It quickly became clear to me that reviewing a solar panel is more involved than reviewing a toaster! I have a "decent" basic knowledge of electricity, but I must say I've learned a LOT more since purchasing my four 175 watt (@ 20 volts, 9 amps each) Renogy Solar Panels for my Promaster Van. 1) Order "Must Have" Items to attach to van/RV roof without drilling holes and allow future removal : Eternabond 3"×50" 1 roll - use sparingly. Velcro,15' x 2" Industrial Self Sticking, 1 box per panel. See pictures. OK, You will probably need to drill ONE necessary hole to bring the final two cables to the inside- also get an entry gland for that. The Velcro should be attached in strips on the raised roof ridges. Renogy says an insulated layer is unnecessary. After 3 months of searing heat, and some rain, all four panels are still secure. 2) Purchase the max wattage, and max # of Panels that will fit up on your van/RV roof. Get the BEST and as MANY Solar Panels (and MC4 connectors, cable, and Y branch adapter) you can afford- you don't want to regret your buying decision on every future road trip, especially after all your work installing these panels. A good crimper like the WISS Solar PV Cable Crimping Tool will help a lot. Incidentally, Renogy has EXCELLENT Customer Support. Contact them with ANY questions. 3) Install an EVEN NUMBER of panels, so you can connect your setup in a "series and parallel combination"(Google that to view examples). Per Renogy, they should all be of equal size/power. 4) With 4 175 watt panels, I put 1 pair in series, I put the other pair also in series, then I put these two sets of pairs in parallel, so I now had a series parallel COMBINATION that yields 40 volts @ 700 watts, but only 17 amps, going to the Yeti or charge controller. Always Remember, WAV: Watts=Amps x Volts. (My 3000X Yeti will allow a max of 50 volts and about 1000 watts of charge). If you put ALL 4 of your 175 watt panels in parallel, you'll have an output of only 20 volts and 37 amps, and your panels won't start to charge your batteries until direct sunlight hits them. The high amperage will also cause your cables to get very hot. If you use the series AND parallel combination, you'll get 40 volts and only 17 amps, which means you can use smaller wiring (10 gauge) that won't overheat. You will also see charging as soon as daylight starts until dusk. You'll achieve the SAME charge rate of rated watts either way! Speaking of advertised panel wattage claims, you'll find that the time of year, where you are parked, air quality (smog/haze), and of course, time of day, WILL AFFECT the rate of charge. Don't panic if you don't get the listed wattage, it's a fact of life! Realistically, expect about 80% of the listed watts rating, on average. It definitely helps to keep them clean. Hose off and squeegee them after it rains. The dust does not disappear after rainstorms, but instead makes a muddy layer up there. Do not get hung up on "positive" and "negative" ends when you build your 'array' of panels, just have your multimeter with you the whole time and make sure you correctly identify the positive and negative final ends that are connected to the batteries. 5) If your Van/RV has 6 or 8 little T posts on the roof, you'll get a LOT of peace of mind attaching each panel to the posts. Use some 1/16" wire rope cables to connect to a grommet anywhere on the panels parameters that you can. After driving around with these 4 Renogy Flexible Solar Panels on my Promaster for 2 months +, I am very happy overall. Their super thin, light design makes them ideal for zero wind drag, and they are absolutely INVISIBLE from ground level. They are a solidly built and well performing panel, and I am glad I made the investment to get the best Solar Panels available.