualifying experience, that is, being in responsible charge of engineering work. P.E''s know what I'm writing about and know that drill.

I was trained (some would say formally educated) in the 60's as a physicist. Not being able to afford further education, and finding that the job market in the field for mere baccalaureate physicists being slim, I became a peddler of industrial equipment and made decent $$ in a boring way for ~ 10 years. I got the solar bug ~ '75 while trying to learn how to stay warm in a cold climate. The curiosity I had, lucky circumstances and getting tired of the B./S. I got from other peddlers (of solar products) all seemed to coalesce at one time and place: I quit working, got more training (returned to school and parked my ass in classrooms long enough to get another tuition receipt), began a real engineering education and got a job as a mechanical engineer designing power and process equipment not unlike some of the stuff I formerly peddled, and, most importantly, learning more of how to think and see the world like an engineer sees and interprets the world. All the while keeping and developing the interest in solar and renewable energy that sparked my return to school in the first place. Along the way, as well as learning to think and see the world like an engineer, and speaking what I believed to be truth to the often B.S. from solar conmen and peddlers, I obtained a P.E. license (mechanical) and got more training (M.S.M.E.) that took about 6 years on a part time basis + 2 yrs. to write the required thesis, the subject of which was far from solar or R.E. and dealt with vibration analysis with respect to some particular aspects of the failure modes of shell and tube heat exchangers of the type and nature that would later produce the San Onofre failures. In true Peter Principle fashion, over the years, I progressed into several levels of engineering management. Last job title (which admittedly means little in the bigger scheme of things) before retirement was Director of Special Projects. I was always active in promoting my profession and was active in professional organizations such as he ASME, ASHRAE, local P.E. society chapters and others, and also the International Solar Energy Society, particularly the Resource Assessment div. I've also kept active and up to date in solar and R.E. developments as less than a job but more than a hobby. I've also, from the '70's on been active in community pro bono work, usually of the type that tries to educate and help folks understand and improve their lives through energy conservation and more efficient ways to use (or not use) energy. My recent stint on the ARC in my HOA is probably a continuation of that effort at community involvement. 10,000+ posts here may also perhaps be attributed to some sense of maybe giving back.

I've never been reimbursed by or been involved with companies that mfg. or installed solar equipment, but I have worked for a few companies that have what I believe to be good reputations in the engineering and manufacture of power generation and process equipment.

As for why I have S.P. on my roof while railing about it's poor cost effectiveness relative to other equipment, and the level of half truth I see in their marketing: Biggest reason is I wanted to investigate the S.P. claims of superiority on my own. I believe I've satisfied my curiosity. I've described my efforts at investigating their equipment's performance at some length on this forum, probably ad nauseum in some opinions. I'll not repeat them here. If you're curious, start digging. They're public record. I knew S.P stuff was not cost effective long before I signed a contract. I didn't get S.P. for its for cost effectiveness. Hell, no PV is cost effective for me by my criteria. I only use about 7,000 kWh/yr. The LCOE for most any system I'd consider is still greater than the LCOE of what the POCO would supply me. Most passions about things (what some call hobbies) are not cost effective anyway. For me, the PV on my roof satisfies my curiosity and keeps me off the streets. Knowing nothing else, the knowledge of local PV pricing and vendor quality gained from my HOA/ARC experience would have shown that S.P. is not cost effective even if I didn't have other means to see it.

Jealous or remorseful about my choice ? No. Quite the contrary. I accomplished what I set out to do - see the truth or B.S. of the S.P. claims on my own terms as best as my own engineering abilities allow me to analyze. I also learned and continue to learn a lot about residential PV that I would not know of without having made the effort. Some of which information I've shared here. Some agree with some of my spoor, some don't. Most probably either don't understand it, or care, or both, or something else. Either or any way, it matters naught to me. I'm having fun. That I do so while having the good fortune and luck to have made a buck off S.P. stock while saving some $$ in electric bills (but in so doing gaining less by not having used the funds for alternate and more productive investments rather than PV equipment) is icing on the cake.

My guess is I've probably forgotten more about the engineering aspects of solar and renewable energy and resource assessment, as well as how to market and peddle such products (and so more easily spot he B.S. that goes with the marketing) than some others may know for quite some time to come. Maybe even you.

Rant mode off.

[littleharbor]

Fine, I won't waste my time then. I've got better things to do than quibble incessantly. There was a comment made earlier about the copper backed cells being no better for heat dissipation and jokingly suggesting adding cooling fins to the cells. I showed some pix clearly showing overheated cells and now we have you with your panties in a bunch over it.

Work out your issues here with the others. I'm done. If it makes you feel better that you may have won the argument because I don't have the facts you desire, whatever.

BTW SunPower wasn't selling commercial solar panels in the 70's. As far as I can tell SunPower modules weren't available for residential systems until the 2000's. I'll leave it to you to show otherwise.

Have a great day

[LLB]

Tell you what, I'll pull out the panels I have and have already explained the history on and take some pics just for you. See you Tuesday.

Why bother sending more pics that look like the ones you just sent? I see no need to do that.

"have already explained the history" You must be referring to "costal Southern California", hmm, seems a little thin.
Does that mean LID, the inter-connect or the encapsulant failed?

[LLB]

As a result, a typical conventional cell has a breakdown voltage of approximately -15V to -20V [30], whereas the SunPower cells breakdown voltage is only about -5.5V for its second generation Maxeon cells (E-Series modules) and -2.5V for its third generation Maxeon cells (X-Series modules). With a lower reverse bias voltage there is less power, and therefore less heat, to dissipate. Table 1 shows a side-by-side comparison of the heat dissipation between the two designs.

Manufacturers generally install diodes across substrings within the module (Figure 20). These substrings almost always divide the module into thirds (20 cells in a 60-cell Conventional Module or 24 cells in a 72- cell Conventional Module). When a conventional cell is shaded, the voltage drop across the cell is limited to the voltage produced by the other cells within its sub-string, and a large fraction of the current is shunted through the bypass diode, deactivating the substring.

It might seem counterintuitive that a higher reverse bias voltage is generally a desired trait for
Conventional Module manufacturers, since it raises the temperature of a cell in reverse bias. However, a higher reverse bias voltage ensures a bypass diode will activate at lower threshold, making the module more sensitive to reverse bias conditions, such as partial shading or cell defects. While this module design initially protects against thermal breakdown, there are two potential side effects, production and long term reliability.

A lower threshold for bypass diode activation means partial shading or soiling are more likely to activate the diode. When the bypass diode activates, the voltage contribution from that substring is eliminated, reducing power proportionally. In a typical Conventional Module, a single cell perpetually in reverse bias will effectively reduce a 240W module into a 160W module.

Further, an activated diode runs at an elevated temperature reducing the remaining life of the diode. All diodes will eventually fail and the life depends on temperature as well as several other factors, including module design, diode quality, junction box heat transfer, and module installation. Depending on how a diode fails, it can either permanently remove a substring from that modules production or allow a shaded cell to run in reverse bias unmitigated, causing high heating in areas of a conventional cell which allow current to flow, generally causing backsheet damage.

SunPower cells operate in reverse bias with uniform breakdown across the cell, resulting in much lower temperatures, so bypass diodes are not required to ensure long term reliability. SunPower does include diodes in its J-boxes, but the diodes do not turn on when only one cell is shaded. The voltage drop across a single reverse-biased cell is not sufficient to drive significant current through the diode.

SunPower includes diodes only to increase the production of the system in the case that several cells in the same substring go into reverse bias. In this case, the diodes limit the total amount of power that can be dissipated by reverse-biased cells.

Light-induced degradation (LID) is a very fast degradation mechanism which drives an efficiency loss of
1-4% in p-type silicon within hours of exposure [33], [34], [35]. It was first discovered in 1972 by R. L. Crabb [36], and since then, the mechanisms have been comprehensively studied, culminating with a model and strong evidence for boron-oxygen complex formation by Schmidt [34] and Glunz [37]. The fact that it occurs only in p-type, and specifically boron-doped silicon (e.g. gallium-doped Si does not exhibit
LID) leads to an obvious advantage for Maxeon cells, which are n-doped both on the front surface and in the bulk. This mechanism has been covered in numerous journal articles and trade publications.
The End

[LLB]

damp heat, humidity-freeze, and mechanical load. These tests have been identified as important in assessing reliability [38]; however, they are not designed to estimate useful lifetime because they do not show a strong correlation with field performance and degradation. Instead, these tests are designed to ensure safety and identify infant mortality issues due to basic manufacturing quality [28] [21].

SunPowers current generation module has a rate of only 27 returns per million modules built. This includes all post-site-commissioning world-wide warranty returns of E-Series modules (Jan 2006 through July-2012, 6.5 million modules).

Various field studies have measured the degradation rate of conventional crystalline modules at between 0.6% per year to 1.5% per year, so a reasonable assessment is 1.0% per year [8], [9], [10], [11], [12] (Figure 4). These studies are discussed further in Appendix A.

In order to perform a more robust assessment, SunPower recently completed its own fleet-wide system level degradation study of 445 systems within the SunPower operating fleet. The study included 266 systems (86 MW) using the previous generation of SunPower modules as old as 3.5 years, and 179 systems (42 MW), using Conventional Modules as old as 6 years. Data spanning back to the site commissioning date were used to determine fleet-wide degradation rates, representing 3.2 million module-years of monitored data. The study [13], and a review by independent engineering firm Black and
Veatch, are available upon request.

A key result from this study is shown graphically below in Figure 5. The annual system power degradation rate (including inverter) for SunPower systems with the previous generation of modules was found to be -0.32 +0.32 % (95% confidence) per year, while non-SunPower conventional systems were found to degrade at -1.25 +0.25% (95% confidence) per year, and in both cases were shown to be linear with time.

SunPower design differences
Cell architecture and metallization
Conventional cells are made of various grades of monocrystalline or multicrystalline p-type silicon.
The front-surface is also an n-type emitter, typically doped with phosphorus; the back is typically a p-type emitter doped with boron. When the conventional cell is illuminated, electron-hole pairs are formed within the cell, and they are collected at these doped regions and transferred into metal conductors.

Cell-to-cell interconnects
To create a module, cells have to be interconnected. From a reliability perspective, these interconnects are crucial, since failure to maintain electrical contact between cells results in total failure of the module to perform, and in the worst-case scenario could potentially result in an arc-fault failure.

Conventional Module manufacturers typically rely on tin-coated copper ribbons, which are soldered along the length of the cell to printed grid lines (Figure 7). Soldering metal and crystalline materials together is considered state of the art and still leads to reliability challenges from manufacturing induced micro-cracks and stress from differences in thermal expansion [14]. The cells are connected by daisy chaining ribbons that alternate from the front of one cell to the back of the next. As modules heat and cool, the gaps between cells expand and contract, kneading these ribbons back and forth [15].

A recent NREL study [16] has shown that as a result of thermal expansion, they are much more likely to fail within 25 years if not properly strain relieved (in the tabbing ribbon where it traverses between cells, Figure 7).

In contrast, the SunPower cell interconnection is an engineered tab (Figure 8). Instead of bonding ribbons along the entire length of the cell, a stamped metal interconnect is soldered to the edges of the cell.

Secondly, they have cut-outs which allow expansion and contraction as the cells grow and shrink with temperature, providing strain relief.

Third, there are three solder pads on each side of the inter-connect, providing redundancy. In the case a solder joint ever fails, current is rerouted through the remaining pads onto the cell surface, which also has parallel bus-bars to distribute current as necessary.
Finally, when there is a (hot cell) due to shading or local soiling, the solder joint does not get as hot because the thick copper interconnect efficiently draws heat away from the hot cell [18], keeping the solder pads cooler.

The design does not look very different to the casual observer, both have cells encapsulated in a polymer encapsulant that is bonded both to the front side glass and a polymer backsheet. However, the materials and their quality can vary widely and their specific properties can have important impacts on performance.

Materials and suppliers for other laminate components, such as glass, encapsulant, and backsheet, vary between manufacturers, and their specific properties can have important ramifications for long-term reliability. It is beyond the scope of this white paper to do exhaustive comparisons, but SunPowers materials qualification processes have identified a wide variation in quality for these materials.

SunPower has produced high efficiency cells for decades. The original cell design was intended for use in concentrating applications; however, in the mid-2000s, non-concentrated flat plate modules came into widespread production.

The generations of these SunPower modules can be put into three categories:
- Previous generation: 2005-2011. These modules required positive grounding. One version:
- Gen 2 Maxeon cells. Module efficiencies up to 18%.
- Current generation: 2011 onward. No positive grounding required. Two versions:
- E series: Gen 2 Maxeon cells. Module efficiencies up to 20%.
- X series: Gen 3 Maxeon cells. Module efficiencies up to 22% and better shade tolerance.

SunPowers patented back-contact design is substantially different from the designs used by Conventional Module manufacturers.

Part of SunPowers design qualification includes a dynamic load test (DLT). In this test, a force of 2400Pa is repeatedly applied to the front and back of the module, deflecting it back and forth.
This test is designed to ensure that a product can withstand a lifetime of shipping, installation, and environmental stresses and that there are no unfavorable characteristics inherent in the design.

A side-by-side comparison of a conventional multi-crystalline silicon module and a SunPower module in this dynamic load test is shown in Figure 13. After 1000 cycles, the standard efficiency module shows several broken cells in the center, and a power loss of nearly 4%. The shunt resistance of this module has dropped by more than 20%, which results in parasitic yield losses at lower irradiance levels [23]. Low shunt resistance can also push cells into reverse bias which leads to more frequent diode activation and yield loss. If the shunt resistance is low enough, or if the diode fails, the cell may form a catastrophic hotspot [24].

2400Pa of stress corresponds to extreme winds (130 mph, 209 kph) or snow loads (about
3m deep, assuming 80 kg/m3 snow density) that are unlikely to be observed in real life at most, but not all, installations. Nonetheless a basic tenet of design qualification testing is that larger safety factors are generally better, since real-world stresses can come from unexpected events. For example, stresses occur during shipping and installation. An installer weighing 80 kg (175 lbs) stepping on a module with a boot that has a contact area of roughly 3inch x 10inch (0.019 m2) induces local normal stress on the surface of the glass of about 41,000 Pa. Fortunately, the glass spreads this stress over a larger area (it bows relatively smoothly), reducing the strain on the cells; but, it is not as forgiving as a uniform pressure applied over the entire surface.

Results for Partial Shading and Reverse Bias Stress
Solar cells in a module are essentially current sources connected in series. When their current flow is not perfectly matched, mismatch losses occur and the weakest cells can operate in reverse bias. When a cell is in reverse bias it essentially consumes power from neighboring cells and converts it into heat.

In agricultural areas, airborne dust settles on modules and sticks due to the morning dew; if the dew and dust preferentially collects at one end or corner of the module, the partial shading can also cause reverse bias.

Finally, cell manufacturing defects can also push cells into permanent reverse bias.
SunPowers back contact design performs differently than a conventional cell, due to fundamental design differences. In the conventional cell, heavily doped layers (regions rich with charge carriers) are separated by bulk silicon, which is lightly doped, creating space between heavily p-doped and n-doped areas on the front and back (see Figure 6, left).

SunPowers back contact design has steep doping profiles on the backside of the cell, which can be seen where the p-doped and n-doped areas are immediately adjacent (Figure 6, right). These regions are rich in charge carriers, so when a cell is in reverse bias, current flows more easily, resulting in a lower reverse-bias voltage.

[LLB]

I was simply responding to Bruce's question. We, or at least I, learned that the removed area of the triangles = ~ 1.8 % of a square of 15,375mm^2 area. It doesn't prove anything.

As for being upset...

No neighbors were harmed in the making of this post.

Apparently posts can only be 11,000 words so I'm going to have to break this into 3 posts.
What a nightmare this is to upload. This editor will not take quotes or apostrophes or the three dots after etc, finding more all the time.

From 2015 when I started reading your posts I thought for certain you were some 30-40yr. electrical engineer solar veteran. Who had worked for multiple big brand name companies, knew all the back room conversations and dirty laundry of the solar industry. And now I find out you do not like (despise) SP because the 3 (one being yours) installations you know of that do not out-perform the others like you think they should, because of their marketing techniques. Crikey! You are going to make me pull an all-nighter here because now I have a few things to say/show. Starting with your comment about ignorance, seriously? Ignorance pisses you off? Arrogance sure, but ignorance?

You do know the definition is (a lack of knowledge) it is not laziness, more accurately it is (individuals who do not deliberately ignore or disregard important information or facts). You should feel empathy for them not admonish them. Basically everyone who does not research things as much as you do, you get mad at. I think you might be in for some disappointment. I think you should have stuck with, I hate SP because I think their marketing is unethical and deplorable. I am fine with that, you can have that opinion all day. But to brow beat the newb and then put on the halo of IMO. Nope does not fly with me, not imho.

Believe it or not I hope to make you feel better, because I think you are mad at yourself for buying SP and not getting the performance you thought you should have received. I hope to show you that you did not make as bad a decision as you think you did. I think as the years roll on and your panels hold up better than your neighbors it will be more obvious. But hey, are not these forums great were we get to agree to disagree.

To everyone else who came here because of the title and are still trying to get to an answer, please read on.

I am attaching a few files that I pulled the following info from (2013 NREL, 2013 IEEE conference, Panasonic-HIT 2018, SP Maxeon X/E Gen 2, 3 2013 )

I am just going to do it bullet style, otherwise this post would be 100 pages and no one wants to read that.

These are all the points I was hoping to find and discuss in this forum. Many the original OP brought up and according to my searching of this forum was always met with, IMO Anyone who knows anything and most on this forum, about SP knows they are not worth the hype, its only for the ignorant, sucker born every minute, that is why I bought the stock and did well, etc.

I judge a person by their actions, not their words. I saw no action/facts, just words/opinion.

If any of the snippets peak your interest you might find it worthwhile to look at some of the attachments.

Before I get started I will say I do not like how SP compares their best mono panel to probably a 5yr. older poly panel, but they do state that fact in their document. Also the SP doc is simply a more in depth discussion but definitely not a brochure that is handed out (61pgs.) And they do use some adjective that I would not use, but I do not think it is anywhere near as bad as JPM makes it out to be. I mean seriously would you say you product is a little bit better or your product is measurably better?

I also think they stretch the degradation numbers to the legal limit. They often say conventional panels are .5 to 1.25% and that they are .25%. NREL says mono panels are ~.5% and poly are ~1%.

I think every time SP says conventional you have to think poly, because your brain is going to keep thinking LG/Pana 330 mono and that would be wrong.

So except for some marketing vocabulary and the degradation numbers I think they make the most durable, resistant to fatigue cell out there and it is worth a reasonable premium, less than 10%.

I just do not think it is a commodity like iron or nickel. Even a hot water heater (the closest thing I can think of that should be priced like a commodity is not. You find different prices at HD and Walmart, etc. Why is solar equipment any different? Maybe it should be, but it is not.

OK, lets get started, apologies in advance for formatting issues.

- A 2013 study at the National Renewable Energy Lab (NREL) found that the primary underlying causes of module failures in the field were due to cell/interconnect breakage (40.7%), and corrosion (45.3%)

This is one of the main papers that the SP paper references.
Validation of the PVLife Model Using 3 Million Module-Years of Live Site Data 2012
Ernest Hasselbrink, Mike Anderson, Zoe Defreitas, Mark Mikofski, Yu-Chen Shen, Sander Caldwell, Akira Terao, David Kavulak, Zach Campeau, David DeGraaff

I included this because it is an independent 3^rd party reference.
NREL Photovoltaic Degradation Rates - An Analytical Review Dirk C Jordan and Sarah R Kurtz 6/2012 51664

I hope somebody finds LG, Panasonic, Canadian Solar, etc, equivalent papers. I could not find any.

Some 3^rd party info first.

Failure Rate Data

In addition to degradation rates, failure rates are another important concern. SunPowers installed fleet has not been in the field long enough to provide a good basis for validation, so we shall not attempt to validate PVLifes failure models in this paper. Nonetheless, SunPower, Powerlight, and Tenesol (another front-contact module manufacturer that SunPower acquired in 2012) have significant installed fleets, and a Pareto of failures from these fleets may lead to some insights about what modes cause earlier-than-expected module failures, providing motivation for future modeling.

SunPower is in the unique position of having purchased two companies which deployed Conventional Modules. PowerLight was a project development company which installed 240 MW of modules from 20 different manufacturers before it was bought by SunPower. This fleet has an average age of 6.7 years, and has a failure rate of 8,700 warrantable returns per million modules installed, nearly 1%. SunPower also purchased a relatively high quality European Conventional Module manufacturer (Tenesol) which had installed over 500 MW. This fleet has an average age of 4.6 years and has a failure rate of 1,450 returns per million or 0.14%.

Some general comments and observations on the fleets studied and the overall return rate:
- The overall return rate for the front-contact (FC) fleet is approximately 0.44%, compared to less than 0.005% for the Maxeon II fleet.

- The FC fleet is comprised of about 0.8M modules installed by Powerlight (average age 6.8 years), and 2.6M modules installed by Tenesol (average age 4.3 years).

The weighted-average age of the entire front-contact fleet is 4.9 years.

The Maxeon II fleet is comprised of >8M modules, with an average age of 2.1 years. Thus the Maxeon II fleet is significantly younger (and of a newer design) than the FC fleet. However, given only a 2.3X difference in age, the nearly 100X difference in return rate is remarkable.

Investigating the data for each failure mode in turn, we note the following:
- For the FC fleet, laminate cell/ribbon/solder failures (primarily cell interconnections) dominate the Pareto, resulting in about 66% of returns.

- For Maxeon II, the return rate is more than 1000 times lower for this defect type. We believe this is likely due to significant design differences in cell interconnection.

In particular, (a) FC interconnects are two or three ribbons that connect the backside of one cell to the front side of the adjacent cell. In contrast, the SunPower interconnect is a wide tin-coated copper bar and has cutouts for strain relief. This additional copper can conduct heat away from the cell and the solder joints in case of temporary reverse bias [10]. (b) SunPowers cells have an on-cell busbar which can redistribute current evenly, in event of a solder joint failure in any of the 3 solder pad connections, providing double redundancy.

- For the FC fleet, backsheet and encapsulant are the next largest return category, with about 22% of returns. We note the FC returns are dominated by one particular type of module. The returns data indicate about 1 per million for the Maxeon II fleet attributed to this defect.

The remaining modes have relatively low failure rates, under 100 per million in total. Glass damage has a return rate of ~40 per million. The SunPower Maxeon II fleet has a rate of only 2 per million; in both cases the statistics are based on a relatively small number of observations. FC and SunPowers modules both show very similar low (30 DPPM) failure rates for J-boxes, diodes, and cables. Cell failures, that is, electrical failures that lead to damaged modules, are only a few per million for both the FC and SunPower Maxeon II fleet.

There is reasonable agreement between the Pareto from our FC fleet and those found by previous researchers [11-12]. Wohlgemuth et al [11] found 86% of failures could be attributed to either corrosion (45.3%) or interconnect failure (40.7%). Kato [12] found that 28 out of 32 systems (88%) in a field survey of residential systems of approximately 10 years of age had at least one module in the system exhibiting evidence of solder bond or cell interconnect ribbon failure.

Unlike Wohlgemuths data, our Laminate (cell/ribbon/solder) category does not distinguish corrosion damage from fatigue damage, thus it makes sense to compare our value (66%) with his combined value for both corrosion + cell or interconnect failure (86%, classifying both as metallization damage).

Conclusions
We believe the data analysis method (median YOYPIX) used in this paper is a powerful technique that has significant advantages for proving system degradation rates to investors.
In particular, the methods key advantages are:
- It uses data from real-world systems, and measures system-level AC-power production
- It is tolerant of data acquisition failures and other practical realities of real-world systems
- It is unbiased, and minimal data scrubbing is necessary
- It derives a median degradation rate with low uncertainty, given a sufficient number of sites.

Summary: Design Differences
SunPower modules have several intrinsic differences over Conventional Modules which result in superior resistance against real world stresses.
- The use of n-type silicon prevents early degradation due to LID.
- The thickly plated, tin coated copper foundation of the Maxeon cell is highly resistant against the forces of moisture and oxidation.
- This metal foundation allows for thinner, more flexible silicon, resulting in a cell which can withstand repeated snow and wind loading and can crack without significant power loss.
- Electroplating the metal directly onto the cell ensures a strong and uniform bond with low residual stresses.
- Solder pads and an interconnect that allows for thermal expansion are used to connect the cells instead of a process intensive copper ribbon solder bond.

Reliability Research and Performance Degradation Model (PVLife)
Introduction
SunPower has developed a physical model based on extensive research that addresses SunPowers degradation mechanisms. However, models quantifying Conventional Module degradation is not included, since data and research is, for obvious reasons, primarily focused on the SunPower design. The ability to quantify degradation rate has been vital to SunPower in order to securely offer its current industry-leading twenty five year warranty. Degradation rates cannot be determined through industry standard certification tests such as thermal cycling,

[LLB]

Determining better accuracy requires no justification. Bruce Roe

Bruce sorry my query came across the wrong way. Just because I was being spicy with littleharbor (which I assumed was all in fun-apologies to littleharbor while I'm at it) doesn't mean I can't have serious conversations at the same. I was hoping to get more details about the pics you posted on using my identical strings to see if I can tease out if my stepped on panel is under-performing. No worries I will read the post again and certain your explanation was clear enough to figure it out.

It was a serious question and I take your answer to be "curiosity/accuracy". I was certain there was going to be something about poly panels having x amount of more surface area in their modules, making them possibly even a less cost effective choice to mono than previously thought. Obviously 384 (96x4) triangles are going to add up to a few more square inches of real estate, but not enough to make a difference because of polys lower efficiency I'm guessing.

[bcroe]

Bruce / JPM
Can JPM or Bruce explain what we learned or the reasoning for doing the math?

Determining better accuracy requires no justification. Bruce Roe

[J.P.M.]

and from #98
"...I personally have a couple of the same failed panels in my possession..."

littleharbor
I thought in the quote above you said you had some of these panels or panels that looked just like them? So just some random picture from the net of some "not even sure if they're dead" SP panels. I'm sure I can't similar pictures of LG or Pana, that seals it, I hate SP they're a much of liars.
Seems my version of the story is more likely than yours, since you're not providing one that is. The picture is more likely from 1970, improperly designed system in the Salton Sea area, that's my story and I'm sticking to it.

And the dealers should take the fall, why should SP? The dealer decides so many things SP has no control over; which inverter, panel location, electrical runs, grounding, etc...

Bruce / JPM
Can JPM or Bruce explain what we learned or the reasoning for doing the math? Obviously it doesn't matter mono to mono as my joke might have been misconstrued as meaning. So were you guys figuring out what advantage poly had in surface area (1.8%) and if it moves the needle in any significant way?

Also I have been meaning to say I think the old guards attitude towards SP has been misguided as I think it is really the installers markup that upsets them. Obviously SP doesn't paint the installer into a corner forcing them to charge higher prices, because we hear of some SP installers (granted not enough) bidding with a reasonable premium. That alone puts it squarely on the installer in my eyes. Again websites assisting in transparency are the key.

What I think I'm resenting is this "don't buy SP" attitude or as some like to say only the ignorant buy SP. When in reality they contradict themselves by saying they make a solid product, its just "they" feel SP stretches the marketing too much. Yet deep down if a newb comes along and says I have 2 bids one from SP and the other "X", they are the same price who should I go with, I think they would say, "you can't go wrong with either of those manufacturers, its the reputation of the installer you want to consider."

You can try to bring bad customer service into this, but to that I say manufacturers are just that. Their job is to provide a quality product (high QC and materials) and brand recognition (marketing). The customer service they outsource (pay for) to the dealer, so lets leave it out. Just because you bought a Ford doesn't mean you get to call the factory and ask questions. They would likely ask you which dealer you bought it from and send you packing. If you picked a bad dealer like I did, then thems the breaks. (It just seems a un-proportionately high percentage of them are bad -from all manu., not just SP) but that's a systemic industry money-grab problem for another day.

I was simply responding to Bruce's question. We, or at least I, learned that the removed area of the triangles = ~ 1.8 % of a square of 15,375mm^2 area. It doesn't prove anything.

As for being upset (if I'm the old guard), I'm not, particularly upset about vendor markup. Those who can DIY can save a bundle. Vendors have costs that ignorant and simple minds do not have a clue about. One of the few things that does piss me off is ignorance, especially when coupled with arrogance, and especially so when it leads to waste.

Sunpower is a good product. It is just not worth a premium price. That price is not supported by process economics or life cycle costing methods when compared to the cost and reliability of other equally fit for purpose equipment that costs less.

Among lots of things and among many mfgs'. and vendors' practices that I've got problems with, to the degree Sunpower uses peoples ignorance to get a marketing advantage in ways I believe to be unethical and then extract a premium when one cannot be logically justified pisses me off. They are not alone in such practices by any means, but they do seem to have, IMO only, raised it to the level close to that of an art form. To my personal experience, and similar to what can be read on this forum most any day, most who consider and then later buy S.P. over other equally fit for purpose equipment are woefully ignorant of what they are doing, and that ignorance is, IMO only, what S.P. preys on. Most buyers are marks wasting a lot of money buying any PV before other, more cost effective measures that aren't as sexy, but that's a separate issue.

I'm the guy on the HOA Arch. Rev. Comm. that reviews and recommends member solar energy system proposals to the entire comm. for approval and installation. There's a pretty high solar penetration in this HOA: ~ 120 homes out of ~ 550 that have PV. I know all 120 systems on something bordering on intimately. I reviewed each one, spoke with each owner and vendor, watch each installation and spoke with the AHJ for each install. Of those 120 PV systems, 24 use Sunpower panels (including - GASP ! - mine). I also, with the help of cooperative neighbors, monitor about 10 or so of the systems with 3 of them S.P., a few LG's and a couple other panel mfgs. Those systems have orientations similar to mine. All those systems , as best as I can figure it, produce about the same output as mine per STC kW.

The 120 systems in the HOA probably have about 2500 or so panels between them. After 8 yrs. of monitoring things, probably less than perfectly, 1 panel has failed. It was a Sanyo and it died of infant mortality about/less than a week after install. All other ~ 2500 panels are, to the best of my knowledge, operating nominally - S.P.'s and everyone else's . One string inverter needed replacement. Several string inverters have needed service, and maybe a dozen micros, probably/mostly Enphase 190's I think, have failed. There have been a few wiring issues that have been resolved, all early on after install. There have been no big monitoring issues that I'm aware of, probably because most folks in this HOA, being of the old guard, could care less about such things. The S.P. vendors run from among the best to mundane.

Service, when needed is generally best from local vendors as are the installations, although installs are not always perfect. The big, national lease outfits are hit/run, blow & go nightmares for installation.

Most all owners/lessors/PPA users of PV systems in my HOA are ignorant of what they purchased. Those who bought S.P. all 24 of them it seems, sing one tune - and it sounds just like yours: Highest efficiency, best warranty, etc., and after talking to all of them, as neighbors and friends, I'm quite sure none of them have much of any understanding of what they are saying. If I suggest that most every system produces about equal annual output per installed kW regardless of panel, the S.P. owners usually become indignant and what looks to me to be defensive, and display an attitude and opinions that, to me seem not unlike yours. That's understandable to me in many ways, one such way being as a denial or defensive response to avoid the reality of acknowledging a mistake. I have suggested they not take my word but simply check PVOutput.org and offer to help understanding what it has to offer. No takers so far. Only a lot of denial of reality, or at least what looks like reality to me.


Take what you want of the above. Scrap the rest.

No neighbors were harmed in the making of this post.

[Mike90250]

My feeling of the gist of this, is unless you are really tight on space, and need the extra % that SP offers, they are over priced, with lotsa technobabble in their sales pitch

[littleharbor]

Tell you what, I'll pull out the panels I have and have already explained the history on and take some pics just for you. See you Tuesday.