Eric, I'm assuming AC means Air Conditioning.
In areas where freezing or snow occurs, a few loops under the driveway to bring the Earth's latent heat up to melt the snow would also be welcome.
I wonder if anyone has tried to put together a low-grade energy generation system utilizing a solar collector for the heat, and a geothermal loop for the cooling? While it would be somewhat weather dependent, the investment costs seem affordable enough to make it worth while for a small plant. Some heat and cooling would be secondary benefits of such a system.
Or to look at it another way, keeping your house cool in the Summertime, and your driveway free of snow and ice in the Wintertime, would be the primary benefits, and a steady stream of low-wattage energy for lights and the refrigerator would be secondary benefits.
We do get snow in mid-Missouri and you're correct. The snow melts on the cement driveway, courtesy of this system. Check it out at www.waterfurnace.com.
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...