- Ecological characteristics and management of geothermal systems of the Taupo Volcanic Zone, New Zealand
Ian K. G. Boothroyd.
Geothermics, Vol. 38, No. 1, Mar. 2009, pp. 200-209.
New Zealand has an array of geothermal systems with distinctive ecological features, with many occurring in the Taupo Volcanic Zone in the Central North Island. Associated with these geothermal features are characteristic geophysical and geochemical components, and distinctive terrestrial and aquatic ecosystems with many attributes that are common across a range of the biotic groups. Zonation amongst vegetation communities is closely related to soil temperature and these associations generally occur in a predictable sequence along the soil temperature gradient. Similarly, clear distinctions in aquatic flora and fauna occur longitudinally downstream from the source of thermal springs and vertically on geyser mounds. The characteristic vegetation communities associated with geothermal fields and the invertebrate and algal communities found in geothermally influenced springs and streams are described, in particular the features of the Wairakei geothermal field. At this field four plant associations are recognized (non-vegetated soilfield, prostrate kanuka shrubland, prostrate kanuka scrub, mixed fernland), but all the major aquatic macroinvertebrate groups are represented and commonly found in natural freshwaters throughout New Zealand. The current management of geothermal ecosystems is reviewed with particular reference to the Waikato region of New Zealand. Management of geothermal resources in New Zealand aims to balance development with the protection of highly valued surface features via a series of regional policies, rules and regulations. Geothermal habitats, ecological gradients, and at-risk geothermal plants are included in the definition of geothermal systems for management purposes. With the recognition of the unique ecological diversity and function of geothermal ecosystems, knowledge and understanding of their ecological characteristics will be critical to the ability to utilize and sustain geothermal resources into the future.
- Fifty years of geothermal power generation at Wairakei
Ian A. Thain and Brian Carey.
Geothermics, Vol. 38, No. 1, Mar. 2009, pp. 48-63.
The challenges and changes that have occurred over the last 50 years of remarkable service from the Wairakei Geothermal Power Project are reviewed. The project was initially constructed during the 1953-1963 period. Plant changes including the decommissioning of the high-pressure turbine generators, the installation of a 3.5-MW intermediate-low pressure steam turbine at the Wairakei Power Station in 1996, the commissioning of the 55 MW Poihipi Power Station in 1997, the 14 MW binary power plant at the Wairakei Power Station in 2005, and a proposed new station to be constructed in the Te Mihi area in 2011-2016 are briefly discussed. Also reviewed are steamfield aspects including steam separation processes, a pilot scheme that was designed to carry hot geothermal water some distance before flash steam generation by pressure reduction, steam production from vapor-dominated regions in the Wairakei reservoir, geothermal water injection, and cascade and direct heat uses. Finally, various aspects of the Wairakei development that have contributed to its success are described. It is anticipated that the geothermal resource will be producing beyond 2028 at generation levels 50% above the current (2008) level.
- Information and Decision-Making Aid Systems on Near-Surface Geothermal Energy in Bavaria
KW - Korrespondenz Wasserwirtschaft, No. 1, Jan 2009, pp.
The planning and construction of near-surface geothermal energy plants requires detailed information on water resources management as well as the geological, hydro-geological and geothermal conditions at the site of the plant. When relying on flat-rate values, for example according to VDI 4640, for the design of geothermal energy collectors, ground source heat pumps, or groundwater heat pumps, the desired results cannot always be achieved, or it may lead to a sub-optimum design of such plants. At the Department for geological services, economic geology and soil protection of the Bavarian Environmental Agency, a comprehensive information system on near-surface geothermal energy is being developed. In charts of different scales, through an internet application, and via a special geothermal energy portal, basic data, planning data, and further information are made available.
- Utilisation of geothermal resources
John W. Lund.
Proceedings of the Institution of Civil Engineers, Energy, Vol. 162, No. 1, Feb. 2009, pp. 3-12.
For centuries, geothermal energy has been used for bathing, cooking and space heating. More recently, district heating, industrial processing and geothermal heat pumps have become part of the direct-use mix. Geothermal electric power generation began in Italy in 1904, with the first commercial plant operational in 1913. Presently, the total installed global capacity for direct use is 29 000 MWt, producing 76 000 GW h/year in 72 countries; the installed capacity for electric power is 9700 MWe, generating 60 000 GW h/year in 24 countries. Recent trends are to maximise the use of geothermal resources in a combined heat and power project. Geothermal resources of around 100 deg C have been used in binary (organic Rankine) cycle plants and then cascaded for district heating. Geothermal energy is considered to be both renewable and sustainable as a green energy resource, but certain environmental aspects must be considered and mitigated.
- Effect of Non-Condensable Gases on geothermal power plant performance. Case study: Kizildere Geothermal Power Plant-Turkey
Gulden Gokcen and Nurdan Yildirim.
International Journal of Exergy, Vol. 5, No. 5-6, 17 Oct 2008, pp. 684-695.
Non-Condensable Gases (NCGs) are natural components of geothermal fluids, and they are a source of considerable capital and operating costs for power plants. The NCG content of geothermal steam varies over the world from almost zero to as much as 250#37; (wt). In this work, the influence of NCGs on the thermodynamic performance of geothermal power plants is analysed for various NCG content and turbine inlet temperatures. The results obtained can be useful on the feasibility study of single flash geothermal power plants. Depending on the NCG content of the field, the performance of the power plant can be determined roughly.
- Going Underground
New Scientist, Vol. 200, No. 2677, pp. 37-40, 2008, pp. October 11.
Geothermal energy is clean, inexhaustible, provides predictable 24-hour power, and can be obtained from just about anywhere. A 2006 report by researchers at the Massachusetts Institute of Technology (MIT) estimated that there is enough geothermal energy in the U.S. alone to meet the country's energy needs 2000 times over. According to the Geothermal Energy Association (GEA) based in Washington, D.C., the best sites can generate electricity for as little as 5.5 cents per kilowatt (kW)-hour, compared with 8 or 9 cents per kW-hour for natural gas plants. However, outside of geologically blessed places such as Iceland, Japan, and New Zealand, where volcanically active rocks are close to the surface, Earth's heat is locked away beneath several kilometers of rock. New developments are making these depths easier and more cost-effective to reach, and the world is beginning to realize the potential of geothermal energy. The key to tapping geothermal energy is a relatively new technology called enhanced geothermal systems (EGS), which can create a geothermal hotspot almost anywhere. The process involves fracturing hot rocks and then injecting water, which heats up as it circulates through them. It is then pumped back to the surface and passed through a heat exchanger, which drives a turbine, generating electricity. A number of EGS projects have recently come online. The world's first commercial plant in Landau, Germany, was commissioned in 2007 and is producing 22 gigawatt (GW)-hours of electricity per year. A 1.5-megawatt (MW) pilot plant in Soultz, France, began operating in June 2008, and a test plant in Germany should be online by the end of next year. In southern Australia, a 1-MW demonstration plant should be producing electricity by January. In the U.S., the Department of Energy has invested more than million to add an EGS system to a conventional geothermal well, where water is pumped through naturally hot rocks, east of Reno, Nevada, in the hope of increasing its productivity.
- History of geothermal exploration in Indonesia from 1970 to 2000
Manfred P. Hochstein and Sayogi Sudarman.
Geothermics, Vol. 37, No. 3, June 2008, pp. 220-266.
Reconnaissance surveys undertaken since the 1960s show that more than 200 geothermal prospects with significant active surface manifestations occur throughout Indonesia. Some 70 of these were identified by the mid-1980s as potential high-temperature systems using geochemical criteria of discharged thermal fluids. Between 1970 and 1995, about 40 of these were explored using geological mapping, geochemical and detailed geophysical surveys. Almost half of the surveyed prospects were tested by deep (0.5-3 km) exploratory drilling, which led to the discovery of 15 productive high-temperature reservoirs. Several types of reservoirs were encountered: liquid-dominated, vapour-dominated, and a vapour layer/liquid-saturated substratum type. All three may be modified by upflows (plumes) containing magmatic fluid components (volcanic geothermal systems). Large, concealed outflows are a common feature of liquid-dominated systems in mountainous terrain. All explored prospects are hosted by Quaternary volcanic rocks, associated with arc volcanism, and half occur beneath the slopes of active or dormant stratovolcanoes. By 1995, five fields had been developed by drilling of production wells; three of them supplied steam to plants with a total installed capacity of 305 MWe. By 2000, with input from foreign investors, the installed capacity had reached 800 MWe in six fields, but geothermal developments had stalled because of the 1997-1998 financial crisis.
- Inverse modeling and forecasting for the exploitation of the Pauzhetsky geothermal field, Kamchatka, Russia
Alexey V. Kiryukhin, Natalia P. Asaulova and Stefan Finsterle.
Geothermics, Vol. 37, No. 5, Oct. 2008, pp. 540-562.
A three-dimensional numerical model of the Pauzhetsky geothermal field has been developed based on a conceptual hydrogeological model of the system. It extends over a 13.6-km2 area and includes three layers: (1) a base layer with inflow; (2) a geothermal reservoir; and (3) an upper layer with discharge and recharge/infiltration areas. Using the computer program iTOUGH2 [Finsterle, S., 2004. Multiphase inverse modeling: review and iTOUGH2 applications. Vadose Zone J. 3, 747-762], the model is calibrated to a total of 13,675 calibration points, combining natural-state and 1960-2006 exploitation data. The principal model parameters identified and estimated by inverse modeling include the fracture permeability and fracture porosity of the geothermal reservoir, the initial natural upflow rate, the base-layer porosity, and the permeabilities of the infiltration zones. Heat and mass balances derived from the calibrated model helped identify the sources of the geothermal reserves in the field. With the addition of five make-up wells, simulation forecasts for the 2007-2032 period predict a sustainable average steam production of 29 kg/s, which is sufficient to maintain the generation of 6.8 MWe at the Pauzhetsky power plant.
- Mexico: Renewable Energy. Solar, Wind, Mini-Hydroelectric, Geothermal
PB2008114052, Aug 2008, pp. 13.
Renewable energy used for the generation of electricity, including mini-hydroelectric, biomass, photovoltaic-solar, wind power, and geothermal energies, has experienced slow growth in Mexico. The existence of state owned oil and electricity companies has led to little innovation beyond fossil fuels. To this point, hydroelectric and geothermal energy have been Mexicos most prolific renewable sources, and its geothermal production is the third largest in the world. But the market looks to be changing as the Mexican Government has recently proposed new renewable energy goals. The increasing level of pollution, higher costs of fossil fuels, difficulties in the reform of the state oil company, and heightened awareness of global warming have all led the government to press for the adoption of more clean energy sources. The recent addition of several new wind turbine plants in Oaxaca shows promise, and as prices for renewable resources continue to fall we can expect the market to open even further. The electricity generated in Mexico by hydroelectric and geothermal plants already represents 25% of the capacity and 15% of the total generation of the National Electric System, but the government has expressed a desire to further increase other renewable sources.
- Understanding the Chena Hot Springs, Alaska, geothermal system using temperature and pressure data from exploration boreholes
Kamil Erkan, Gwen Holdmann, Walter Benoit and David Blackwell.
Geothermics, Vol. 37, No. 6, Dec. 2008, pp. 565-585.
Chena Hot Springs is a small, moderate temperature, deep circulating geothermal system, apparently typical of those associated to hot springs of interior Alaska. Multi-stage drilling was used in some exploration boreholes and was found to be useful for understanding subsurface flow characteristics and developing a conceptual model of the system. The results illustrate how temperature profiles illuminate varying pressure versus depth characteristics and can be used alone in cases where staged drilling is not practical. The extensive exploration activities helped define optimal fluid production and injection areas, and showed that the system could provide sufficient hot fluids (57 deg C) to run a 400-kWe binary power plant, which came on line in 2006.