A few years ago, flexible solar panels became popular with RV owners as they represented a innovative solution for smaller RV’s, where weight reduction played an important role. Less weight meant more panels and more power to stay off-grid longer.
With a weight difference of about 20 lbs per panel, easy installation without holes in the roof, conformation with the curvature of vehicle roofs, it is easy to understand the potential for these panels among boondockers and alike.
Their popularity rose when several videos showed them improperly used by bending the panels at extreme angles, both inward as outward or by sitting or walking on them. It made for good watching, but in the end was bad for business. The extreme bending led to broken contacts and premature failing of these panels. The walking and sitting led to scratches and reduced power.
Be that as may be, this first generation of Flexibles had other unresolved issues too. Whereas rigid panels are usually installed with an airspace between them and the surface of the roof of the vehicle, flexible panels often are installed directly onto the roof, reducing the ability to dissipate excess heat and leading to an efficiency reduction of around 10%. While this issue has been addressed somewhat with some of the newer panels by using an aluminum background panel, it is much easier to compensate by applying more panels.
The major issue resulting in many complaints was the use of PET (Polyethylene Terephthalate) as a protective layer for the panels. It’s reflective properties reduce the panel’s output. More seriously, the likely incorrect application of this Thermoplastic foil, resulted in separation of the material along the edges of the panels, lessening it’s efficiency and damaging the solar panels.
The new generation Flexibles use the expensive ETFE (Ethylene Tetrafluoroethylene); this material can absorb sunlight, but not reflect light. While the new generation of Flexibles will allow for some misuse, it is highly recommended to use it as a solar panel and not a grown-up toy.
What is reality in 2017?
Creating a slight curve, that conforms to the roof of your vehicle, is a major advantage of flexible panels.
- Only bend backwards.
- Only bend if necessary.
- Bend up to 20%, much less if possible.
- DO NOT walk on the panels.
PET vs PVDF vs ETFE protective foils
- PVDF is a new and untested material in the fabrication of flexible solar panels. It seems to have a price point and efficiency that lies between PET and ETFE.
- Choose ETFE.
- DO NOT use PET foils.
- The most popular cells have silver contact lines strewn across its surface.
- With the new ‘Backcontact’ Sunpower cells, these silver pathways are moved to the back of the cell, increasing exposure to sunlight and thus maximizing efficiency of up to 23%. Choose these if available.
- Most flexible panels are produced with a white PCB (fiberglass) background.
- Choose a black PCB (fiberglass) background for stealth on dark colored vehicles.
- Choose an aluminum background for improved heat dissipation along its surface.
- Most panels on the market are 100W.
- Some are 135W or 150W, and optimized to make a better fit on the roof, thus maximizing capacity.
- Some companies will build custom sizes on request.
- The standard procedure has always been to use bolts & nuts AND holes, to attach solar panels to the roof.
- If the roof surface allows for it, a better way might be to use a 3M VHB tape. Besides an incredible adhesion, it also avoids the otherwise necessary holes, which can result in unwanted leaks.
- Most rigid panels have a 25-year warranty that specifies an efficiency of 90% for the first 5/10yr and 80% up to 25 years.
- Only few flexible panels have a similar warranty. Most of these panels haven’t been long enough on the market and are untested at 25 years.
- Most PET produced panels may only last a couple of years.
- Rigid panels can be had for as low as $0.50/watt.
- The first generation of flexible solar panels (PET) are approx. $1.50/watt.
- The newest generation (ETFE) cost approx. $3.00/watt.
How efficient are your solar cells?
With 3.7 watt and 5” x 5” inch, the Sunpower solar cells probably have the highest efficiency in the world and many companies in China, eBay or in on-line stores, offer Sunpower cells at super low prices, resulting in a consumer focus on low prices and the ultimate stride to find the cheapest panel.
Reality is that many suppliers are selling low quality or flawed Sunpower cells that are a byproduct from the regular production process.
A-grade Sunpower cells at 3.7 watt are never on sale because of their high cost. Currently the most popular Sunpower cell is Bin Q grade at approx. 3.2 watt and while it can have many kinds of flaws, it can be used to produce flexible solar panels and other solar products.
The lowest level of Sunpower cells are X, R level with under 2.8 watt; their lifespan likely won’t be much longer than 2 years.