Wire-wound pressure vessels for small scale CAES

This paper explores the use of steel wire wound pressure vessels for reducing the cost of aboveground air storage for small-scale CAES systems. CAES technology is often only considered for large scale applications because underground salt caverns are only cost-effective for capacities in the order of hundreds of MWh. Besides the size restriction, CAES systems are geographically limited to places with suitable salt deposits. The cheapest pressure vessels available on the market have a nominal pressure of 250 bar (suitable for CAES applications) and can be found for about similar to 80$/kWh; which is approximately 12 times the overall cost per unit exergy storage of an underground cavern. Such high costs would impede a CAES system to be competitive. The wire-winding approach proposed allows reducing the volume of steel required to fabricate a vessel up to a 35%, depending on the specific configuration of the vessel. A conventional container made from solid plates and rated for 250 bar, requires between 0.08 and 0.11 m(3) of steel per m(3) of storage volume, which translates into material costs in the range of $16.5 to $21.7 per kWh of exergy storage capacity. In contrast, a wire-wound vessel (rated for the same pressure) requires between 0.068 and 0.07 m(3) of steel wire per m(3) of capacity (considering wires with a yield strength of 1700 MPa). This represents material costs between $8.5 and $12.4 per kWh of exergy storage capacity. Considering that wire-winding is much simpler than the fabrication of a conventional tank made of solid steel plates, it is estimated that wire-wound vessels can be produced for less than 35 $/kWh.