>Speaker: Robert Fournier
>Dr. Robert Fournier is a retired super grade USGS researcher who has
>spent most of his career investigating geothermal energy-related
>topics. He has served on the Boards of Directors of the Geothermal
>Resources Council and the International Geothermal Association. In
>addition he has served on United Nations and USAID Panels to evaluate
>geothermal energy exploration programs in numerous developing
>countries, and also served for many years as Chairman of Advisory
>Panels for the Development of Geothermal Resources in Costa Rica,
>El Salvador, and Panama. In his talk he will discuss where geothermal
>energy resources are found and how they can be utilized.
>Temperature gradients in the earth's crust generally are about 17-30
>deg C per kilometer of depth (50-87 deg F per mile). This is sufficient
>for the economically competitive use of ground-based heat pumps to
>heat homes in the winter and cool them in the summer. In contrast, the
>economically competitive generation of electricity from geothermal
>resources requires abnormally high temperatures (>150 deg C) at
>relatively shallow depths (>2-3 km). Superheated water and/or steam
>in fractures and pores ("reservoirs") within these anomalously hot
>rocks are brought to the surface through drilled wells and used in
>various ways to turn turbines. About 6% of California's electrical
>needs are now met by Geothermal. World-wide, the electrical needs
>of about 46 million people in 17 countries are met by Geothermal. In
>addition to easing the dependence on fossil fuels, geothermal is far
>less damaging to the environment.
Dr. Fournier's first interesting slide showed where Geothermal power is currently being utilized, and how much of the energy demand of those populations was being supplied by it. Highlights from the table: Iceland gets the highest percentage of its energy from energy, 90%. The Swiss get about 10% of the energy from Geothermal that Americans do. China and the US get about the same amount of geothermal power, but the Chinese are expected to expand their Geothermal energy use much quicker over the next few years. He is particularly proud of the fact that Costa Rica gets 20% of their power from Geothermal sources, because he had a lot to do with getting them to install their first unit.
Dr. Fournier then explained what a home Geothermal system looks like. It is a well about 300 feet deep with a circulating water pipe in it. A pump circulates the water from the well past a heat pump, which draws heat from, or puts heat in the water (depending on the season). Circulating the water through the well allows the huge thermal mass of the earth to work as a source or sink. Such a system is generally about 20% more efficient than an air exchange heat pump, primarily because those do air conditioning by putting heat in hot air, and drawing heat from cold air, which is more work than dealing with the constant temperature earth.
Currently such systems are unusual because of the expense of building the well, which adds several thousand dollars to the price of a heating system, which developers are usually unwilling to invest because consumers aren't willing to pay for the feature yet. One utility has gotten a lot of units installed by loaning consumers the money for the project and then taking the payments as part of the utility bill, promising to cap the bill at current levels. The payoff for the consumer is five to eight years down the road, when the loan is paid off and the bill falls.
Many of the big Geothermal installations that are currently being done are happening in the developing world, where the money to import lots of energy is not available, and such plants make lots of economic sense. Industrial scale Geothermal installations are not currently being installed in the US because they have a several year development cycle, which short term capital doesn't seem to want to wait through. Dr. Fournier expects that the option will get more attractive here after energy prices have risen considerably from where they are now.
For more information see: www.geothermal.marin.org