October 9, 2023
To Roll or not to Roll; that is the question for a solar awning!
RV’ers need ever increasing amounts of energy to power all of their electrical appliances, particularly when going off-grid or boondocking. RV Solar systems offer a great way to generate clean and quiet power during off-grid camping adventures. However, there’s limited space on the roof for adequate solar power generation. That’s where solar awnings come in! A retractable and stowable RV solar awning is an ideal solution to add solar beyond what’s possible on the roof of an RV.
One seemingly simple solution is to just replace the fabric in a traditional awning with a flexible sheet of solar panels that rolls onto the roller bar of the traditional awning. The flexible solar panels in such an awning could be fabricated using either thin film solar ‘cells’ which are a layer only a few microns thick that’s deposited on a thin metal foil; or by using traditional brittle solar cells that are cut into small sizes.
At first glance, a rolled awning seems like a simple no-brainer solution, regardless of the type of solar cells used to make the solar panels, but digging in a bit deeper uncovers some inherent issues with a rollable design.
The first fundamental issue is that solar cells, when rolled up into a tight small roll diameter are prone to cracking due to the mechanical stresses on the cells from repeated rolling and unrolling. In the case of traditional cut solar cells, one can try to mitigate this problem by cutting the cells much smaller and stringing them together so that they conform more easily to the roller bar.
However, such an approach does not eliminate cracking altogether and leads to another problem, namely, there are now thousands of little cells which need to be electrically joined together. These electrical interconnections, typically soldered joints, experience tremendous mechanical fatigue from constant rolling and unrolling of the awning (and from constant movements due to wind) resulting in debonding and loss of performance over time.
A bigger issue is safety. A rollable solar awning uses flexible polymeric materials to protect the front and back of the solar cells instead of the high strength tempered glass that’s used in the traditional solar systems. These polymer materials are very prone to cuts and tears from both from constant rolling and unrolling and also from accidents like from falling pinecones, for example. Once a tear develops, unbeknownst to the user it opens an electrically conductive path to the solar cell underneath posing a major safety concern, and can become particularly dangerous when water starts to pool on the fabric during rain.
Polymers, when left rolled up for extended periods of time, have memory and stay rolled up and resist unrolling into a completely flat sheet. The act of extending the awning after an extended period, particularly after a cold winter, causes mechanical stress which causes damage to the polymer sheet and the solar cell.
Lastly, an unrolled solar awning has one big drawback similar to that of a regular fabric awning i.e., it is not wind tolerant. It easily flaps around as it catches wind and acts as a sail. This can cause significant damage to the solar cells on the awning and to the soldered ribbon connections between the cells.
In summary, a rolled solar awning may look like a simple and obvious solution, but a closer look reveals multiple issues that impact its performance, reliability, and more importantly its safety.