Environmental Engineering Reference
In-Depth Information
Hard Rock
Although hard rock is an option for CAES design, the cost of mining a new
reservoir is often relatively high (typically $30/kWh produced). However, in
some cases existing mines may be used, in which case the cost will typically
be about $10/kWh produced [1,40,41] as is the case for the proposed Norton
CAES plant that plans to use an idle limestone mine.
Detailed methodologies have been developed for assessing rock stability,
leakage, and energy loss in rock-based CAES systems including concrete-
lined tunnels [45-47]. Several such systems have been proposed [48] and
known field tests include two recent programs in Japan: a 2 MW test sys-
tem using a concrete-lined tunnel in the former Sunagaawa coal mine and
a hydraulic confinement test performed in a tunnel in the former Kamioka
mine [1].
In addition, a test facility was developed and evaluated by the Electric
Power Research Institute (EPRI) and Luxembourg's Societé Electrique de
l´Our SA utility using an excavated hard rock cavern with water compensa-
tion [49]. The site was used to determine the feasibility of such a system for
CAES operation and characterize and model water flow instabilities result-
ing from the release of dissolved air in the upper portion of the water shaft
(i.e., the “champagne effect”).
Hard rock geologies suitable for CAES are widely available in the
continental United States and overlap well with high-quality wind resources
[82]. However, because development costs are high relative to other geologies
(especially given the limited availability of preexisting caverns and aban-
doned mines [37]), it is unlikely that this option will be the first one pur-
sued for a large-scale deployment of CAES. Although future developments
in mining technology may reduce the costs of utilizing such geologies, it
appears that other geological structures may offer the best near-term oppor-
tunities for CAES development.
Porous Rock
Porous rock formations (Figure 5.6) such as saline aquifers are also suitable
for CAES development. Figure 5.7 shows that large, homogeneous aquifers
can be found throughout the Central United States. Because this area also
has high quality wind and because of the limited availability and/or cost
effectiveness of other options, aquifer CAES will be especially relevant to the
discussion of energy storage for balancing wind.
Although the total cost of developing a porous rock formation for CAES
will depend on the characteristics of the storage stratum (e.g., thinner, less
permeable structures will require more wells and therefore higher devel-
opment costs), it appears that this type of geology is often the lowest cost
option. CAES estimates indicate that total development costs are in the range
$2 to $6 million/Bcf of total volume (working gas and base gas)—similar to
