Energy Systems Analysis

A.J. Simon, Energy Systems Analyst, GCEP, Rebecca Hunt, Software Engineer, GCEP; Ian Coe, Kelsey Lynn, Brooks Moses, Katie Plzak, Adam Simpson, Graduate Researchers

The goal of the Energy Systems Analysis Group is to create an interconnected set of models that tracks transformations of matter and energy through various energy technologies.

This set of models serves four functions: innovation, integration, tool-building, and education. Detailed insight into the operation of existing and proposed technologies aids in identification of opportunities to improve those technologies. The goal of this project, as an integral part of the GCEP analysis framework (including Technical Assessments and Integrated Assessments), is to develop a methodology for measuring the impact of technologies from an energy- and materials-usage standpoint. The systems analysis group also trains the next generation of energy systems engineers to think critically about the efficiency potential of new technologies and about "round-trip" consequences of returning harvested energy and materials to the environment.

All material conversions and energy transactions can be characterized by a thermodynamic efficiency. The Energy Systems Analysis group uses a quantitative definition of efficiency, the Second Law Thermodynamic Efficiency, to assess various energy technologies and the value of various energy resources. This efficiency is defined as the exergy of the outputs of a process divided by the exergy of the inputs of the process, where exergy is defined as the maximum amount of mechanical work that can be harvested when material or energy is transformed from a well-defined state to a state in equilibrium with the environment. The second law of thermodynamics states that there is no process whose efficiency can exceed unity. However, all processes can be modeled as "reversible," and could theoretically have second law efficiencies approaching unity. In this way, all actual technologies can be evaluated against a theoretical ideal, and can therefore be quantitatively compared.

The Energy Systems Analysis Group is taking a "bottom-up" approach to energy system modeling. Individual energy harvesting, conversion, distribution and usage systems are being scrutinized. Each system is identified with its associated inputs and outputs. The relationships between the properties of mass and energy as they enter and exit the system are determined by the system model. Model parameters are linked to known state transitions within the system and to material and kinetic constraints.

Individual component models are be combined together for "fuel-chain-analysis." This first step of integration requires a framework in which the system models can share information. An application programming interface is in development which will allow system models of any level of complexity to share information about input and output material and energy streams, exergy flow and destruction, and second law efficiency.

In addition to development of the software framework in which individual energy system models can operate, there is ongoing work in generating component modules. Completed modules include: Molten Carbonate Fuel Cell, Anaerobic Digester, Proton Exchange Membrane Electrolyzer and Fission-Based Nuclear Reactor. These models incorporate varying levels of detail, but all are sufficient to describe the second law efficiency of the device in question. Further development continues on the following models:

1. Energy Storage: Various energy storage methods are investigated to determine suitability for load-leveling and CO₂ emissions reduction potential in association with the electrical grid. Technologies studied include: Pumped Hydro, Compressed Air, Flywheels, Super-capacitors and Superconducting Magnetics. Chemical Batteries and Hydrogen Flow-Batteries were omitted from this study.

Figure 1: Process Diagram for Gaseous Fuel Liquefaction

2. Gaseous Fuel Storage: The energy penalty for storing gaseous fuels such as propane, methane and hydrogen is quantified, and the compression and liquefaction processes are studied (Figure 1) to identify the exergy loss mechanisms. The capability to recover stored physical exergy will be explored.
3. Solar Energy: The exergy of sunlight is quantified, as are the ability to capture and convert that exergy to electrical work. Single and multi-bandgap devices are considered, as are some of the major known loss mechanisms such as radiative recombination.
4. Gasification: A gasifier model is built with the capability to examine oxygen-separation, post-gasification hydrogen-shift and post-shift CO₂ separation. Multiple CO₂ separation options are explored including amines and hydrates.
5. Natural resource characterization from the point of view of exergy (thermodynamic availability) has been conducted for a wide range of energy reservoirs. This characterization is technology independent, and so adheres to a slightly different theme than the other technology investigations. A set of code modules has been developed that return exergy on a normalized basis from descriptive parameters particular to each resource type.