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What You Should Know About Flexible Solar Panel Performance

What You Should Know About Flexible Solar Panel Performance

At first glance, flexible solar panels seem like they would be a superior product to alternative rigid solar panels, and in some regards, they are. But in other ways, flexible solar panels are much worse.  We have had both rigid and flexible panels on our RV and will be sharing our real-world experience in this article. There are situations in which each type should or should not be used, so keep reading to find out which type you need.

What Are Flexible Solar Panels?

Flexible solar panels are just what their name implies – they are solar panels that can bend. However, by “flexible,” we don’t mean they can be folded up. Rather, they can usually curve to a reasonable extent. If they are bent too much, the internal cells and electrical structure will still fail. So be sure to note the limits from the manufacturer.  

Flexible panels can be made with thin-film, polycrystalline, or monocrystalline solar cells -just like rigid glass panels. However, they are usually encapsulated in plastic instead of glass. The top of the plastic is clear so the sun can hit the cells to produce electricity.

Like rigid panels, there are thin electrical wires inside flexible solar panels that connect the cells and a connection point at one end of the panel that usually has MC4 connectors on it. Depending on the manufacturer, these panels can be wired in series and parallel to one another, like a standard panel. Usually, they include blocking diodes at the electrical connection, but many are not accessible like a rigid solar panel.    

The Advantages of Flexible Solar Panels

The biggest advantages of flexible solar panels are space and weight. They are much thinner and lighter than rigid solar panels. Sometimes they weigh up to 80% less than a comparable rigid glass panel. Being thinner and, of course, flexible allows them to be installed in locations where rigid panels could not be mounted.

Flexible panels are usually mounted with an adhesive instead of mounting brackets, allowing them to eliminate screws that add leak points in roofs. Some even come with an adhesive backing so they can be stuck down like a big sticker. Many flexible panels have grommets and can be mounted with rope temporarily because they are so lightweight.      

The Disadvantages of Flexible Solar Panels

The first drawback to flexible solar panels is the cost. They typically cost twice as much or more than comparable rigid glass solar panels. Their flexible design can also be a drawback as they are not easily mounted in a suspended fashion. This is because they need a solid surface to support them. Because they are usually firmly mounted to a solid surface, they also have issues with heat. Conversely, rigid solar panels usually have airflow around them that helps cool the panels. 

Flexible Solar Panels and Heat

Flexible panels mounted to a roof do not get this airflow and can get very hot. Hot solar cells perform worse, so flexible panels that get hot usually have an additional capacity loss due to the heat. 

Heat can also be an issue for the surface they are mounted to. Their dark color contributes to this heat problem. And when they get hot, they will transfer this extra heat onto the surface beneath them. If this is an RV, car, or boat, this could mean extra heat in the interior space.  In cold weather, this is not a problem as it will help keep your RV nice and toasty. But on a hot summer day, this is not what you want.  

Life Expectancy 

Most flexible panels will have a much shorter life expectancy than rigid panels. Because their surface is a polymer instead of glass, it has the potential to degrade and cloud up. Usually, 10 to 15 years is the max life expectancy for flexible panels, whereas 20-30 years is expected for ridged glass ones.  

However, not all flexible solar panels are created equal. Many are built with lower quality plastics that do not allow for the flex of the cells. This can cause the metal busbars to break prematurely. It’s not uncommon to hear about flexible panels failing after only a year or two due to thermal stresses. Rigid glass panels are less likely to have this problem. 

Our Flexible vs. Rigid RV Solar Panel Experience

In our travels, we have had both flexible and rigid solar panel systems. The first system we installed was a 1200W rigid glass solar panel set. This was a set of four 300 watt panels weighing 50 lbs apiece.  We later upgraded our system to twelve 230 watt panels weighing 15 lbs apiece. If you do the math, we gained 1500Watts of installed capacity but lost 20lbs on the roof! 

The new panels were adhered down with adhesives as well, removing almost 200 screws that held down the old panels. We also installed the panels in the places where we couldn’t have them before, like on the front curved cap of our fifth-wheel.

Ultimate RV Off-Grid Solar System Build - 2760 Watts of Solar ☀️ 11Kwh Battery, on a 32' Fifth wheel

This all sounds great, right?  Well, there have been a few drawbacks. First, the new flexible panels are mounted directly to the roof, which transmits heat into the RV. The original panels actually shaded the roof and helped keep the RV cooler, where the new panels make it hotter. 

We were also surprised to notice that the rain noise on the roof was louder because the rigid panels had been acting as an umbrella of sorts. 

Flexible Panel Performance Compared to Rigid Panels

As we mentioned earlier, because the panels get so hot, they also perform worse power-wise. It’s not uncommon to see the panels get up to 160F, or 71C, in the summer. 

You can calculate power degradation by looking at the panel’s temperature coefficient. Our flexible solar panels have a  -.42% coefficient, meaning that for every degree Celcius above 25C, the panels lose .42% of their rated capacity. Thus, we can do the following calculation and find our loss:

71C – 25C =46 x -.42% = 19.3% Loss

(19% is the max. We actually calculated a 17% loss most of the summer.) 

So, at the hottest time of the day, we could be seeing a 19% loss. Now, our 2760-watt rated system typically produces around 1700W max in the summer, which is 38% less than its max capacity. A lot of this is how the panels are mounted, but some of that is heat loss.  

Our rigid panels would regularly produce about 1000W max, which is only 23% less than rated. This means that the flexible panels perform 15% worse overall than the original rigid panels, and much of that has to do with the heat loss.

Interestingly, the flexible solar panels still produce around 1400W max in the winter, whereas the rigid system would only produce about 600W.  The chart below shows our panel performance in summer vs winter.

Panel
Section
Summer Peak
Performance*
Winter Peak
Performance**
Difference
Front Panels200W/460W = 43.5%340W/460W = 73.9%+30.4%
Roof Panels1500W/2300W = 65.2%1020W/2300W = 44.3%-20.9%
Total System1700W/2760W = 61.6%1360W/2760W = 49.3%-12.6%
*Sunny July Day in Michigan data; **Sunny December Day in Arizona data

Some of this is due to the lower temperatures in the winter, and some of it is due to the set of panels on the front of our RV. These have a much more aggressive angle that works great for catching the low-angle rays of winter.

Overall the system performance works well for us because the winter capacity loss is not as bad as before, enabling more power in the lower-solar winter months.

Does Couregated Plastic Under the Panel Help?

In our detailed install video we showed how we installed some of the panels on corrugated plastic.

Ultimate RV Solar System Build Details - Turning an electrical Schematic into Reality (PART 2 )

Did the corrugation help? Well yes and no.

We took temperatures of the top surfaces of the panels and found no statistical benefit in the panel temperature meaning the corrugation is not helping us make any more power.

On the other hand we saw about a 5 degree temperature decrease inside the RV from heat being transmitted through the roof. This in my opinion is a significant benefit to adding a small amount of insulation under the panels.

The video below is a quick temp test I did on the hottest black panels on a 90 degree summer day mid day with direct sun.

Which Panel Type Is Right for You?

If we look solely at the cost of the flexible solar panels, it did not stack up with their actual performance. But, we would not have been able to add more weight or install rigid panels where the flexible panels were installed. To max out our system, it had to be lightweight panels. We were able to more than double the solar panel capacity on our roof because of these panels.

We considered the lifecycle of the panels and selected the highest quality panels, which we got from Battle Born Batteries. They are Merlin solar panels that include really cool technology, which should give us the best longevity possible. Find out what makes these solar panels special here.

If you have the weight capacity and are ok with installing firm mounts, rigid panels will perform much better for the cost. Plus, they keep the heat at bay. If however, you have weight or location requirements that require flexible panels, they are a great option. 

The best solution might be a combination of both types. We could have left our rigid installation in place and added flexible panels with minimal weight impact. If you choose to install both types of panels, always use separate charge controllers for each set as their performance characteristics are so different they will perform worse if installed on the same circuit. 

Flexible Solar Panels Are Great For Mobile Applications

Personally, I would never consider flexible panels for a stationary application on a house or building, but they have lots of use in mobile applications. Overall, it really comes down to the needs of each particular installation. But now that you know the advantages and disadvantages of each type and have seen our real-world experience, you can make the best choice possible for your needs.

Need some help understanding how RV solar systems work? Read The Beginner’s Complete Guide to RV Solar Battery Chargers


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Hardy

Wednesday 13th of October 2021

Thanks for a marvelous posting! I definitely enjoyed reading it, you may be a great author.

Chris Probert

Tuesday 17th of August 2021

My RV roof is aluminum, I would imagine the aluminum would dissipate the heat better than most RV roofs. Doing a flexible solar install and have been going back and forth on if I should use the coroplast or not…. Do you think I will see an improvement of the interior temp of the RV given the aluminum roof?

Mortons on the Move

Wednesday 18th of August 2021

Hmm That's a good question, I think your are right the aluminum will dissipate heat much better around the panel, where a fiberglass or rubber roof would not. In another sense, however, it will act as a conductor and could absorb more heat. Im no thermodynamics expert but if you have decent insulation between the roof and interior I would think installing it directly on the metal would help dissipate heat outside better like a heat sink.

Lance Garrett

Monday 11th of January 2021

hey tom, so a question as we are looking at a low to middle size solar setup on our rv. we spend a fair amount of time in rv campgrounds like state parks, small site camping areas and enjoy the less crowded and off grid camping situations but most have only dappled sun during different parts of the day, some more than others. we dont need or think at this point we are high users of power but have faced chasing keeping things charged, running the gen each day for an hour or so has been frustrating. so our use is a bit of tv, some lights, charging our devices, water pump for showers and the daily like things. what can we expect from solar if we are not fully in the sun each day but have some sun through the day??? though question but I haven't found people talking about how this works in some sort of shade during the day. sitting in the open during hot summer days is tough on night sleeping without air, so we try to find some part of the day that is shaded... thanks for your incite as we investigate solar for our needs. for us anything would be better then 2- 12v dry cell batteries which is our current power. we usually plan a power hookup every week to 2 weeks when we are out. thanks

Mortons on the Move

Monday 11th of January 2021

Shading has a very big negative impact on solar performance, but usually, you need most of the sun in the morning so trying to find a spot that allows for morning sun is best. Partial shading can also have a negative effect on panels that are on the same system even if they are in full sun. For this reason its usually advisable to put RV panels in parallel to mitigate this issue, but also install multiple charge controllers for each end of the RV if panels are across the whole roof as partial shading will only affect panels on the same charge controller. Although it requires a little more setup a ground-based Panel system is a great option for allowing you to be in the shade but run a wire out to panels in the sun. We have auxiliary panels that we hook up like this when on our property in the summer, but smaller arrays can be setup for portability. I have it on my list to write a detailed article about how shading affects solar performance :)

John

Wednesday 6th of January 2021

Were you ever able to determine how much extra power you produce when driving into the sun and amount of wore on those front panels compared to those mounted on top of the rig?

Mortons on the Move

Monday 11th of January 2021

Take a look at the chart in the post, those are all facing into the sun. Facing away from the sun the front panels hardly do anything at all. I am sure I have the data facing away from the sun and add it to the post.

Bruce Honig

Monday 4th of January 2021

Tom if you used corrugated plastic under the panels to help dissipate the heat , how much do you think it would improve the efficiency? If the corrugated plastic was mounted on a slight pitch would that dissipate the heat better than if the corrugated plastic was perfectly level?

Mortons on the Move

Tuesday 9th of February 2021

Hey Bruce, We actually tried that and I updated the article to reflect what we did. You will see we saw no panel temp improvement but we did see heat transmission into the rv reduced.

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