Session: 09-04 Techno-Economic Analysis and System Integration of Energy Storage

Submission Number: 176638

Framework for Techno-Economic Analysis of Energy Storage Systems 

Energy Storage Systems (ESS) involve the transformation of energy from and to a useful form to a form that can be stored safely, conveniently, and economically.  ESS are commonly classified by the form of energy storage: Thermal, Mechanical, Chemical, and Electrical.  Electrochemical batteries that transform valence states are commonly considered as Electrical storage devices, although strictly speaking only inductors and capacitors would qualify. However, this high-level classification approach obscures the characteristics by which ESS are evaluated as fit for purpose.  Moreover, the utility of this classification schema for evaluation of actual ESS designs is compromised by the multiplicity of different types of mass and energy streams, and even multiple storage reservoirs and storage media of different types.

This paper proposes an alternative framework that encompasses the functionality, equipment, performance, and cost of the key elements of an ESS: the charging process, the discharging process, and the storage subsystem itself, which includes the storage reservoir, storage medium, and any streams needed to support and maintain the storage subsystem.  To be sure, the storage system is key to the functional requirements, cost, and performance of the charging and discharging subsystems, and the size, cost, and duration of the overall ESS. 

Yet, to use thermal energy storage as an example, there are a host of differences between molten salt, fire bricks, and cryogenic air: the first is both heat transfer fluid and storage medium, the second is a storage medium needing a separate heat transfer fluid, and the last is a working fluid capable of directly operating a turbo machine.  Likewise, there are substantial differences between mechanical energy storage systems: both pumped storage hydro and railcars employ gravitational potential but are completely different in function and cost structure.

Accordingly, this paper identifies distinguishing functional characteristics that affect the cost, performance, and capability of ESS.  These characteristics form the basis for technoeconomic analysis of the ESS to assess fitness according to cost-benefit analysis to identify the optimal capacity of the charge, storage, and discharge subsystems.  The cost of energy includes capital amortization, operations and maintenance expenses, and the costs of the energy streams used for charging, standby, and discharging.

Capital amortization charges dominate the cost of energy delivered by ESS, which generally have low capacity factors or utilization rates (the ratio of energy discharged to energy that could be produced in a year if discharged continually at full power).  The principal reason for this is the need to charge the ESS, which consumes a substantial number of hours.  Discharge hours are also limited by the need for positive net revenue, i.e., the payments for discharge energy must exceed the costs of charge energy, which depends on hourly price.  The energy capacity of the storage subsystem also limits capacity factor, as low-price energy cannot be stored when the reservoir is full, nor may energy be discharged when the reservoir is empty.  Consideration must also be given to off-design ESS performance under varying ambient conditions.

Performance metrics, derived partly from ASME PTC53 Performance Test Code for Thermal and Mechanical Energy Storage Systems, support the modeling of ESS economic dispatch to determine capacity factor, hourly revenue, and the net annual benefit. Use cases can be derived based on ambient conditions and commodity prices. ESS characteristics can then be evaluated using parametric studies to support the selection of storage media, the type and size of the charging and discharging processes, and the size and duration of the storage sub-system. In some cases, the net benefit of energy discharge is insufficient, requiring additional financial support, such as via capacity payments or subsidies.

Presenting Author: William Conlon Pintail Power

Presenting Author Biography: Dr. William M. (Bill) Conlon, P.E. is the founder and President of Pintail Power LLC, and inventor of patented liquid air and liquid salt energy storage technologies that bridge renewable and conventional generation by synergistic integration of thermal energy storage with thermal generation.

After receiving a Ph.D. in Nuclear Engineering and Science from Rensselaer Polytechnic Institute, he worked on Pacific Gas & Electric Company’s Diablo Canyon Project. At International Power Technology he was responsible for control systems and received three patents for the Cheng Cycle steam injected gas turbine, led new product development, and transferred technology to international licensees.

Following forays in water treatment, industrial controls and software, Bill returned to energy to lead Ausra’s turn-around to price-performance leadership in the solar thermal market and was instrumental in its merger with AREVA. As Chief Engineer and Senior VP he helped secure more than $1 billion of new business within 18 months of the merger and was responsible for Engineering, Commissioning and Operations teams on three continents.

Bill is a licensed Mechanical Engineer in California, a life member of IEEE and ASME. and serves on the ASME PTC-53 Committee.

Authors:

William Conlon Pintail Power
Pablo Enrique Rodríguez De Arriba Universidad de Sevilla
Milton Venetos Pintail Power LLC
David Tomas Sanchez Martinez Universidad de Sevilla