First house I had the solar installed a few years after the house and pool were built. Current house we bought used and I did the solar install myself with some used panels I found on Craigslist.
There is no way they will raise the water from 50 into the 80s. They are good for slightly extending the season in the spring and fall and boosting the temp some in the summer if needed. In the summer mine are not used at all as the water is already warm enough. If you add a cover to the pool, that will help a good bit to maintain the heat. In April (I think) I was getting about a 5 degree temperature rise throughout the day, but was losing about the same overnight with no cover.
Solar will not allow you to just quickly heat up the pool in the winter. I am about to shut off mine as the water is not really warm enough anymore that anyone wants to swim, so why waste the electricity running the pump on high for the solar?
If that is something you want to do ... then you will need to get a bigger propane tank. There are some members here that use propane, but I am not sure how much gas is used.