Re: Roll-up solar panels
There are basically 2 types of panel construction for solar panels out there (warning, this information may be a little dated in a rapidly changing market).
Crystalline panels are by FAR the most common. They are divided up into cells, which are usually square and visible. Each cell provides a set voltage. The total number of cells, with sunlight applied, provide the charging current and sufficient voltage to "push" electrons into your batteries.
The problem arises when you shade a cell. Now, you've got enough current for lots of charge, but suddenly you don't have enough voltage to "push" that current into your battery. No charging happens now.
Manufacturers get around this by putting more than the required number of cells into a panel in order to allow for partial shading. If the voltage is too high, it can always be down-regulated. Still, shade enough panels and you get zilch current.
The other type of panel is the thin film panel. These are the ones that have been around for a long time and you have likely seen them in solar powered calculators (remember those?). These panels are MUCH more shade tolerant and will always produce the correct voltage so long as there is some light. They will just produce less and less current as the amount of light decreases.
Solar calculators with their thin film panels work indoors with ambient light remember? They have excellent shade tolerance. Thin film panels are also CHEAPER to manufacture per watt (once again this info may be dated). The reason they're not as popular as crystiline is that they're less efficient in the WATT/SQUARE FOOT measurement. i.e. it takes a bigger (but less expensive) panel to create the same number of watts.
I did some experiments with my Unisolar thin film flexible panel a few years ago. I measured the voltage (19.something volts) with a voltmeter and slowly turned the panel upside down. With only a corner of the panel turned slightly off the deck it would read 19V. I couldn't measure amps and it would have been 0.0001amps I'm sure, but it proved how shade tolerant they are. For me, living in the PNW shade tolerance was key.
I really like the thin film panels myself. On top of the bimini is a great spot for them and on a sailboat, everything gets partially shaded, and they're cheaper. But if maximum power in the smallest space is your goal and you don't mind rigid panels, then crystalline is the way to go.
PS I like the look of that 97W panel!
PPS There was a European company a couple years back that was marketing a stick-on thin-film panel that would be mounted on the topsides of the hull of a sailboat. It was about 6" wide and looked quite decorative (think racing stripe) and used the reflected sun from the water for power. Remember, thin-film can use any available light.
I have a sauna on my boat, therefore I win.
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Last edited by MedSailor; 04-24-2012 at 03:01 PM.