Analysis of thermal/mechanical energy-conversion concepts. Final report

Project activities and publications are listed. (MHR

Temperature Effects on Biomass and Regeneration of Vegetation in a Geothermal Area.

Understanding the effects of increasing temperature is central in explaining the effects of climate change on vegetation. Here, we investigate how warming affects vegetation regeneration and root biomass and if there is an interactive effect of warming with other environmental variables. We also examine if geothermal warming effects on vegetation regeneration and root biomass can be used in climate change experiments. Monitoring plots were arranged in a grid across the study area to cover a range of soil temperatures. The plots were cleared of vegetation and root-free ingrowth cores were installed to assess above and below-ground regeneration rates. Temperature sensors were buried in the plots for continued soil temperature monitoring. Soil moisture, pH, and soil chemistry of the plots were also recorded. Data were analyzed using least absolute shrinkage and selection operator and linear regression to identify the environmental variable with the greatest influence on vegetation regeneration and root biomass. There was lower root biomass and slower vegetation regeneration in high temperature plots. Soil temperature was positively correlated with soil moisture and negatively correlated with soil pH. Iron and sulfate were present in the soil in the highest quantities compared to other measured soil chemicals and had a strong positive relationship with soil temperature. Our findings suggest that soil temperature had a major impact on root biomass and vegetation regeneration. In geothermal fields, vegetation establishment and growth can be restricted by low soil moisture, low soil pH, and an imbalance in soil chemistry. The correlation between soil moisture, pH, chemistry, and plant regeneration was chiefly driven by soil temperature. Soil temperature was negatively correlated to the distance from the geothermal features. Apart from characterizing plant regeneration on geothermal soils, this study further demonstrates a novel approach to global warming experiments, which could be particularly useful in low heat flow geothermal systems that more realistically mimic soil warming

Economics of geothermal power

Geothermal, steam, nuclear, and hydraulic construction costs, power generating costs, and utilization rate are compared. The risk factor in exploratory geothermal wells is discussed. (MHR

Geothermal power plants of the United States: a technical survey of existing and planned installations

The development of geothermal energy as a source of electric power in the United States is reviewed. A thorough description is given of The Geysers geothermal power project in northern California. The recent efforts to exploit the hot-water resources of the Mexicali-Imperial Rift Valley are described. Details are given concerning the geology of the several sites now being used and for those at which power plants will soon be built. Attention is paid to the technical particulars of all existing plants, including wells, gathering systems, energy conversion devices, materials, environmental impacts, economics and operating characteristics. Specifically, plants which either exist or are planned for the following locations are covered: The Geysers, CA; East Mesa, CA; Heber, CA; Roosevelt Hot Springs, UT; Valles Caldera, NM; Salton Sea, CA; Westmorland, CA; Brawley, CA; Desert Peak, NV; and Raft River, ID. The growth of installed geothermal electric generating capacity is traced from the beginning in 1960 and is projected to 1984

Geothermal power plants of New Zealand, Philippines, and Indonesia: a technical survey of existing and planned installations. Report No. CATMET/17

This report is the fourth in a series dealing with the geothermal power plants of the world. Here the existing and planned stations in the south Pacific area are surveyed including New Zealand, the Philippines and Indonesia. Details are given for the plants at Wairakei and Kawerau, and for the one proposed at Broadlands in New Zealand; for the plants proposed for Tiwi and Los Banos, and the wellhead units operating at Los Banos and Tongonan in the Philippines; and for the wellhead unit soon to be installed at Kawah Kamojang on Java in Indonesia. The geologic characteristics of the fields are described along with wellflow particulars, energy conversion systems, environmental impacts, economic factors and operating experiences, where available. The geothermal resource utilization efficiency is computed or estimated for the power plants covered. Furthermore, some discussion is devoted to the other sites which may prove exploitable for the production of electricity

Introduction to electric energy conversion systems for geothermal energy resources

The types of geothermal energy conversion systems in use are classified as follows: direct, dry steam; separated steam; single-flash steam; double-flash steam; multi-flash steam; brine/Freon binary cycle; and brine/isobutane binary cycle. The thermodynamics of each of these is discussed with reference to simplified flow diagrams. Typical existing power plants are identified for each type of system. (MHR

The effect of expansion-ratio limitations on positive-displacement, total-flow geothermal power systems

Combined steam-turbine/positive-displacement engine (PDE) geothermal power systems are analyzed thermodynamically and compared with optimized reference flash-steam plants. Three different configurations of combined systems are considered. Treated separately are the cases of self-flowing and pumped wells. Two strategies are investigated that help overcome the inherent expansion-ratio limitation of PDE's: pre-flashing and pre-mixing. Parametrically-obtained results show the required minimum PDE efficiency for the combined system to match the reference plant for various sets of design conditions