In from the Cold: Geothermal Energy is Making a Comeback
Well-read science fiction fans are pretty familiar with geothermal energy production concepts. Geothermal is one of the most popular forms of energy production in sci-fi novels and stories, and many futuristic worlds are powered by tapping the virtually limitless heat inside the planet to generate energy, but there is nothing fantastical about the technology involved. In fact, geothermal energy has been around in one form or another since the days of Ancient Rome where hot springs were used to heat public baths like the one that gave Bath, England its name.
Geothermal was a popular energy source at the turn of the 20th century and remained so until cheap oil had a chilling effect on development following the Second World War, and while popularity peaked again during the energy crisis of the 70s it once again dropped off when that crisis ended and oil prices returned to previous levels. However, like a fickle teenager, the world is once again in love with geothermal energy.
“Geothermal energy production is going through a kind of a renaissance right now,” says Robert Hegger, Segment Manager Geothermal, Clean Technology & Renewable Energy for Siemens Industry, Inc. “Geothermal was very popular in the 70s and 80s, but dropped off after the cost of oil dropped. Now, with all the interest in sustainable energy production and high gas prices it’s on the bounce and new technologies are being introduced that make it very competitive and reliable.”
Iceland’s Nesjavellir geothermal power plant is a case in point. The plant began operations in September 1990 and has undergone a series of upgrades in the intervening years as it produces both electricity for the power grid and hot water for district heating. The most recent stage of development began with the installation of two 30 MW turbine generators bringing output up to 60 MWe electric and 200 MWt thermal power. There are three major types of geothermal electricity production plants:
“If the water is hot enough – typically 400°F or higher – you can bring it to the surface and it will flash into steam …you can then direct that into a specially configured steam turbine which generates electricity. This is the most efficient process and the preferred method.
More common are binary cycle power plants which use water that isn’t hot enough to flash into steam efficiently. These plants push geothermal fluid to the surface and direct it through a heat exchanger where it is used to heat a secondary fluid which boils at a much lower temperature than water. This secondary fluid then turns into steam and powers the turbines.
“We’re finding a lot of these cooler reservoirs in the US,” says Hegger, adding that most future geothermal plants will use this technology.
The final type of plant is the oldest and the rarest. Dry steam power plants produce steam that is directly from the geothermal reservoir which in turn runs the turbine that powers the generator and produces electricity. Excess steam is sent back to the source via the injection well making the circuit self-sustaining.
Says Hegger, “Once you get the power it’s the same as conventional turbine power plant. Take rotational mechanical energy, turn it into electricity, get it into the grid and sell it. From output to the grid, these power plants are not going to look terribly different than traditional power plants.”
At Nesjavellir geothermal steam and water is collected from 10 production wells and piped into a central separator station, which then supplies up to 132 kg/s of steam and 240 kg/s of water. Two steam condensing turbines generate electricity while the exhaust steam from the turbines is used to preheat fresh water in the condensers. The separated geothermal water is used in heat exchangers to heat the preheated water up to the required temperature. Finally, the water is treated in de-aerators to suit the requirements of the distribution system. According to research conducted by MIT for the US department of Energy and published in 2006 in a report entitled The Future of Geothermal Energy – Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century “Geothermal energy from EGS represents a large, indigenous resource that can provide base-load electric power and heat at a level that can have a major impact on the United States, while incurring minimal environmental impacts.”
The report goes on to state that a reasonable R&D investment could lead to providing 100 GWe or more of cost-competitive generating capacity by the middle of the century. “Further, EGS provides a secure source of power for the long term that would help protect America against economic instabilities resulting from fuel price fluctuations or supply disruptions. Most of the key technical requirements to make EGS work economically over a wide area of the country are in effect, with remaining goals easily within reach. This achievement could provide performance verification at a commercial scale within a 10- to 15-year period nationwide.”
EGS is still an immature flavor of Geothermal technology, but it shows that there is both a great deal of work being done to enhance yields and that the technology has a bright future, says Hegger.
Despite its enormous potential, geothermal energy has suffered fits and starts that have caused it to lag behind Wind and Solar options as the world seeks out renewable energy sources. Paris, France-based Societe Generale – one of the oldest financial services companies in Europe – examined the geothermal market in depth and identified four reasons for this.
1) Location of resources – geothermal reservoirs are often found near active tectonic plates and in volcanic regions.
2) Availability of skilled human labor and drilling equipment – geothermal plants need deep drilling equipment and the human expertise to use them, putting them in direct competition with the highly lucrative oil and gas sector.
3) Lengthy plant construction – a geothermal project will usually take about six years to develop.
4) Difficulty in financing initial capex – 2009 wasn’t a good year to be looking for investment in anything, but geothermal energy has problems beyond the economy. Initial development costs will total as much as 40 percent of total development costs and it can be hard to find investors to start drilling operations until the presence of a geothermal reservoir is confirmed.
These challenges notwithstanding, Societe Generale says the market for geothermal energy is accelerating rapidly. Geothermal sector capex was $3 billion in 2007, up 183 percent over 2006. By 2015, Societe Generale expect the US geothermal market to see $16.9 billion in investment. Today the US has 4,000MW in projects under development and this has grown by about 20 percent since 2008.
There are several excellent reasons for the way geothermal has bounced back, says Hegger. Today’s climate conscious society has fostered a frenzy of research and development into harnessing sustainable/renewable forms of energy production including Wind, Solar, Biomass and Geothermal and more. It only makes sense that a technology like geothermal, that offers better than 90 percent uptime (as opposed to wind and solar which are weather dependent), has minimal environmental impact and produces energy for a very competitive cost would come back into favor.
Additional Resources:
Geothermal Energy Association
http://www.geo-energy.org/
International Energy Agency Geothermal webpage
http://www.iea-gia.org/
Report: The Future of Geothermal Energy – Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century
http://geothermal.inel.gov/publications/future_of_geothermal_energy.pdf
Wikipedia entry on Geothermal energy
http://en.wikipedia.org/wiki/Geothermal_power
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