MemberOctober 6, 2021 at 9:22 pm
I know solar cell efficiency decreases with increasing temperature. It will be interesting to learn how wind cooling affects the cells while driving– they may get more efficient as your speed increases.
Conversely, on a hot day the cells on the dashboard would presumably do better than exterior cells when the car is stationary and interior cooling is on.
MemberOctober 7, 2021 at 6:18 am
My primary (some would say exclusive) interest in solar race cars is the solar array. As such, I’ve sort of coined a bit of an inside joke with the solar racing community. I tell them that if they want more power they should simply drive faster!
MemberOctober 7, 2021 at 8:19 am
Heat does affect solar cells/arrays.
Of course, arrays composed of different materials will respond differently to temperature, but a general range for panels at max efficiency is between 59F and 95F. For every degree increase in temperature above 77F degrees, a solar panel can lose10-25 percent of its efficiency.
Solar array output for an Aptera under cold and hot climatic conditions will be performed during Aptera testing
MemberOctober 7, 2021 at 8:47 am
I’m pretty sure you have a typo or three. Your “for every degree increase in temperature above 77F degrees, a solar panel can lose 10-25 percent of it’s efficiency” is not correct (for practically all crystalline cell panels). A SunPower/Maxeon panel might lose 15% (relative) of it’s efficiency when it goes from a cell temperature of 25 C to 75 C. That’s equivalent to taking a 700 watt rated array to just under 600 watts. A 75 C solar cell, by the way, is likely only under the hottest, most stagnant conditions.
MemberOctober 7, 2021 at 8:04 pm
25C is 77F in my experience the baseline for testing solar cells. 75C is 167F. Probably not a factor for an Aptera sitting in the sun. You are right about typos.
I have no experience that would relate to the Aptera “Granular”, compound curve cells and how different they would be from the common, flat, crystalline cells. I guess that will be resolved/published from testing of the appropriate Aptera Prototype and hopefully close to the advertised performance.
MemberOctober 7, 2021 at 9:00 pm
Yes, 25C/77F is one of the three key things for “standard test conditions” when rating cells/modules/arrays. Although it appears that you do, what most others don’t realize is that it’s the actual cell temperature and not ambient. For a cell to be at 25C when 1000 W/M^2 of 1.5G spectrum sunlight is hitting them would require a LOT of “forced” cooling of some sort. With respect to the 75C number, I would not be surprised if it’s hit in some cases. I’ll look through some of my data from testing solar race car arrays (typically in summer) and report back!
Aptera’s cells really are, more or less, common, flat, crystalline cells. Being IBC type, however, makes them premium ones, to be sure. It’s a great choice for many a reason. In short, however, I’m pretty sure there’s such a thing as a “granular”, compound curve cell. I’ve tried to address this in other threads and hopefully folks will start to get it. Myths can be difficult to extinguish. I’m not trying to be combative. Just accurate.
MemberOctober 7, 2021 at 9:36 pm
Thanks for the tech data on solar cells. Nice to have an expert on the forum. Look forward to your report out. Also any additional information you would care to share would be useful. I think the more we know about Aptera technology the better we will be at both appreciating it and promoting it to others.
An added thought. It would be interesting to hear you reasoning on why the cell technology selected by Aptera was the right choice. Would help to strengthen confidence in Aptera engineering.
MemberOctober 8, 2021 at 8:05 am
(side note/question – I used to be able to edit a comment but the editing function doesn’t seem to exist anymore. Any ideas? In the comment I made October 7, 9:00 PM (just above), I meant to say “…there’s NO such thing as a “granular”, compound curve cell….” and would like to correct it.)
With respect to peak cell temperatures, I’ve looked through the data I collected during the last 2 events held at “Circuit of the Americas” in Austin, Texas and found a series of current vs voltage (a.k.a. IV) curves taken between 2:17 PM and 2:34 PM local time on July 7, 2017 for a solar car team’s array. Peak temperatures of the array were between 68 and 76 C. Nominal co-planer insolation was between 990 and 1006 W/m^2 at the time. I don’t know with 100% certainty but I suspect the testing was done with the car in the “cold pit” (between garages and “hot pit”) of the track. I wish I had wind data too but, alas, I don’t. I suspect, however, it was quite still in the area because of the garages to the rear of us and the track grand stands to the front.
If interested, the team’s array was composed of full size SunPower cells encapsulated such that the finished “laminates” had an “areal weight” of about 800 grams/m^2 (it’s my “Legacy” encapsulation scheme). These laminates were bonded to the team’s upper shell. The upper shell, as I recall, was a fiber reinforced resin skinned honeycomb core sandwich structure w/o foam filler.
With respect to why the cells are the right choice, it boils down to, essentially 3 characteristics. First, raw efficiency. SunPower/Maxeon still have the best efficiencies. Second, of all the conventional single junction Silicon cells, they have one of the lowest (if not the lowest) peak power temperature coefficient. Third, at least in the more recent generations, they have a lower “breakdown” voltage. Having a lower breakdown voltage helps mitigate mis-match losses. Mis-match is all but guaranteed on curved arrays.
ModeratorOctober 16, 2021 at 5:15 am
Alain, I am grateful for your well-informed and in-depth comments in this thread. I’ve learned a good deal from them.
I have 18 Silfab Solar panels on my home here in Ohio which is not known for great insolation but gets enough sun to make the panels worthwhile. I knew from my previous research that the panels are more efficient in cooler temps and that summer sun can raise the all-black panels that I have to about 120 degrees or more. I was not aware of the particular percentage drop engendered by higher temps that you and John Malcom reference. This is good information. Of course, my roof panels are fixed and use cells different from those that Aptera will use. Regardless of composition though, the effect of temperature on cells applies.
As has been hinted, it remains to be seen what we will experience in the real world when finished vehicles get into our hands. The efficiency drop in temperature in the end is less of a factor affecting output than how many hours of sun and how intense that sunshine is for any given Aptera owner. I note a good 10%+ or more variation in output from my roof panels comparing one sunny day to another sunny day. Even a light cloud haze in my area (such that I would subjectively say “it’s a sunny day”) can make a detectable difference in the amount of electricity I produce.
MemberOctober 16, 2021 at 6:57 am
I’m happy to contribute and thanks for the detail of your experiences.
Where I live and work (same place), for the 9 years it’s been running, my 12 SolarWorld nominally 255 w-DC rated panels/modules produces, on average, 16.4 KW-Hr per day whereas my daily average consumption is 16.2 KW-Hr. We are all electric. To be fair, it’s a small house/shop and it’s just two of us.
MemberOctober 8, 2021 at 12:38 am
Just read through your other post. Very informative. Looking forward to your next assessment.
MemberOctober 7, 2021 at 4:15 pm
MemberOctober 7, 2021 at 11:43 pm
A couple of guesses here. The middle area (between the cells) is like a loading area and may subject cells located there to more damage. But at only a little over 20 watts, I have kind of thought of those chevrons as a functional styling feature. They might use that much just to light up the logo????, and that’s ok by me!
MemberOctober 15, 2021 at 11:26 pm
I have a question that I think fits this topic. In some other forum topics, some have wondered if the rear hatch camera dedicated to the rear view monitor (virtual rear view mirror), would fog up in some winter weather conditions, blocking rear visibility in the absence of an old school rear view mirror. Is it possible for the heat generated by the solar cells covering the rear hatch act as a defroster for the rear view camera? If they did, it would make a lot of rust belt customers (like myself) very happy!
MemberOctober 16, 2021 at 5:00 am
Great practical question!
While “fogging up” of camera lens’ is not my area of expertise, and I live in a dry/warm area (a.k.a., rust – what’s that?), I think I understand what you’re getting at.
While the solar cells covering the rear hatch, do indeed, warm up when hit with sunshine, they tend to warm up LESS than non-solar cells of similar material/color. This is because they are “converting” a significant percentage of the incoming radiation into electricity. Were it not for that conversion, practically all the incoming radiation would, instead, be converted to heat and thus making the solar cells hotter.
With the physics lesson out of the way, maybe a better idea would be to simply have a tiny “resistor” on/near the camera lens and run a small amount of electricity through it to “de-fog” it as needed. Come to think of it, it’s probably already a thing in camera tech!
ModeratorOctober 16, 2021 at 10:17 am
Philip, being a fellow rust belt customer I find your question about fogging of the rear camera very relevant.
I can offer for comparison my 2 years of experience with the rearview camera in my Hyundai Ioniq hybrid. Even in the most severe winter conditions, the most my rear visibility was impaired took the form of moisture blotches on parts of the image. It was never so bad that my rear vision was completely blocked. Position of and shrouding of the lens are variables. I assume that will be considered as part of the final Aptera design.
MemberOctober 18, 2021 at 4:03 am
So in my experience, the problem won’t be moisture with a rear camera, it’ll be road grime (based on my Prius).
However, it’s possible that with the camera being mounted especially low, and on a very narrow section of body, that that may not be a problem – airflow past the sides of the camera might prevent that. (Typically on the flat rear of a vehicle, road grime ends up in a turbulent area of airflow and thrown up against the back, and in winter, there’s a lot of road grime to throw up.)
MemberOctober 18, 2021 at 5:56 am
bhtooefr: As I recall, (Might be from Aptera, might be from discussions.) There are 2 rear cameras, a back up camera on the end of the tail (Should be low turbulence area thanks to the vehicle design.) and the main rear view camera mounted at the top of the hatch.
MemberOctober 16, 2021 at 10:32 am
Unless there is some evaporative material on their surface, driving faster will only cool the cells if they are hotter that the ambient temperature to begin with, and then will only cool them down to ambient. Driving faster will reduce the time it takes to drop the temp to ambient, however.
MemberOctober 17, 2021 at 6:51 am
You nailed it!
A “trick” used in solar racing (especially in the dry Australian outback) was to spray the array with distilled water just before setting off and boy did the array voltage/power jump as the car got to speed. Didn’t last long, of course. Also, in some scenarios, water on the array was a dust magnet and when the water evaporated, guess what was left behind? Orange tinted dirt! Not good for light transmission as one would expect.
MemberOctober 16, 2021 at 11:53 am
Alain, thanks for taking the time to go back through your data and do the research. Wow! was surprised at the peak temperatures. 68-76C (154-169F) Would not have thought that high especially if taken between garages I assume a cool are relative to the track.
Also glad for the identification/description of the factors that contribute to Apera’s selection of SunPower’s Maxeon cells. This should provide a level of comfort to forum followers coming from an expert in the field of solar cell engineering and performance.
Have some additional questions for you.
– How do you think the cells in the Aptera areas are connected? Series or parallel
– What measures do you think they are taking to avoid shading effects in the configuration you think they are employing
– In one video, Chris is showing a cell, breaks it and says that even if the cell is broken, it will not lose “Much” of its power. I have a different understanding of a broken cells performance and affect on the arrays performance. Your thoughts?
– The full array is rated at 700Wh. I am assuming that rating would be of the arrays are flat, all facing the optimum angle of the sun. Or do you think that is some “Average” that comes from exposing the curved arrays on the vehicle to the sun under some set of varying conditions?
– A claim is made that if a cell is broken the owner can replace the cell “easily” If a new cell(s) are added to an older array, would that not degrade the array performance?
– Is it possible for a layman to replace cells?
I know a lot of questions. But I believe you are our only exper in solar that is willing to speak up.
<font face=”inherit”>WRT editing. You can edit for a short time after posting. But after the post has been </font>reviewed<font face=”inherit”> or has been in place for a time, we loose the editing ability.</font>
MemberOctober 16, 2021 at 12:25 pm
The individual cells appear to be sealed into the resin coating of the panels on which they’re mounted – except for the dashboard. I would assume, then, that by “replaceable” they’re talking about the entire panel (ie. hood (bonnet), roof, hatch or tail).
My hope is that the wider roof panel will allow the six tail-cells to be moved to the roof, simplifying the system.
MemberOctober 17, 2021 at 3:33 pm
My pleasure John and thanks for letting me know about the forum editing question.
I’ll try to answer your additional questions as best I can but understand that there may be some details I can’t share as they are somewhat “trade secrets” for me.
Series/parallel – It’s unlikely full size SunPower cells are connected in parallel prior to the controllers. What’s usually done in racing is series strings of cells are put into a single controller then the outputs of the controllers are paralleled.
Shading – With relatively small compound curved arrays that move somewhat randomly, shading mitigation is a challenge. Regrettably, from what I’ve been able to discern, it doesn’t look like Aptera has adopted any tricks commonly used in solar racing. (There’s quite a bit I’m NOT telling you here)
Breaking cells – The section of the video you refer to really, really caused me “discomfort”. I’m sure even Mr. Anthony knew the shattered cell is, ahem, toast. The dialog around that section should have been edited differently to differentiate between shattered cells and, what I call, “simple breaks/cracks” which is likely what Mr. Anthony was referring to. Simple breaks do have minimal influence on power in, at least, the short term. Especially with SunPower/Maxeon cells. Longer term, it’s a crap-shoot on when but significant power loss is all but guaranteed. In solar racing, with some of the better teams, known cracked cells are “monitored”. When the cell begins to lead to more power loss than can be tolerated, it’s “shorted out” or replaced (technically the module within which the cracked cell is in is replaced should that luxury exist) (Again, there’s quite a bit I’m NOT telling you here)
Full array rating – The 700 watt number has been mentioned more than a few times and has caused a certain amount of consternation in some circles. Here’s something I wrote in another forum: The most efficient solar panel available in the recent past/today
(certain models of SunPower/Maxeon) calculates out to having individual
cells (125 mm x 125 mm) at just about 3.8 watts each. These factory
made panels are incredibly well made (~25 year power warranty) and, more
importantly, have ALL their cells pointed nearly identically (normal)
to the great ball-o-fire in the sky. Aptera’s nominally 180 cells are
not and hence simply will not deliver 700 watts even under Standard Test
Conditions let alone real conditions (with the possible exception for
brief periods when it’s really cold out and there are “edge of cloud”
Cell replacement – There are claims (I believe “aspirational”at best) being tossed about that Aptera has IP specifically for easy replacement of cells or panels or something. I’m skeptical (I’ve read Aptera’s patent applications related to solar). Individual cell replacement is likely out of the question. Whole “sections”?, more than doable I would imagine. On your second point, generally newer cells, assuming they are of higher current, which is typical, would not degrade overall array performance but they, individually, would not be operating at their own peak capacity.
Cell replacement by the layman – Cell level replacement by ANYONE is not likely going to happen. I hope I am wrong and I would really love to chat with whomever develops such a clever individual cell replacement scheme (if I’m properly motivated to do the development needed, I could imagine having that chat with myself ????). Panel level replacements? Quite possible if it’s engineered well.
Hope that helps. A lot of generalizations but please feel free to ask for clarification should anything not make sense or should anything trigger additional questions.
MemberOctober 17, 2021 at 6:43 pm
Thanks SO much for this and taking the time to be so thorough. The ” Generalities” are more than sufficient. Certainly would not want you to give away your competitors edge. I have familiarity but by no means expertise in this area but felt uncomfortable with the 700 watt claim and ” Right to repair” owner replacement.
I feel comfortable with Aptera’s solar cell selection with your comments on their choice. Appears they picked the best available.
Thanks again for being a part of this forum and so willingly lending your expertise. Always a pleasure to read you posts
MemberOctober 19, 2021 at 7:12 pm
While not about cell temperature, I have a question about the flexibility of cells:
If a number of these cells were mounted on a flexible thin sheet, could it be rolled up (above some reasonable-yet-still-compact minimum radius) without damaging the cells?
If so, would they survive long to being un-rolled and re-rolled repeatedly for many deployments?
Hoping there is a way to increase the solar collection of a parked Aptera without such flexible panels taking up a lot of room in the stored condition (like around a tube of something like 4 or 5 inches (10 or 12 cm) diameter but when deployed would extend from the back end of the vehicle to the wheel pants (one panel on each side). Depending on the practicality of the basic idea (the answer to the questions above) and the feasibility of the deployment structure and panel width, these “Solar Wings” might actually double the solar collection of the vehicle.
MemberOctober 20, 2021 at 4:46 am
No one, so far, has been very successful with using “conventional” crystalline silicon cells (such as what’s on Aptera) in reasonably low weight and “robust”panels/modules that can be repeatedly “rolled up”/ “unrolled” to such a degree that you describe. I’m hopeful, however, that in the relatively near future (<10 years), NON-conventional cells will be available to enable such products.
ModeratorOctober 20, 2021 at 11:36 am
Alain, this video was released recently and presents evidence that the SunPower Maxeon cells are the ones being used for the Aptera.
I share your skepticism about getting 700w from the solar array on a fully optioned Aptera. While it is OK to advertise the 700w figure, we must keep in mind that “your mileage may vary”. I can offer the real-world example of the single 180w solar panel I use to charge a battery at home. In full Summer sun, I see 130w, not 180w. I’m posting this in the spirit of managing customer expectations. The company doesn’t need a smattering of new-to-solar Aptera customers whining about how they are not getting the full 700W the Aptera “promised”. My two cents.
MemberOctober 21, 2021 at 11:32 am
There are so many technical errors in this video. I’m happy to detail them but it may take some time….(I will immediately, however, state unequivocally that SunPower/Maxeon cells that are shattered to the extent shown in the video(s) WILL NOT PRODUCE ALMOST THE SAME POWER as unbroken cells!!!!)
ModeratorOctober 21, 2021 at 1:33 pm
My spider sense was tingling about that “almost the same power” statement when I heard it.
MemberNovember 10, 2021 at 4:07 pm
Set up and tested 2 identical SunPower/Maxeon E60 cells today. One un-broken and one broken. Quick vid of results here: https://www.youtube.com/watch?v=uUlyg7UOXx4
Note, I didn’t break the broken one nearly as much as either gentlemen did in the Aptera Owner’s Club vid above.