Edited by : Graham Morfitt (BSc Physics)
Maybe you’ve seen them. Flexible solar modules without aluminum frames, glued directly onto the roofs of vans & trailers, or boat decks. Ever wonder what they’re all about, and whether they would be appropriate for your application? This article will review the technology, several leading product options, and what to look for when buying.
Why Flexible Solar?
The idea behind semi-flexible and fully flexible solar modules is that without the glass & aluminum frame, these are the lightest solar options available. No frames also means that they can be attached to surfaces without the use of bolts, clamps, or rails. This is something that our van conversion, motorhome, trailer, and boat clients are very keen on. Being flexible also means that they can match the contour of a moulded roof or other surface. Wiring is also provided on the face of the panel header instead of the back of the panel, thereby making the wiring process a lot simpler. Lots of reasons to like this approach!
Crystalline vs Thin Film Cells
The next thing to know about these modules, is that you have two different types of solar cell to choose from. Crystalline (usually monocrystalline), and thin film (CIGS or Amorphous).
The crystalline variety use the same high-efficiency solar cells used in standard rooftop modules. The cells are extremely thin and brittle, so they are laminated between layers of encapsulation, and mounted onto a backing material that is either a type of thermo plastic (Tedlar: TPT or TPE), or fiberglass.
Thin Film Cells…
CIGS or ASi thin film cells use a light-sensitive material that is adhered to a backing material in a process resembling a printing press. The cells are not rigid, and so are not subject to cracking & breaking. This makes them even thinner, lighter, and more flexible than their crystalline cousins.
This is not to say that crystalline cells are much like thin film solar modules. While crystalline cells are more efficient, thin film is more sensitive. So in all practicality, a 100W thin film solar panel will generate more total energy over the course of any day than a 100W crystalline panel.
Because a thin film module is more sensitive, it will reach a usable charging output threshold under lower light conditions than crystalline. This means more energy produced at 25%, 50%, 75% of full sunlight. The rated peak output at 100% full sun might be the same, but more energy will be harvested by thin film cells at all other light levels, resulting in a greater daily total.
Thin film cells are less ‘efficient’, which means that it takes a greater surface area to generate the same power, which means that a thin film solar module will be 25-100% larger (depending on the type of thin film) than a crystalline module with the same power rating.
Choosing the Cell Type for Your Needs
Our recommendation is usually based on the following considerations…
1. 3-Season/Summer-Only/Lower Latitudes : Crystalline
During the months of greatest solar radiation, you might as well harvest using the most efficient cells type, and maximize your energy. This is especially true if you have limited space available for mounting solar modules.
2. Off-Season/Winter/High Latitudes/Shade : Thin Film
Not going to see a lot of intense sunlight where you are headed? Shade? Morning fog? Cloud? Low sun angle? Then you need a module that will give you the best chance of collecting some minimal amount of energy.
3. Portability : Thin Film
Although the semi-flexible crystalline panels are lightweight, they are not foldable, rollable, or very easily shipped. They need to be protected during transport. By contrast, most thin film flexible modules can be folded like tarps, or rolled into tubes for easy transport or storage.
4. Critical Equipment : Thin Film
Needing to keep communication or research equipment charged? Vaccine fridges? Using a CPAP machine? Then you’d better go with a thin film solution that will provide the most consistent base level performance over the widest range of light conditions.
Not All Modules Are Created Equal
Just because you found a great deal on a semi-flexible crystalline solar module, doesn’t mean that it is like every other semi-flexible solar module. There are important differences, and most of them will determine if you enjoy long years of charging bliss, or rapid failure.
First & foremost is the type of cells used. The best modules use SunPower cells, with back-of-cell bus wire connections for improved durability & performance. Front-of-cell wiring, combined with standard cells, have been known to fail through electrical shorts & burns. Not what you want when you are hundreds of miles from utility power. Also be sure of the encapsulation process used. ETFE is the top material for the top sheet, providing UV stability and durability against de-lamination.