@georgesplane- I would tell you to examine your energy use. The use of geothermal energy in a geo-exchange system will be used to heat or cool some fluid to increase efficiency in your HVAC system. You will improve heating efficiency by up to 70% and increase your cooling efficiency by up to 50%, and you will also reduce your maintenance costs. Of course, the amount of increase in efficiency and reduction of costs depends on how efficient your current HVAC system is.
Installing a PV and solar water heating system will reduce the total amount of energy use, and significantly reduce your energy consumption for water heating. The efficiency of your solar system however, ultimately depends on how much sunshine you get and the amount of money you are willing to spend. I would recommend that you get an energy audit and discuss these options with your auditor. That person will be able to help you make an informed decision specific to your circumstances.