ok so remember when I was telling you aout the eveloution of residential panels, one thing I do not recomend is buying used panels especialy with the wires cut, but thats nto a big deal if you have the right kind of crimper and MC4 ends, it will just limit the length of the cables if you ever have to undo them you might have to remove the panel.
but I will tell you why I don't like used panels. the first reason is how old are they? they don't say. Why were they being replaced, were they not preforming properly? what are the physical dimentions, can you fit them where you want to? what technology are they?
now having said that, the add actualy lists the info I would want, except the age. the 235 watters would be a hard no for me because the pigtails are to short and they would never be serviceable after an instalation, the 310's if you can fit them would be ok. still older technology but that usaly just means not as good shade preformance, not as efficient which translates to larger for the same wattage. I just did three 200 watt 24V panels on my rv as I couldnt fit anything larger and they had to be the new N type panels to get the size that small for the wattage.
are you picking them up? highly recomended, but things to look for , scuff/scratches on the front face, bent frames, and have them do a open circuit voltage and an open circut amprae test and make sure it is with in 5% of the numbers listed on the back sticker.
now I would recomend you go up on the rv roof and do some measuring and at that price buy as many as you can fit up there. if you can get 4 great, if you can only get three thats good, if only two that will be good also. from my 600 watts (three panels ran in series) I was getting 8 amps of charging at 8:30am last weekend and 34 amps at 10:30am. the battery was full so I shortly after that so I still have of yet to see how many amps Iget during the best hours of the day, but it should be over 40. so two panels in series will alomost give you that preformance, little less early because the total voltage will be lower. the benifit you would have if you decide to spend a tiny bit more and get what I now think is the best solar charge controler for a rv, victron with two you can get a 100/50 the first number is the total voltage in your string, the second is the output to the battery. if you go parralel you sacrafice early morning charging with the even lower voltage, but you gain a bit of shade preformance.
