I'm thinking of building a country home with a passive solar design. To augment the passive solar I'm thinking of a geothermal heating system. To run the geothermal pump I'm thinking of a pv solar panel that will produce enough electricity in the daylight to compensate for night time usage, (I'm in a state with net metering). I've heard you can put geothermal cooling loops in a pond instead of a trench or well. Since I like the idea of having a pond, would it be more economical to build a pond than dig wells or trenches? When done, in theory, I would have no heating or cooling costs, (I don't like AC, so if the geothermal can cool the house that should be fine). Am I crazy to think this can be done?

If I understand you correctly, you want to produce enough electricity during the day and sell it back to the Power Company to cover the cost of running the geothermal system at night. I don't see why this wouldn't work. but if you wanted to generate enough power during the day, store it and run the geothermal system at night off the grid, then no, it wouldn't work.

As far as building a pond, it would be far cheaper just to dig the trenches than to dig a pond big enough for a geothermal system to run the loop to. People who go this route, have existing ponds they can use, I never heard of anyone building there own pond for the express purpose of using it for a geothermal system. I would think the pond would have to be at least the size of 4 to 6 large swimming pools in size, that's a sizable hole.  
 

Can it be done? Absolutely. How much $ is another question. The pond would have to be at least 6 to 8 feet deep so it doesn't freeze in the winter. The size of the pond required would depend on your heating load. A pond that is too small would basically freeze solid as your extracting heat from it to heat your house.

I believe this can be done. I live in CT and have a 3kw PV system on my house. It went online 3/18/08 and has produced 3.2Mw of power to date. It was estimated to produce about 3.6Mw/year, so I think I'll be ahead of this projection with 3 months to go. I am in the process of installing a 3 1/2 ton 2 stage closed loop Geo system now. My house 1600 sq.ft. cape. I don't have it up and running yet, so I can't say for sure. My PV system is relatively small, 14 - 215w panels. I plan on adding more panels when I determine how much power the Geo is using over the year. You can see pics of my house and PV system at the following link. http://pjcgeo.synthasite.com

When you decide to add more panels look into nano solar , they are manufacturing " high end " grids at 30 cents per watt

Thanks for the info. I'm not looking to store the electricity. With net metering, you spin the meter backwards as long as the PV panels are making more than you are using, then at night the meter spins forward as you run off the power grid. With a big enough PV array you end up not paying for electricity. Though I don't think you get paid if you make more than you use. That would be too good.

That's quite some drilling rig. Are you a professional driller or a "hobbyist"? If you don't drill professionally, is it more cost effective to buy a rig than to hire a driller?

Hobby, It's NOT cost effective to buy a drill. Most are toys and cannot drill rock formations effectively. If you have the land available, a trench loop, I believe is the most cost effective way.

geofan.......do you have a link to that nano tech for .30 watt?

Google " solar cheaper then coal " Its a great article/ad.

from what I understand first orders are now being sent , so no cust/ installer reviews yet but very exciting .

I'm on the Nanosolar mailing list- waiting for when they start shipping to non-commercial customers. They say their cost is about .30 per watt and you should expect to pay about $1w when they get the capacity to handle residential. I'm hoping for next year.

I hate to be a nay sayer, I have been in to solar RE for over 10 years now and nano solar is "just around the corner", has been for at least 5 years now. I do hope they eventually figure it out, but right now the cheapest place I know of for solar panels is Sun Electronics, they have panels you can actually buy for $3.18 / watt (Dec 2008) a watt in large quantities. I have bought from them and never had any issues.

There are so many other variables to consider to obtain good PV panels other than $ per Watt.

Long term degradation / durability, performance at higher ambient temperatures, efficiiency (watts per square foot or meter), physical robustness (think of high wind, snow, hail, etc).

So where does one find data on the durability of PV panels?

HomePower magazine is a great source for PV and alternative energy info. You can buy years of back issues on CD. One clue as to panel durability is manufacturers warranty - If an established manufacturer guarantees 90% of rated output for 20+ years, that is worth considering, even at higher first cost.