Alternative Heat Sources
Geothermal Energy
With the Geo Exchange system, the Earth’s natural heat is collected in winter through a series of bore holes, called a loop, known as a “wellfield”.
The vertical bore holes used in Geo Exchange are typically drilled in the range of 4 to 6 inches in diameter and from 150 to 600 ft deep. The holes are fully grouted with a hole-sealing mixture of self- expanding diatomaceous earth from top to bottom, sealing the complete hole. The same approach is used in water well capping to prevent surface water contamination of the drinking water supplies.
Fluid circulating in the loop carries this heat from the earth to the home or building.. An indoor Geo Exchange system then uses electrically-driven compressors and heat exchangers in a vapor compression cycle–the same principle employed in a refrigerator (but operating in reverse)–to concentrate the Earth’s energy and release it inside the home or building at a higher temperature. The system is versatile and can work with radiant (hydronic) heat and forced air delivery systems.
Geo Exchange systems have very high efficiency and, unlike solar, have a constancy of performance, in that they rely on a constant below surface earth temperature of 55 degrees year-round. Also, due to very few moving parts, maintenance is low. Geo-exhange systems do have a relatively high initial cost and also a 30% tax rebate for the until 2012.
The electric operation of the system’s pumps must be kept in mind with these systems. At 40 cents+ per kWh in Kirkwood, the system is approximately break-even on an operating basis, compared with traditional boilers using propane (at today’s cost). If kWh prices drop
or if combined with solar roofs, geothermal can potentially be an attractive choice for heating. A potentially highly cost effective application would replace a 100% electrically heated building with a GeoExhange system., where an 85% or higher gain of efficiency is likely. Base Camp condominiums would be a prime target for this type of application.
One home in Kirkwood has used a Geo Exchange system, successfully for 9 years.Another prime local example of a working vertical bore Geo Exchange system is the new Truckee Middle School. The 100,000 square foot school is fully heated and cooled using a vertical bore system. Other examples of successfully operating vertical bore systems include many private
residences in the Western Sierra mountain area. Walter Roosli invited us to his home and a look at his geothermal system.
Here are some links to information on geothermal:
Here is some good information found by Al Graf:
A couple of interesting DOE pages.
heating fuel cost per BTU calculator
http://www.eia.doe.gov/neic/experts/heatcalc.xls
CO2 content per btu for fuels
http://www.eia.doe.gov/oiaf/1605/coefficients.html
With $0.39 per kWhr plugged into the spreadsheet cell for the cost of electricity, the cost per million BTU of geothermal is the same as for propane (using a fuel cost of $2.47 per gallon – I don’t know what our cost is). My boiler mfg claims that my boiler is 80 percent efficient rather than the 78 percent efficient used in the DOE spreadsheet. For this efficiency the break even electricity cost would be $0.38 per kWhr for a propane cost of $2.47 per gallon.
When reading all this (discussion relating to the impacts of geothermal systems as it impacts grid connection), a light bulb went on for me.
1) If we are not connected to PG&E, then using solar to power geothermal is essentially replacing propane with solar energy. But by doing that, we probably give up opportunity
to use solar to replace diesel. I’m not sure that’s a good tradeoff.
2) But if we are connected to PG&E, then PG&E’s natural gas plus array of renewable sources replaces our diesel, which is good.
3) At the same time, if we are connected to PG&E, any solar we do to satisfy normal electric needs (resort, lights, appliances, etc) hurts our ability to repay the bonds issued to
build the connection.
4) In that case, solar to run geothermal (rather than compete with PG&E electricity for all other electric needs) may make a lot of sense. Then, using solar to replace propane may be a great idea…maybe best of all worlds!