I've been watching solar
technology for quite a few years now, and had bought only mono panels when I added solar to our Scamp
5th wheel and made a portable, folding 40w setup from two 20w panels. Recently, however, I ordered a 100w poly panel for our Surfside
project trailer. It arrived last week, and I set about the process of testing it and comparing it to our 40w mono panel.
It used to be that poly panels had a faster, steeper fall-off for energy production as the sun came in at steeper angles than mono panels did. I found that wasn't the case with the new acid-etching and coating process they use on poly cells. The poly cells actually outperformed my mono panel at steeper angles of the sun, though not by much.
Where mono panels still rule the roost is in their thermal performance. Solar panel
performance is at its optimum when the panels are at or around room temperature. When they get cooler, their performance degrades somewhat, and when they get warmer, their performance degrades somewhat, right until they hit about 113F/45C degrees. At 45C, their power output falls by about 10%, but starts to fall
rapidly, by about 4% per degree Celsius/1.8 degrees Farenheit for poly panels and about 3.8% per degree C for mono. Solar panels get hot in the sun; if you're flat-mounting your panel on the roof, that can make a big difference on a sunny day.
Power output on our new 100w poly panel fell from 100w to 28w when I put it out in the sun on a 95F/35C day tucked neatly into its cardboard packing box so air couldn't move underneath. The panel was so hot when I took it back inside that I needed gloves to handle it, and gave myself a minor burn where it came into contact with the skin of my forearm for several seconds as I moved it inside.
You can compensate for the heat problem to some extent by providing an air gap under your panel so air can circulate freely and cool it from underneath. Better yet, use the contours of your trailer to help move the air around, ramping your solar panel
at an angle and creating a somewhat larger gap toward the top/centerline of your trailer so the hot air will naturally rise and expand up as it follows the line of your trailer shell.
One of my failings when I installed my mono panels on the roof of our Scamp
was I didn't provide for adequate air circulation under the panels to help keep them cool. This time I plan to make sure there's a 1"+/25mm+ gap at the top edge of my panel, and I'll tilt the panel with the natural curvature of the trailer so hot air is encouraged to escape