So you’ve decided to go with flexible solar panels. Which type of flexible solar panel should you choose – thin film or crystalline silicon? What are their pros and cons?
Which of these two should you select for a stationary and flat roof, a curved roof on a mobile home, or even for camping? What characteristics should you look out for when it comes to flexible solar panels? How do you decipher the technical terms used in product descriptions?
This article addresses these issues and provides short answers to a few commonly asked questions.
What are flexible solar panels?
As the name suggests, flexible solar panels are not rigid but can be curved to a certain degree. However, if the panels are bent too much, the internal cells and electrical structure within the photovoltaic (pv) panel will be damaged.
Different flexible solar panel brands have different limits as to how much the pv panel can be bent. This will be indicated by the manufacturer.
The photovoltaic materials used in solar panels are varied. Depending on the type, the pv material can be monocrystalline or polycrystalline silicon, cadmium telluride, or copper indium gallium selenide.
However, recent research at the Massachusetts Institute of Technology has paved the way for advances in organic solar cells. Instead of using silicon as the basis for solar cells, researchers have found a way to use graphene. This development may someday lead to thinner, more flexible, and more stable solar panels than what the solar industry currently produces.
Flexible solar panels vs rigid
A rigid, standard solar panel consists of many solar cells connected by a system of thin electrical wires. The silicon layer in a rigid panel is typically up to 200 micrometers thick, which is just slightly thicker than human hair. The pv cells are then wrapped in a layer of glass.
With flexible solar panels, the pv cells are encapsulated in plastic instead. The photovoltaic material inside is much thinner, down to just a few micrometers. It is these features that give flexible solar panels their flexibility.
Similar to rigid panels, flexible solar panels also have thin electrical wires. The wires connecting the solar cells to a connection point at one end of the panel usually have MC4 connectors.
Types of flexible solar panels
There are two types of flexible solar panels – thin film and crystalline silicon. Each of them is suitable for different applications due to their slightly different natures.
Knowing the characteristics as well as pros and cons of both types will help you decide the best one for your needs.
1. Crystalline silicon solar panel
The pv material in this type of flexible solar panel is either monocrystalline or polycrystalline silicon. With this type of flexible solar panels, the pv material is cut thinner than that of the standard solar panel.
This makes the solar panel fairly flexible while retaining the photovoltaic properties of crystalline silicon. At the most, the solar cells of this type of flexible solar panel can only bend about 30 degrees.
- portable solar systems
- curved surfaces such as on the roof of an RV or a boat
- roofs of structures that cannot take the weight of standard rigid solar panels
Advantages of flexible crystalline silicon solar panels
Flexible panels made from monocrystalline silicon, in particular, have a high efficiency when it comes to solar power conversion. As such, this type is as efficient as its rigid version.
In terms of durability, this type of solar panel also scores higher points than thin-film. This makes it the more favoured option for mobile homes such as RVs, tiny homes and boats.
As it is thinner and wrapped in plastic instead of glass, it is many times lighter than the standard one. It does not need heavy-duty roof mounting systems. Instead, it can be mounted with adhesives or rope only. This makes installation much easier, thus costing less for labour.
Disadvantages of flexible crystalline silicon solar panels
This type is less durable than a standard solar panel over the long-term because it does not enjoy the protection of a thick layer of glass and a rigid aluminium frame like that of standard pv panels.
Crystalline silicon is rigid in nature. That is why, when these solar cells are attached to flexible sheets, it is easy to subject them to more stress over their lifetime. Eventually, the wiring can fail or the solar cells can crack.
For these reasons, flexible solar panels have shorter warranties. Instead of a 25-year warranty, some products may get as short as a 2-year material warranty and a 5-year power warranty.
The flexible design also means these solar panels cannot be easily mounted in a suspended fashion, as they need a solid surface to support them. Since they are not mounted on a bracket above the solid surface, there is no airflow between the panel and surface.
This causes heat to transfer directly from the panel to the surface, warming up the interior of the house or RV. Solar cells generally don’t perform well when they are too hot. Therefore, the heat build-up results in an additional capacity loss.
2. Thin-film solar panel
The photovoltaic materials used to make thin solar panels are different from crystalline silicon solar panels. Examples of a thin-film solar panel are cadmium telluride and copper indium gallium selenide.
Thin-film solar panel is so thin because the photovoltaic material is printed onto a plastic surface, instead of being sandwiched between a top and bottom protective layer like other types of solar panels.
The photovoltaic layer in a thin-film can be over 300 times smaller than that of a standard silicon solar panel. It is also thinner than the crystalline silicon solar panel.
This makes the thin-film the most flexible among all solar panels. Some can even be rolled up like a yoga mat. Thin-film can be placed on many different materials including glass, metal, and even fabrics.
- small solar panels
- rooftop installations
- solar kits for camping
- portable solar systems
- solar panels on backpacks
- solar-integrated structures or products such as solar tents
Advantages of thin-film solar panels
As thin-film is not made from the more brittle crystalline silicon, it is less likely to be damaged by bending. This makes it ideal for small solar projects, where it may experience physical wear and tear that would not occur on a stationary roof.
Its durability combined with the reduced weight also makes it ideal for smaller mobile solar projects that don’t need large amounts of energy. In addition to that, its malleability makes it a good candidate for a wide variety of applications where there is no solid surface. For instance, solar backpacks and solar tents.
Disadvantages of thin-film solar panels
Cost-wise it is more expensive than the crystalline silicon one and doubles that of a conventional rigid solar panel. This is because it is a relatively newer solar product than the other two.
Aside from its price, the thin-film is less efficient than crystalline silicon and the pv materials used are toxic. Consequently, thin-film is not very widely used.
The efficiency ratings for thin-film solar panels is also lower than average monocrystalline or polycrystalline panels. Crystalline silicon cells have between 16 and 20 per cent efficiency ratings while thin-film offers between 7 and 15 per cent. This means you would need more thin film panels and more space to produce the same amount of solar power.
The life expectancy of thin-film is also lower than that of standard rigid solar panels. One of the reasons for this is the plastic layers. The polymer surface has the potential to degrade and cloud up faster than glass.
Features of flexible solar panels to look out for when you buy
1. Solar panel wattage
The power output advertised for the panel usually does not reflect actual performance. The figure is based on ideal conditions during laboratory testing to get the Standard Test Conditions (STC) rating of a solar panel (in watts). The ideal conditions in the test are rarely encountered in the real world.
Instead, you should look for more realistic test ratings such as the CEC, PTC, or NOTC test standards. These ratings are always provided with solar panels for residential or commercial use. However, cheaper flexible solar panels don’t always come with such detailed specifications.
In such situations, you can assume that the flexible solar panel will produce only about 75% of the advertised STC rate in ideal conditions. This means cool weather, bright sun, and an orientation perpendicular to the sun.
2. Nominal, operating, and open circuit voltage
Most flexible solar panels in the market are fashioned for portable applications such as RVs and camping. The products of these industries are designed around 12 volt DC devices.
Consequently, flexible solar panels are typically advertised as either 12 volt or 18 volt panels. However, this is not the actual voltage that is produced. You might see these terms to describe their capacity:
- Nominal voltage refers to the advertised voltage. Most of the time the solar panel will be listed as 12v or 18v.
- Operating voltage is the maximum voltage output of the panel in bright sun. The typical rating for this category is between 15 and 22 volts.
- Open circuit voltage is the maximum potential voltage of the panel. This rating can be ignored for the most part.
What you should note is that if you want to charge a 12v battery, you need a panel with a higher voltage, say around 18v. If you don’t have 18v panels, you can wire multiple lower voltage panels together to gain enough operating voltage.
3. MC4 connectors and cables
MC4 connectors are found at both ends of a wiring cable. They are a standard for wiring cables between flexible solar panels because it allows for a waterproof connection that clicks easily into place. Each pair of MC4 connectors is linked to a junction box at the solar panel.
Cables for connecting the panel to your battery or device may either have MC4 connectors at both ends or a different type of connector at one end, such as a round DC plug. Check whether your purchase comes with these cables.
4. Strength ratings
Strength rating refers to how much pressure a solar panel can withstand on the front (snow load) and rear (wind load). This is relevant for panels that will be installed on rooftops or exposed to the elements. The rating is usually 5,400Pa/2,400Pa, but not all flexible panels have one.
The part to look out for when it comes to rain or salt spray is the junction box. Look for a waterproof rating for this. Typical ratings are between IP65 and IP68. A higher number is more waterproof.
6. Type of material for the pv skin
Flexible (crystalline silicon) solar panels are constructed by sandwiching solar cells between pv skins made from plastic. Cheaper panels use a polymer called polyethylene terephthalate (PET) while pricier ones will use ETFE (ethylene tetrafluoroethylene).
ETFE has slightly better light transmittance compared to PET. ETFE is also more durable, which is an important attribute to consider if the panel has to be constantly exposed to the elements.
Commonly asked questions about flexible solar panels
1. Which flexible solar panels should you get for RVs and campervans?
Both types of flexible solar panels can be used. However, the crystalline silicon type has a higher efficiency rate than thin-film panels.
2. Are flexible solar panels any good?
Yes, they are for applications where their lightweight and flexibility are an advantage over traditional rigid solar panels.
3. Do flexible solar panels last?
Yes, but nowhere near as long as rigid panels. Factors such as type of solar panel, nature of use, brand and model play a role in determining how long they can last. Generally, the lifespan of flexible solar panels is less than half of rigid ones.
4. What is the highest watt flexible solar panel?
Most of the products in the market start with 100 watts. The highest so far is 300 watts by Portamax Power.
5. How do you clean flexible solar panels?
Those that come with a polymer top coating are mostly self-cleaning, as the rain will wash away any dust and debris. To remove bird droppings, rinse it with fresh water.
For more persistent dirt or grease, use neutral soap and water with a non-abrasive sponge or cloth. The dirt build-up in corners can be removed with a gentle brush, but do not use a pressure washer at any point.
6. How to mount flexible solar panels
They are normally mounted using adhesives. Some DIYers have also managed to use rope instead.
Whether it is thin-film or crystalline silicon, the type of flexible solar panel you choose should fit the purpose and nature of use. Crystalline silicon is better for tiny homes, including RVs and marine applications, where higher solar output is needed. Thin film is great for camping due to its incredibly lightweight and flexibility.
However, this doesn’t mean you have to stick to only flexible solar panels. Many who live off the grid have successfully used a combination of both rigid and flexible solar panels to cater to their needs. To do this, you should install separate charge controllers.