In the Electric Reliability Council of Texas (ERCOT) compressed air energy storage (CAES) is currently viewed as the most promising energy storage technology due to Texas having suitable geology for CAES and few locations suitable for pumped-hydro storage. CAES is a proven technology but the economics for new facilities are uncertain. This work quantified the economic prospects for CAES in ERCOT as a function of installed wind capacity, natural gas price, and CAES capital cost. Two types of models were developed and used in this work. The first type of model was a CAES dispatch optimization model, which determined the maximum operating profits a CAES facility could earn given a set of electricity and ancillary services market prices. These models were used to examine several separate research questions relating to the maximum potential for CAES and the impact of uncertainty and other real-world complications. The models determined that the maximum operating profit from 2002-2010 varied widely from year to year and averaged $120-140/kW-year, which is likely below the operating profits required to justify investing in CAES. The models also determined that current price forecasting methods are sufficient to earn approximately 95% of the operating profits achievable with perfect knowledge of all prices in the year. The second type of model was a unit commitment model of ERCOT, which determined the least-cost operation of all the generators in the generation fleet to meet given load. The unit commitment model was used to determine electricity and ancillary service market prices under different assumptions about natural gas price, installed wind capacity, and installed CAES capacity. The CAES dispatch optimization model was then used to determine the operating profits of a CAES facility under these scenarios. CAES operating profits were found to increase with increasing natural gas price and installed wind capacity and to decrease with increasing installed CAES capacity. CAES operating profits were estimated to support installed CAES capacities from zero to more than 6 GW, depending on the natural gas price, installed wind capacity, installed CAES capacity, and the CAES capital costs. The strongest determinant of the maximum CAES capacity that would be profitable is the natural gas price, followed by the CAES capital costs. / text

Renewable Energy is by nature intermittent and matching the supply of energy to specific time dependent demand poses huge challenges. Energy storage is a useful tool in handling this temporal disparity, although except for regions very suitable for pumped hydroelectric storage schemes, it suffers from being technically difficult to implement and costly as a result. This study investigates the potential benefits offered by various scales of energy storage to different types of renewable energy generation. It also explores the economic drivers behind energy storage operating as part of an electricity spot market. A stochastic optimisation algorithm for determining the maximum possible arbitrage revenue available to energy storage devices is presented and schedule of operation of storage acting in this manner is analysed. The schedule of operation for maximising the revenue is compared to the schedule of operation for minimising the fuel cost to the network and it is demonstrated that because prices are more volatile than the demand which drives them, storage devices do not always act to decrease the fuel cost to the network. It is shown that storage behaving in the right manner can offer significant benefits to electricity systems, and increases the usage of base-load generation, reducing peak electricity demands and the need for expensive peaking plants. The value of storage also increases as the penetration of renewable energy generation increases, although the current electricity market framework is perhaps not the best way to encourage this behaviour. Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) is also identified as a theoretical storage option which deserves further scrutiny. Using thermodynamic modelling the efficiency of this type of system is estimated in the range of 63-67%, and we suggest that this may be increased closer to 73% by using direct contact heat exchangers rather than indirect contact heat exchangers (and a separate thermal fluid), as described in the currently available literature. However, dealing with large pressure ranges (leading to large variations in pressure ratios) encountered in the expansion process is a problematic area which will have to be resolved before this type of system can be constructed with “off-the-shelf” components. Some small scale experiments are used to gain valuable insights into a AA-CAES system. While these suffer from a very low overall efficiency, they highlight the effect of variable pressure ratio on expander efficiency. We conclude that AA-CAES is thermodynamically sound and will be achieved one of two ways: either through the construction of expanders that can work with high efficiency over large pressure ratios, or by resolving the engineering issues with maintaining a constant storage pressure.

As energy systems shift away from fossil-fuel based electricity, the non-dispatchability of renewable energy converters (REC) continue to stress the grid infrastructure and conventional thermal generating units. These hybrid electricity systems require energy storage systems to buffer the variabilities of electricity supply and demand. Regenerative air energy storage (RAES) is an emerging technology that shows promise to overcome the barriers of REC variability. RAES uses a novel compressor/expander that approaches isothermal operation by spraying water into the piston/cylinder to absorb/release heat. RAES can be sized for power and energy independently, and has a high round-trip efficiency that can be boosted using low grade waste heat. Because of its novelty, new numerical models are necessary to investigate the sizing and performance of RAES systems. In this thesis a numerical simulation tool is developed to allow flexible and intuitive analysis of a range of hybrid energy systems involving RAES.

This study investigates Compressed Air Energy Storage (CAES) application in the electrical power and transportation industries. Information concerning current CAES projects is presented. A thorough thermodynamic analysis of the CAES process is completed; including theoretical efficiency determination for several variants of the compression and expansion processes. Industry claimed efficiencies ranging from 26% to 82% are presented and explained. Isothermal and Isentropic efficiency baselines are developed. Energy density of compressed air on both a mass and volume basis is compared to other energy storage methods. Best expected efficiency of a hypothetical CAES system is determined to be 34% using currently achievable efficiencies and 63% considering 100% efficient compression and expansion. A .5 kW CAES system, built from commercial off the shelf components (COTS) to demonstrate the CAES concept, is documented and discussed. This system includes a LabView data acquisition system which was used to record all test results. LabView was also used to develop a complete test bed program that determined real time thermodynamic state properties, component efficiencies, mass flow rates, power outputs and several other performance characteristics of the demonstration system. The LabView program allowed real time efficiency and power optimization of the demonstration system. Results of demonstration system testing are thoroughly discussed. Total system efficiency was very poor; 3.6% electrical conversion efficiency, .040 refrigeration coefficient of performance (COP) and a 5.0% overall efficiency which considers both cooling and electrical storage properties. Several paths for possible future projects involving the demonstration system and CAES are presented.

Energy storage is becoming a crucial element to the renewable energy grid, and new facilities will have to go somewhere. This thesis will propose to co-locate compressed air energy storage on a site with residential units, and a community park. This thesis will make the argument that co-locating a compressed air energy storage system with residential units could create a new start for the communities most harmed by fossil fuel infrastructure. This thesis will propose a design for a site in East Boston; a community badly scarred by heating oil and natural gas storage; with the goal of creating a model for healing both the physical site, and the social injustices created by the fossil fuel grid, arguing for using compressed air energy storage as both a spatial and an economic resource.

Wind and solar technologies have experienced rapid market growth recently as a result of the growing interest for implementation of renewable energy. However, the intermittency of wind and solar power is a major obstacle to their broader use. The additional risks of unexpected interruptions and mismatch with demand have hindered the expansion of these two primary renewable resources. The goal of this research is to analyze an integrated energy system that includes a novel configuration of wind and solar coupled with two storage methods to make both wind and solar sources dispatchable during peak demand, thereby enabling their broader use. Named DSWiSS for Dispatchable Solar Wind Storage System, the proposed system utilizes compressed air energy storage (CAES) that is driven from wind energy and thermal storage supplied by concentrating solar thermal power in order to achieve this desired dispatchability. Although DSWiSS mimics the operation of a typical CAES facility, the replacement of energy derived from fossil fuels with energy generated from renewable resources makes this system unique. While current CAES facilities use off peak electricity to power their compressors, this system uses power from wind turbines. Also, rather than using natural gas for heating of the compressed air before its expansion through a turbine, DSWiSS uses solar thermal energy and thermal storage. For this research, two models were created; the first is a dynamic model of a 1.5 MW variable speed wind turbine, programmed in PSCAD/EMTDC, that utilizes rotor resistive control to maintain rated power output. This model simulates the dynamic response of the wind turbine to changing wind conditions as well as the nominal performance parameters at all wind speeds. The second model is a steady state thermodynamic simulation of the turbomachinery power unit in the DSWiSS facility. By assuming conditions similar to those of a currently operating CAES facility in McIntosh, Alabama, the model calculates the performance parameters of DSWiSS and estimates the relative energy input requirements. By combining these models with a levelized lifetime cost analysis estimates of the power system performance and the cost of energy for the DSWiSS facility were estimated. The combination of these components yielded an efficiency greater than 46% for the main power block and a nearly equal utilization of both renewable resources. It was also estimated that the overall system is only slightly more expensive per unit of electricity generated than the current technologies employed today, namely coal, nuclear, and natural gas, but is comparable to a stand-alone solar thermal facility. However, this economic analysis, though accurate with regard to the technologies chosen, will not be complete until cost values can be placed on some of the externalities associated with power generation such as fuel cost volatility, national security, and emissions. / text

Water or steam is added into the working fluid (often air) in gas turbines to improve the performance of gas turbine cycles. A typical application is the humidified gas turbine that has the potential to give high efficiencies, high specific power output, low emissions and low specific investment. A heat recovery system is integrated in the cycle with a humidifier for moisturizing the high-pressure air from the compressor as a kernel. Based on today’s gas turbines, the operating temperature and pressure in the humidifier are up to about 523 K and 40 bar, respectively. The operating temperature of the heat exchanger after the humidifier is up to 1773 K. The technology of water or steam addition is also used in the process of compressed air energy storage (CAES), and the operating pressure is up to 150 bar. Reliable thermodynamic properties of humid air are crucial for the process simulation and the traceable performance tests of turbomachinery and heat exchanger in the cycles. Several models have been proposed. However, the application range is limited to 400 K and 100 bar because of the limited experimental data for humid air. It is necessary to investigate the thermodynamic properties of humid air at elevated temperatures and pressures to fill in the knowledge gap. In this thesis, a new model is proposed based on the modified Redlich-Kwong equation of state in which a new cross interaction parameter between molecular oxygen and water is obtained from the fitting of the experimental data of oxygen-water system. The liquid phase is assumed to follow Henry’s law to calculate the saturated composition. The results of the new model are verified by the experimental data of nitrogen-water and oxygen-water systems from ambient temperature and pressure to 523 K and 200 bar, respectively. Properties of air-water system are predicted without any additional parameter and compared with the available experimental data to demonstrate the reliability of the new model for air-water system. The results of air-water system predicted using the new model are compared with those calculated using other real models. The comparison reveals that the new model has the same calculation accuracy as the best available model but can be used to a wider temperature and pressure range. The results of the new model are also compared with those of the ideal model and the ideal mixing model from ambient temperature and pressure to 1773 K and 200 bar to investigate the effect of the models on the thermodynamic properties of humid air. To investigate the impact of thermodynamic properties on the simulation of systems and their components, different models (ideal model, ideal mixing model and two real models) are used to calculate the thermodynamic properties of humid air in the simulation of the compressor, humidification tower, and heat exchanger in a humidified gas turbine cycle. The simulation reveals that a careful selection of a thermodynamic property model is crucial for the cycle design. The simulation results provide a useful tool for predicting the performance of the system and designing the humidified cycle components and systems. / QC 20100902

This diploma thesis deals with the underground compressed air enery storage. Thesis can be divided into several parts. The first part focuses on the theoretical analysis which decribes reason of renewable resources implementation to the electric grid and how renewable resources affect electric grid. Second part describes compression and expansion stage. Last part deals with design of storage facility which is suitable for different energy supplies. Extracted coal mines of Rosicko-Oslavany area is used as suitable underground storage.

The global electricity generation industry is very reliant on the use of fossil fuels, particularly natural gas and coal. However, it is quickly becoming a reality that the over-consumption of these resources will continue to lead to significant global damage via global warming, ecosystem destruction, and the depletion of these so-called non-renewable re-sources. To combat this issue, renewable sources such as wind, biofuels and solar are be-coming much more prevalent in the power generation industry, but significant economic, reliability and availability barriers to entry will prevent these sources from being major contributors to the power industry for decades. To this end, this thesis focuses on the design, operation, optimization and life cycle analysis of an integrated solid-oxide fuel (SOFC) cell power plant integrated with com-pressed air energy storage (CAES). This plant, fueled by either natural gas or coal, can make much more efficient use of their limited non-renewable fuel sources, and are capable of achieving nearly 100% carbon capture at the plant boundary. This plant is intended to serve as a more efficient and environmentally responsible alternative to current power generation methods while still exploiting remaining fossil fuels to their fullest extent. This thesis details the design, sizing and simulation of integrated SOFC/CAES plants in Aspen Plus so that full feasibility and techno-economic analyses may be performed, the results of which are then compared to the current state-of-the-art (SOTA) options. In order to compare the plants on an environmental level, full cradle-to-grave life-cycle analyses using the ReCiPe 2008 method are completed for each SOFC-based plant and all comparable SOTA options under a wide range of assumptions and plant configurations, such as the use of carbon capture strategies. Furthermore, detailed reduced-order dynamic models of the integrated SOFC/CAES plants are developed and simulated with a newly developed rolling-horizon optimization method to assess the load-following capabilities of the integrated plant. Real scaled demand data for the market of Ontario, Canada for the years 2013 and 2014 are used as the demand data for the simulations. This thesis takes strides in proving the feasibility of an integrated SOFC/CAES power plant for providing clean, efficient, reliable and cost-effective power using fossil fuels. The next steps for this project involve the development of a lab-scale pilot plant, which would be used to validate simulation results and provide an opportunity for the real-time application and assessment of the potential of this plant design. / Thesis / Doctor of Philosophy (PhD)

Emerging integration of renewable energy has prompted a wide range of research on the use of energy storage to compensate for the added uncertainty that accompanies these resources. In the Electric Reliability Council of Texas (ERCOT), compressed air energy storage (CAES) has drawn particular attention because Texas has suitable geology and also lacks appropriate resources and locations for pumped hydroelectric storage (PHS). While there have been studies on incorporation of renewable energy, utilization of energy storage, and dispatch optimization, this is the first body of work to integrate all these subjects along with the proven ability to recreate historical dispatch and price conditions. To quantify the operational behavior, economic feasibility, and environmental impacts of CAES, this work utilized sophisticated unit commitment and dispatch (UC&D) models that determine the least-cost dispatch for meeting a set of grid and generator constraints. This work first addressed the ability of these models to recreate historical dispatch and price conditions through a calibration analysis that incorporated major model improvements such as capacity availability and sophisticated treatment of combined heat and power (CHP) plants. These additions appreciably improved the consistency of the model results when compared to historical ERCOT conditions. An initial UC&D model was used to investigate the impacts on the dispatch of a future high wind generation scenario with the potential to utilize numerous CAES facilities. For all future natural gas prices considered, the addition of CAES led to reduced use of high marginal cost generator types, increased use of base-load generator types, and average reductions in the total operating costs of 3.7 million dollars per week. Additional analyses demonstrated the importance of allowing CAES to participate in all available energy and ancillary services (AS) markets and that a reduction in future thermal capacity would increase the use of CAES. A second UC&D model, which incorporated advanced features like variable marginal heat rates, was used to analyze the influence of future wind generation variability on the dispatch and resulting environmental impacts. This analysis revealed that higher amounts of wind variability led to an increase in the daily net load ramping requirements which resulted in less use of coal and nuclear generators in favor of faster ramping units along with reductions in emissions and water use. The changes to the net load also resulted in increased volatility of the energy and AS prices between daily minimum and maximum levels. These impacts were also found to increase with compounding intensity as higher levels of wind variability were reached. Lastly, the advanced UC&D model was also used to evaluate the operational behavior and potential economic feasibility of a first entrant conventional or adiabatic CAES system. Both storage systems were found to operate in a single mode that enabled very high utilization of their capacity indicating both systems have highly desirable characteristics. The results suggest that there is a positive case for the investment in a first entrant CAES facility in the ERCOT market. / text