Portable Solar Panel Testing- Results

[conqueror4x4usa]

I know that I will probably offend some of the panel manufacturers with this testing. I believe that the results would be useful to those that are seeking to purchase panels in the future or simply want to know why their panels are not performing as anticipated.

I will start off here with some background of why I am posting this. Over the last few years we have sold most of the major bands of fixed and portable panels to our customers with varying results of durability and output. Each panel had its strengths and weaknesses. Some panels were super portable but lacked the output and some panels were large and bulky but had reasonable output. The one thing that almost all of them had in common was that the all seemed to not produce their stated power. As an engineer I really want to dig down to the bottom of it and find out why.

The first set of benchmark tests was relatively easy. Simply stated, put the panel in the sun and test its actual output and compare that to its stated rating. After doing the field testing I realized that some more in depth lab testing was needed to figure out why some of the panels fell short. We did a whole host of lab tests on each panel in a real solar lab, yep a real deal solar lab. If we are going to do the testing we should do it right. Each panel was even dismantled to test the solder joints and connections. I will do another post on portable panel construction in the near future to address those issues also. The one test that stood out the most as to why some panels performed poorly was the electroluminscence testing. For results please read on.



Panels To Be Tested- All of the panels are brand new and have not been used except for this testing.
1) Overland Solar 120 Watt: Sunpower mono-crystalline cell, busbar, soldered wire connections between panes
2) Flexopower 105 Watt: Solarworld mono-crystalline cell, busbar, soldered wire connections between panes
3) GoPower 100 Watt Flexible Panel: Sunpower mono-crystalline cell, busbar
4) Merlin Solar 160 Watt: Mono PERC CSi, Merlin Grid, solid copper band between panes
5) GoPower 100 Watt Glass Panel (reference panel): Carmana mono-crystalline cell. Not a portable panel but by far and away the most prolific panel on the market.

Test Method-
1) Place the panels at the same angle on the test jig facing the sun and measure the power coming out of the panel using a Thornwave Blutoooth PowerMon. We want to measure at the panel to limit any influence that the MPPT may have. (As a side note If you guys have not heard of this the Thornwave Blutoooth PowerMon then you are really missing out. It is has a 60 amp current shunt or you can attach up to 1000 amp current shunt. Bluetooth, control relays, monitor power etc, it can also control the charging from your vehicle to any type of battery.)

2) The panels will be fed into a Redarc BCDC1240D, 40 amp DC-DC and MPPT solar controller

3) The Redarc will then feed the power into two 100Ah lithium batteries. It is a battery bank that we made up for us to use at shows and around the shop and will be perfect for this testing.

4) A constant load will be applied to the the batteries in the form of two 12V led light bars so that the panels will be working at their peak output. Everyone knows that solar panels do not work well when the battery is full.

5) Each panels will be tested 3 times at a random selection to mitigate the variability in the angle of the sun. No clouds were present when testing.

Test Condition:
Temp: 42°F
Sun: Approx 10:00-11:00 AM

Picture of the Test Jig:




Field Testing and Results:

Please see table below showing the results of the field test we did with the panels on the test jig. There are also pictures down the line showing the panels on the test jig.

Portable Panel Results: The Merlin Solar panel exceeded the stated rating by 10%. It is rated at 160 watts and it produce 176.15 watts. That is incredible considering we did not have lab level conditions for the field testing. The next closest panels in the portable category was the Flexible 100 Watt panel. It is rated at 100 watts and it produce 98.53 watts. Much father down the line were the Overland Solar 120 watt panel and the Flexopower 105 watt panel. Neither one reached its rated output.

Fixed Panel Result: There was really no surprise here. The glass panels performed as it show just barely beating its rated power of 100 watts.




Overland Solar
Rated: 120 Watts
As Tested: 113.37 Watts


Flexopower
Rated: 105 Watts
As Tested: 75.63 Watts


GoPower Flexible
Rated: 100 Watts
As Tested: 98.53 Watts


Merlin Solar
Rated: 160 Watts
As Tested: 176.15 Watts


Glass Panel
Rated: 100 Watts
As Tested: 101.1 Watts


Lab Testing and Results:

The panels were tested in a lab capable of testing solar panels. There was a host of tests that were run but the test that easily showed why some panels were performing below the rated amount, Electroluminescence .

From Mr Google:

Electroluminescence relies on the same principle as a light emitting diode (LED). Current is fed into a solar cell (essentially a large diode) and radiative recombination of carriers causes light emission. As an indirect bandgap semiconductor, most of the recombination in silicon occurs via defects or Auger recombination. The amount of band-to-band recombination producing radiative emission is relatively low. However, there is a small amount of radiative recombination that happens even in silicon and this signal can be sensed using an external detector. The technique requires electrical contact and so can only be used once the metallization has been applied and the cell is substantially complete. Electroluminsecence provides a wealth of data about the area related uniformity of solar cells and modules. It is non descructive and relatively fast with measurement times of 1 s possible.

It other words. It can detect very easily if the solar cell has been compromised from cracking. See results below:




And for everyone out there that cares about cost...Merlin is also the least expensive per watt in the portable category.

 

[john61ct]

Great contribution. Don't worry about "offending" any vendors. . .

 

[luthj]

Thanks for posting this testing. Very useful

The micro cracking of the cells is a major bane, even in home mounted rigid panels. Damage during handling is the primary cause of this cracking. However, if the cell soldering process is not well controlled, the cells will crack from thermal stress.

I think most of those panels would have hit near their rated power if cracks/solder failures had not been present. Of course that is the challenge with flexible panels. I have long thought that to make a "flexible" panel more robust, each cell needs backed or faced with rigid material (glass/metal/composite).

The overland panel looks like it took several point impacts, possibly during shipping? Which is a very common issue, poor packaging! The flexopower panel looks like it is lacking in cell support completely? Or maybe the cells are just too thin?


Finally, the low temp conditions are likely really helping the output of those panels. In warmer temps, with longer exposure, I would bet those panels would drop another 10-20% in output.

 

[conqueror4x4usa]

Thanks for posting this testing. Very useful

The micro cracking of the cells is a major bane, even in home mounted rigid panels. Damage during handling is the primary cause of this cracking. However, if the cell soldering process is not well controlled, the cells will crack from thermal stress.

I think most of those panels would have hit near their rated power if cracks/solder failures had not been present. Of course that is the challenge with flexible panels. I have long thought that to make a "flexible" panel more robust, each cell needs backed or faced with rigid material (glass/metal/composite).

The overland panel looks like it took several point impacts, possibly during shipping? Which is a very common issue, poor packaging! The flexopower panel looks like it is lacking in cell support completely? Or maybe the cells are just too thin?


Finally, the low temp conditions are likely really helping the output of those panels. In warmer temps, with longer exposure, I would bet those panels would drop another 10-20% in output.

Yes, all really good points. I believe that some of the cracking also comes from the smaller companies that do not have the relationships with the cell manufactures to be able to buy "A" grade cells. Most likely the cells are lower grade cells from day one. Also some of the damage will come from the sewing up of the panels and like you said handling. We have finished the lab testing and put all the panels through some durability testing. I will post the results soon.

 

[dwh]

STC is 77F. At 42F all of those "should" have produced more than their "STC Rated" output. Were the panels allowed to acclimate to the ambient temp? Or rolled out into the sun from a heated building?

Latitude and time of year (miles of atmosphere traveled) also plays a role (outside of the lab, of course).

Where is the table showing the electroluminescence test results?

Was there any cell cracking (crazing?) whatsoever on the glass panel? I've seen quite a few glass panels with crazing/cracking in the cells.

 

[conqueror4x4usa]

Lab Testing Results: From a power point presentation I made.

Full Disclosure: About 6 months ago, one of our Air Con suppliers recommended that we take a look at using the Merlin Solar thin film flexible panels to mount permanently on the roof of our trailers to help with recharging the batteries. Merlin's specialty is making panels for the big rig trucking industry by providing solar for the aircon battery banks and lift gates in delivery trucks. After doing some more research online, I reached out to Merlin and purchased some of their 330W, 220W, 165W and 80W fixed panels to install on the Conqueror UEV-440, UEV-490 and also on my Chevy van. The installs went super quick, (30 minutes or less). After that we started to test those fixed panels with customers and on our own rigs. We were getting great results from the fixed panels so we asked Merlin if they could make a portable panel version. After a bunch of discussions on what I had learned about the shortfalls of the portable panels that are currently on the market the 160W Merlin Portable panel was born. Merlin has been in the portable market for a while with military applications (Nishati Panel) so this was not their first hay ride. The Merlin Panel meets all the military requirements but is a fraction of the cost.


Cell to Cell Connections: We also took apart the panels to inspect them further.

1) Flexopower: Each of the tri-fold panels were connected together with wires that were soldered to the adjacent tri-fold panel. Overtime those connections will fail in fatigue and they will also be a point for arcing. I believe that if this panel was wet or that connection point was compromised it could be a source of a fire.

2) Overland Solar: Same as Flexopower. Each of the panels were connected together with wires that were soldered to the adjacent panel. Overtime those connections will fail in fatigue and they will also be a point for arcing. I believe that if this panel was wet or that connection point was compromised it could be a source of a fire.

3) Glass Panel: The cell to cell connections are embedded into the panel its self so there is little chance of them failing.

4) Flexible Panel: The cell to cell connections are embedded into the panel its self but is a bus bar connection. These will also fail if bent too far. More on bus bar below.

5) Merlin Solar: Each of the tri-fold panels are connected to the adjacent tri-fold panel with a solid 2.5" copper ribbon that is laminated on both sides with some tough flexible plastic. We opened and closed the panel 14,000 times and that is when the copper ribbon failed. As a side note the Merlin panel will also meet the UL 1703 and IEC 61215/61730 test requirements

Internal Cell Grid:

1) All the panels tested except the Merlin panels use a bus bar grid design. The little lines that you see in most panels are small wires that collect the current from the cells and bring it to the larger flat bars, (bus bar) in the cell and transfer that current on down the line. You can't see the wires in the SunPower cells because they are behind the solar cell, but they are there and they are still the bus bar technology. In my research I learned that the bus bar design is 30+ year old technology that was really designed for fixed panels. It is a very fragile type connection that is prone to breakage due to bending and vibrations. If that bus bar is compromised in any way then you loose the collection ability of that cell.

2) Merlin grid is different: It does not use the bus bar design. Instead it uses a special grid that has 1,000+ redundant connections. If you look closely at the grid you will also see that the wires are thicker on one end and gradually get thinner as it moves across the cell. It is supposed to help with the current flow. Merlin claims that they can get 20% more current off of the cell with their grid. They are also made in the USA which is a plus.

 

[Rando]

Let me guess, you happen to sell Merlin Solar Panels?

I am not saying anything you are saying is untrue, but you need to be upfront in your motivations and conflicts here and that this is not an 'independent test' but most likely a marketing presentation from Merlin Solar.

 

[conqueror4x4usa]

Let me guess, you happen to sell Merlin Solar Panels?

I am not saying anything you are saying is untrue, but you need to be upfront in your motivations and conflicts here and that this is not an 'independent test' but most likely a marketing presentation from Merlin Solar.

Hello Rando. Thank you for your comment and I do understand your concerns. If you take a look at my post above I do disclose that after two years of having issues with panels from other manufactures I started to research for a better solution. Over those two years I literally have tested the output on probably 200 different solar panel modules. My independent testing was done way before I even knew Merlin existed. With respect to the output testing that I have summarized above in the leading post, I purchased all of those panels, brand new from each supplier and then I personally did the testing at my shop. I wanted an apples to apples comparison that was done by me. All the OE's (including Merlin) were claiming that their panels were the best and I wanted to test them all at the same time to verify. I was an Test Engineer at Honda Research and Development in the Engine Research department (ER2) for 12 years and I took the same approach to testing the panels as I would have when bench marking an engine or any other system. Based on my engine testing experience I have learned that other OE's like BMW, Ford, Chevy, Toyota, Hyundai are all less than truthful about their numbers. With the solar panel testing, I assumed that all the solar panel OE's were also less truthful about their performance. I know it is a cynical approach but that is what my experience had taught me. I wanted to find out what the real numbers were when all the panels were in the same test condition and that is what I presented in the first post.

Merlin was recommended to me by another supplier of ours for a fixed panel application on our trailers. Those fixed panels worked really well so we approached Merlin asking for a portable solution. At the time Merlin did not have a portable so together we took the knowledge and experience that I had with the failures of the panels we had been selling and together we developed the portable panel. Yes, we do now sell Merlin panel now. Why? Because based on the testing that I did and the lab did they are the best out there.

The lab testing (Electroluminescence ) was done outside of my control but after reviewing the data it does make sense why some of the other panels have issues.

Quoting from my post above about being forthright in my summary:

"Full Disclosure: About 6 months ago, one of our Air Con suppliers recommended that we take a look at using the Merlin Solar thin film flexible panels to mount permanently on the roof of our trailers to help with recharging the batteries. Merlin's specialty is making panels for the big rig trucking industry by providing solar for the aircon battery banks and lift gates in delivery trucks. After doing some more research online, I reached out to Merlin and purchased some of their 330W, 220W, 165W and 80W fixed panels to install on the Conqueror UEV-440, UEV-490 and also on my Chevy van. The installs went super quick, (30 minutes or less). After that we started to test those fixed panels with customers and on our own rigs. We were getting great results from the fixed panels so we asked Merlin if they could make a portable panel version. After a bunch of discussions on what I had learned about the shortfalls of the portable panels that are currently on the market the 160W Merlin Portable panel was born. Merlin has been in the portable market for a while with military applications (Nishati Panel) so this was not their first hay ride. The Merlin Panel meets all the military requirements but is a fraction of the cost."

 

[Rando]

I guess my interpretation of 'up front' is a little different .

There is a fine line between marketing and engineering, and one of the tricks here is choosing the performance metric. It does appear that Merlin solar does well under abuse and meets specification. However, I notice that there is no mention of efficiency (where front metalized cells do not do well) which is a key metric for performance in space limited applications such as portables and vehicle mount panels.

I am sure most retailers think their products are the best option, based on the metrics that they think are most important.

 

[conqueror4x4usa]

I guess my interpretation of 'up front' is a little different .

There is a fine line between marketing and engineering, and one of the tricks here is choosing the performance metric. It does appear that Merlin solar does well under abuse and meets specification. However, I notice that there is no mention of efficiency (where front metalized cells do not do well) which is a key metric for performance in space limited applications such as portables and vehicle mount panels.

I am sure most retailers think there products are the best option, based on the metrics that they think are most important.

There are a few things to take into account when designing a portable solar panel. Regardless of where the grid is placed, front, back or middle, if the cell structure, the method of cell layup, how you package the final panel and the grid to collect the current off of the cell is not robust for the portable application then the actual cell efficiency really does not matter that much. If your cell, as a whole, is not working and is cracked or the grid are compromised because it cannot withstand the abuse of normal wear and tear then cell efficiency is a moot point. I think for too long, panel OE's make their claim that their's is the best cell purely based on the claims that their cells are the "most efficient" cells but ignore the application that the cell will be in and the total packaging of the cell (grid and cell layup). For a rigid panel application like a glass panel, as the test result showed, they performed according to spec. But for a portable application that is using the fragile bus bar, thin film technology that was really designee to used in a rigid or static application (house or solar array) then those panels will fall on their face every time, just as the test results show. For years Merlin's panels have been used in the big rig trucking industry. The had to take into account the vibrations, temperatures and the abuse of that industry. The guys making panels for houses simply did not have to take those extremes into account.

 

[amenges45]

These panels are fantastic!

 

[amenges45]

We are running the set up Dave sold us ... truly fantastic. Topped off our lithium batteries much much faster than expected and is extremely durable and super easy to deploy

 

[amenges45]

Really appreciate the testing you did....paid off for your customers!