I think a solar collector for the heat, while nice, is a bit of a waste if you have a geothermal system to begin with.
In the summer you get A/C dirt cheap and you get free hot water (using waste heat off the system). In the winter your heat is dirt cheap but you may not get enough hot water free - only then and when the A/C or heat isn't on would a solar collector provide much use...
Whatever your source of energy for the hot water, a solar heat collector will save energy by acting as a pre-heater for the water, especially in the Wintertime.
The additional cost is marginal, and the collector can house and protect the pumps of the system.
In fact, on mild cool days, distributing the aolar heat collected could mean that compressors may not even need to run.