Editing Pieee (section)

===Mechanical storage===
 
====The present state and future prospects for advanced adiabatic compressed air energy storage====
*'''Authors:''' Giuseppe Grazzini (University of Florence, Italy), Adriano Milazzo (University of Florence, Italy) 
*'''Contact email:''' adriano.milazzo@unifi.it
*'''Scope:''' Adiabatic compressed air energy storage represents a valuable and environmental friendly option for massive energy storage. Some examples in this field refer to underground storage at medium pressure level. In view of a widespread utilization, independent from the availability of underground storage volumes, an artificial reservoir is required. This prompts for rather high air pressure within the storage, which in turn requires carefully optimized recovery of the thermal energy released in the compression phase. Starting from a thermodynamic tutorial of the relevant design parameters and their influence on the system efficiency, we propose a comprehensive set of criteria for the design of the system; with particular attention on heat transfer devices. A possible application within a wind energy plant is analyzed. 
 
====The history, present state, and future prospects of underground pumped hydro====
*'''Authors:'''  William F. Pickard (Washington University, USA)
*'''Contact email:''' wfp@ese.wustl.edu
*'''Scope:''' To stabilize the future national or regional electricity grid supplied by sustainable but intermittent sources will require multiple gigawatt-day-sized energy storage modules.  Devices of such functionality do not at present exist but can be created using extant technology.  This paper discusses one possible realization based upon the familiar pumped hydro facility, only now with the lower reservoir directly under the upper and many hundred meters below ground surface. 
 
====Geotechnical issues in the creation of underground reservoirs for massive energy storage====
*'''Authors:''' Nasim Uddin (University of Alabama at Birmingham, USA)
*'''Contact email:''' nuddin@uab.edu
*'''Scope:''' Pumped storage is currently an economically viable alternative to the conventional above ground type of facility, and is made increasingly attractive by consideration of the reduced environmental impact, which the underground concept make possible. This paper is intended to provide an introduction to the engineering challenges of underground pumped storage.