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Mines, Greg

Publications and source records attributed to Mines, Greg.

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Binary Power Plant CO2 Life Cycle Emissions Including Isobutane Fugitive Emission

Geothermal energy production has one of the lowest life cycle CO2 emission factors (~ 15 g-CO2/kWh) for plants producing electricity (Hondo, 2005). This life cycle factor includes indirect emissions from plant construction as well as ongoing operations such as additional well drilling and equipment replacement. Not included in this calculation are direct emissions from geothermal power production. Geothermal flash plants emit CO2 at rates related to the reservoir concentration. Binary plants report “near zero” emissions of high global warming potential gases because of their closed loop system design. Binary plants use working fluids to drive the turbine generators and leakage of these working fluids have not yet been quantified. To assess the working fluid emissions from geothermal power production using an Organic Rankine Cycle, reported isobutane emissions were accessed for 3 California binary plants from the Great Basin Unified and Imperial County Air Pollution Control Districts as well as the California Air Resource Board. Each binary plant used in this study has been operating for more than 25 years. From the data, two types of isobutane emissions were accounted for over a 15 month period: ‘normal’ equipment leakage and equipment breakdown emissions. This preliminary analysis of working fluid emissions from these plants suggest that if a binary plant has equipment failures, the majority of the isobutane releases can be due to these events. The results indicate that a well maintained binary plant releases approximately 0.13 g-Isobutane/kWh where as a plant with equipment failures releases approximately 6 g-Isobutane/kWh. Assuming a greenhouse warming potential of 3 for isobutane, these emission values become 0.4 and 18 g-CO2e/kWh (where CO2e is the CO2 equivalent effect). The direct operation isobutane leakage for a well maintained binary plant does not significant increase the life cycle CO2 emission factor whereas a plant with significant equipment issues can effectively double the life cycle CO2 emissions. This limited data set suggests that when direct CO2e fugitive emission are add to the indirect CO2 emissions, the total CO2 emissions from binary power plants are equivalent or less than nuclear, as well as other renewables power production such as wind and solar.

15 GEOTHERMAL ENERGY↗
DOE OSTI2015

Geothermal Risk Reduction via Geothermal/Solar Hybrid Power Plants. Final Report

There are numerous technical merits associated with a renewable geothermal-solar hybrid plant concept. The performance of air-cooled binary plants is lowest when ambient temperatures are high due to the decrease in air-cooled binary plant performance that occurs when the working fluid condensing temperature, and consequently the turbine exhaust pressure, increases. Electrical power demand is generally at peak levels during periods of elevated ambient temperature and it is therefore especially important to utilities to be able to provide electrical power during these periods. The time periods in which air-cooled binary geothermal power plant performance is lowest generally correspond to periods of high solar insolation. Use of solar heat to increase air-cooled geothermal power plant performance during these periods can improve the correlation between power plant output and utility load curves. While solar energy is a renewable energy source with long term performance that can be accurately characterized, on shorter time scales of hours or days it can be highly intermittent. Concentrating solar power (CSP), aka solar-thermal, plants often incorporate thermal energy storage to ensure continued operation during cloud events or after sunset. Hybridization with a geothermal power plant can eliminate the need for thermal storage due to the constant availability of geothermal heat. In addition to the elimination of the requirement for solar thermal storage, the ability of a geothermal/solar-thermal hybrid plant to share a common power block can reduce capital costs relative to separate, stand-alone geothermal and solar-thermal power plant installations. The common occurrence of long-term geothermal resource productivity decline provides additional motivation to consider the use of hybrid power plants in geothermal power production. Geothermal resource productivity decline is a source of significant risk in geothermal power generation. Many, if not all, geothermal resources are subject to decreasing productivity manifested in the form of decreasing production fluid temperature, flow rate, or both during the life span of the associated power generation project. The impacts of geothermal production fluid temperature decline on power plant performance can be significant; a reduction in heat input to a power plant not only decreases the thermal energy available for conversion to electrical power, but also adversely impacts the power plant efficiency. The impact of resource productivity decline on power generation project economics can be equally detrimental. The reduction in power generation is directly correlated to a reduction in revenues from power sales. Further, projects with Power Purchase Agreement (PPA) contracts in place may be subject to significant economic penalties if power generation falls below a specified default level. While the magnitude of PPA penalties varies on a case-by-case basis, it is not unrealistic for these penalties to be on the order of the value of the deficit power sales such that the utility may purchase the power elsewhere. This report evaluates the use of geothermal/solar-thermal hybrid plant technology for mitigation of resource productivity decline, which has not been a primary topic of investigation in previous analyses in the open literature.

14 SOLAR ENERGY↗
DOE OSTI2015

DOE-GTO Low Temperature Project Case Study

The US Department of Energy (DOE), Geothermal Technologies Office (GTO) has funded low temperature projects to demonstrate the technical and economic feasibility of power generation from geothermal resources at temperatures of 150 degrees C and lower. To date three of the funded projects have completed their two year operation phase during which they supplied operating data to the GTO. This paper discusses the operation of two of these plants while they were providing data, including a review of facility performance, as well as an initial economic assessment of each.

15 GEOTHERMAL ENERGY↗
DOE OSTI2015

Stillwater Hybrid Geo-Solar Power Plant Optimization Analyses

Solar field and power plant models have been developed to predict the performance of the Stillwater geothermal / solar-thermal hybrid power plant. The models have been validated using operational data from the Stillwater plant. The validated models will be used to optimize performance of the Stillwater hybrid plant and explore next-generation hybrid plant design concepts. A preliminary effort to improve performance of the Stillwater hybrid plant using optical characterization of the solar field has been completed. The Stillwater solar field optical characterization involved measurement of mirror reflectance, mirror slope error, and receiver position error. Subsequent analyses of the optical characterization results indicate that the solar field is currently operating at approximately 90% of the manufacturer’s performance specifications. Control system and hardware modifications expected to improve solar array performance by XX% have been identified.

14 SOLAR ENERGY↗
DOE OSTI2015

DOE-GTO Low Temperature Project Case Study

The US Department of Energy (DOE), Geothermal Technologies Office (GTO) has funded low temperature projects to demonstrate the technical and economic feasibility of power generation from geothermal resources at temperatures of 150°C and lower. To date three of the funded projects have completed their two year operation phase during which they supplied operating data to the GTO. This paper discusses the operation of two of these plants while they were providing data, including a review of facility performance, as well as an initial economic assessment of each.

15 GEOTHERMAL ENERGY↗
DOE OSTI2015

David Blackwell’s Forty Years in the Idaho Desert, The Foundation for 21st Century Geothermal Research

Dr. David Blackwell has had a profound influence on geo-thermal exploration and R&D in Idaho. Forty years have elapsed since the first Southern Methodist University (SMU) temperature logging truck rolled onto the high desert in Southern Idaho, yet even after so much time has elapsed, most recent and ongoing geothermal R&D can trace its roots to the foundational temperature studies led by Dr. Blackwell. We believe that the best way to honor any scientist is to see their work carried forward by others. As this paper demonstrates, it has been an easy task to find a host of Idaho researchers and students eager to contribute to this tribute paper. We organize this paper by ongoing or recent projects that continue to benefit left to Idaho by Dr. David Blackwell.

15 GEOTHERMAL ENERGY↗
DOE OSTI2015

Geothermal Plant Capacity Factors

The capacity factors recently provided by the Energy Information Administration (EIA) indicated this plant performance metric had declined for geothermal power plants since 2008. Though capacity factor is a term commonly used by geothermal stakeholders to express the ability of a plant to produce power, it is a term frequently misunderstood and in some instances incorrectly used. In this paper we discuss how this capacity factor is defined and utilized by the EIA, including discussion on the information that the EIA requests from operations in their 923 and 860 forms that are submitted both monthly and annually by geothermal operators. A discussion is also provided regarding the entities utilizing the information in the EIA reports, and how those entities can misinterpret the data being supplied by the operators. The intent of the paper is to inform the facility operators as the importance of the accuracy of the data that they provide, and the implications of not providing the correct information.

15 GEOTHERMAL ENERGY↗
DOE OSTI2014

Economics of Developing Hot Stratigraphic Reservoirs

Stratigraphic geothermal reservoirs at 3 – 4 km depth in high heat-flow basins are capable of sustaining 100 MW-scale power plants at about 10 c/kWh. This paper examines the impacts on the levelized cost of electricity (LCOE) of reservoir depth and temperature, reservoir productivity, and drillhole/casing options. For a reservoir at 3 km depth with a moderate productivity index by hydrothermal reservoir standards (about 50 L/s/MPa, 5.6 gpm/psi), an LCOE of 10c/kWh requires the reservoir to be at about 200°C. This is the upper temperature limit for pumps. The calculations assume standard hydrothermal drilling costs, with the production interval completed with a 7 inch liner in an 8.5 inch hole. If a reservoir at 4 km depth has excellent permeability characteristics with a productivity index of 100 L/s/MPa (11.3 gpm/psi), then the LCOE is about 11 c/kWh assuming the temperature decline rate with development is not excessive (< 1%/y, with first thermal breakthrough delayed by about 10 years). Completing wells with modest horizontal legs (e.g. several hundred meters) may be important for improving well productivity because of the naturally high, sub-horizontal permeability in this type of reservoir. Reducing the injector/producer well ratio may also be cost-effective if the injectors are drilled as larger holes.

15 GEOTHERMAL ENERGY↗
DOE OSTI2014

Summary of Historical Production for Nevada Binary Facilities

The analysis described was initiated to validate inputs used in the US Department of Energy’s (DOE) economic modeling tool GETEM (Geothermal Electricity Technology Evaluation Model) by using publically available data to identify production trends at operating geothermal binary facilities in the state of Nevada. Data required for this analysis was obtained from the Nevada Bureau of Mines and Geology (NBMG), whom received the original operator reports from the Nevada Division of Minerals (NDOM). The data from the NBMG was inputted into Excel files that have been uploaded to the DOE’s National Geothermal Data System (NGDS). Once data was available in an Excel format, production trends for individual wells and facilities could be established for the periods data was available (thru 2009). Additionally, this analysis identified relationships existing between production (temperature and flow rates), power production and plant conversion efficiencies. The data trends showed that temperature declines have a significant impact on power production, and that in some instances operators increased production flow rate to offset power declines. The production trends with time that were identified are being used to update GETEM’s default inputs.

15 GEOTHERMAL ENERGY↗
DOE OSTI2014

Use of a Geothermal-Solar Hybrid Power Plant to Mitigate Declines in Geothermal Resource Productivity

Many, if not all, geothermal resources are subject to decreasing productivity manifested in the form of decreasing brine temperature, flow rate, or both during the life span of the associated power generation project. The impacts of resource productivity decline on power plant performance can be significant; a reduction in heat input to a power plant not only decreases the thermal energy available for conversion to electrical power, but also adversely impacts the power plant conversion efficiency. The reduction in power generation is directly correlated to a reduction in revenues from power sales. Further, projects with Power Purchase Agreement (PPA) contracts in place may be subject to significant economic penalties if power generation falls below the default level specified. A potential solution to restoring the performance of a power plant operating from a declining productivity geothermal resource involves the use of solar thermal energy to restore the thermal input to the geothermal power plant. There are numerous technical merits associated with a renewable geothermal-solar hybrid plant in which the two heat sources share a common power block. The geo-solar hybrid plant could provide a better match to typical electrical power demand profiles than a stand-alone geothermal plant. The hybrid plant could also eliminate the stand-alone concentrated solar power plant thermal storage requirement for operation during times of low or no solar insolation. This paper identifies hybrid plant configurations and economic conditions for which solar thermal retrofit of a geothermal power plant could improve project economics. The net present value of the concentrated solar thermal retrofit of an air-cooled binary geothermal plant is presented as functions of both solar collector array cost and electricity sales price.

14 SOLAR ENERGY↗
DOE OSTI2013

Production and Injection data for NV Binary facilities

Excel files are provided with well production and injection data for binary facilities in Nevada. The files contain the data that reported montly to the Nevada Bureau of Mines and Geology (NBMG) by the facility operators. this data has been complied into Excel spreadsheets for each of the facilities given on the NBMG web site.

15 GEOTHERMAL ENERGY↗