Sunpower Maxeon Solar Cell - Discussion

[Zucca]

Folks,

I was thinking to start a home made solar panel project. I tipped in google "best solar cell" (I know I know, please have mercy on me) and I ended up here.
To me it looks clever, but I don´t have any deep know how regardig a solar cell. I searched Maxeon in the EEVBlog but nothing was there, so here the post.

Now, what is a Maxeon Solar Cell?
They claim over 21% efficiency, with a lot of nice details and improvement, see attached details on the X-Series panels made with those cells, or here

http://us.sunpower.com/why-sunpower/high-efficiency-solar-technology/

there is also a nice video here



and here a nice white paper (very slow server, be patience):

http://us.sunpowercorp.com/cs/Satellite?blobcol=urldata&blobheader=application%2Fpdf&blobheadername3=Content-Disposition&blobheadervalue3=attachment%3B+filename%3Dsunpower-module-degradation-rate%252C0.pdf&blobkey=id&blobtable=MungoBlobs&blobwhere=1300290935416&ssbinary=true

What I like is the fact of the +/- connections on the bottom



and the reverse diode integrated in the cell itself, see video here:



You can also buy those here:

http://www.alibaba.com/trade/search?fsb=y&IndexArea=product_en&CatId=&SearchText=Maxeon++Solar+Cell 

http://www.aliexpress.com/store/product/Sunpower-Maxeon-Solar-Cell-21-8-Efficiency-3-34W-Semi-flexible-125x125mm-Mono-20pcs-lot-Solar/129132_1541941540.html

or simply on ebay here:

eBay auction: #251627066704
eBay auction: #251648370523

looks too cool to me, now what do you think?

Thanks!

[tom66]

I'd be very cautious buying solar cells off eBay. Who knows if they are the genuine article? So many fakes.

Just my two pence.

[Zucca]

You are right, like the eneloop battery

[NiHaoMike]

For most applications, the figure that matters is $/W.

[Zucca]

What about the warranty?

For most applications, the figure that matters is $/W.

They claim a 25 year life cycle/warranty. This is relevant for both quotes above.

[Zucca]

No hope. I would have the beautiful classic DIY warranty (about 0 seconds), but I hope you know how to fix the crap you build  .

[Psi]

Do you have info on what one of those panels weighs?
I'm curious if i could add some to my big RC plane for extra flight time.


Also, be careful with cutting edge stuff on aliexpress at a good price. It maybe genuine, but also a factory reject.

[Zucca]

Apparently this cell is the one they choose for a solar powered plane and boat, check this links:

http://www.solarimpulse.com/timeline/view/6544#.VCKk3373aK0

http://www.planetsolar.org/

This could also be useful:

In 2005, Alan Cocconi, founder of AC Propulsion, succeeded in flying an unmanned airplane (drone) with a 5-metre wingspan for 48 hours non-stop, propelled entirely by solar energy. This was the first time a device of this type was able to fly through a whole night, thanks to the energy collected by, and stored in, the solar batteries mounted on the plane.

[Artlav]

Well, i've ordered a dozen cells from Ebay linked here.
They claim to be coming from Poland, but ship with USPS, and sound a bit chinglish-y.
Hm...

Will report back in a few weeks, i guess.

[Zucca]

Cool Artlav, please if you can force an inverted voltage on the cell and see how the buid in diode is performing...

[Psi]

And please report back on the weight of  a single cell

[amyk]

Okay, but if you buy from eBay and install yourself will they honour that 25 year promise?

I'd be more inclined to wonder whether they'd be around in 25 years...

[Artlav]

The cells have arrived.

Beautiful blue-weird colour.

Back side:

They were fine overall, but there is some discolourations near the edges:

Not sure if it's ok or not.

The cells are paper-thin, flexible and feel very fragile.
The front surface is changing colours of blue in a rather peculiar fashion.

Don't ever touch the front surface - it absorbs fingerprints and contaminants with no hope of removal.

My father, who made solar cells in the 90s, said that the surface is likely a dense pack of tiny pyramids, giving the colour changes and responsible for the dirt absorption.

Each cell weights exactly 7g, on +-0.05g scale.
It's night out (and winter is approaching), so not sure what performance they would get in the sun - i'll test on the nearest sunny day.

Being put 10cm away from a 150W metal halide arc lamp it gives 0.65V open circuit and 3.5A short circuit.
A luxmeter gives 80000lux at this distance, which is close enough, but the spectrum is likely wrong.
The cell heats uniformly when in front of the lamp, getting warm almost instantly.

One thing is certain - these won't survive any time exposed to the elements, so i'll better find something to encase them into.
Any ideas?

What else to test?
Zucca asked about reverse voltage test, but i'm not sure what exactly to look for.

[Zucca]

NICE! Thanks brother  O0! It looks like it will be a little bit hardcore for a DIY solar panel, they look very delicate devices; but I like the challenge.

Zucca asked about reverse voltage test, but i'm not sure what exactly to look for.

This is the theory on normal Solar Cell[SC]/panel:
http://pveducation.org/pvcdrom/modules/bypass-diodes

Just imagine for this one there is a reverse diode implemented in the cell itself. Like This:
Negative SC Terminal ---|>|--- Positive SC Terminal

Just take a lab power supply unit [PSU], set the voltage to (my best guess) 5V and turn the current to 0A. Connect the + of the PSU to the - of the SC, and the - of the PSU to the + of the SC.
SC must be in dark condition, no light on it. Now increase the current on the PSU and see how the SC voltage reacts. I would like to know what is the forward voltage (best case the I/V plot) of that diode and how the cell is handling the thermal dissipation. If needed increase the 5V.

Don´t destroy the cell for me though... keep one eye on the temperature. It would be very interesting but I do it only if you can/have time!

[solarcross]

I've used the same cells for a couple projects...I bought a whole stack of 150 cells for just over $500 about 1.5 years ago..

[Zucca]

Funky bike! Are you happy with those solar cells? Any tips for the DIYer out there?

[solarcross]

cells are pretty good,  cant wait for +28% efficiency PV cells to hit the market..
good rule of thumb.. build your PV array at double the watts of the output you need

[Artlav]

In the end, i decided against trying to connect and laminate them myself.
The things are too damn fragile.
Fortunately, my father still had contacts in the industry, so i found a place that laminated them professionally for me.

They also measured the performance of the completed panel under the standard conditions:

For the 10 cells in series:
Each cell is 0,01522 m^2 (including lack of corners), so total area is 0.152 m^2.
Isc=6.35A
Uoc=7V
Im=6.04A
Um=5.4V
Total power: 33W
That comes out to about 21.6% efficiency.
2% losses in the lamination, so the cells themselves give out about 22.1%

Seems legit.

The voltage range is good for a single cell li-po battery charging, or USB charging.

No testing yet on the diode performance - i'd like to see how the panel as a whole performs under partial shading conditions, rather than doing shenanigans with a power supply.

[Zucca]

COOL! Nice Job! The  efficiency>20% is a very good news. Do you know the SC temperature (at least the ambient temperature) when it was spitting out the 33W?

Regarding the connections I was thinging to build me a spot welder, like this one
http://www.avdweb.nl/tech-tips/spot-welder.html

but it seems to me that you can just solder a tab wire on it, but with my poor hands it could end up in a dirty job....

No testing yet on the diode performance - i'd like to see how the panel as a whole performs under partial shading conditions, rather than doing shenanigans with a power supply.

Reasonable. Since you have already a solar panel, you could cover just one cell (a piece of paper or plastic?) when the sun is shining and look on what happen to the voltage across that covered cell... or if you don´t have the access on the single cell terminals just report the variation in voltage/current with or without one cell covered.
By choosing another cell to cover you could test is the variations are pretty much the same (so diodes are equals in the cells, as expected).

[Artlav]

Do you know the SC temperature (at least the ambient temperature) when it was spitting out the 33W?

979 W/m^2, 27 *C ambient, as measured in the chamber.

Regarding the connections I was thinging to build me a spot welder, like this one

Bad idea.
These are silicon, that won't weld itself.
And, they are only 0.2mm thick - any pressure enough for a good spot welder current would punch through them or crack them. And, perhaps, burn through them.
In the panel they are just soldered together, with a special flux i presume.

[Zucca]

979 W/m^2, 27 *C ambient, as measured in the chamber.

I overlooked that in the report. Sorry... BTW I would love to know your language.

These are silicon, that won't weld itself.

Got it, you are right. Interesting, which means that the "solid copper base"
http://us.sunpower.com/why-sunpower/high-efficiency-solar-technology/
it at the end a paper thin layer.... of silicon? WOW

[madmalkav]

Hi everyone. First of all, sorry for the thread necromancy, but I'm quite lost.

I'm a computer technician and recently I got unemployed. I have been considering to buy some of this Sunpower cells to play a little but I'm quite lost in some aspects.

First aspect: how to laminate the cells. Something like this will be ok? http://www.instructables.com/id/Make-rad-solar-panels-with-a-sweet-desktop-laminat/?ALLSTEPS
Second aspect: how to solder the cells. OP says they are somewhat delicate, so I don't know what will be the proper method to connect them.
Third aspect: electronics. Will connecting the output of the cells to a regulator like this be correct? http://eud.dx.com/product/mini-dc-dc-voltage-stabilizer-regulator-module-red-844126106#.VRGGKOEYHlY

Thanks and sorry if all this is already explained elsewhere, I swear I couldn't find it.

[Psi]

I'm working on a quadcopter which can fly on solar power alone (will still have battery) and I'm using these panels too (after reading this thread a while back)

As you say, The real issue with them is protection from cracking. You basically have a paper thin silicon wafer. I'm working on a carbon fiber reinforced epp sheet and transparent film covering. Most important for me is keeping weight down.

madmalkav, yeah they are bendable but any impact force cracks them.
You can solder wire to them as long as you do it on a flat surface and dont press the iron down much. (Best to let the solder ball up and bridge the iron to the tab)

[madmalkav]

Please keep us informed on your progress. I think I will try that way of laminating just to see if it works, but I won't order anything until I can find a DC booster that can take three of this cells and boost it to 5V 2A.

[Zucca]

+1
I would love to see a EEVBlog procedure to build a DIY Solar Panel....