You could consider a ground source heat pump system. The uses pipes/rods that are buried in the ground either horizontally or if space is an issue vertically (the latter costing more). They draw the natural heat from the grounds and feed an underfloor heating system in the house, in the summer, this can be reversed to draw heat from the house back into the ground outside. They can also be used to heat the pool. Expensive to install and you need to get a proper company to do the work, and then there is the issue of lifting the tiles in the house to lay the underfloor.
Alternatively, you could consider an air source heat pump to draw the warm air in to heat the pool. I wouldn't bother with solar to heat the pool, as i don't believe the technology is there yet to do so effectively at a cost effective price.
also consider the CoE (co-effeciency of energy) - this means that although ground source heat/cooling systems are effectively free to use, you still need to pump the heat/cool which requires some electricity. The CoE compares how much benefit you get for the outlay. For example if it costs € 50 to pump the heat to warm the pool as opposed to € 200 to use electric say, then the CoE of the heat pump is is 4:1. It's a really easy to understand example of what the true costs still are and you can combine this along with the installation to determine just how cost effective each option is.
Regards, Carl