IIRC, a program called PV Watts is useful for determining the PV potential of your house. You need to crunch numbers for this kind of decision. The DOE has some worksheets for this. Where is solar thermal, BTW? Your answer might be "neither".

If you are building an Energy Star Home, your energy rater should be able to help you do the math.

Followed you're advice contacted DOE and here is their reply which is a lot of info but I will sift thru it all:

Thank you for contacting the EERE Information Center. I understand you are seeking information on the efficiency of solar photovoltaic systems versus geothermal systems. Additionally, you want to verify that your home site is suitable for solar energy.

The following resources provide energy calculators that may help you evaluate the efficiency of a particular system. You may need to use different calculators to compare the results in order to decide which is the best system for your circumstances:

U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy (EERE)
Energy Calculators & Software
Renewable Energy Systems
This website provides tools to help you evaluate your options for generating your own electricity with a small renewable energy system. System technologies include microhydropower, small solar electric, and small wind electric.
http://www.eere.energy.gov/calculators/renewable_energy_systems.html

National Renewable Energy Laboratory (NREL)
In My Backyard
The In My Backyard (IMBY) tool estimates the electricity you can produce with a solar photovoltaic (PV) array or wind turbine at your home or business.
http://www.nrel.gov/eis/imby/

National Renewable Energy Laboratory (NREL)
PVWatts
NREL's PVWattsTM calculator determines the energy production and cost savings of grid connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, installers, manufacturers, and researchers to easily develop estimates of the performance of hypothetical PV installations.
http://www.nrel.gov/rredc/pvwatts/

U.S. Energy Information Administration (EIA)
Heating Fuel Comparison Calculator
This calculator can be used to compare residential heating fuel prices and costs. It factors in the relative price based on the fuel heat content and the heating appliance�s efficiency. Geothermal heat pump is one of the options for heating appliance type.
http://www.eia.doe.gov/neic/experts/heatcalc.xls

Western Area Power Authority (WAPA)
Energy Experts
Heating System Cost Calculator
This calculator also incudes ground source (geothermal) heat pump as a heating option.
http://www.energyexperts.org/CalculatorsTools/HeatingCostCalculator.aspx

The following resources provide general information on small solar electric systems and geothermal heat pumps and may also be of interest to you with regard to this request:

SOLAR

U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy (EERE)
Energy Savers
Small Solar Electric Systems
http://www.energysavers.gov/your_home/electricity/index.cfm/mytopic=10710

U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy (EERE)
Solar Energy Technologies Program
Own Your Power!
A Consumer Guide to Solar Electricity for the Home
http://www.eere.energy.gov/solar/pdfs/43844.pdf

U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy (EERE)
Solar Energy Technologies Program
Related Links on Solar Electricity for Homes
http://www.eere.energy.gov/solar/solar_electricity_homes.html

National Renewable Energy Laboratory (NREL)
A Consumer's Guide: Get Your Power from the Sun
This booklet provides basic information on photovoltaic systems.
http://www.nrel.gov/docs/fy04osti/35297.pdf

American Solar Energy Society
Go Solar: How to get started with solar energy
http://www.ases.org/index.php?option=com_content&view=article&id=162&Itemid=7

GEOTHERMAL

U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy (EERE)
Energy Savers
Geothermal Heat Pumps
http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12640

ENERGY STAR
Geothermal Heat Pumps
http://www.energystar.gov/index.cfm?c=geo_heat.pr_geo_heat_pumps

ENERGY STAR
Geothermal Heat Pumps Key Product Criteria
http://www.energystar.gov/index.cfm?c=geo_heat.pr_crit_geo_heat_pumps

International Ground Source Heat Pump Association (IGSHPA)
Frequently Asked Questions
http://www.igshpa.okstate.edu/geothermal/faq.htm

Finally, you may also be interested in the following resource on designing and remodeling a home:

U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy (EERE)
Energy Savers
Designing and Remodeling a Home
Before you design a new home or remodel an existing one, you should consider investing in its energy efficiency. You'll save energy and money in the long run. It's also a good time to invest in a renewable energy system that will provide your home with electricity, water heating, or space heating and cooling.
http://www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10080

Please contact the EERE Information Center if you need further assistance or have other energy-related questions by calling 877-EERE-INFO (877-337-3463), Monday through Friday, 11 a.m. to 5 p.m. Eastern Time, or through our web submittal form at https://www.eere.energy.gov/informationcenter/.

After more research and talking to various people, I was given some good advice. My first question should not be geo. vs. solar. Since we are comtemplating constructing a new house the question s/b what HVAC system are we going to install - above ground high effeciency heat pump, propane, geothermal or a hybrid system? I believe we need to make that decision first before contemplating installing a PV solar system.

The advice given by Springtime is good. If you don't have an energy rater, you might hire one (Resnet). For a job like this, I'd do at least a phone interview of three or more. They should be able to help you sift through the options that are most economic for your area. You might also try the University of Delaware or the land grant universities in the same climate as you are (MD maybe).

We built a new green home and did both geothermal and active solar to help pay for the electric costs. We also did passive solar and closed cell insulation and wood stove. We use LP fired tankless hot water heaters.

In terms of energy savings and comfort, I'd put my money first into insulation. Then I would do geothermal. Then I would do passive solar and then I would do active solar.

A. Regardless of how you create a BTU, the longer you hang onto it, the better. Insulation will do that. Closed cell is the best...and adds structural rigidity to the house and the house is very quiet.

B. geothermal provides both heating and cooling. The system works steadily, unlike air sourced heat pumps which fail in the cold or solar which relies on sunshine vs clouds or snow cover. We also use our system to circulate the air from the wood stove through the house. The difference in cost vs a traditional system was the cost of the wells, which we got back with our 30% tax credit. This for us would be a no brainer if we ever built again.

C. Passive solar because it always works and is "free" in that you need walls and windows anyway so its all in the design. We gain 4 degrees in temp on sunny days in the winter.

D. Active solar will take us about 7-10 years to pay back...but what other appliance do you buy that pays for itself? I'd be concerned about your roofline though. Our house has a 10-12 roof that faces due solar south and no shade so we get maximum generation out of our 5kw system. But it does not meet our total electricity needs.

We are in southern new england, so have had a mild winter. House is about 2100 sq ft on the main floor with a finished walkout basement below....built into a southern-facing slope. Our total energy costs for the last 12months was $1200 with electricity about $900 and the rest for LP. In our old, smaller house, it would cost about $900 just to fill the oil tank once. We don't heat the lower level as it maintains a temp of at least 63 deg all winter...warms up to 67 on sunny days.

The first costs of Geothermal will be more than conventional PV systems, but the savings are very substantial. And, as energy prices continue to rise, the investment return gets better and better.

You're right, shouldn't be a solar vs. geo scenario but what HVAC system. Geothermal is an excellent investment. A good installer can give you an energy analysis including a pay back analysis. If you are on propane the paybacks are very good, if you have natural gas the paybacks can be very good also. Good insulation of the house is key too as this can reduce the size of your geo thus saving you $. Also make sure you find good contractors and make apples to apples comparisons on the type of system they propose. Many times a contractor may be less$ but may be installing a smaller system or a hybrid that may not save you as much in utilities. Not bad, just be aware of what you are getting and not just to compare price. Ask yourself what your end result is- have low utility bills? Comfort? Heating and cooling? Decrease green house emissions? You are definitely on the right track and arm yourself with as much knowledge as you can!