For solar charging of the “house” batteries, we decided to use the 110w flexible panels from SunPower.
We like the technical specs of the Sunpower panels and their advanced cell design. We figure the brand-name panel should hold up a little better under adverse conditions, plus there is a hint that the SunPower panels have some better partial shade performance.
Rack or flat install
There is the argument of using a lower performance panel and putting more panel area up there. Perhaps valid, but not my style. I have seen many van solar installs that use the lower-cost, perhaps-higher-efficiency rigid panels, but then they have to build some kind of bulky rigid frame to hold the rigid panels. That seemed like a lot of work. Plus I just can’t bring myself to build a rack to hold rigid panels, only to have it ruin what minimal aerodynamics the Promaster has.
Temperature and efficiency
I had read a few threads where there was concern presented about the panel temperature–and the argument is put forward that the rack allows air to flow around the panel and keep them cool. The way I see it when the temperature is highest (reducing efficiency slightly), that is when you have the most sun and are least worried about efficiency. When there is good airflow, you are driving and the batteries are being charged by the Promaster’s alternator, so again, you would not be as worried if the solar panels are cranking at their maximum efficiency. As with all aspects of this build, we shall see how the assumptions work out.
Panel installation step-by-step
We used some 3/4″ wide 3M VHB 4910 tape that we had some excess stock of at work. You can get the same product here.
Here is a detail of how we placed the tape for the panels. We figured that more of the aerodynamic pressure would be concentrated on the leading edge of the panel, so we used three passes of the tape on the front few inches, then two passes of tape for the full length of the rib:
We used Windex and a clean rag to make sure the back of the panels and the top of the van roof was clean for a good bond.
On the edges of the panel, we put the tape on the panel, to make sure the edge of the tape was nicely lined up with the edge of the panel:
You definitely need to have some care, and some extra hands are nice when you place the panel on the adhesive. It is possible to reposition the panel if you just barely touch it, but since the panel is flexible, if you lift the edge, the panel flexes and presses the tape down in the middle, so it is really touchy. Using some masking tape would be a good idea to make it easier to see when the panel is positioned perfectly.
The second panel goes on much the same. There is a gap in the ribs in that section–the panel seems to be rigid enough to span the gap.
We used some feed sacks to weigh the panels down overnight to make sure the VHB made good contact.
Here is a picture of three panels in the array. We held off on installing the 4th panel since we were not exactly sure of the placement of the front fan: