
582 Principles of Sustainable Energy Systems
© 2008 Taylor & Francis Group, LLC
10.2 Mechanical Technologies
Two of the mechanical storage systems discussed later are at this time the only technolo-
gies available for large-scale and long-term utility size storage, as shown in Figure 10.2:
pumped hydro and compressed air energy storage (CAES).
10.2.1 Pumped Hydroelectric Energy Storage
Pumped hydroelectric energy storage (PHES) is a mature technology that has been deployed for
over a century. Examples as early as the 1890s exist in Italy and Switzerland. PHES uses electric-
ity to pump water uphill into a reservoir where it can be stored. The energy ...