ASTM E974-21

Standard Guide for Specifying Thermal Performance of Geothermal Power Systems

SIGNIFICANCE AND USE
2.1 Thermal efficiency and heat rate are frequently utilized to evaluate the thermodynamic quality of fossil fuel-fired power plants.2 Evaluation of geothermal systems using similar definitions of thermal efficiency and heat rate is inappropriate, except for plants which operate on a cycle, such as binary plants. A utilization efficiency, defined as the ratio of net work output to the ideal work available from the geofluid, provides a more equitable basis for evaluation of the thermodynamic excellence of geothermal systems.
SCOPE
1.1 This guide covers power plant performance terms and criteria for use in evaluation and comparison of geothermal energy conversion and power generation systems. The special nature of these geothermal systems makes performance criteria commonly used to evaluate conventional fossil fuel-fired systems of limited value. This guide identifies the limitations of the less useful criteria and defines an equitable basis for measuring the quality of differing thermal cycles and plant equipment for geothermal resources.  
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2021
• ICS: 07.060 - Geology. Meteorology. Hydrology
• ICS: 27.100 - Power stations in general
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources
• Drafting Committee: E44.15 - Geothermal Field Development, Utilization and Materials

Overview

ASTM E974-21 - Standard Guide for Specifying Thermal Performance of Geothermal Power Systems provides crucial terminology, evaluation criteria, and guidance for assessing the thermal performance of geothermal energy conversion and power generation systems. Developed by ASTM International under recognized global standards principles, this guide helps ensure that geothermal plant performance is measured equitably and comparably, recognizing the unique characteristics of geothermal resources and systems.

Unlike fossil fuel-fired plants, which are evaluated by established metrics such as thermal efficiency and heat rate, geothermal plants require different approaches. The standard identifies the limitations of directly applying traditional efficiency metrics to geothermal systems, offering a more equitable and thermodynamically valid basis for comparison through utilization efficiency.

Key Topics

• Performance Evaluation Criteria:
  • Guides the selection of appropriate terms and criteria for evaluating geothermal energy conversion systems.
  • Recognizes the limited value of applying fossil fuel-based efficiency measures to geothermal applications.
• Utilization Efficiency:
  • Introduces the concept of utilization efficiency as the ratio of net work output to the ideal work available from the geofluid.
  • Establishes this metric as an equitable benchmark for comparing different geothermal power plant designs.
• Limitations of Traditional Metrics:
  • Explains why standard metrics like thermal efficiency and heat rate are only applicable to geothermal plants with cyclic operations (e.g., binary cycles).
  • Discourages the misuse of such metrics for other geothermal plant types.
• Thermodynamic Analysis:
  • Defines key terms such as net power, wellhead flow rate, and ideal specific work.
  • Details the process for determining the quality of differing thermal cycles and the performance of plant equipment.
• Auxiliary Power Considerations:
  • Stresses the importance of accounting for auxiliary power needs, such as gas venting or fluid transport, in performance evaluations.

Applications

ASTM E974-21 supports practical use in several critical activities within the geothermal energy sector:

• Plant Design Optimization:
  • Assists engineers and project developers in optimizing geothermal power plants by enabling direct comparison of alternative designs and operating conditions.
• Resource Assessment:
  • Provides a robust framework for evaluating the power potential of geothermal resources using utilization efficiency and geofluid consumption rates.
• Performance Benchmarking:
  • Facilitates fair benchmarking of different geothermal technologies, such as flash steam, double-flash, binary, and hybrid systems.
• Project Feasibility and Reporting:
  • Supports the transparent reporting and comparison of plant performance metrics to stakeholders and regulatory bodies.
• Cost Analysis:
  • Connects plant thermodynamic quality with development and operating costs, aiding in investment and field development decisions.
• Regulatory and Environmental Compliance:
  • Encourages the consideration of safety, health, and environmental practices during the application of the guide.

Related Standards

For comprehensive project and performance evaluation, the following standards are frequently referenced alongside ASTM E974-21:

• ASTM Standards:
  • ASTM E957 – Standard Terminology Relating to Geothermal Energy
  • ASTM E1675 – Guide for Specification and Evaluation of Geothermal Well Cement Materials
• International Standards:
  • ISO 50001 – Energy Management Systems
  • IEC/TS 62862 – Solar Energy - Terminology (useful for hybrid systems)
• Sector Guidance:
  • DOE and EPRI guidelines for geothermal power cycle selection and project design.
  • World Trade Organization TBT Principles for standard development and application.

By using ASTM E974-21, stakeholders can ensure that geothermal power generation projects are evaluated with accurate, fair, and internationally recognized criteria, driving improvement and reliability in the growing field of geothermal energy.

Keywords: geothermal energy, thermal performance, geothermal power systems, utilization efficiency, plant performance, geothermal power generation, ASTM E974-21, energy conversion, renewable energy standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E974 − 21
Standard Guide for
Specifying Thermal Performance of Geothermal Power
Systems
This standard is issued under the fixed designation E974; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The following sections describe a guide for determining the thermodynamic excellence of
geothermal power systems. This guide may be used to establish and compare performance levels of
alternative geothermal plant designs using any resource conditions and is intended as a means for
supplying information in support of geothermal plant optimization.
It is also the purpose of this guide to encourage the common use of pertinent comparison criteria
for geothermal power systems, and to discourage the use of certain criteria which may range from less
useful to misleading.
1. Scope power plants. Evaluation of geothermal systems using similar
definitions of thermal efficiency and heat rate is inappropriate,
1.1 This guide covers power plant performance terms and
except for plants which operate on a cycle, such as binary
criteria for use in evaluation and comparison of geothermal
plants. A utilization efficiency, defined as the ratio of net work
energy conversion and power generation systems. The special
output to the ideal work available from the geofluid, provides
nature of these geothermal systems makes performance criteria
a more equitable basis for evaluation of the thermodynamic
commonly used to evaluate conventional fossil fuel-fired
excellence of geothermal systems.
systems of limited value. This guide identifies the limitations
of the less useful criteria and defines an equitable basis for
3. Calculations
measuring the quality of differing thermal cycles and plant
3.1 Fossil Fuel-fired Power Plants—Thermal efficiency and
equipment for geothermal resources.
heat rate are useful and valid criteria for evaluation and
1.2 This standard does not purport to address all of the
comparison of fossil fuel-fired power plants. Thermal effi-
safety concerns, if any, associated with its use. It is the
ciency is the ratio of net work generated to the heat that is
responsibility of the user of this standard to establish appro-
theoretically available from the fuel. Conventional usage
priate safety, health, and environmental practices and deter-
within the electric generating industry defines thermal effi-
mine the applicability of regulatory limitations prior to use.
ciency (in dimensionless form) as:
1.3 This international standard was developed in accor-
η 5 3600/HR (1)
t
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
where:
Development of International Standards, Guides and Recom-
3600 = kJ equivalent of 1 kWh, and
mendations issued by the World Trade Organization Technical
HR = heat rate, the ratio of thermal energy supplied to the
Barriers to Trade (TBT) Committee.
net electrical output, kJ/kWh.
3.1.1 Forfossilfuel-firedpowerplantsheatrateisexpressed
2. Significance and Use
as:
2.1 Thermal efficiency and heat rate are frequently utilized
˙
to evaluate the thermodynamic quality of fossil fuel-fired
HR 5 m˙ 3FC⁄WHR (2)
f
where:
This guide is under the jurisdiction of ASTM Committee E44 on Solar,
m˙ = fuel flow rate, kg/h,
f
Geothermal and OtherAlternative Energy Sources and is the direct responsibility of
SubcommitteeE44.15onGeothermalFieldDevelopment,UtilizationandMaterials.
Current edition approved April 1, 2021. Published April 2021. Originally
approved in 1983. Last previous edition approved in 2006 as E974 - 00 (2006) Kestin, J., DiPippo, R., Khalifa, H. E., and Ryley, D. J., “Source Book on the
which was withdrawn in January 2015 and reinstated in April 2021. DOI: Production of Electricity From Geothermal Energy,” DoE/RA/28320-2, U.S. De-
10.1520/E0974-21. partment of Energy, 1980, pp. 243–257.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E974 − 21
significant differences in auxiliary power requirements, and
FC = fuel higher heating value, kJ/kg, and
differing methods of providing auxiliary power, in the cases
W = net electrical output, kW.
being evaluated. This applies particularly to auxiliary power
3.1.2 Thermal efficiency and heat rate are applicable to
allowancesforventinggasesorfortransportingworkingfluids.
plants which operate on a cycle, and include the effectiveness
3.3.2 Utilizationefficiencyispresentedasaguidefordesign
of energy conversion associated with the fuel combustion, the
evaluations and the selection of suitable design conditions for
effect of heat rejected in exhaust gases and condensate, and
equipment specifications. Utilization efficiency for a typical
allowance for equipment and balance of plant auxiliary power
single-flash steam plant is presented as a function of steam
losses. Thus, thermal efficiency and heat rate provide an
separation temperature in Fig. 2; the temperature that results in
equitable basis for ranking and comparing fossil fuel-fired
the highest utilization efficiency is referred to as the optimum
plants of alternative design.
separator temperature. For multi-flash systems (including
3.2 Geothermal Power Plants—Geothermal plants using
flash-binary) optimum values can be identified for each flash
flashed steam (see Fig. 1a and Fig. 1b) do not operate on a
level. For binary cycles, optimum temperatures depend on the
cycle but involve a series of e
...