Flexible Solar panels... Opinions?

[72Alumacoach]

Ok, I feel silly posting my pics after seeing the beautiful pics BigAl posted. I wish I had thought of painting the roof! Anyway, like BigAl I bought some inexpensive flexible panels online a few years back. Haven't ever regretted that purchase. I am not a solar expert and we haven't logged the output we are getting but after three years we are still able to camp for several days off grid and the battery maintains it charge. My panels are not adhesive and they have rubber spacers underneath creating a small gap. The only change over years is that the panels have yellowed. That is probably impacting performance but we haven't noticed yet. Crossing our fingers that we get a couple more years out of them. Hopefully new flex panels will have come down in price.


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[AirSolarGuy]

Since it seems like there are only a few people commenting on the subject of flexible solar modules I would like to provide additional input.

First let’s look at the obvious benefits:

• Flexible solar modules are frameless and can couture to the shape of the RV roof, making them far more aerodynamic.

• They are virtually unbreakable when mounted and they are up to 82% lighter than standard framed modules of the same size.

• You can walk on these modules without worry of breaking them and they look aesthetically a lot better on an RV roof.

• These avoid the need for custom mounts and they can be mounted with adhesives or screwed down.

Here's some additional information on the comments made by lewster on May 16th, 2014:

• “the panels get extremely hot as they are bonded to the roof and have no way for cooling air to flow under the panels” – MY COMMENT - Obviously the more the panel heats up, the less efficient it will be. Also having more ventilation to the backside of a panel will help that efficiency by cooling the panel. – See below for actual temperature calculations.

• “due to the extreme surface heat, the panels tend to cup in a concave fashion ever so slightly, capturing morning dew and the associated dirt....they are extremely hard to clean when this happens.” – MY COMMENT - I have not found this to be the case with smooth flex modules. Maybe this is something other people have found with older non-smooth flexible modules.

• “the biggest problem, which is also heat related, is panel over heating. As solar cells heat, they loose efficiency. With no way to cool down, they can reach surface temperatures of up to 160ºF, which can reduce the output by as much as 50%, making your 100 watt, $600 flex panel essentially a 50 watt, $600 flex panel.” – MY COMMENT – Using Standard Test Conditions (STC) here’s a rough calculation using temperature co-efficients:

If the roof of an RV heats up to 160ºF which is 71.1°C. That’s 46.1°C above the STC (Irradiance of 1000W/m2, AM 1.5G, cell temperature 77°F/25°C). Basically at 77°F/25°C a 100 watt flex panel can produce 100 watts of power. Note any temperature above 77°F/25°C will see some form of power loss.
At 46.1°C x Temperature Co-efficient Power Loss -0.38% = -17.52% of power lost
100 Watts – 17.52% = 82.48 Watts. This means at a temperature of 71°C/160 ºF a 100 watt flex panel will still produce approximately 82 watts of power, not 50 watts.
These are pretty high temperatures, which not all RVer’s will experience.
Framed are also tested to STC which means they lose power efficiency at the same rate. They might stay a bit cooler because of they are raised off the roof allowing some airflow, which is the trade off between framed vs flexible solar panels.

• “That 1000 watt output specification was measured at 'standard test conditions, or STC, which is a lab figure calculated at 77ºF and assuming 1000 watts/sq. meter. Not a real world measurement!” – MY COMMENT - NOCT (Normal Operating Cell Temperatures) is a better way of getting a realistic sense of what your panels would be producing. That's why NOCT is used for the design of large scale solar arrays. Also, you can't compare STC values to NOCT values. It's not apples to apples due to the difference in temperature and irradiance.

The STC temperature is 77°F/25°C. Using the standard test condition method for rating panels is an industry standard which is referenced in UL 1703. There's nothing strange about using the STC method of rating a module.

[gandttimes]

Thanks AirSolarGuy.
I understand from some of your other posts that you are connected with the company that Airstream uses for it's solar supply?
Do you have enough influence to get them to prewire with something heavier than the 10Awg that they are presently using especially since most who are installing themselves or using after market installers are putting 2 to 300 Watts minimum to start with which should have at least 6Awg at a minimum?
George

[BigAl]

I hooked my four panels up in series which results in about 70 volts and 4.5 amps max in full sun. That does not require the heavy gauge wiring others use when hooking up in parallel. Something to think about. I used the same gauge wire that the panels have.
Al

[switz]

We used a pair of #10 wires from each AM solar 100 watt panel to the common junction box on the roof. From the Junction box we used a pair of 2-0 wires to the TriStar 60 MPPT Solar Charge Controller and then onwards to the battery bus.

The proper wire size for the current to be carried reduces power loss in the wires. The Airstream pre-wire of a pair of #10 wire is barely adequate for the two 53 watt panels they sell for the Airstream solar option.

The Airstream 1,000 watt inverter option is inadequate to power the convection microwave (1,650 watts or 13 amps) option some dealers insist on ordering for a few hundred dollars more profit. There real expensive issues to convert back to a propane oven what with changing out cabinets in some models. The other issue with the Airstream inverter is they typically power only three outlets in the coach. What about all the other outlets?

I realized it would be a waste of my money to order any of the Airstream factory options for their solar and inverter equipment as they would all have to all be replaced when we did our major conversion.

[lewster]

Allow me reply point by point to the most recent post from AirSolarGuy. And if you are unfamiliar with my work in the RV solar field, it comes from 8 years of direct installation experience and real world measurements, not lab calculations.

First, here is a long term use report from Greg Holder, owner of AM Solar on the 2500 watts of flex panels he is testing on the roof of his Winnebago motor home. If you are interested, I can get the actual numbers mentioned for you. PM me any time.


We have had these on the roof of our RV since June of 2013. They are made with SunPower's back contact cells (like the ones we use in our GS100 solar panel). We used 3M VHB tape to hold them to the roof and that seems to work well so far. They worked very well during the summer months when the sun was high. However, we have noticed a fairly dramatic drop off in power with low angle sun during the winter and early morning/late afternoon sun angles when compared to the output of the glass/aluminum GS100.

The most serious problem we noticed was during a spell of 90 to 95 degree temperatures last summer. The thin covering over the cells (3mm thick) was not sufficient to keep the cells from "cupping". This, in essence, caused each cell to form a shallow bowl which collects dust that any moisture will push to the middle of the cell. When the water evaporates, there is a small circle of dried mud that blocks enough sun to cause a power loss.

Simply spraying them with a hose didn't completely remove that spot. I had to use a soft brush to scrub it off and then I noticed I was actually scratching the plastic surface of the panel (made from a UV resistant P.E.T. or "polyester"). Scratching the surface means less transparency which means less light hitting the cells which means loss of power.

Given that they scratch easily, have reduced output at off angles of the Sun, cupping cells from high heat and a limited 10 year warranty. We consider them "Not Ready for Prime Time". We are working on ways to address these problems and will offer them for sale when we have something we can heartily recommend.

Until then ... Buyer Beware!

Lewster comment: Perhaps this problem has been overcome by Go Power, but I have not seen their panels to test yet.

• Regarding the use of STC (standard test conditions) in selling panels: Yes, it is the standard for being able to look at various panels with an apples to apples comparison, but you will NEVER SEE the conditions used in the lab to calculate these values. You have to look at what is really happening on the real world at real operating conditions.

Here are a few practical observations from AM Solar's solar education section regarding STC vs. NOTC (normal operating test conditions):

Let's say you just purchased a 100 watt solar panel ... how much power (watts) can you expect to get from that panel given the conditions of an "average" day? First, you need to understand how that panel was given that 100 watt rating to begin with.

STC ... Solar Panel manufacturers use what is called Standard Test Conditions (STC). This means they put the solar panels in a flash tester in their factory that has been calibrated to deliver the equivalent of 1000 watts per square meter of sunlight intensity, hold a cell temperature of 25'C (77'F), and assume an airmass of 1.5. This flash test gives them their STC ratings. Consider these as you would EPA mileage ratings ... how many of you actually get the mileage they post?

NOTE: Airmass is the optical path length through the Earth's atmosphere for light from a celestial source. As it passes through the atmosphere, light is attenuated by scattering and absorption; the more atmosphere through which it passes, the greater the attenuation. Consequently, celestial bodies at the horizon appear less bright than when at the zenith. An airmass of 1 is looking straight up from sea level at the sun when it is directly overhead (which it never is in North America).

If you are anywhere north of the Tropics (23.5 degrees of Latitude), the sun is never directly overhead and so it will never give you an airmass of 1. A number had to be agreed upon so 1.5 has become the one used for STC. It is because solar panel manufacturers operate at varying degrees of latitude and altitude that some sort of standard had to be developed so that all solar panels were tested and rated under the same conditions so you have some basis for comparison.

NOCT ... Do Standard Test Conditions resemble "Real World" conditions? ... Not Hardly! Because of this, when utilities and municipalities are trying to calculate real available wattage on an average day (in order to issue tax credits, etc.) they use what is called Normal Operating Cell Temperature (NOCT) ratings. NOCT recognizes a bit of reality and assumes the following: 800 watts per square meter of Sunlight Irradiance, an average of 20'C (68'F) Air Temperature, an average wind velocity of 1 meter per second (2.24 miles per hour), with the back side of the solar panel open to that breeze (as opposed to being on a roof where heats builds up under the panels).

Given those conditions, what is the Temperature of the Solar CELL (not the air)? The average was found to be about 48'C (118.4'F). Some panels are a little higher and some a little lower. What you need to know is that ALL solar panels experience a voltage drop as they heat up. Since Volts x Amps = Watts, the power of the solar panel diminishes as they heat up.

Now think about this ... since most solar panels in use on RVs are laying flat on the roof, they are operating at even higher cell temperatures than what is expected from NOCT (as described above) with the back of the solar panel open. This is why you want to keep the panels raised up off of the roof by a few inches or so. Even then, I have measured cell temperatures as high as 70'C (158'F) on a day when the air temperature was only 80'F.

So what does all this mean to you? It means that on AVERAGE, you will be getting about 75% to 80% of the power you paid for. So that 100 watt solar panel you just bought will give you about 75 to 80 watts of power on the AVERAGE day. There will be days when you get the full rating of the panels but those days are few and far between. Likewise, there will be days when it is dark and cloudy and you will get only about 10 to 20 watts out of that 100 watt panel.

Here are some links to the sites where the data I used came from. Spend some time studying these and you will see that panels laying flat on the roofs of RVs do not operate anywhere near their STC ratings. Here's one in my backyard at the University of Oregon (UO SRML: Summary files) and here's one at the National Renewable Energy Lab in Arizona (National Solar Radiation Data Base). These go back for decades and can be relied upon for good averages.

• heating of solar panels vs. efficiency and output:

Don't confuse the temperature of an RV roof with the temperatures of a blue/black solar panel as the temperature differential can be over 60ºF.

Here is a bit more information on 'real world' solar panel usage from AM Solar:


"Real World" conditions for a solar system on an RV are quite a bit different than they are for the same system used in an off-grid solar home. One giant difference is the placement of the solar panels.

An off-grid home can put the panels on a pole mounted, dual-axis tracking mechanism where the panels face the sun squarely and track it across the sky from dawn to dusk. Panels mounted on RVs are usually laid flat on the roof, don't face the sun squarely and don't track it across the sky throughout the day. The difference in the amount of power being delivered by the solar panels in each situation is substantial! Using solar panels on RVs has some challenges but they can be minimized.

Let's look at all the places where solar power is lost in a typical RV installation and see how we can address them. First, a quick review of the equation for power. Power is measured in watts and Watts = Volts x Amps. So, anyplace that the Voltage and/or Amps is reduced there will be a drop in the power (watts).

What causes Voltage Drop?
1) Anytime the temperature of the solar cell exceeds 25'C (77'F), there will be a drop in voltage from heat. As the heat increases, so does the amount of voltage dropped. When you consider that I've measured cell temperatures of solar panels on the roof of RVs above 65'C (150'F), this is significant. This is one reason why we have custom panels built with higher operating voltages. It is also why solar panels should be mounted with a few inches of clearance under them so the heat can escape instead of building up.

2) Every Amp traveling through every foot of copper wire has a known and measurable voltage drop. Smaller wire will have more voltage drop than a larger wire if they are carrying the same amperage. Voltage drop is also relative to the temperature of the wire. The higher the temperature of the wire, the greater the voltage drop. This is why we use larger wire sizes as the wattage of our systems increase and yet another reason we use higher voltage solar panels. Example: Our GO100 solar panel operates at 18.5 volts and 5.42 amps (18.5 x 5.42 = 100.27 watts). A competitor's 100 watt panel operates at 17.0 volts and 5.88 amps (17.2 x 5.88 = 99.96 watts). Assuming 15 feet of 10 gauge wire between the solar panel and the combiner box, our solar panel will deliver 99.39 watts to the combiner box. Their's will deliver 98.9 watts. That 0.49 watts may seem small but it is a significant difference in power delivered, especially as you add more solar panels to the equation. The difference in power also grows when you add in the rest of the wire harness and the path it takes to get to the batteries through the charge controller.

3) Every connection made in the wire harness has some resistance which causes some voltage drop including the connections to the solar panel, combiner box, charge controller, fuse or circuit breaker and batteries. Corrosion at these connections also causes voltage drop. This is why we use high quality copper lugs, crimps and ring terminals in our kits and protect them from corrosion by using glue-filled, heat-shrink tubing there.

4) Just passing the power through the electronics of a charge controller causes voltage drop. There is no charge controller out there that operates at 100% efficiency. They all have varying degrees of voltage drop depending on the quality of the electronic components used and how much power they are processing. This is why we choose high quality, high efficiency controllers to put in our systems.

5) Fuses and circuit breakers are designed to make the current (amps) pass through a small section of wire or metal so that if the current rating of the fuse or breaker is exceeded the wire will melt or the circuit breaker will open. There are varying degrees of voltage drop at these devices depending on how much power is passing through them.

What causes a reduction in Amperage?

1) The amperage (or current) a solar panel puts out is a straight line correlation with the intensity of sunlight shining on it. If the panel is receiving the equivalent of 1000 watts per square meter of sunlight, you will get the rated amperage of that panel. If it is receiving 500 watts per square meter, you will get half of the rating. If it is 100 watts per square meter, you will only get 10% of the rating.

2) Shade causes a rather dramatic drop in amperage. Even if only a portion of a few cells are shaded, it can cut the amperage by half or more! So pay attention to where the panels are placed. Keep them away from antennas, satellite dishes, and air-conditioners. Try to assure that they will at least see the 3 hours either side of solar noon without any shade because this is when you will get 90% to 95% of the day's solar power. Morning and evening light are less powerful and are basically "icing on the cake" so you needn't be too worried about those times of the day. However, zero shade from dawn to dusk is ideal.

3) The charge controller requires some power to operate its logic, LED lights and display. This is expressed as "Self Consumption" or "Quiescent Current Draw" in the technical specifications of the controller's data sheet. These little parasitic draws can add up. This is why we choose high efficiency controllers to use in our systems.

Summary of "Real World" Operating Conditions for RV Solar Systems:

1) Solar panels on RVs operate at higher temperatures than those used to define Standard Test Conditions (STC) and Normal Operating Cell Temperature (NOCT) ratings. This means the power ratings for solar panels used on the roofs of RVs will be less than the same panels used in other applications.

2) Solar panels on RVs are typically laid flat which means they are not squarely facing the sun. Even if you tilt them up to the south in winter, they only face the sun squarely for about an hour per day since you are not tracking the sun from dawn to dusk. This means the power output from solar panels used on the roofs of RVs will be less than the same panels used on a pole mounted rack facing the sun.

3) The wire used in RV solar systems is typically exposed to higher temperatures (because it is exposed to direct sunlight on the roof) and somewhat longer runs than in other applications (because it travels odd paths to get from the roof to the controller and from the controller to the batteries). This will cause some power to be lost in transmission between components. Our roof wire is round and light grey in color so it will operate at cooler temperatures than black wire that is flat like the commonly used "Tray Cable" in other systems.

4) Charge controllers used in RV systems are typically placed in areas where there is limited availability to move air over them to dissipate the heat generated when they are processing power from the solar panels. Higher temperatures mean less efficiency which means some power lost.

These conditions are different than almost every other application and require some thought when you are considering a system for use on an RV. The next topic will include these considerations when we go about designing RV solar systems for use in their unique "Real World" conditions.

• PRICING:

The only thing NOT mentioned above is what you get with a flex panel and at what cost? The lowest price I could find on the net was at Amazon for the 100 watt flex panel and 30 amp PWM controller was $643. The controller alone can be found for $120. That means that the 100 watt flex panel alone will run $540 alone.

I still maintain that flex panels will be the wave of the future. Unfortunately, that future that is available now comes at a pretty steep price.....and as always.............YMMV

[mansaj]

Prices keep getting more tempting.
$220 for a bendable 100W monocrytaline panel:
Amazon.com : Renogy® 100W Monocrystalline Bendable Solar Panel : Patio, Lawn & Garden

Would be nice to see the MPPT controller prices come down too.

[Safari Tim]

I'm finishing up my installation of 400 watts of GoPower! Solar Flex.

I used two panels in front of my A/C and two behind it. I'm one cable short of getting them all connected But I did pull in over 10amps with just two panels.

My install blog post is here:
400W of Sun Power… almost | 1960 Airstream Ambassador Blog!

The best part is you can't even see them when standing around the trailer. They disappear

[0557]

Sweet !

[VintageRV]

Lookin Good Tim!

[Hudsoncamp]

I'm also looking at Go Power. Let us know how they're performing in the heat. Any cupping, etc.

[Safari Tim]

So far they are great. I just completed the installation, so I don't know about your cupping concerns yet. We are going to have GoPower! on the show on the 26th. Hopefully we can address some concerns. It would be great for anyone interested to call in their solar questions to theVAP voicemail line @ 707-533-4VAP. We can play them for GoPower!

I just put together a video on my solar flex installation. You can check it out here.

[Landrum]

Do solar panels stop producing if any piece of the panel is in the shade?

[47WeeWind]

Mr. Ambassador Tim:

You are doing a great job with your blog and video about installing the GoPower flexible solar panels on your 1960 Ambassador. Both are wonderfully informative. I look forward to hearing about your experiences with these solar panels while traveling and especially while boondocking. Thanks for sharing!

[SuperTrouper]

Maybe its just the AIRFORUMS app but I don't get sound for videos unless I go direct to the origin site or youtube.

Ipad IOS 7. something Brad

[Hudsoncamp]

Tim, I'm following your lead. Two GP Solar Flex panels. One 100 watt and one 30 watt. I have an 19 foot Bambi with limited roof space. I know it's a bit unproven, but I'm willing to give it a shot.
I too will use the 3M VHB tape. What was the width of the tape you used? Half inch? Three-quarter?

[Arcticfox]

This is an interesting thread. Tim your video and instructions were great.
I don't know much (really nothing) about these systems but it looks to me that it might be the way to go. I don't boondocks much but it is always good to have some options as time moves forward.

Tim (or anyone else) - I have a 2013 Flying Cloud 28', in a perfect world how many panels would you put on and is this something I could do myself or should I have a dealer do it?

If the feeling is one can do this (DIY) what would I need for parts and were is the best place to buy the required items.

Thanks

Doug

[SuperTrouper]

Yes Tim, Thank you. I'm seriously considering this set up for my solar requirements. I'd be interested in your actual power generation over time. I also read some of the discussion with cooling (heat reduces the output) and I find this true with my home panels but I'm curious if air circulation around panels actually works better than the heat sink capability of the roof when panels are applied directly as you have done. Having the panels contacting the roof and shell might actually draw more heat away from the panels than air underneath can. Some heat conductive grease underneath would be even better but the chemicals may not react well with the panel base. Just thinking out loud.

[Safari Tim]

Hey guys,

We did our big show on solar, its available here:

Episode 212: Go Solar! | The Vintage Airstream Podcast

I also did a video walk through of my flex solar install in case you might be interested.

GoPower! Solar Flex Installation Video | 1960 Airstream Ambassador Blog!

Thanks!

[Hudsoncamp]

I haven't even seen it in person yet, but here's a photo of my SolarFlex installation. One 100 watt and two 30 panels. With limited room on our 19', it fit pretty well. Looks good, now I just hope it actually works!



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